Merge pull request #8617

e44e8b164 wallet: background sync with just the view key (j-berman)

15 files changed, 1849 insertions, 94 deletions

diff --git a/src/cryptonote_basic/account.cpp b/src/cryptonote_basic/account.cpp
index 2ac455fda..4e87d4477 100644
--- a/src/cryptonote_basic/account.cpp
+++ b/src/cryptonote_basic/account.cpp
@@ -152,6 +152,17 @@ DISABLE_VS_WARNINGS(4244 4345)
     m_keys.m_multisig_keys.clear();
   }
   //-----------------------------------------------------------------
+  void account_base::set_spend_key(const crypto::secret_key& spend_secret_key)
+  {
+    // make sure derived spend public key matches saved public spend key
+    crypto::public_key spend_public_key;
+    crypto::secret_key_to_public_key(spend_secret_key, spend_public_key);
+    CHECK_AND_ASSERT_THROW_MES(m_keys.m_account_address.m_spend_public_key == spend_public_key,
+        "Unexpected derived public spend key");
+
+    m_keys.m_spend_secret_key = spend_secret_key;
+  }
+  //-----------------------------------------------------------------
   crypto::secret_key account_base::generate(const crypto::secret_key& recovery_key, bool recover, bool two_random)
   {
     crypto::secret_key first = generate_keys(m_keys.m_account_address.m_spend_public_key, m_keys.m_spend_secret_key, recovery_key, recover);
diff --git a/src/cryptonote_basic/account.h b/src/cryptonote_basic/account.h
index 2ee9545d4..93d1d28f0 100644
--- a/src/cryptonote_basic/account.h
+++ b/src/cryptonote_basic/account.h
@@ -95,6 +95,7 @@ namespace cryptonote
     bool store(const std::string& file_path);
 
     void forget_spend_key();
+    void set_spend_key(const crypto::secret_key& spend_secret_key);
     const std::vector<crypto::secret_key> &get_multisig_keys() const { return m_keys.m_multisig_keys; }
 
     void encrypt_keys(const crypto::chacha_key &key) { m_keys.encrypt(key); }
diff --git a/src/cryptonote_config.h b/src/cryptonote_config.h
index 3077349fe..d69556acd 100644
--- a/src/cryptonote_config.h
+++ b/src/cryptonote_config.h
@@ -241,6 +241,8 @@ namespace config
   const unsigned char HASH_KEY_ENCRYPTED_PAYMENT_ID = 0x8d;
   const unsigned char HASH_KEY_WALLET = 0x8c;
   const unsigned char HASH_KEY_WALLET_CACHE = 0x8d;
+  const unsigned char HASH_KEY_BACKGROUND_CACHE = 0x8e;
+  const unsigned char HASH_KEY_BACKGROUND_KEYS_FILE = 0x8f;
   const unsigned char HASH_KEY_RPC_PAYMENT_NONCE = 0x58;
   const unsigned char HASH_KEY_MEMORY = 'k';
   const unsigned char HASH_KEY_MULTISIG[] = {'M', 'u', 'l', 't' , 'i', 's', 'i', 'g', 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
diff --git a/src/simplewallet/simplewallet.cpp b/src/simplewallet/simplewallet.cpp
index 011b1c761..89691e9f7 100644
--- a/src/simplewallet/simplewallet.cpp
+++ b/src/simplewallet/simplewallet.cpp
@@ -155,6 +155,17 @@ typedef cryptonote::simple_wallet sw;
     } \
   } while(0)
 
+#define CHECK_IF_BACKGROUND_SYNCING(msg) \
+  do \
+  { \
+    if (m_wallet->is_background_wallet() || m_wallet->is_background_syncing()) \
+    { \
+      std::string type = m_wallet->is_background_wallet() ? "background wallet" : "background syncing wallet"; \
+      fail_msg_writer() << boost::format(tr("%s %s")) % type % msg; \
+      return false; \
+    } \
+  } while (0)
+
 static std::string get_human_readable_timespan(std::chrono::seconds seconds);
 static std::string get_human_readable_timespan(uint64_t seconds);
 
@@ -325,7 +336,7 @@ namespace
     auto pwd_container = tools::password_container::prompt(verify, prompt);
     if (!pwd_container)
     {
-      tools::fail_msg_writer() << sw::tr("failed to read wallet password");
+      tools::fail_msg_writer() << sw::tr("failed to read password");
     }
     return pwd_container;
   }
@@ -335,6 +346,11 @@ namespace
     return password_prompter(verify ? sw::tr("Enter a new password for the wallet") : sw::tr("Wallet password"), verify);
   }
 
+  boost::optional<tools::password_container> background_sync_cache_password_prompter(bool verify)
+  {
+    return password_prompter(verify ? sw::tr("Enter a custom password for the background sync cache") : sw::tr("Background sync cache password"), verify);
+  }
+
   inline std::string interpret_rpc_response(bool ok, const std::string& status)
   {
     std::string err;
@@ -452,6 +468,41 @@ namespace
     return "invalid";
   }
 
+  const struct
+  {
+    const char *name;
+    tools::wallet2::BackgroundSyncType background_sync_type;
+  } background_sync_type_names[] =
+  {
+    { "off", tools::wallet2::BackgroundSyncOff },
+    { "reuse-wallet-password", tools::wallet2::BackgroundSyncReusePassword },
+    { "custom-background-password", tools::wallet2::BackgroundSyncCustomPassword },
+  };
+
+  bool parse_background_sync_type(const std::string &s, tools::wallet2::BackgroundSyncType &background_sync_type)
+  {
+    for (size_t n = 0; n < sizeof(background_sync_type_names) / sizeof(background_sync_type_names[0]); ++n)
+    {
+      if (s == background_sync_type_names[n].name)
+      {
+        background_sync_type = background_sync_type_names[n].background_sync_type;
+        return true;
+      }
+    }
+    fail_msg_writer() << cryptonote::simple_wallet::tr("failed to parse background sync type");
+    return false;
+  }
+
+  std::string get_background_sync_type_name(tools::wallet2::BackgroundSyncType type)
+  {
+    for (size_t n = 0; n < sizeof(background_sync_type_names) / sizeof(background_sync_type_names[0]); ++n)
+    {
+      if (type == background_sync_type_names[n].background_sync_type)
+        return background_sync_type_names[n].name;
+    }
+    return "invalid";
+  }
+
   std::string get_version_string(uint32_t version)
   {
     return boost::lexical_cast<std::string>(version >> 16) + "." + boost::lexical_cast<std::string>(version & 0xffff);
@@ -805,6 +856,7 @@ bool simple_wallet::spendkey(const std::vector<std::string> &args/* = std::vecto
     fail_msg_writer() << tr("wallet is watch-only and has no spend key");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("has no spend key");
   // don't log
   PAUSE_READLINE();
   if (m_wallet->key_on_device()) {
@@ -836,6 +888,7 @@ bool simple_wallet::print_seed(bool encrypted)
     fail_msg_writer() << tr("wallet is watch-only and has no seed");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("has no seed");
 
   multisig = m_wallet->multisig(&ready);
   if (multisig)
@@ -913,6 +966,7 @@ bool simple_wallet::seed_set_language(const std::vector<std::string> &args/* = s
     fail_msg_writer() << tr("wallet is watch-only and has no seed");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("has no seed");
 
   epee::wipeable_string password;
   {
@@ -1059,6 +1113,7 @@ bool simple_wallet::prepare_multisig_main(const std::vector<std::string> &args,
     fail_msg_writer() << tr("wallet is watch-only and cannot be made multisig");
     return false;
   }
+  CHECK_IF_BACKGROUND_SYNCING("cannot be made multisig");
 
   if(m_wallet->get_num_transfer_details())
   {
@@ -2195,6 +2250,7 @@ bool simple_wallet::save_known_rings(const std::vector<std::string> &args)
 
 bool simple_wallet::freeze_thaw(const std::vector<std::string> &args, bool freeze)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot freeze/thaw");
   if (args.empty())
   {
     fail_msg_writer() << boost::format(tr("usage: %s <key_image>|<pubkey>")) % (freeze ? "freeze" : "thaw");
@@ -2234,6 +2290,7 @@ bool simple_wallet::thaw(const std::vector<std::string> &args)
 
 bool simple_wallet::frozen(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot see frozen key images");
   if (args.empty())
   {
     size_t ntd = m_wallet->get_num_transfer_details();
@@ -3005,6 +3062,57 @@ bool simple_wallet::set_track_uses(const std::vector<std::string> &args/* = std:
   return true;
 }
 
+bool simple_wallet::setup_background_sync(const std::vector<std::string> &args/* = std::vector<std::string>()*/)
+{
+  if (m_wallet->multisig())
+  {
+    fail_msg_writer() << tr("background sync not implemented for multisig wallet");
+    return true;
+  }
+  if (m_wallet->watch_only())
+  {
+    fail_msg_writer() << tr("background sync not implemented for watch only wallet");
+    return true;
+  }
+  if (m_wallet->key_on_device())
+  {
+    fail_msg_writer() << tr("command not supported by HW wallet");
+    return true;
+  }
+
+  tools::wallet2::BackgroundSyncType background_sync_type;
+  if (!parse_background_sync_type(args[1], background_sync_type))
+  {
+    fail_msg_writer() << tr("invalid option");
+    return true;
+  }
+
+  const auto pwd_container = get_and_verify_password();
+  if (!pwd_container)
+    return true;
+
+  try
+  {
+    boost::optional<epee::wipeable_string> background_cache_password = boost::none;
+    if (background_sync_type == tools::wallet2::BackgroundSyncCustomPassword)
+    {
+      const auto background_pwd_container = background_sync_cache_password_prompter(true);
+      if (!background_pwd_container)
+        return true;
+      background_cache_password = background_pwd_container->password();
+    }
+
+    LOCK_IDLE_SCOPE();
+    m_wallet->setup_background_sync(background_sync_type, pwd_container->password(), background_cache_password);
+  }
+  catch (const std::exception &e)
+  {
+    fail_msg_writer() << tr("Error setting background sync type: ") << e.what();
+  }
+
+  return true;
+}
+
 bool simple_wallet::set_show_wallet_name_when_locked(const std::vector<std::string> &args/* = std::vector<std::string>()*/)
 {
   const auto pwd_container = get_and_verify_password();
@@ -3237,6 +3345,7 @@ bool simple_wallet::apropos(const std::vector<std::string> &args)
 
 bool simple_wallet::scan_tx(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot scan tx");
   if (args.empty())
   {
     PRINT_USAGE(USAGE_SCAN_TX);
@@ -3458,6 +3567,8 @@ simple_wallet::simple_wallet()
                                   "  Ignore outputs of amount below this threshold when spending.\n "
                                   "track-uses <1|0>\n "
                                   "  Whether to keep track of owned outputs uses.\n "
+                                  "background-sync <off|reuse-wallet-password|custom-background-password>\n "
+                                  "  Set this to enable scanning in the background with just the view key while the wallet is locked.\n "
                                   "setup-background-mining <1|0>\n "
                                   "  Whether to enable background mining. Set this to support the network and to get a chance to receive new monero.\n "
                                   "device-name <device_name[:device_spec]>\n "
@@ -3876,6 +3987,7 @@ bool simple_wallet::set_variable(const std::vector<std::string> &args)
     success_msg_writer() << "ignore-outputs-above = " << cryptonote::print_money(m_wallet->ignore_outputs_above());
     success_msg_writer() << "ignore-outputs-below = " << cryptonote::print_money(m_wallet->ignore_outputs_below());
     success_msg_writer() << "track-uses = " << m_wallet->track_uses();
+    success_msg_writer() << "background-sync = " << get_background_sync_type_name(m_wallet->background_sync_type());
     success_msg_writer() << "setup-background-mining = " << setup_background_mining_string;
     success_msg_writer() << "device-name = " << m_wallet->device_name();
     success_msg_writer() << "export-format = " << (m_wallet->export_format() == tools::wallet2::ExportFormat::Ascii ? "ascii" : "binary");
@@ -3894,6 +4006,7 @@ bool simple_wallet::set_variable(const std::vector<std::string> &args)
   }
   else
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot change wallet settings");
 
 #define CHECK_SIMPLE_VARIABLE(name, f, help) do \
   if (args[0] == name) { \
@@ -3947,6 +4060,7 @@ bool simple_wallet::set_variable(const std::vector<std::string> &args)
     CHECK_SIMPLE_VARIABLE("ignore-outputs-above", set_ignore_outputs_above, tr("amount"));
     CHECK_SIMPLE_VARIABLE("ignore-outputs-below", set_ignore_outputs_below, tr("amount"));
     CHECK_SIMPLE_VARIABLE("track-uses", set_track_uses, tr("0 or 1"));
+    CHECK_SIMPLE_VARIABLE("background-sync", setup_background_sync, tr("off (default); reuse-wallet-password (reuse the wallet password to encrypt the background cache); custom-background-password (use a custom background password to encrypt the background cache)"));
     CHECK_SIMPLE_VARIABLE("show-wallet-name-when-locked", set_show_wallet_name_when_locked, tr("1 or 0"));
     CHECK_SIMPLE_VARIABLE("inactivity-lock-timeout", set_inactivity_lock_timeout, tr("unsigned integer (seconds, 0 to disable)"));
     CHECK_SIMPLE_VARIABLE("setup-background-mining", set_setup_background_mining, tr("1/yes or 0/no"));
@@ -4900,7 +5014,10 @@ std::string simple_wallet::get_mnemonic_language()
 //----------------------------------------------------------------------------------------------------
 boost::optional<tools::password_container> simple_wallet::get_and_verify_password() const
 {
-  auto pwd_container = default_password_prompter(m_wallet_file.empty());
+  const bool verify = m_wallet_file.empty();
+  auto pwd_container = (m_wallet->is_background_wallet() && m_wallet->background_sync_type() == tools::wallet2::BackgroundSyncCustomPassword)
+    ? background_sync_cache_password_prompter(verify)
+    : default_password_prompter(verify);
   if (!pwd_container)
     return boost::none;
 
@@ -5203,6 +5320,8 @@ boost::optional<epee::wipeable_string> simple_wallet::open_wallet(const boost::p
       prefix = tr("Opened watch-only wallet");
     else if (m_wallet->multisig(&ready, &threshold, &total))
       prefix = (boost::format(tr("Opened %u/%u multisig wallet%s")) % threshold % total % (ready ? "" : " (not yet finalized)")).str();
+    else if (m_wallet->is_background_wallet())
+      prefix = tr("Opened background wallet");
     else
       prefix = tr("Opened wallet");
     message_writer(console_color_white, true) <<
@@ -5411,6 +5530,10 @@ void simple_wallet::stop_background_mining()
 //----------------------------------------------------------------------------------------------------
 void simple_wallet::check_background_mining(const epee::wipeable_string &password)
 {
+  // Background mining can be toggled from the main wallet
+  if (m_wallet->is_background_wallet() || m_wallet->is_background_syncing())
+    return;
+
   tools::wallet2::BackgroundMiningSetupType setup = m_wallet->setup_background_mining();
   if (setup == tools::wallet2::BackgroundMiningNo)
   {
@@ -6275,6 +6398,7 @@ bool simple_wallet::show_blockchain_height(const std::vector<std::string>& args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::rescan_spent(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot rescan spent");
   if (!m_wallet->is_trusted_daemon())
   {
     fail_msg_writer() << tr("this command requires a trusted daemon. Enable with --trusted-daemon");
@@ -6532,10 +6656,27 @@ void simple_wallet::check_for_inactivity_lock(bool user)
           "                ||     ||" << std::endl <<
           "" << std::endl;
     }
+
+    bool started_background_sync = false;
+    if (!m_wallet->is_background_wallet() &&
+        m_wallet->background_sync_type() != tools::wallet2::BackgroundSyncOff)
+    {
+      LOCK_IDLE_SCOPE();
+      m_wallet->start_background_sync();
+      started_background_sync = true;
+    }
+
     while (1)
     {
       const char *inactivity_msg = user ? "" : tr("Locked due to inactivity.");
-      tools::msg_writer() << inactivity_msg << (inactivity_msg[0] ? " " : "") << tr("The wallet password is required to unlock the console.");
+      tools::msg_writer() << inactivity_msg << (inactivity_msg[0] ? " " : "") << (
+        (m_wallet->is_background_wallet() && m_wallet->background_sync_type() == tools::wallet2::BackgroundSyncCustomPassword)
+            ? tr("The background password is required to unlock the console.")
+            : tr("The wallet password is required to unlock the console.")
+      );
+
+      if (m_wallet->is_background_syncing())
+        tools::msg_writer() << tr("\nSyncing in the background while locked...") << std::endl;
 
       const bool show_wallet_name = m_wallet->show_wallet_name_when_locked();
       if (show_wallet_name)
@@ -6548,8 +6689,16 @@ void simple_wallet::check_for_inactivity_lock(bool user)
       }
       try
       {
-        if (get_and_verify_password())
+        const auto pwd_container = get_and_verify_password();
+        if (pwd_container)
+        {
+          if (started_background_sync)
+          {
+            LOCK_IDLE_SCOPE();
+            m_wallet->stop_background_sync(pwd_container->password());
+          }
           break;
+        }
       }
       catch (...) { /* do nothing, just let the loop loop */ }
     }
@@ -6576,6 +6725,7 @@ bool simple_wallet::on_command(bool (simple_wallet::*cmd)(const std::vector<std:
 bool simple_wallet::transfer_main(const std::vector<std::string> &args_, bool called_by_mms)
 {
 //  "transfer [index=<N1>[,<N2>,...]] [<priority>] [<ring_size>] <address> <amount> [<payment_id>]"
+  CHECK_IF_BACKGROUND_SYNCING("cannot transfer");
   if (!try_connect_to_daemon())
     return false;
 
@@ -7004,6 +7154,7 @@ bool simple_wallet::transfer_main(const std::vector<std::string> &args_, bool ca
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::transfer(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot transfer");
   if (args_.size() < 1)
   {
     PRINT_USAGE(USAGE_TRANSFER);
@@ -7016,6 +7167,7 @@ bool simple_wallet::transfer(const std::vector<std::string> &args_)
 
 bool simple_wallet::sweep_unmixable(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sweep");
   if (!try_connect_to_daemon())
     return true;
 
@@ -7123,6 +7275,7 @@ bool simple_wallet::sweep_unmixable(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sweep_main(uint32_t account, uint64_t below, const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sweep");
   auto print_usage = [this, account, below]()
   {
     if (below)
@@ -7404,6 +7557,7 @@ bool simple_wallet::sweep_main(uint32_t account, uint64_t below, const std::vect
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sweep_single(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sweep");
   if (!try_connect_to_daemon())
     return true;
 
@@ -7642,12 +7796,14 @@ bool simple_wallet::sweep_single(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sweep_all(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sweep");
   sweep_main(m_current_subaddress_account, 0, args_);
   return true;
 }
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sweep_account(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sweep");
   auto local_args = args_;
   if (local_args.empty())
   {
@@ -7668,6 +7824,7 @@ bool simple_wallet::sweep_account(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sweep_below(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sweep");
   uint64_t below = 0;
   if (args_.size() < 1)
   {
@@ -7686,6 +7843,7 @@ bool simple_wallet::sweep_below(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::donate(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot donate");
   std::vector<std::string> local_args = args_;
   if(local_args.empty() || local_args.size() > 5)
   {
@@ -7747,6 +7905,7 @@ bool simple_wallet::donate(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::accept_loaded_tx(const std::function<size_t()> get_num_txes, const std::function<const tools::wallet2::tx_construction_data&(size_t)> &get_tx, const std::string &extra_message)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot load tx");
   // gather info to ask the user
   uint64_t amount = 0, amount_to_dests = 0, change = 0;
   size_t min_ring_size = ~0;
@@ -7927,6 +8086,7 @@ bool simple_wallet::sign_transfer(const std::vector<std::string> &args_)
      fail_msg_writer() << tr("This is a watch only wallet");
      return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("cannot sign transfer");
 
   bool export_raw = false;
   std::string unsigned_filename = "unsigned_monero_tx";
@@ -8034,6 +8194,8 @@ std::string get_tx_key_stream(crypto::secret_key tx_key, std::vector<crypto::sec
 
 bool simple_wallet::get_tx_key(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get tx key");
+
   std::vector<std::string> local_args = args_;
 
   if (m_wallet->key_on_device() && m_wallet->get_account().get_device().get_type() != hw::device::TREZOR)
@@ -8074,6 +8236,8 @@ bool simple_wallet::get_tx_key(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::set_tx_key(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot set tx key");
+
   std::vector<std::string> local_args = args_;
 
   if(local_args.size() != 2 && local_args.size() != 3) {
@@ -8150,6 +8314,8 @@ bool simple_wallet::set_tx_key(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::get_tx_proof(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get tx proof");
+
   if (args.size() != 2 && args.size() != 3)
   {
     PRINT_USAGE(USAGE_GET_TX_PROOF);
@@ -8356,6 +8522,7 @@ bool simple_wallet::check_tx_proof(const std::vector<std::string> &args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::get_spend_proof(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get spend proof");
   if (m_wallet->key_on_device())
   {
     fail_msg_writer() << tr("command not supported by HW wallet");
@@ -8440,6 +8607,7 @@ bool simple_wallet::check_spend_proof(const std::vector<std::string> &args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::get_reserve_proof(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get reserve proof");
   if (m_wallet->key_on_device())
   {
     fail_msg_writer() << tr("command not supported by HW wallet");
@@ -9126,6 +9294,8 @@ bool simple_wallet::unspent_outputs(const std::vector<std::string> &args_)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::rescan_blockchain(const std::vector<std::string> &args_)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot rescan");
+
   uint64_t start_height = 0;
   ResetType reset_type = ResetSoft;
 
@@ -9423,6 +9593,7 @@ bool simple_wallet::account(const std::vector<std::string> &args/* = std::vector
   if (command == "new")
   {
     // create a new account and switch to it
+    CHECK_IF_BACKGROUND_SYNCING("cannot create new account");
     std::string label = boost::join(local_args, " ");
     if (label.empty())
       label = tr("(Untitled account)");
@@ -9453,6 +9624,7 @@ bool simple_wallet::account(const std::vector<std::string> &args/* = std::vector
   else if (command == "label" && local_args.size() >= 1)
   {
     // set label of the specified account
+    CHECK_IF_BACKGROUND_SYNCING("cannot modify account");
     uint32_t index_major;
     if (!epee::string_tools::get_xtype_from_string(index_major, local_args[0]))
     {
@@ -9474,6 +9646,7 @@ bool simple_wallet::account(const std::vector<std::string> &args/* = std::vector
   }
   else if (command == "tag" && local_args.size() >= 2)
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot modify account");
     const std::string tag = local_args[0];
     std::set<uint32_t> account_indices;
     for (size_t i = 1; i < local_args.size(); ++i)
@@ -9498,6 +9671,7 @@ bool simple_wallet::account(const std::vector<std::string> &args/* = std::vector
   }
   else if (command == "untag" && local_args.size() >= 1)
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot modify account");
     std::set<uint32_t> account_indices;
     for (size_t i = 0; i < local_args.size(); ++i)
     {
@@ -9521,6 +9695,7 @@ bool simple_wallet::account(const std::vector<std::string> &args/* = std::vector
   }
   else if (command == "tag_description" && local_args.size() >= 1)
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot modify account");
     const std::string tag = local_args[0];
     std::string description;
     if (local_args.size() > 1)
@@ -9638,6 +9813,7 @@ bool simple_wallet::print_address(const std::vector<std::string> &args/* = std::
   }
   else if (local_args[0] == "new")
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot add address");
     local_args.erase(local_args.begin());
     std::string label;
     if (local_args.size() > 0)
@@ -9650,6 +9826,7 @@ bool simple_wallet::print_address(const std::vector<std::string> &args/* = std::
   }
   else if (local_args[0] == "mnew")
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot add addresses");
     local_args.erase(local_args.begin());
     if (local_args.size() != 1)
     {
@@ -9675,6 +9852,7 @@ bool simple_wallet::print_address(const std::vector<std::string> &args/* = std::
   }
   else if (local_args[0] == "one-off")
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot add address");
     local_args.erase(local_args.begin());
     std::string label;
     if (local_args.size() != 2)
@@ -9693,6 +9871,7 @@ bool simple_wallet::print_address(const std::vector<std::string> &args/* = std::
   }
   else if (local_args.size() >= 2 && local_args[0] == "label")
   {
+    CHECK_IF_BACKGROUND_SYNCING("cannot modify address");
     if (!epee::string_tools::get_xtype_from_string(index, local_args[1]))
     {
       fail_msg_writer() << tr("failed to parse index: ") << local_args[1];
@@ -9839,6 +10018,8 @@ bool simple_wallet::print_integrated_address(const std::vector<std::string> &arg
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::address_book(const std::vector<std::string> &args/* = std::vector<std::string>()*/)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get address book");
+
   if (args.size() == 0)
   {
   }
@@ -9899,6 +10080,8 @@ bool simple_wallet::address_book(const std::vector<std::string> &args/* = std::v
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::set_tx_note(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot set tx note");
+
   if (args.size() == 0)
   {
     PRINT_USAGE(USAGE_SET_TX_NOTE);
@@ -9927,6 +10110,8 @@ bool simple_wallet::set_tx_note(const std::vector<std::string> &args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::get_tx_note(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get tx note");
+
   if (args.size() != 1)
   {
     PRINT_USAGE(USAGE_GET_TX_NOTE);
@@ -9952,6 +10137,8 @@ bool simple_wallet::get_tx_note(const std::vector<std::string> &args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::set_description(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot set description");
+
   // 0 arguments allowed, for setting the description to empty string
 
   std::string description = "";
@@ -9968,6 +10155,8 @@ bool simple_wallet::set_description(const std::vector<std::string> &args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::get_description(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot get description");
+
   if (args.size() != 0)
   {
     PRINT_USAGE(USAGE_GET_DESCRIPTION);
@@ -10026,6 +10215,8 @@ bool simple_wallet::wallet_info(const std::vector<std::string> &args)
     type = tr("Watch only");
   else if (m_wallet->multisig(&ready, &threshold, &total))
     type = (boost::format(tr("%u/%u multisig%s")) % threshold % total % (ready ? "" : " (not yet finalized)")).str();
+  else if (m_wallet->is_background_wallet())
+    type = tr("Background wallet");
   else
     type = tr("Normal");
   message_writer() << tr("Type: ") << type;
@@ -10037,6 +10228,7 @@ bool simple_wallet::wallet_info(const std::vector<std::string> &args)
 //----------------------------------------------------------------------------------------------------
 bool simple_wallet::sign(const std::vector<std::string> &args)
 {
+  CHECK_IF_BACKGROUND_SYNCING("cannot sign");
   if (m_wallet->key_on_device())
   {
     fail_msg_writer() << tr("command not supported by HW wallet");
@@ -10144,6 +10336,7 @@ bool simple_wallet::export_key_images(const std::vector<std::string> &args_)
     fail_msg_writer() << tr("command not supported by HW wallet");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("cannot export key images");
   auto args = args_;
 
   if (m_wallet->watch_only())
@@ -10197,6 +10390,7 @@ bool simple_wallet::import_key_images(const std::vector<std::string> &args)
     fail_msg_writer() << tr("command not supported by HW wallet");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("cannot import key images");
   if (!m_wallet->is_trusted_daemon())
   {
     fail_msg_writer() << tr("this command requires a trusted daemon. Enable with --trusted-daemon");
@@ -10305,6 +10499,7 @@ bool simple_wallet::export_outputs(const std::vector<std::string> &args_)
     fail_msg_writer() << tr("command not supported by HW wallet");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("cannot export outputs");
   auto args = args_;
 
   bool all = false;
@@ -10354,6 +10549,7 @@ bool simple_wallet::import_outputs(const std::vector<std::string> &args)
     fail_msg_writer() << tr("command not supported by HW wallet");
     return true;
   }
+  CHECK_IF_BACKGROUND_SYNCING("cannot import outputs");
   if (args.size() != 1)
   {
     PRINT_USAGE(USAGE_IMPORT_OUTPUTS);
diff --git a/src/simplewallet/simplewallet.h b/src/simplewallet/simplewallet.h
index 652708f5a..159da2c45 100644
--- a/src/simplewallet/simplewallet.h
+++ b/src/simplewallet/simplewallet.h
@@ -147,6 +147,7 @@ namespace cryptonote
     bool set_ignore_outputs_above(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_ignore_outputs_below(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_track_uses(const std::vector<std::string> &args = std::vector<std::string>());
+    bool setup_background_sync(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_show_wallet_name_when_locked(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_inactivity_lock_timeout(const std::vector<std::string> &args = std::vector<std::string>());
     bool set_setup_background_mining(const std::vector<std::string> &args = std::vector<std::string>());
diff --git a/src/wallet/api/wallet.cpp b/src/wallet/api/wallet.cpp
index 2ed14bfbd..8fda0bab7 100644
--- a/src/wallet/api/wallet.cpp
+++ b/src/wallet/api/wallet.cpp
@@ -54,6 +54,40 @@ using namespace cryptonote;
 #undef MONERO_DEFAULT_LOG_CATEGORY
 #define MONERO_DEFAULT_LOG_CATEGORY "WalletAPI"
 
+#define LOCK_REFRESH() \
+    bool refresh_enabled = m_refreshEnabled; \
+    m_refreshEnabled = false; \
+    m_wallet->stop(); \
+    m_refreshCV.notify_one(); \
+    boost::mutex::scoped_lock lock(m_refreshMutex); \
+    boost::mutex::scoped_lock lock2(m_refreshMutex2); \
+    epee::misc_utils::auto_scope_leave_caller scope_exit_handler = epee::misc_utils::create_scope_leave_handler([&](){ \
+        /* m_refreshMutex's still locked here */ \
+        if (refresh_enabled) \
+            startRefresh(); \
+    })
+
+#define PRE_VALIDATE_BACKGROUND_SYNC() \
+  do \
+  { \
+    clearStatus(); \
+    if (m_wallet->key_on_device()) \
+    { \
+        setStatusError(tr("HW wallet cannot use background sync")); \
+        return false; \
+    } \
+    if (m_wallet->watch_only()) \
+    { \
+        setStatusError(tr("View only wallet cannot use background sync")); \
+        return false; \
+    } \
+    if (m_wallet->multisig()) \
+    { \
+        setStatusError(tr("Multisig wallet cannot use background sync")); \
+        return false; \
+    } \
+  } while (0)
+
 namespace Monero {
 
 namespace {
@@ -792,6 +826,8 @@ bool WalletImpl::close(bool store)
 
 std::string WalletImpl::seed(const std::string& seed_offset) const
 {
+    if (checkBackgroundSync("cannot get seed"))
+        return std::string();
     epee::wipeable_string seed;
     if (m_wallet)
         m_wallet->get_seed(seed, seed_offset);
@@ -805,6 +841,8 @@ std::string WalletImpl::getSeedLanguage() const
 
 void WalletImpl::setSeedLanguage(const std::string &arg)
 {
+    if (checkBackgroundSync("cannot set seed language"))
+        return;
     m_wallet->set_seed_language(arg);
 }
 
@@ -828,6 +866,8 @@ void WalletImpl::statusWithErrorString(int& status, std::string& errorString) co
 
 bool WalletImpl::setPassword(const std::string &password)
 {
+    if (checkBackgroundSync("cannot change password"))
+        return false;
     clearStatus();
     try {
         m_wallet->change_password(m_wallet->get_wallet_file(), m_password, password);
@@ -988,6 +1028,8 @@ bool WalletImpl::lightWalletImportWalletRequest(std::string &payment_id, uint64_
 
 void WalletImpl::setRefreshFromBlockHeight(uint64_t refresh_from_block_height)
 {
+    if (checkBackgroundSync("cannot change refresh height"))
+        return;
     m_wallet->set_refresh_from_block_height(refresh_from_block_height);
 }
 
@@ -1105,6 +1147,8 @@ void WalletImpl::refreshAsync()
 
 bool WalletImpl::rescanBlockchain()
 {
+    if (checkBackgroundSync("cannot rescan blockchain"))
+        return false;
     clearStatus();
     m_refreshShouldRescan = true;
     doRefresh();
@@ -1113,6 +1157,8 @@ bool WalletImpl::rescanBlockchain()
 
 void WalletImpl::rescanBlockchainAsync()
 {
+    if (checkBackgroundSync("cannot rescan blockchain"))
+        return;
     m_refreshShouldRescan = true;
     refreshAsync();
 }
@@ -1136,7 +1182,7 @@ int WalletImpl::autoRefreshInterval() const
 UnsignedTransaction *WalletImpl::loadUnsignedTx(const std::string &unsigned_filename) {
   clearStatus();
   UnsignedTransactionImpl * transaction = new UnsignedTransactionImpl(*this);
-  if (!m_wallet->load_unsigned_tx(unsigned_filename, transaction->m_unsigned_tx_set)){
+  if (checkBackgroundSync("cannot load tx") || !m_wallet->load_unsigned_tx(unsigned_filename, transaction->m_unsigned_tx_set)){
     setStatusError(tr("Failed to load unsigned transactions"));
     transaction->m_status = UnsignedTransaction::Status::Status_Error;
     transaction->m_errorString = errorString();
@@ -1156,6 +1202,8 @@ UnsignedTransaction *WalletImpl::loadUnsignedTx(const std::string &unsigned_file
 
 bool WalletImpl::submitTransaction(const string &fileName) {
   clearStatus();
+  if (checkBackgroundSync("cannot submit tx"))
+    return false;
   std::unique_ptr<PendingTransactionImpl> transaction(new PendingTransactionImpl(*this));
 
   bool r = m_wallet->load_tx(fileName, transaction->m_pending_tx);
@@ -1179,6 +1227,8 @@ bool WalletImpl::exportKeyImages(const string &filename, bool all)
     setStatusError(tr("Wallet is view only"));
     return false;
   }
+  if (checkBackgroundSync("cannot export key images"))
+    return false;
   
   try
   {
@@ -1199,6 +1249,8 @@ bool WalletImpl::exportKeyImages(const string &filename, bool all)
 
 bool WalletImpl::importKeyImages(const string &filename)
 {
+  if (checkBackgroundSync("cannot import key images"))
+    return false;
   if (!trustedDaemon()) {
     setStatusError(tr("Key images can only be imported with a trusted daemon"));
     return false;
@@ -1222,6 +1274,8 @@ bool WalletImpl::importKeyImages(const string &filename)
 
 bool WalletImpl::exportOutputs(const string &filename, bool all)
 {
+    if (checkBackgroundSync("cannot export outputs"))
+        return false;
     if (m_wallet->key_on_device())
     {
         setStatusError(string(tr("Not supported on HW wallets.")) + filename);
@@ -1252,6 +1306,8 @@ bool WalletImpl::exportOutputs(const string &filename, bool all)
 
 bool WalletImpl::importOutputs(const string &filename)
 {
+    if (checkBackgroundSync("cannot import outputs"))
+        return false;
     if (m_wallet->key_on_device())
     {
         setStatusError(string(tr("Not supported on HW wallets.")) + filename);
@@ -1284,6 +1340,8 @@ bool WalletImpl::importOutputs(const string &filename)
 
 bool WalletImpl::scanTransactions(const std::vector<std::string> &txids)
 {
+    if (checkBackgroundSync("cannot scan transactions"))
+        return false;
     if (txids.empty())
     {
         setStatusError(string(tr("Failed to scan transactions: no transaction ids provided.")));
@@ -1322,8 +1380,86 @@ bool WalletImpl::scanTransactions(const std::vector<std::string> &txids)
     return true;
 }
 
+bool WalletImpl::setupBackgroundSync(const Wallet::BackgroundSyncType background_sync_type, const std::string &wallet_password, const optional<std::string> &background_cache_password)
+{
+    try
+    {
+        PRE_VALIDATE_BACKGROUND_SYNC();
+
+        tools::wallet2::BackgroundSyncType bgs_type;
+        switch (background_sync_type)
+        {
+            case Wallet::BackgroundSync_Off: bgs_type = tools::wallet2::BackgroundSyncOff; break;
+            case Wallet::BackgroundSync_ReusePassword: bgs_type = tools::wallet2::BackgroundSyncReusePassword; break;
+            case Wallet::BackgroundSync_CustomPassword: bgs_type = tools::wallet2::BackgroundSyncCustomPassword; break;
+            default: setStatusError(tr("Unknown background sync type")); return false;
+        }
+
+        boost::optional<epee::wipeable_string> bgc_password = background_cache_password
+            ? boost::optional<epee::wipeable_string>(*background_cache_password)
+            : boost::none;
+
+        LOCK_REFRESH();
+        m_wallet->setup_background_sync(bgs_type, wallet_password, bgc_password);
+    }
+    catch (const std::exception &e)
+    {
+        LOG_ERROR("Failed to setup background sync: " << e.what());
+        setStatusError(string(tr("Failed to setup background sync: ")) + e.what());
+        return false;
+    }
+    return true;
+}
+
+Wallet::BackgroundSyncType WalletImpl::getBackgroundSyncType() const
+{
+    switch (m_wallet->background_sync_type())
+    {
+        case tools::wallet2::BackgroundSyncOff: return Wallet::BackgroundSync_Off;
+        case tools::wallet2::BackgroundSyncReusePassword: return Wallet::BackgroundSync_ReusePassword;
+        case tools::wallet2::BackgroundSyncCustomPassword: return Wallet::BackgroundSync_CustomPassword;
+        default: setStatusError(tr("Unknown background sync type")); return Wallet::BackgroundSync_Off;
+    }
+}
+
+bool WalletImpl::startBackgroundSync()
+{
+    try
+    {
+        PRE_VALIDATE_BACKGROUND_SYNC();
+        LOCK_REFRESH();
+        m_wallet->start_background_sync();
+    }
+    catch (const std::exception &e)
+    {
+        LOG_ERROR("Failed to start background sync: " << e.what());
+        setStatusError(string(tr("Failed to start background sync: ")) + e.what());
+        return false;
+    }
+    return true;
+}
+
+bool WalletImpl::stopBackgroundSync(const std::string &wallet_password)
+{
+    try
+    {
+        PRE_VALIDATE_BACKGROUND_SYNC();
+        LOCK_REFRESH();
+        m_wallet->stop_background_sync(epee::wipeable_string(wallet_password));
+    }
+    catch (const std::exception &e)
+    {
+        LOG_ERROR("Failed to stop background sync: " << e.what());
+        setStatusError(string(tr("Failed to stop background sync: ")) + e.what());
+        return false;
+    }
+    return true;
+}
+
 void WalletImpl::addSubaddressAccount(const std::string& label)
 {
+    if (checkBackgroundSync("cannot add account"))
+        return;
     m_wallet->add_subaddress_account(label);
 }
 size_t WalletImpl::numSubaddressAccounts() const
@@ -1336,10 +1472,14 @@ size_t WalletImpl::numSubaddresses(uint32_t accountIndex) const
 }
 void WalletImpl::addSubaddress(uint32_t accountIndex, const std::string& label)
 {
+    if (checkBackgroundSync("cannot add subbaddress"))
+        return;
     m_wallet->add_subaddress(accountIndex, label);
 }
 std::string WalletImpl::getSubaddressLabel(uint32_t accountIndex, uint32_t addressIndex) const
 {
+    if (checkBackgroundSync("cannot get subbaddress label"))
+        return "";
     try
     {
         return m_wallet->get_subaddress_label({accountIndex, addressIndex});
@@ -1353,6 +1493,8 @@ std::string WalletImpl::getSubaddressLabel(uint32_t accountIndex, uint32_t addre
 }
 void WalletImpl::setSubaddressLabel(uint32_t accountIndex, uint32_t addressIndex, const std::string &label)
 {
+    if (checkBackgroundSync("cannot set subbaddress label"))
+        return;
     try
     {
         return m_wallet->set_subaddress_label({accountIndex, addressIndex}, label);
@@ -1366,12 +1508,16 @@ void WalletImpl::setSubaddressLabel(uint32_t accountIndex, uint32_t addressIndex
 
 MultisigState WalletImpl::multisig() const {
     MultisigState state;
+    if (checkBackgroundSync("cannot use multisig"))
+        return state;
     state.isMultisig = m_wallet->multisig(&state.isReady, &state.threshold, &state.total);
 
     return state;
 }
 
 string WalletImpl::getMultisigInfo() const {
+    if (checkBackgroundSync("cannot use multisig"))
+        return string();
     try {
         clearStatus();
         return m_wallet->get_multisig_first_kex_msg();
@@ -1384,6 +1530,8 @@ string WalletImpl::getMultisigInfo() const {
 }
 
 string WalletImpl::makeMultisig(const vector<string>& info, const uint32_t threshold) {
+    if (checkBackgroundSync("cannot make multisig"))
+        return string();
     try {
         clearStatus();
 
@@ -1524,6 +1672,9 @@ PendingTransaction *WalletImpl::createTransactionMultDest(const std::vector<stri
     PendingTransactionImpl * transaction = new PendingTransactionImpl(*this);
 
     do {
+        if (checkBackgroundSync("cannot create transactions"))
+            break;
+
         std::vector<uint8_t> extra;
         std::string extra_nonce;
         vector<cryptonote::tx_destination_entry> dsts;
@@ -1690,6 +1841,9 @@ PendingTransaction *WalletImpl::createSweepUnmixableTransaction()
     PendingTransactionImpl * transaction = new PendingTransactionImpl(*this);
 
     do {
+        if (checkBackgroundSync("cannot sweep"))
+            break;
+
         try {
             transaction->m_pending_tx = m_wallet->create_unmixable_sweep_transactions();
             pendingTxPostProcess(transaction);
@@ -1823,11 +1977,15 @@ uint32_t WalletImpl::defaultMixin() const
 
 void WalletImpl::setDefaultMixin(uint32_t arg)
 {
+    if (checkBackgroundSync("cannot set default mixin"))
+        return;
     m_wallet->default_mixin(arg);
 }
 
 bool WalletImpl::setCacheAttribute(const std::string &key, const std::string &val)
 {
+    if (checkBackgroundSync("cannot set cache attribute"))
+        return false;
     m_wallet->set_attribute(key, val);
     return true;
 }
@@ -1841,6 +1999,8 @@ std::string WalletImpl::getCacheAttribute(const std::string &key) const
 
 bool WalletImpl::setUserNote(const std::string &txid, const std::string &note)
 {
+    if (checkBackgroundSync("cannot set user note"))
+        return false;
     cryptonote::blobdata txid_data;
     if(!epee::string_tools::parse_hexstr_to_binbuff(txid, txid_data) || txid_data.size() != sizeof(crypto::hash))
       return false;
@@ -1852,6 +2012,8 @@ bool WalletImpl::setUserNote(const std::string &txid, const std::string &note)
 
 std::string WalletImpl::getUserNote(const std::string &txid) const
 {
+    if (checkBackgroundSync("cannot get user note"))
+        return "";
     cryptonote::blobdata txid_data;
     if(!epee::string_tools::parse_hexstr_to_binbuff(txid, txid_data) || txid_data.size() != sizeof(crypto::hash))
       return "";
@@ -1862,6 +2024,9 @@ std::string WalletImpl::getUserNote(const std::string &txid) const
 
 std::string WalletImpl::getTxKey(const std::string &txid_str) const
 {
+    if (checkBackgroundSync("cannot get tx key"))
+        return "";
+
     crypto::hash txid;
     if(!epee::string_tools::hex_to_pod(txid_str, txid))
     {
@@ -1946,6 +2111,9 @@ bool WalletImpl::checkTxKey(const std::string &txid_str, std::string tx_key_str,
 
 std::string WalletImpl::getTxProof(const std::string &txid_str, const std::string &address_str, const std::string &message) const
 {
+    if (checkBackgroundSync("cannot get tx proof"))
+        return "";
+
     crypto::hash txid;
     if (!epee::string_tools::hex_to_pod(txid_str, txid))
     {
@@ -2002,6 +2170,9 @@ bool WalletImpl::checkTxProof(const std::string &txid_str, const std::string &ad
 }
 
 std::string WalletImpl::getSpendProof(const std::string &txid_str, const std::string &message) const {
+    if (checkBackgroundSync("cannot get spend proof"))
+        return "";
+
     crypto::hash txid;
     if(!epee::string_tools::hex_to_pod(txid_str, txid))
     {
@@ -2044,6 +2215,9 @@ bool WalletImpl::checkSpendProof(const std::string &txid_str, const std::string
 }
 
 std::string WalletImpl::getReserveProof(bool all, uint32_t account_index, uint64_t amount, const std::string &message) const {
+    if (checkBackgroundSync("cannot get reserve proof"))
+        return "";
+
     try
     {
         clearStatus();
@@ -2090,6 +2264,9 @@ bool WalletImpl::checkReserveProof(const std::string &address, const std::string
 
 std::string WalletImpl::signMessage(const std::string &message, const std::string &address)
 {
+    if (checkBackgroundSync("cannot sign message"))
+        return "";
+
     if (address.empty()) {
         return m_wallet->sign(message, tools::wallet2::sign_with_spend_key);
     }
@@ -2217,6 +2394,16 @@ bool WalletImpl::isDeterministic() const
     return m_wallet->is_deterministic();
 }
 
+bool WalletImpl::isBackgroundSyncing() const
+{
+    return m_wallet->is_background_syncing();
+}
+
+bool WalletImpl::isBackgroundWallet() const
+{
+    return m_wallet->is_background_wallet();
+}
+
 void WalletImpl::clearStatus() const
 {
     boost::lock_guard<boost::mutex> l(m_statusMutex);
@@ -2285,9 +2472,7 @@ void WalletImpl::doRefresh()
             if(rescan)
                 m_wallet->rescan_blockchain(false);
             m_wallet->refresh(trustedDaemon());
-            if (!m_synchronized) {
-                m_synchronized = true;
-            }
+            m_synchronized = m_wallet->is_synced();
             // assuming if we have empty history, it wasn't initialized yet
             // for further history changes client need to update history in
             // "on_money_received" and "on_money_sent" callbacks
@@ -2391,6 +2576,24 @@ bool WalletImpl::doInit(const string &daemon_address, const std::string &proxy_a
     return true;
 }
 
+bool WalletImpl::checkBackgroundSync(const std::string &message) const
+{
+    clearStatus();
+    if (m_wallet->is_background_wallet())
+    {
+        LOG_ERROR("Background wallets " + message);
+        setStatusError(tr("Background wallets ") + message);
+        return true;
+    }
+    if (m_wallet->is_background_syncing())
+    {
+        LOG_ERROR(message + " while background syncing");
+        setStatusError(message + tr(" while background syncing. Stop background syncing first."));
+        return true;
+    }
+    return false;
+}
+
 bool WalletImpl::parse_uri(const std::string &uri, std::string &address, std::string &payment_id, uint64_t &amount, std::string &tx_description, std::string &recipient_name, std::vector<std::string> &unknown_parameters, std::string &error)
 {
     return m_wallet->parse_uri(uri, address, payment_id, amount, tx_description, recipient_name, unknown_parameters, error);
@@ -2409,6 +2612,8 @@ std::string WalletImpl::getDefaultDataDir() const
 bool WalletImpl::rescanSpent()
 {
   clearStatus();
+  if (checkBackgroundSync("cannot rescan spent"))
+    return false;
   if (!trustedDaemon()) {
     setStatusError(tr("Rescan spent can only be used with a trusted daemon"));
     return false;
diff --git a/src/wallet/api/wallet.h b/src/wallet/api/wallet.h
index ec2d7e9b3..1f199a72c 100644
--- a/src/wallet/api/wallet.h
+++ b/src/wallet/api/wallet.h
@@ -171,6 +171,13 @@ public:
     bool importOutputs(const std::string &filename) override;
     bool scanTransactions(const std::vector<std::string> &txids) override;
 
+    bool setupBackgroundSync(const BackgroundSyncType background_sync_type, const std::string &wallet_password, const optional<std::string> &background_cache_password = optional<std::string>()) override;
+    BackgroundSyncType getBackgroundSyncType() const override;
+    bool startBackgroundSync() override;
+    bool stopBackgroundSync(const std::string &wallet_password) override;
+    bool isBackgroundSyncing() const override;
+    bool isBackgroundWallet() const override;
+
     virtual void disposeTransaction(PendingTransaction * t) override;
     virtual uint64_t estimateTransactionFee(const std::vector<std::pair<std::string, uint64_t>> &destinations,
                                             PendingTransaction::Priority priority) const override;
@@ -239,6 +246,7 @@ private:
     bool isNewWallet() const;
     void pendingTxPostProcess(PendingTransactionImpl * pending);
     bool doInit(const std::string &daemon_address, const std::string &proxy_address, uint64_t upper_transaction_size_limit = 0, bool ssl = false);
+    bool checkBackgroundSync(const std::string &message) const;
 
 private:
     friend class PendingTransactionImpl;
@@ -253,6 +261,10 @@ private:
     mutable boost::mutex m_statusMutex;
     mutable int m_status;
     mutable std::string m_errorString;
+    // TODO: harden password handling in the wallet API, see relevant discussion
+    // https://github.com/monero-project/monero-gui/issues/1537
+    // https://github.com/feather-wallet/feather/issues/72#issuecomment-1405602142
+    // https://github.com/monero-project/monero/pull/8619#issuecomment-1632951461
     std::string m_password;
     std::unique_ptr<TransactionHistoryImpl> m_history;
     std::unique_ptr<Wallet2CallbackImpl> m_wallet2Callback;
diff --git a/src/wallet/api/wallet2_api.h b/src/wallet/api/wallet2_api.h
index 71991df0d..e349df176 100644
--- a/src/wallet/api/wallet2_api.h
+++ b/src/wallet/api/wallet2_api.h
@@ -445,6 +445,12 @@ struct Wallet
         ConnectionStatus_WrongVersion
     };
 
+    enum BackgroundSyncType {
+        BackgroundSync_Off = 0,
+        BackgroundSync_ReusePassword = 1,
+        BackgroundSync_CustomPassword = 2
+    };
+
     virtual ~Wallet() = 0;
     virtual std::string seed(const std::string& seed_offset = "") const = 0;
     virtual std::string getSeedLanguage() const = 0;
@@ -936,6 +942,42 @@ struct Wallet
      */
     virtual bool scanTransactions(const std::vector<std::string> &txids) = 0;
 
+    /*!
+     * \brief setupBackgroundSync       - setup background sync mode with just a view key
+     * \param background_sync_type      - the mode the wallet background syncs in
+     * \param wallet_password
+     * \param background_cache_password - custom password to encrypt background cache, only needed for custom password background sync type
+     * \return                          - true on success
+     */
+    virtual bool setupBackgroundSync(const BackgroundSyncType background_sync_type, const std::string &wallet_password, const optional<std::string> &background_cache_password) = 0;
+
+    /*!
+     * \brief getBackgroundSyncType     - get mode the wallet background syncs in
+     * \return                          - the type, or off if type is unknown
+     */
+    virtual BackgroundSyncType getBackgroundSyncType() const = 0;
+
+    /**
+     * @brief startBackgroundSync - sync the chain in the background with just view key
+     */
+    virtual bool startBackgroundSync() = 0;
+
+    /**
+     * @brief stopBackgroundSync  - bring back spend key and process background synced txs
+     * \param wallet_password
+     */
+    virtual bool stopBackgroundSync(const std::string &wallet_password) = 0;
+
+    /**
+     * @brief isBackgroundSyncing - returns true if the wallet is background syncing
+     */
+    virtual bool isBackgroundSyncing() const = 0;
+
+    /**
+     * @brief isBackgroundWallet - returns true if the wallet is a background wallet
+     */
+    virtual bool isBackgroundWallet() const = 0;
+
     virtual TransactionHistory * history() = 0;
     virtual AddressBook * addressBook() = 0;
     virtual Subaddress * subaddress() = 0;
diff --git a/src/wallet/wallet2.cpp b/src/wallet/wallet2.cpp
index bee27e12a..dfb8b23cb 100644
--- a/src/wallet/wallet2.cpp
+++ b/src/wallet/wallet2.cpp
@@ -157,6 +157,8 @@ static const std::string MULTISIG_SIGNATURE_MAGIC = "SigMultisigPkV1";
 
 static const std::string ASCII_OUTPUT_MAGIC = "MoneroAsciiDataV1";
 
+static const std::string BACKGROUND_WALLET_SUFFIX = ".background";
+
 boost::mutex tools::wallet2::default_daemon_address_lock;
 std::string tools::wallet2::default_daemon_address = "";
 
@@ -1009,14 +1011,14 @@ uint64_t num_priv_multisig_keys_post_setup(uint64_t threshold, uint64_t total)
  * @param keys_data_key the chacha key that encrypts wallet keys files
  * @return crypto::chacha_key the chacha key that encrypts the wallet cache files
  */
-crypto::chacha_key derive_cache_key(const crypto::chacha_key& keys_data_key)
+crypto::chacha_key derive_cache_key(const crypto::chacha_key& keys_data_key, const unsigned char domain_separator)
 {
   static_assert(HASH_SIZE == sizeof(crypto::chacha_key), "Mismatched sizes of hash and chacha key");
 
   crypto::chacha_key cache_key;
   epee::mlocked<tools::scrubbed_arr<char, HASH_SIZE+1>> cache_key_data;
   memcpy(cache_key_data.data(), &keys_data_key, HASH_SIZE);
-  cache_key_data[HASH_SIZE] = config::HASH_KEY_WALLET_CACHE;
+  cache_key_data[HASH_SIZE] = domain_separator;
   cn_fast_hash(cache_key_data.data(), HASH_SIZE+1, (crypto::hash&) cache_key);
 
   return cache_key;
@@ -1104,7 +1106,7 @@ wallet_keys_unlocker::wallet_keys_unlocker(wallet2 &w, const boost::optional<too
   boost::lock_guard<boost::mutex> lock(lockers_lock);
   if (lockers++ > 0)
     locked = false;
-  if (!locked || w.is_unattended() || w.ask_password() != tools::wallet2::AskPasswordToDecrypt || w.watch_only())
+  if (!locked || w.is_unattended() || w.ask_password() != tools::wallet2::AskPasswordToDecrypt || w.watch_only() || w.is_background_syncing())
   {
     locked = false;
     return;
@@ -1221,6 +1223,11 @@ wallet2::wallet2(network_type nettype, uint64_t kdf_rounds, bool unattended, std
   m_ignore_outputs_above(MONEY_SUPPLY),
   m_ignore_outputs_below(0),
   m_track_uses(false),
+  m_is_background_wallet(false),
+  m_background_sync_type(BackgroundSyncOff),
+  m_background_syncing(false),
+  m_processing_background_cache(false),
+  m_custom_background_key(boost::none),
   m_show_wallet_name_when_locked(false),
   m_inactivity_lock_timeout(DEFAULT_INACTIVITY_LOCK_TIMEOUT),
   m_setup_background_mining(BackgroundMiningMaybe),
@@ -1869,6 +1876,9 @@ bool has_nonrequested_tx_at_height_or_above_requested(uint64_t height, const std
 //----------------------------------------------------------------------------------------------------
 void wallet2::scan_tx(const std::unordered_set<crypto::hash> &txids)
 {
+  THROW_WALLET_EXCEPTION_IF(m_background_syncing || m_is_background_wallet, error::wallet_internal_error,
+    "cannot scan tx from background wallet");
+
   // Get the transactions from daemon in batches sorted lowest height to highest
   tx_entry_data txs_to_scan = get_tx_entries(txids);
   if (txs_to_scan.tx_entries.empty())
@@ -2176,11 +2186,11 @@ void wallet2::scan_output(const cryptonote::transaction &tx, bool miner_tx, cons
   THROW_WALLET_EXCEPTION_IF(i >= tx.vout.size(), error::wallet_internal_error, "Invalid vout index");
 
   // if keys are encrypted, ask for password
-  if (m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only && !m_multisig_rescan_k)
+  if (m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only && !m_multisig_rescan_k && !m_background_syncing)
   {
     static critical_section password_lock;
     CRITICAL_REGION_LOCAL(password_lock);
-    if (!m_encrypt_keys_after_refresh)
+    if (!m_encrypt_keys_after_refresh && !m_processing_background_cache)
     {
       boost::optional<epee::wipeable_string> pwd = m_callback->on_get_password(pool ? "output found in pool" : "output received");
       THROW_WALLET_EXCEPTION_IF(!pwd, error::password_needed, tr("Password is needed to compute key image for incoming monero"));
@@ -2192,7 +2202,7 @@ void wallet2::scan_output(const cryptonote::transaction &tx, bool miner_tx, cons
   crypto::public_key output_public_key;
   THROW_WALLET_EXCEPTION_IF(!get_output_public_key(tx.vout[i], output_public_key), error::wallet_internal_error, "Failed to get output public key");
 
-  if (m_multisig)
+  if (m_multisig || m_background_syncing/*no spend key*/)
   {
     tx_scan_info.in_ephemeral.pub = output_public_key;
     tx_scan_info.in_ephemeral.sec = crypto::null_skey;
@@ -2449,6 +2459,22 @@ void wallet2::process_new_transaction(const crypto::hash &txid, const cryptonote
         THROW_WALLET_EXCEPTION_IF(tx.vout.size() != o_indices.size(), error::wallet_internal_error,
             "transactions outputs size=" + std::to_string(tx.vout.size()) +
             " not match with daemon response size=" + std::to_string(o_indices.size()));
+
+        // we're going to re-process this receive when background sync is disabled
+        if (m_background_syncing && m_background_sync_data.txs.find(txid) == m_background_sync_data.txs.end())
+        {
+          size_t bgs_idx = m_background_sync_data.txs.size();
+          background_synced_tx_t bgs_tx = {
+            .index_in_background_sync_data = bgs_idx,
+            .tx                            = tx,
+            .output_indices                = o_indices,
+            .height                        = height,
+            .block_timestamp               = ts,
+            .double_spend_seen             = double_spend_seen
+          };
+          LOG_PRINT_L2("Adding received tx " << txid << " to background sync data (idx=" << bgs_idx << ")");
+          m_background_sync_data.txs.insert({txid, std::move(bgs_tx)});
+        }
       }
 
       for(size_t o: outs)
@@ -2474,7 +2500,7 @@ void wallet2::process_new_transaction(const crypto::hash &txid, const cryptonote
 	    td.m_tx = (const cryptonote::transaction_prefix&)tx;
 	    td.m_txid = txid;
             td.m_key_image = tx_scan_info[o].ki;
-            td.m_key_image_known = !m_watch_only && !m_multisig;
+            td.m_key_image_known = !m_watch_only && !m_multisig && !m_background_syncing;
             if (!td.m_key_image_known)
             {
               // we might have cold signed, and have a mapping to key images
@@ -2664,10 +2690,25 @@ void wallet2::process_new_transaction(const crypto::hash &txid, const cryptonote
         set_spent(it->second, height);
         if (!ignore_callbacks && 0 != m_callback)
           m_callback->on_money_spent(height, txid, tx, amount, tx, td.m_subaddr_index);
+
+        if (m_background_syncing && m_background_sync_data.txs.find(txid) == m_background_sync_data.txs.end())
+        {
+          size_t bgs_idx = m_background_sync_data.txs.size();
+          background_synced_tx_t bgs_tx = {
+            .index_in_background_sync_data = bgs_idx,
+            .tx                            = tx,
+            .output_indices                = o_indices,
+            .height                        = height,
+            .block_timestamp               = ts,
+            .double_spend_seen             = double_spend_seen
+          };
+          LOG_PRINT_L2("Adding spent tx " << txid << " to background sync data (idx=" << bgs_idx << ")");
+          m_background_sync_data.txs.insert({txid, std::move(bgs_tx)});
+        }
       }
     }
 
-    if (!pool && m_track_uses)
+    if (!pool && (m_track_uses || (m_background_syncing && it == m_key_images.end())))
     {
       PERF_TIMER(track_uses);
       const uint64_t amount = in_to_key.amount;
@@ -2681,7 +2722,27 @@ void wallet2::process_new_transaction(const crypto::hash &txid, const cryptonote
           {
             size_t idx = i->second;
             THROW_WALLET_EXCEPTION_IF(idx >= m_transfers.size(), error::wallet_internal_error, "Output tracker cache index out of range");
-            m_transfers[idx].m_uses.push_back(std::make_pair(height, txid));
+
+            if (m_track_uses)
+              m_transfers[idx].m_uses.push_back(std::make_pair(height, txid));
+
+            // We'll re-process all txs which *might* be spends when we disable
+            // background sync and retrieve the spend key. We don't know if an
+            // output is a spend in this tx if we don't know its key image.
+            if (m_background_syncing && !m_transfers[idx].m_key_image_known && m_background_sync_data.txs.find(txid) == m_background_sync_data.txs.end())
+            {
+              size_t bgs_idx = m_background_sync_data.txs.size();
+              background_synced_tx_t bgs_tx = {
+                .index_in_background_sync_data = bgs_idx,
+                .tx                            = tx,
+                .output_indices                = o_indices,
+                .height                        = height,
+                .block_timestamp               = ts,
+                .double_spend_seen             = double_spend_seen
+              };
+              LOG_PRINT_L2("Adding plausible spent tx " << txid << " to background sync data (idx=" << bgs_idx << ")");
+              m_background_sync_data.txs.insert({txid, std::move(bgs_tx)});
+            }
           }
         }
       }
@@ -2691,7 +2752,24 @@ void wallet2::process_new_transaction(const crypto::hash &txid, const cryptonote
           continue;
         for (uint64_t offset: offsets)
           if (offset == td.m_global_output_index)
-            td.m_uses.push_back(std::make_pair(height, txid));
+          {
+            if (m_track_uses)
+              td.m_uses.push_back(std::make_pair(height, txid));
+            if (m_background_syncing && !td.m_key_image_known && m_background_sync_data.txs.find(txid) == m_background_sync_data.txs.end())
+            {
+              size_t bgs_idx = m_background_sync_data.txs.size();
+              background_synced_tx_t bgs_tx = {
+                .index_in_background_sync_data = bgs_idx,
+                .tx                            = tx,
+                .output_indices                = o_indices,
+                .height                        = height,
+                .block_timestamp               = ts,
+                .double_spend_seen             = double_spend_seen
+              };
+              LOG_PRINT_L2("Adding plausible spent tx " << txid << " to background sync data (idx=" << bgs_idx << ")");
+              m_background_sync_data.txs.insert({txid, std::move(bgs_tx)});
+            }
+          }
       }
     }
   }
@@ -3066,8 +3144,8 @@ void wallet2::pull_blocks(bool first, bool try_incremental, uint64_t start_heigh
   req.start_height = start_height;
   req.no_miner_tx = m_refresh_type == RefreshNoCoinbase;
 
-  req.requested_info = first ? COMMAND_RPC_GET_BLOCKS_FAST::BLOCKS_AND_POOL : COMMAND_RPC_GET_BLOCKS_FAST::BLOCKS_ONLY;
-  if (try_incremental)
+  req.requested_info = (first && !m_background_syncing) ? COMMAND_RPC_GET_BLOCKS_FAST::BLOCKS_AND_POOL : COMMAND_RPC_GET_BLOCKS_FAST::BLOCKS_ONLY;
+  if (try_incremental && !m_background_syncing)
     req.pool_info_since = m_pool_info_query_time;
 
   {
@@ -3094,7 +3172,7 @@ void wallet2::pull_blocks(bool first, bool try_incremental, uint64_t start_heigh
       << ", height " << blocks_start_height + blocks.size() << ", node height " << res.current_height
       << ", pool info " << static_cast<unsigned int>(res.pool_info_extent));
 
-  if (first)
+  if (first && !m_background_syncing)
   {
     if (res.pool_info_extent != COMMAND_RPC_GET_BLOCKS_FAST::NONE)
     {
@@ -3606,6 +3684,9 @@ void wallet2::process_unconfirmed_transfer(bool incremental, const crypto::hash
 // incremental update anymore, because with that we might miss some txs altogether.
 void wallet2::update_pool_state(std::vector<std::tuple<cryptonote::transaction, crypto::hash, bool>> &process_txs, bool refreshed, bool try_incremental)
 {
+  process_txs.clear();
+  if (m_background_syncing)
+    return;
   bool updated = false;
   if (m_pool_info_query_time != 0 && try_incremental)
   {
@@ -4177,6 +4258,8 @@ void wallet2::refresh(bool trusted_daemon, uint64_t start_height, uint64_t & blo
   }
 
   m_first_refresh_done = true;
+  if (m_background_syncing || m_is_background_wallet)
+    m_background_sync_data.first_refresh_done = true;
 
   LOG_PRINT_L1("Refresh done, blocks received: " << blocks_fetched << ", balance (all accounts): " << print_money(balance_all(false)) << ", unlocked: " << print_money(unlocked_balance_all(false)));
 }
@@ -4262,6 +4345,14 @@ wallet2::detached_blockchain_data wallet2::detach_blockchain(uint64_t height, st
       td.m_uses.pop_back();
   }
 
+  for (auto it = m_background_sync_data.txs.begin(); it != m_background_sync_data.txs.end(); )
+  {
+    if(height <= it->second.height)
+      it = m_background_sync_data.txs.erase(it);
+    else
+      ++it;
+  }
+
   if (output_tracker_cache)
     output_tracker_cache->clear();
 
@@ -4336,8 +4427,12 @@ void wallet2::handle_reorg(uint64_t height, std::map<std::pair<uint64_t, uint64_
   //               C
   THROW_WALLET_EXCEPTION_IF(height < m_blockchain.offset() && m_blockchain.size() > m_blockchain.offset(),
       error::wallet_internal_error, "Daemon claims reorg below last checkpoint");
+
   detached_blockchain_data dbd = detach_blockchain(height, output_tracker_cache);
 
+  if (m_background_syncing && height < m_background_sync_data.start_height)
+    m_background_sync_data.start_height = height;
+
   if (m_callback)
     m_callback->on_reorg(height, dbd.detached_blockchain.size(), dbd.detached_tx_hashes.size());
 }
@@ -4347,6 +4442,7 @@ bool wallet2::deinit()
   if(m_is_initialized) {
     m_is_initialized = false;
     unlock_keys_file();
+    unlock_background_keys_file();
     m_account.deinit();
   }
   return true;
@@ -4373,6 +4469,7 @@ bool wallet2::clear()
   m_device_last_key_image_sync = 0;
   m_pool_info_query_time = 0;
   m_skip_to_height = 0;
+  m_background_sync_data = background_sync_data_t{};
   return true;
 }
 //----------------------------------------------------------------------------------------------------
@@ -4391,13 +4488,30 @@ void wallet2::clear_soft(bool keep_key_images)
   m_scanned_pool_txs[1].clear();
   m_pool_info_query_time = 0;
   m_skip_to_height = 0;
+  m_background_sync_data = background_sync_data_t{};
 
   cryptonote::block b;
   generate_genesis(b);
   m_blockchain.push_back(get_block_hash(b));
   m_last_block_reward = cryptonote::get_outs_money_amount(b.miner_tx);
 }
-
+//----------------------------------------------------------------------------------------------------
+void wallet2::clear_user_data()
+{
+  for (auto i = m_confirmed_txs.begin(); i != m_confirmed_txs.end(); ++i)
+    i->second.m_dests.clear();
+  for (auto i = m_unconfirmed_txs.begin(); i != m_unconfirmed_txs.end(); ++i)
+    i->second.m_dests.clear();
+  for (auto i = m_transfers.begin(); i != m_transfers.end(); ++i)
+    i->m_frozen = false;
+  m_tx_keys.clear();
+  m_tx_notes.clear();
+  m_address_book.clear();
+  m_subaddress_labels.clear();
+  m_attributes.clear();
+  m_account_tags = std::pair<serializable_map<std::string, std::string>, std::vector<std::string>>();
+}
+//----------------------------------------------------------------------------------------------------
 /*!
  * \brief Stores wallet information to wallet file.
  * \param  keys_file_name Name of wallet file
@@ -4409,16 +4523,35 @@ bool wallet2::store_keys(const std::string& keys_file_name, const epee::wipeable
 {
   boost::optional<wallet2::keys_file_data> keys_file_data = get_keys_file_data(password, watch_only);
   CHECK_AND_ASSERT_MES(keys_file_data != boost::none, false, "failed to generate wallet keys data");
-
+  return store_keys_file_data(keys_file_name, keys_file_data.get());
+}
+//----------------------------------------------------------------------------------------------------
+bool wallet2::store_keys(const std::string& keys_file_name, const crypto::chacha_key& key, bool watch_only, bool background_keys_file)
+{
+  boost::optional<wallet2::keys_file_data> keys_file_data = get_keys_file_data(key, watch_only, background_keys_file);
+  CHECK_AND_ASSERT_MES(keys_file_data != boost::none, false, "failed to generate wallet keys data");
+  return store_keys_file_data(keys_file_name, keys_file_data.get(), background_keys_file);
+}
+//----------------------------------------------------------------------------------------------------
+bool wallet2::store_keys_file_data(const std::string& keys_file_name, wallet2::keys_file_data &keys_file_data, bool background_keys_file)
+{
   std::string tmp_file_name = keys_file_name + ".new";
   std::string buf;
-  bool r = ::serialization::dump_binary(keys_file_data.get(), buf);
+  bool r = ::serialization::dump_binary(keys_file_data, buf);
   r = r && save_to_file(tmp_file_name, buf);
   CHECK_AND_ASSERT_MES(r, false, "failed to generate wallet keys file " << tmp_file_name);
 
-  unlock_keys_file();
+  if (!background_keys_file)
+    unlock_keys_file();
+  else
+    unlock_background_keys_file();
+
   std::error_code e = tools::replace_file(tmp_file_name, keys_file_name);
-  lock_keys_file();
+
+  if (!background_keys_file)
+    lock_keys_file();
+  else
+    lock_background_keys_file(keys_file_name);
 
   if (e) {
     boost::filesystem::remove(tmp_file_name);
@@ -4431,25 +4564,26 @@ bool wallet2::store_keys(const std::string& keys_file_name, const epee::wipeable
 //----------------------------------------------------------------------------------------------------
 boost::optional<wallet2::keys_file_data> wallet2::get_keys_file_data(const epee::wipeable_string& password, bool watch_only)
 {
+  crypto::chacha_key key;
+  crypto::generate_chacha_key(password.data(), password.size(), key, m_kdf_rounds);
+  verify_password_with_cached_key(key);
+  return get_keys_file_data(key, watch_only);
+}
+//----------------------------------------------------------------------------------------------------
+boost::optional<wallet2::keys_file_data> wallet2::get_keys_file_data(const crypto::chacha_key& key, bool watch_only, bool background_keys_file)
+{
   epee::byte_slice account_data;
   std::string multisig_signers;
   std::string multisig_derivations;
   cryptonote::account_base account = m_account;
 
-  crypto::chacha_key key;
-  crypto::generate_chacha_key(password.data(), password.size(), key, m_kdf_rounds);
-
-  // We use m_cache_key as a deterministic test to see if given key corresponds to original password
-  const crypto::chacha_key cache_key = derive_cache_key(key);
-  THROW_WALLET_EXCEPTION_IF(cache_key != m_cache_key, error::invalid_password);
-
   if (m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only)
   {
     account.encrypt_viewkey(key);
     account.decrypt_keys(key);
   }
 
-  if (watch_only)
+  if (watch_only || background_keys_file)
     account.forget_spend_key();
 
   account.encrypt_keys(key);
@@ -4584,6 +4718,9 @@ boost::optional<wallet2::keys_file_data> wallet2::get_keys_file_data(const epee:
   value2.SetInt(m_track_uses ? 1 : 0);
   json.AddMember("track_uses", value2, json.GetAllocator());
 
+  value2.SetInt(m_background_sync_type);
+  json.AddMember("background_sync_type", value2, json.GetAllocator());
+
   value2.SetInt(m_show_wallet_name_when_locked ? 1 : 0);
   json.AddMember("show_wallet_name_when_locked", value2, json.GetAllocator());
 
@@ -4641,6 +4778,12 @@ boost::optional<wallet2::keys_file_data> wallet2::get_keys_file_data(const epee:
   value2.SetInt(m_enable_multisig ? 1 : 0);
   json.AddMember("enable_multisig", value2, json.GetAllocator());
 
+  if (m_background_sync_type == BackgroundSyncCustomPassword && !background_keys_file && m_custom_background_key)
+  {
+    value.SetString(reinterpret_cast<const char*>(m_custom_background_key.get().data()), m_custom_background_key.get().size());
+    json.AddMember("custom_background_key", value, json.GetAllocator());
+  }
+
   // Serialize the JSON object
   rapidjson::StringBuffer buffer;
   rapidjson::Writer<rapidjson::StringBuffer> writer(buffer);
@@ -4667,13 +4810,81 @@ void wallet2::setup_keys(const epee::wipeable_string &password)
     m_account.decrypt_viewkey(key);
   }
 
-  m_cache_key = derive_cache_key(key);
+  m_cache_key = derive_cache_key(key, config::HASH_KEY_WALLET_CACHE);
 
   get_ringdb_key();
 }
 //----------------------------------------------------------------------------------------------------
+void validate_background_cache_password_usage(const tools::wallet2::BackgroundSyncType background_sync_type, const boost::optional<epee::wipeable_string> &background_cache_password, const bool multisig, const bool watch_only, const bool key_on_device)
+{
+  THROW_WALLET_EXCEPTION_IF(multisig || watch_only || key_on_device, error::wallet_internal_error, multisig
+      ? "Background sync not implemented for multisig wallets" : watch_only
+      ? "Background sync not implemented for view only wallets"
+      : "Background sync not implemented for HW wallets");
+
+  switch (background_sync_type)
+  {
+    case tools::wallet2::BackgroundSyncOff:
+    {
+      THROW_WALLET_EXCEPTION(error::wallet_internal_error, "background sync is not enabled");
+      break;
+    }
+    case tools::wallet2::BackgroundSyncReusePassword:
+    {
+      THROW_WALLET_EXCEPTION_IF(background_cache_password, error::wallet_internal_error,
+          "unexpected custom background cache password");
+      break;
+    }
+    case tools::wallet2::BackgroundSyncCustomPassword:
+    {
+      THROW_WALLET_EXCEPTION_IF(!background_cache_password, error::wallet_internal_error,
+          "expected custom background cache password");
+      break;
+    }
+    default: THROW_WALLET_EXCEPTION(error::wallet_internal_error, "unknown background sync type");
+  }
+}
+//----------------------------------------------------------------------------------------------------
+void get_custom_background_key(const epee::wipeable_string &password, crypto::chacha_key &custom_background_key, const uint64_t kdf_rounds)
+{
+  crypto::chacha_key key;
+  crypto::generate_chacha_key(password.data(), password.size(), key, kdf_rounds);
+  custom_background_key = derive_cache_key(key, config::HASH_KEY_BACKGROUND_KEYS_FILE);
+}
+//----------------------------------------------------------------------------------------------------
+const crypto::chacha_key wallet2::get_cache_key()
+{
+  if (m_background_sync_type == BackgroundSyncCustomPassword && m_background_syncing)
+  {
+    THROW_WALLET_EXCEPTION_IF(!m_custom_background_key, error::wallet_internal_error, "Custom background key not set");
+    // Domain separate keys used to encrypt background keys file and cache
+    return derive_cache_key(m_custom_background_key.get(), config::HASH_KEY_BACKGROUND_CACHE);
+  }
+  else
+  {
+    return m_cache_key;
+  }
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::verify_password_with_cached_key(const epee::wipeable_string &password)
+{
+  crypto::chacha_key key;
+  crypto::generate_chacha_key(password.data(), password.size(), key, m_kdf_rounds);
+  verify_password_with_cached_key(key);
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::verify_password_with_cached_key(const crypto::chacha_key &key)
+{
+  // We use m_cache_key as a deterministic test to see if given key corresponds to original password
+  const crypto::chacha_key cache_key = derive_cache_key(key, config::HASH_KEY_WALLET_CACHE);
+  THROW_WALLET_EXCEPTION_IF(cache_key != m_cache_key, error::invalid_password);
+}
+//----------------------------------------------------------------------------------------------------
 void wallet2::change_password(const std::string &filename, const epee::wipeable_string &original_password, const epee::wipeable_string &new_password)
 {
+  THROW_WALLET_EXCEPTION_IF(m_background_syncing || m_is_background_wallet, error::wallet_internal_error,
+      "cannot change password from background wallet");
+
   if (m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only)
     decrypt_keys(original_password);
   setup_keys(new_password);
@@ -4732,8 +4943,24 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
   std::string account_data;
   account_data.resize(keys_file_data.account_data.size());
   crypto::chacha20(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
-  if (json.Parse(account_data.c_str()).HasParseError() || !json.IsObject())
+  const bool try_v0_format = json.Parse(account_data.c_str()).HasParseError() || !json.IsObject();
+  if (try_v0_format)
     crypto::chacha8(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
+
+  // Check if it's a background keys file if both of the above formats fail
+  {
+    m_is_background_wallet = false;
+    m_background_syncing = false;
+    cryptonote::account_base account_data_check;
+    if (try_v0_format && !epee::serialization::load_t_from_binary(account_data_check, account_data))
+    {
+      get_custom_background_key(password, key, m_kdf_rounds);
+      crypto::chacha20(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
+      m_is_background_wallet = !json.Parse(account_data.c_str()).HasParseError() && json.IsObject();
+      m_background_syncing = m_is_background_wallet; // start a background wallet background syncing
+    }
+  }
+
   // The contents should be JSON if the wallet follows the new format.
   if (json.Parse(account_data.c_str()).HasParseError())
   {
@@ -4771,6 +4998,7 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
     m_ignore_outputs_above = MONEY_SUPPLY;
     m_ignore_outputs_below = 0;
     m_track_uses = false;
+    m_background_sync_type = BackgroundSyncOff;
     m_show_wallet_name_when_locked = false;
     m_inactivity_lock_timeout = DEFAULT_INACTIVITY_LOCK_TIMEOUT;
     m_setup_background_mining = BackgroundMiningMaybe;
@@ -4788,6 +5016,7 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
     m_credits_target = 0;
     m_enable_multisig = false;
     m_allow_mismatched_daemon_version = false;
+    m_custom_background_key = boost::none;
   }
   else if(json.IsObject())
   {
@@ -5024,6 +5253,39 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
     m_credits_target = field_credits_target;
     GET_FIELD_FROM_JSON_RETURN_ON_ERROR(json, enable_multisig, int, Int, false, false);
     m_enable_multisig = field_enable_multisig;
+
+    GET_FIELD_FROM_JSON_RETURN_ON_ERROR(json, background_sync_type, BackgroundSyncType, Int, false, BackgroundSyncOff);
+    m_background_sync_type = field_background_sync_type;
+
+    // Load encryption key used to encrypt background cache
+    crypto::chacha_key custom_background_key;
+    m_custom_background_key = boost::none;
+    if (m_background_sync_type == BackgroundSyncCustomPassword && !m_is_background_wallet)
+    {
+      if (!json.HasMember("custom_background_key"))
+      {
+        LOG_ERROR("Field custom_background_key not found in JSON");
+        return false;
+      }
+      else if (!json["custom_background_key"].IsString())
+      {
+        LOG_ERROR("Field custom_background_key found in JSON, but not String");
+        return false;
+      }
+      else if (json["custom_background_key"].GetStringLength() != sizeof(crypto::chacha_key))
+      {
+        LOG_ERROR("Field custom_background_key found in JSON, but not correct length");
+        return false;
+      }
+      const char *field_custom_background_key = json["custom_background_key"].GetString();
+      memcpy(custom_background_key.data(), field_custom_background_key, sizeof(crypto::chacha_key));
+      m_custom_background_key = boost::optional<crypto::chacha_key>(custom_background_key);
+      LOG_PRINT_L1("Loaded custom background key derived from custom password");
+    }
+    else if (json.HasMember("custom_background_key"))
+    {
+      LOG_ERROR("Unexpected field custom_background_key found in JSON");
+    }
   }
   else
   {
@@ -5087,12 +5349,17 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
   const cryptonote::account_keys& keys = m_account.get_keys();
   hw::device &hwdev = m_account.get_device();
   r = r && hwdev.verify_keys(keys.m_view_secret_key,  keys.m_account_address.m_view_public_key);
-  if (!m_watch_only && !m_multisig && hwdev.device_protocol() != hw::device::PROTOCOL_COLD)
+  if (!m_watch_only && !m_multisig && hwdev.device_protocol() != hw::device::PROTOCOL_COLD && !m_is_background_wallet)
     r = r && hwdev.verify_keys(keys.m_spend_secret_key, keys.m_account_address.m_spend_public_key);
   THROW_WALLET_EXCEPTION_IF(!r, error::wallet_files_doesnt_correspond, m_keys_file, m_wallet_file);
 
   if (r)
-    setup_keys(password);
+  {
+    if (!m_is_background_wallet)
+      setup_keys(password);
+    else
+      m_custom_background_key = boost::optional<crypto::chacha_key>(key);
+  }
 
   return true;
 }
@@ -5107,11 +5374,12 @@ bool wallet2::load_keys_buf(const std::string& keys_buf, const epee::wipeable_st
  * can be used prior to rewriting wallet keys file, to ensure user has entered the correct password
  *
  */
-bool wallet2::verify_password(const epee::wipeable_string& password)
+bool wallet2::verify_password(const epee::wipeable_string& password, crypto::secret_key &spend_key_out)
 {
   // this temporary unlocking is necessary for Windows (otherwise the file couldn't be loaded).
   unlock_keys_file();
-  bool r = verify_password(m_keys_file, password, m_account.get_device().device_protocol() == hw::device::PROTOCOL_COLD || m_watch_only || m_multisig, m_account.get_device(), m_kdf_rounds);
+  const bool no_spend_key = m_account.get_device().device_protocol() == hw::device::PROTOCOL_COLD || m_watch_only || m_multisig || m_is_background_wallet;
+  bool r = verify_password(m_keys_file, password, no_spend_key, m_account.get_device(), m_kdf_rounds, spend_key_out);
   lock_keys_file();
   return r;
 }
@@ -5129,7 +5397,7 @@ bool wallet2::verify_password(const epee::wipeable_string& password)
  * can be used prior to rewriting wallet keys file, to ensure user has entered the correct password
  *
  */
-bool wallet2::verify_password(const std::string& keys_file_name, const epee::wipeable_string& password, bool no_spend_key, hw::device &hwdev, uint64_t kdf_rounds)
+bool wallet2::verify_password(const std::string& keys_file_name, const epee::wipeable_string& password, bool no_spend_key, hw::device &hwdev, uint64_t kdf_rounds, crypto::secret_key &spend_key_out)
 {
   rapidjson::Document json;
   wallet2::keys_file_data keys_file_data;
@@ -5146,9 +5414,22 @@ bool wallet2::verify_password(const std::string& keys_file_name, const epee::wip
   std::string account_data;
   account_data.resize(keys_file_data.account_data.size());
   crypto::chacha20(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
-  if (json.Parse(account_data.c_str()).HasParseError() || !json.IsObject())
+  const bool try_v0_format = json.Parse(account_data.c_str()).HasParseError() || !json.IsObject();
+  if (try_v0_format)
     crypto::chacha8(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
 
+  // Check if it's a background keys file if both of the above formats fail
+  {
+    cryptonote::account_base account_data_check;
+    if (try_v0_format && !epee::serialization::load_t_from_binary(account_data_check, account_data))
+    {
+      get_custom_background_key(password, key, kdf_rounds);
+      crypto::chacha20(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
+      const bool is_background_wallet = json.Parse(account_data.c_str()).HasParseError() && json.IsObject();
+      no_spend_key = no_spend_key || is_background_wallet;
+    }
+  }
+
   // The contents should be JSON if the wallet follows the new format.
   if (json.Parse(account_data.c_str()).HasParseError())
   {
@@ -5173,6 +5454,7 @@ bool wallet2::verify_password(const std::string& keys_file_name, const epee::wip
   r = r && hwdev.verify_keys(keys.m_view_secret_key,  keys.m_account_address.m_view_public_key);
   if(!no_spend_key)
     r = r && hwdev.verify_keys(keys.m_spend_secret_key, keys.m_account_address.m_spend_public_key);
+  spend_key_out = (!no_spend_key && r) ? keys.m_spend_secret_key : crypto::null_skey;
   return r;
 }
 
@@ -5184,9 +5466,7 @@ void wallet2::encrypt_keys(const crypto::chacha_key &key)
 
 void wallet2::decrypt_keys(const crypto::chacha_key &key)
 {
-  // We use m_cache_key as a deterministic test to see if given key corresponds to original password
-  const crypto::chacha_key cache_key = derive_cache_key(key);
-  THROW_WALLET_EXCEPTION_IF(cache_key != m_cache_key, error::invalid_password);
+  verify_password_with_cached_key(key);
 
   m_account.encrypt_viewkey(key);
   m_account.decrypt_keys(key);
@@ -5862,11 +6142,30 @@ void wallet2::rewrite(const std::string& wallet_name, const epee::wipeable_strin
 {
   if (wallet_name.empty())
     return;
+  THROW_WALLET_EXCEPTION_IF(m_background_syncing || m_is_background_wallet, error::wallet_internal_error,
+    "cannot change wallet settings from background wallet");
   prepare_file_names(wallet_name);
   boost::system::error_code ignored_ec;
   THROW_WALLET_EXCEPTION_IF(!boost::filesystem::exists(m_keys_file, ignored_ec), error::file_not_found, m_keys_file);
   bool r = store_keys(m_keys_file, password, m_watch_only);
   THROW_WALLET_EXCEPTION_IF(!r, error::file_save_error, m_keys_file);
+
+  // Update the background keys file when we rewrite the main wallet keys file
+  if (m_background_sync_type == BackgroundSyncCustomPassword && m_custom_background_key)
+  {
+    const std::string background_keys_filename = make_background_keys_file_name(wallet_name);
+    if (!lock_background_keys_file(background_keys_filename))
+    {
+      LOG_ERROR("Background keys file " << background_keys_filename << " is opened by another wallet program and cannot be rewritten");
+      return; // not fatal, background keys file will just have different wallet settings
+    }
+    store_background_keys(m_custom_background_key.get());
+    store_background_cache(m_custom_background_key.get(), true/*do_reset_background_sync_data*/);
+  }
+  else if (m_background_sync_type == BackgroundSyncReusePassword)
+  {
+    reset_background_sync_data(m_background_sync_data);
+  }
 }
 /*!
  * \brief Writes to a file named based on the normal wallet (doesn't generate key, assumes it's already there)
@@ -5900,6 +6199,16 @@ bool wallet2::wallet_valid_path_format(const std::string& file_path)
   return !file_path.empty();
 }
 //----------------------------------------------------------------------------------------------------
+std::string wallet2::make_background_wallet_file_name(const std::string &wallet_file)
+{
+  return wallet_file + BACKGROUND_WALLET_SUFFIX;
+}
+//----------------------------------------------------------------------------------------------------
+std::string wallet2::make_background_keys_file_name(const std::string &wallet_file)
+{
+  return make_background_wallet_file_name(wallet_file) + ".keys";
+}
+//----------------------------------------------------------------------------------------------------
 bool wallet2::parse_long_payment_id(const std::string& payment_id_str, crypto::hash& payment_id)
 {
   cryptonote::blobdata payment_id_data;
@@ -6135,10 +6444,81 @@ void wallet2::load(const std::string& wallet_, const epee::wipeable_string& pass
     THROW_WALLET_EXCEPTION_IF(true, error::file_read_error, "failed to load keys from buffer");
   }
 
-  wallet_keys_unlocker unlocker(*this, m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only, password);
+  wallet_keys_unlocker unlocker(*this, m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only && !m_is_background_wallet, password);
 
   //keys loaded ok!
   //try to load wallet cache. but even if we failed, it is not big problem
+  load_wallet_cache(use_fs, cache_buf);
+
+  if (!m_persistent_rpc_client_id)
+    set_rpc_client_secret_key(rct::rct2sk(rct::skGen()));
+
+  // Wallets used to wipe, but not erase, old unused multisig key info, which lead to huge memory leaks.
+  // Here we erase these multisig keys if they're zero'd out to free up space.
+  for (auto &td : m_transfers)
+  {
+    auto mk_it = td.m_multisig_k.begin();
+    while (mk_it != td.m_multisig_k.end())
+    {
+      if (*mk_it == rct::zero())
+        mk_it = td.m_multisig_k.erase(mk_it);
+      else
+        ++mk_it;
+    }
+  }
+
+  cryptonote::block genesis;
+  generate_genesis(genesis);
+  crypto::hash genesis_hash = get_block_hash(genesis);
+
+  if (m_blockchain.empty())
+  {
+    m_blockchain.push_back(genesis_hash);
+    m_last_block_reward = cryptonote::get_outs_money_amount(genesis.miner_tx);
+  }
+  else
+  {
+    check_genesis(genesis_hash);
+  }
+
+  trim_hashchain();
+
+  if (get_num_subaddress_accounts() == 0)
+    add_subaddress_account(tr("Primary account"));
+
+  try
+  {
+    find_and_save_rings(false);
+  }
+  catch (const std::exception &e)
+  {
+    MERROR("Failed to save rings, will try again next time");
+  }
+
+  try
+  {
+    if (use_fs)
+      m_message_store.read_from_file(get_multisig_wallet_state(), m_mms_file, m_load_deprecated_formats);
+  }
+  catch (const std::exception &e)
+  {
+    MERROR("Failed to initialize MMS, it will be unusable");
+  }
+
+  try
+  {
+    if (use_fs)
+      process_background_cache_on_open();
+  }
+  catch (const std::exception &e)
+  {
+    MERROR("Failed to process background cache on open: " << e.what());
+  }
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::load_wallet_cache(const bool use_fs, const std::string& cache_buf)
+{
+  boost::system::error_code e;
   bool cache_missing = use_fs ? (!boost::filesystem::exists(m_wallet_file, e) || e) : cache_buf.empty();
   if (cache_missing)
   {
@@ -6165,7 +6545,7 @@ void wallet2::load(const std::string& wallet_, const epee::wipeable_string& pass
       THROW_WALLET_EXCEPTION_IF(!r, error::wallet_internal_error, "internal error: failed to deserialize \"" + m_wallet_file + '\"');
       std::string cache_data;
       cache_data.resize(cache_file_data.cache_data.size());
-      crypto::chacha20(cache_file_data.cache_data.data(), cache_file_data.cache_data.size(), m_cache_key, cache_file_data.iv, &cache_data[0]);
+      crypto::chacha20(cache_file_data.cache_data.data(), cache_file_data.cache_data.size(), get_cache_key(), cache_file_data.iv, &cache_data[0]);
 
       try {
         bool loaded = false;
@@ -6255,60 +6635,76 @@ void wallet2::load(const std::string& wallet_, const epee::wipeable_string& pass
       m_account_public_address.m_view_public_key  != m_account.get_keys().m_account_address.m_view_public_key,
       error::wallet_files_doesnt_correspond, m_keys_file, m_wallet_file);
   }
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::process_background_cache_on_open()
+{
+  if (m_wallet_file.empty())
+    return;
+  if (m_background_syncing || m_is_background_wallet)
+    return;
+  if (m_background_sync_type == BackgroundSyncOff)
+    return;
 
-  if (!m_persistent_rpc_client_id)
-    set_rpc_client_secret_key(rct::rct2sk(rct::skGen()));
+  if (m_background_sync_type == BackgroundSyncReusePassword)
+  {
+    const background_sync_data_t background_sync_data = m_background_sync_data;
+    const hashchain blockchain = m_blockchain;
+    process_background_cache(background_sync_data, blockchain, m_last_block_reward);
 
-  // Wallets used to wipe, but not erase, old unused multisig key info, which lead to huge memory leaks.
-  // Here we erase these multisig keys if they're zero'd out to free up space.
-  for (auto &td : m_transfers)
+    // Reset the background cache after processing
+    reset_background_sync_data(m_background_sync_data);
+  }
+  else if (m_background_sync_type == BackgroundSyncCustomPassword)
   {
-    auto mk_it = td.m_multisig_k.begin();
-    while (mk_it != td.m_multisig_k.end())
+    // If the background wallet files don't exist, recreate them
+    const std::string background_keys_file = make_background_keys_file_name(m_wallet_file);
+    const std::string background_wallet_file = make_background_wallet_file_name(m_wallet_file);
+    const bool background_keys_file_exists = boost::filesystem::exists(background_keys_file);
+    const bool background_wallet_exists = boost::filesystem::exists(background_wallet_file);
+
+    THROW_WALLET_EXCEPTION_IF(!lock_background_keys_file(background_keys_file), error::background_wallet_already_open, background_wallet_file);
+    THROW_WALLET_EXCEPTION_IF(!m_custom_background_key, error::wallet_internal_error, "Custom background key not set");
+
+    if (!background_keys_file_exists)
     {
-      if (*mk_it == rct::zero())
-        mk_it = td.m_multisig_k.erase(mk_it);
-      else
-        ++mk_it;
+      MDEBUG("Background keys file not found, restoring");
+      store_background_keys(m_custom_background_key.get());
     }
-  }
 
-  cryptonote::block genesis;
-  generate_genesis(genesis);
-  crypto::hash genesis_hash = get_block_hash(genesis);
+    if (!background_wallet_exists)
+    {
+      MDEBUG("Background cache not found, restoring");
+      store_background_cache(m_custom_background_key.get(), true/*do_reset_background_sync_data*/);
+      return;
+    }
 
-  if (m_blockchain.empty())
-  {
-    m_blockchain.push_back(genesis_hash);
-    m_last_block_reward = cryptonote::get_outs_money_amount(genesis.miner_tx);
-  }
-  else
-  {
-    check_genesis(genesis_hash);
-  }
+    MDEBUG("Loading background cache");
 
-  trim_hashchain();
+    // Set up a minimal background wallet2 instance
+    std::unique_ptr<wallet2> background_w2(new wallet2(m_nettype));
+    background_w2->m_is_background_wallet = true;
+    background_w2->m_background_syncing = true;
+    background_w2->m_background_sync_type = m_background_sync_type;
+    background_w2->m_custom_background_key = m_custom_background_key;
 
-  if (get_num_subaddress_accounts() == 0)
-    add_subaddress_account(tr("Primary account"));
+    cryptonote::account_base account = m_account;
+    account.forget_spend_key();
+    background_w2->m_account = account;
 
-  try
-  {
-    find_and_save_rings(false);
-  }
-  catch (const std::exception &e)
-  {
-    MERROR("Failed to save rings, will try again next time");
-  }
-  
-  try
-  {
-    if (use_fs)
-      m_message_store.read_from_file(get_multisig_wallet_state(), m_mms_file, m_load_deprecated_formats);
+    // Load background cache from file
+    background_w2->clear();
+    background_w2->prepare_file_names(background_wallet_file);
+    background_w2->load_wallet_cache(true/*use_fs*/);
+
+    process_background_cache(background_w2->m_background_sync_data, background_w2->m_blockchain, background_w2->m_last_block_reward);
+
+    // Reset the background cache after processing
+    store_background_cache(m_custom_background_key.get(), true/*do_reset_background_sync_data*/);
   }
-  catch (const std::exception &e)
+  else
   {
-    MERROR("Failed to initialize MMS, it will be unusable");
+    THROW_WALLET_EXCEPTION(error::wallet_internal_error, "unknown background sync type");
   }
 }
 //----------------------------------------------------------------------------------------------------
@@ -6390,6 +6786,8 @@ void wallet2::store_to(const std::string &path, const epee::wipeable_string &pas
     same_file = canonical_old_path == canonical_new_path;
   }
 
+  THROW_WALLET_EXCEPTION_IF(m_is_background_wallet && !same_file, error::wallet_internal_error,
+    "Cannot save background wallet files to a different location");
 
   if (!same_file)
   {
@@ -6406,6 +6804,21 @@ void wallet2::store_to(const std::string &path, const epee::wipeable_string &pas
       }
     }
   }
+  else if (m_background_sync_type == BackgroundSyncCustomPassword && m_background_syncing && !m_is_background_wallet)
+  {
+    // We're background syncing, so store the wallet cache as a background cache
+    // keeping the background sync data
+    try
+    {
+      THROW_WALLET_EXCEPTION_IF(!m_custom_background_key, error::wallet_internal_error, "Custom background key not set");
+      store_background_cache(m_custom_background_key.get(), false/*do_reset_background_sync_data*/);
+    }
+    catch (const std::exception &e)
+    {
+      MERROR("Failed to store background cache while background syncing: " << e.what());
+    }
+    return;
+  }
 
   // get wallet cache data
   boost::optional<wallet2::cache_file_data> cache_file_data = get_cache_file_data();
@@ -6499,6 +6912,22 @@ void wallet2::store_to(const std::string &path, const epee::wipeable_string &pas
     // store should only exist if the MMS is really active
     m_message_store.write_to_file(get_multisig_wallet_state(), m_mms_file);
   }
+
+  if (m_background_sync_type == BackgroundSyncCustomPassword && !m_background_syncing && !m_is_background_wallet)
+  {
+    // Update the background wallet cache when we store the main wallet cache
+    // Note: if background syncing when this is called, it means the background
+    // wallet is open and was already stored above
+    try
+    {
+      THROW_WALLET_EXCEPTION_IF(!m_custom_background_key, error::wallet_internal_error, "Custom background key not set");
+      store_background_cache(m_custom_background_key.get(), true/*do_reset_background_sync_data*/);
+    }
+    catch (const std::exception &e)
+    {
+      MERROR("Failed to update background cache: " << e.what());
+    }
+  }
 }
 //----------------------------------------------------------------------------------------------------
 boost::optional<wallet2::cache_file_data> wallet2::get_cache_file_data()
@@ -6516,7 +6945,7 @@ boost::optional<wallet2::cache_file_data> wallet2::get_cache_file_data()
     std::string cipher;
     cipher.resize(cache_file_data.get().cache_data.size());
     cache_file_data.get().iv = crypto::rand<crypto::chacha_iv>();
-    crypto::chacha20(cache_file_data.get().cache_data.data(), cache_file_data.get().cache_data.size(), m_cache_key, cache_file_data.get().iv, &cipher[0]);
+    crypto::chacha20(cache_file_data.get().cache_data.data(), cache_file_data.get().cache_data.size(), get_cache_key(), cache_file_data.get().iv, &cipher[0]);
     cache_file_data.get().cache_data = cipher;
     return cache_file_data;
   }
@@ -8592,6 +9021,34 @@ bool wallet2::is_keys_file_locked() const
   return m_keys_file_locker->locked();
 }
 
+bool wallet2::lock_background_keys_file(const std::string &background_keys_file)
+{
+  if (background_keys_file.empty() || !boost::filesystem::exists(background_keys_file))
+    return true;
+  if (m_background_keys_file_locker && m_background_keys_file_locker->locked())
+    return true;
+  m_background_keys_file_locker.reset(new tools::file_locker(background_keys_file));
+  return m_background_keys_file_locker->locked();
+}
+
+bool wallet2::unlock_background_keys_file()
+{
+  if (!m_background_keys_file_locker)
+  {
+    MDEBUG("background keys file locker is not set");
+    return false;
+  }
+  m_background_keys_file_locker.reset();
+  return true;
+}
+
+bool wallet2::is_background_keys_file_locked() const
+{
+  if (!m_background_keys_file_locker)
+    return false;
+  return m_background_keys_file_locker->locked();
+}
+
 bool wallet2::tx_add_fake_output(std::vector<std::vector<tools::wallet2::get_outs_entry>> &outs, uint64_t global_index, const crypto::public_key& output_public_key, const rct::key& mask, uint64_t real_index, bool unlocked, std::unordered_set<crypto::public_key> &valid_public_keys_cache) const
 {
   if (!unlocked) // don't add locked outs
@@ -13924,6 +14381,413 @@ bool wallet2::import_key_images(signed_tx_set & signed_tx, size_t offset, bool o
   return import_key_images(signed_tx.key_images, offset, only_selected_transfers ? boost::make_optional(selected_transfers) : boost::none);
 }
 
+/*
+  In background sync mode, we use just the view key when the wallet is scanning
+  to identify all txs where:
+
+    1. We received an output.
+    2. We spent an output.
+    3. We *may* have spent a received output but we didn't know for sure because
+       the spend key was not loaded while background sync was enabled.
+
+  When the user is ready to use the spend key again, we call this function to
+  process all those background synced transactions with the spend key loaded,
+  so that we can properly generate key images for the transactions which we
+  we were not able to do so for while background sync was enabled. This allows
+  us to determine *all* receives and spends the user completed while the wallet
+  had background sync enabled. Once this function completes, we can continue
+  scanning from where the background sync left off.
+
+  Txs of type 3 (txs which we *may* have spent received output(s)) are txs where
+  1+ rings contain an output that the user received and the wallet does not know
+  the associated key image for that output. We don't know if the user spent in
+  this type of tx or not. This function will generate key images for all outputs
+  we don't know key images for, and then check if those outputs were spent in
+  the txs of type 3.
+
+  By storing this type of "plausible spend tx" when scanning in background sync
+  mode, we avoid the need to query the daemon with key images when background
+  sync mode is disabled to see if those key images were spent. This would
+  reveal key images to 3rd party nodes for users who don't run their own.
+  Although this is not a perfect solution to avoid revealing key images to a 3rd
+  party node (since tx submission trivially reveals key images to a node), it's
+  probably better than revealing *unused* key images to a 3rd party node, which
+  would enable the 3rd party to deduce that a tx is spending an output at least
+  X old when the key image is included in the chain.
+*/
+void wallet2::process_background_cache(const background_sync_data_t &background_sync_data, const hashchain &background_synced_chain, uint64_t last_block_reward)
+{
+  // We expect the spend key to be in a decrypted state while
+  // m_processing_background_cache is true
+  m_processing_background_cache = true;
+  auto done_processing = epee::misc_utils::create_scope_leave_handler([&, this]() {
+    m_processing_background_cache = false;
+  });
+
+  if (m_background_syncing || m_multisig || m_watch_only || key_on_device())
+    return;
+
+  if (!background_sync_data.first_refresh_done)
+  {
+    MDEBUG("Skipping processing background cache, background cache has not synced yet");
+    return;
+  }
+
+  // Skip processing if wallet cache is synced higher than background cache
+  const uint64_t current_height = m_blockchain.size();
+  const uint64_t background_height = background_synced_chain.size();
+  MDEBUG("Background cache height " << background_height << " , wallet height " << current_height);
+  if (current_height > background_height)
+  {
+    MWARNING("Skipping processing background cache, synced height is higher than background cache");
+    return;
+  }
+
+  if (m_refresh_from_block_height  < background_sync_data.wallet_refresh_from_block_height ||
+      m_subaddress_lookahead_major > background_sync_data.subaddress_lookahead_major ||
+      m_subaddress_lookahead_minor > background_sync_data.subaddress_lookahead_minor ||
+      m_refresh_type               < background_sync_data.wallet_refresh_type)
+  {
+    MWARNING("Skipping processing background cache, background wallet sync settings did not match main wallet's");
+    MDEBUG("Wallet settings: " <<
+      ", m_refresh_from_block_height: "  << m_refresh_from_block_height  << " vs " << background_sync_data.wallet_refresh_from_block_height <<
+      ", m_subaddress_lookahead_major: " << m_subaddress_lookahead_major << " vs " << background_sync_data.subaddress_lookahead_major <<
+      ", m_subaddress_lookahead_minor: " << m_subaddress_lookahead_minor << " vs " << background_sync_data.subaddress_lookahead_minor <<
+      ", m_refresh_type: "               << m_refresh_type               << " vs " << background_sync_data.wallet_refresh_type);
+    return;
+  }
+
+  // Sort background synced txs in the order they appeared in the cache so that
+  // we process them in the order they appeared in the chain. Thus if tx2 spends
+  // from tx1, we will know because tx1 is processed before tx2.
+  std::vector<std::pair<crypto::hash, background_synced_tx_t>> sorted_bgs_cache(background_sync_data.txs.begin(), background_sync_data.txs.end());
+  std::sort(sorted_bgs_cache.begin(), sorted_bgs_cache.end(),
+    [](const std::pair<crypto::hash, background_synced_tx_t>& l, const std::pair<crypto::hash, background_synced_tx_t>& r)
+      {
+        uint64_t left_index = l.second.index_in_background_sync_data;
+        uint64_t right_index = r.second.index_in_background_sync_data;
+        THROW_WALLET_EXCEPTION_IF(
+            (left_index < right_index && l.second.height > r.second.height) ||
+            (left_index > right_index && l.second.height < r.second.height),
+            error::wallet_internal_error, "Unexpected background sync data order");
+        return left_index < right_index;
+      });
+
+  // All txs in the background cache should have height >= sync start height,
+  // but not fatal if not
+  if (!sorted_bgs_cache.empty() && sorted_bgs_cache[0].second.height < background_sync_data.start_height)
+    MWARNING("First tx in background cache has height (" << sorted_bgs_cache[0].second.height << ") lower than sync start height (" << background_sync_data.start_height << ")");
+
+  // We want to process all background synced txs in order to make sure
+  // the wallet state updates correctly. First we remove all txs from the wallet
+  // from before the background sync start height, then re-process them in
+  // chronological order. The background cache should contain a superset of
+  // *all* the wallet's txs from after the background sync start height.
+  MDEBUG("Processing " << background_sync_data.txs.size() << " background synced txs starting from height " << background_sync_data.start_height);
+  detached_blockchain_data dbd = detach_blockchain(background_sync_data.start_height);
+
+  for (const auto &bgs_tx : sorted_bgs_cache)
+  {
+    MDEBUG("Processing background synced tx " << bgs_tx.first);
+
+    process_new_transaction(bgs_tx.first, bgs_tx.second.tx, bgs_tx.second.output_indices, bgs_tx.second.height, 0, bgs_tx.second.block_timestamp,
+        cryptonote::is_coinbase(bgs_tx.second.tx), false/*pool*/, bgs_tx.second.double_spend_seen, {}, {}, true/*ignore_callbacks*/);
+
+    // Re-set destination addresses if they were previously set
+    if (m_confirmed_txs.find(bgs_tx.first) != m_confirmed_txs.end() &&
+        dbd.detached_confirmed_txs_dests.find(bgs_tx.first) != dbd.detached_confirmed_txs_dests.end())
+    {
+      m_confirmed_txs[bgs_tx.first].m_dests = std::move(dbd.detached_confirmed_txs_dests[bgs_tx.first]);
+    }
+  }
+
+  m_blockchain = background_synced_chain;
+  m_last_block_reward = last_block_reward;
+
+  MDEBUG("Finished processing background sync data");
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::reset_background_sync_data(background_sync_data_t &background_sync_data)
+{
+  background_sync_data.first_refresh_done = false;
+  background_sync_data.start_height = get_blockchain_current_height();
+  background_sync_data.txs.clear();
+
+  background_sync_data.wallet_refresh_from_block_height = m_refresh_from_block_height;
+  background_sync_data.subaddress_lookahead_major = m_subaddress_lookahead_major;
+  background_sync_data.subaddress_lookahead_minor = m_subaddress_lookahead_minor;
+  background_sync_data.wallet_refresh_type = m_refresh_type;
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::store_background_cache(const crypto::chacha_key &custom_background_key, const bool do_reset_background_sync_data)
+{
+  MDEBUG("Storing background cache (do_reset_background_sync_data=" << do_reset_background_sync_data << ")");
+
+  THROW_WALLET_EXCEPTION_IF(m_background_sync_type != BackgroundSyncCustomPassword, error::wallet_internal_error,
+      "Can only write a background cache when using a custom background password");
+  THROW_WALLET_EXCEPTION_IF(m_wallet_file.empty(), error::wallet_internal_error,
+      "No wallet file known, can't store background cache");
+
+  std::unique_ptr<wallet2> background_w2(new wallet2(m_nettype));
+  background_w2->prepare_file_names(make_background_wallet_file_name(m_wallet_file));
+
+  // Make sure background wallet is opened by this wallet
+  THROW_WALLET_EXCEPTION_IF(!lock_background_keys_file(background_w2->m_keys_file),
+      error::background_wallet_already_open, background_w2->m_wallet_file);
+
+  // Load a background wallet2 instance using this wallet2 instance
+  std::string this_wallet2;
+  bool r = ::serialization::dump_binary(*this, this_wallet2);
+  THROW_WALLET_EXCEPTION_IF(!r, error::wallet_internal_error, "Failed to serialize wallet cache");
+
+  background_w2->clear();
+  r = ::serialization::parse_binary(this_wallet2, *background_w2);
+  THROW_WALLET_EXCEPTION_IF(!r, error::wallet_internal_error, "Failed to deserialize wallet cache");
+
+  // Clear sensitive data from background cache not needed to sync
+  background_w2->clear_user_data();
+
+  background_w2->m_is_background_wallet = true;
+  if (do_reset_background_sync_data)
+    reset_background_sync_data(background_w2->m_background_sync_data);
+  else
+    background_w2->m_background_sync_data = m_background_sync_data;
+  background_w2->m_background_syncing = true;
+
+  background_w2->m_custom_background_key = boost::optional<crypto::chacha_key>(custom_background_key);
+  background_w2->m_background_sync_type = m_background_sync_type;
+  background_w2->store();
+
+  MDEBUG("Background cache stored (" << background_w2->m_transfers.size() << " transfers, " << background_w2->m_background_sync_data.txs.size() << " background synced txs)");
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::store_background_keys(const crypto::chacha_key &custom_background_key)
+{
+  MDEBUG("Storing background keys");
+
+  THROW_WALLET_EXCEPTION_IF(m_wallet_file.empty(), error::wallet_internal_error,
+      "No wallet file known, can't store background keys");
+
+  const std::string background_keys_file = make_background_keys_file_name(m_wallet_file);
+  bool r = store_keys(background_keys_file, custom_background_key, false/*watch_only*/, true/*background_keys_file*/);
+  THROW_WALLET_EXCEPTION_IF(!r, error::file_save_error, background_keys_file);
+  THROW_WALLET_EXCEPTION_IF(!is_background_keys_file_locked(), error::wallet_internal_error, background_keys_file + "\" should be locked");
+
+  // GUI uses the address file to differentiate non-mainnet wallets in the UI
+  const std::string background_address_file = make_background_wallet_file_name(m_wallet_file) + ".address.txt";
+  if (m_nettype != MAINNET && !boost::filesystem::exists(background_address_file))
+  {
+    r = save_to_file(background_address_file, m_account.get_public_address_str(m_nettype), true);
+    if (!r) MERROR("String with address text not saved");
+  }
+
+  MDEBUG("Background keys stored");
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::write_background_sync_wallet(const epee::wipeable_string &wallet_password, const epee::wipeable_string &background_cache_password)
+{
+  MDEBUG("Storing background sync wallet");
+  THROW_WALLET_EXCEPTION_IF(m_background_sync_type != BackgroundSyncCustomPassword, error::wallet_internal_error,
+      "Can only write a background sync wallet when using a custom background password");
+  THROW_WALLET_EXCEPTION_IF(m_background_syncing || m_is_background_wallet, error::wallet_internal_error,
+      "Can't write background sync wallet from an existing background cache");
+  THROW_WALLET_EXCEPTION_IF(wallet_password == background_cache_password,
+      error::background_custom_password_same_as_wallet_password);
+
+  // Set the background encryption key
+  crypto::chacha_key custom_background_key;
+  get_custom_background_key(background_cache_password, custom_background_key, m_kdf_rounds);
+
+  // Keep the background encryption key in memory so the main wallet can update
+  // the background cache when it stores the main wallet cache
+  m_custom_background_key = boost::optional<crypto::chacha_key>(custom_background_key);
+
+  if (m_wallet_file.empty() || m_keys_file.empty())
+    return;
+
+  // Save background keys file, then background cache, then update main wallet settings
+  store_background_keys(custom_background_key);
+  store_background_cache(custom_background_key, true/*do_reset_background_sync_data*/);
+  bool r = store_keys(m_keys_file, wallet_password, false/*watch_only*/);
+  THROW_WALLET_EXCEPTION_IF(!r, error::file_save_error, m_keys_file);
+
+  MDEBUG("Background sync wallet saved successfully");
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::setup_background_sync(BackgroundSyncType background_sync_type, const epee::wipeable_string &wallet_password, const boost::optional<epee::wipeable_string> &background_cache_password)
+{
+  MDEBUG("Setting background sync to type " << background_sync_type);
+  THROW_WALLET_EXCEPTION_IF(m_background_syncing || m_is_background_wallet, error::wallet_internal_error,
+      "Can't set background sync type from an existing background cache");
+  verify_password_with_cached_key(wallet_password);
+
+  if (background_sync_type != BackgroundSyncOff)
+    validate_background_cache_password_usage(background_sync_type, background_cache_password, m_multisig, m_watch_only, key_on_device());
+
+  THROW_WALLET_EXCEPTION_IF(background_sync_type == BackgroundSyncCustomPassword && wallet_password == background_cache_password,
+      error::background_custom_password_same_as_wallet_password);
+
+  if (m_background_sync_type == background_sync_type && background_sync_type != BackgroundSyncCustomPassword)
+    return; // No need to make any changes
+
+  if (!m_wallet_file.empty())
+  {
+    // Delete existing background files if they already exist
+    const std::string old_background_wallet_file = make_background_wallet_file_name(m_wallet_file);
+    const std::string old_background_keys_file = make_background_keys_file_name(m_wallet_file);
+    const std::string old_background_address_file = old_background_wallet_file + ".address.txt";
+
+    // Make sure no other program is using the background wallet
+    THROW_WALLET_EXCEPTION_IF(!lock_background_keys_file(old_background_keys_file),
+        error::background_wallet_already_open, old_background_wallet_file);
+
+    if (boost::filesystem::exists(old_background_wallet_file))
+      if (!boost::filesystem::remove(old_background_wallet_file))
+        LOG_ERROR("Error deleting background wallet file: " << old_background_wallet_file);
+
+    if (boost::filesystem::exists(old_background_keys_file))
+      if (!boost::filesystem::remove(old_background_keys_file))
+        LOG_ERROR("Error deleting background keys file: " << old_background_keys_file);
+
+    if (boost::filesystem::exists(old_background_address_file))
+      if (!boost::filesystem::remove(old_background_address_file))
+        LOG_ERROR("Error deleting background address file: " << old_background_address_file);
+  }
+
+  m_background_sync_type = background_sync_type;
+  m_custom_background_key = boost::none;
+
+  // Write the new files
+  switch (background_sync_type)
+  {
+    case BackgroundSyncOff:
+    case BackgroundSyncReusePassword: rewrite(m_wallet_file, wallet_password); break;
+    case BackgroundSyncCustomPassword: write_background_sync_wallet(wallet_password, background_cache_password.get()); break;
+    default: THROW_WALLET_EXCEPTION(error::wallet_internal_error, "unknown background sync type");
+  }
+
+  MDEBUG("Done setting background sync type");
+}
+//----------------------------------------------------------------------------------------------------
+/*
+  When background syncing, the wallet scans using just the view key, without
+  keeping the spend key in decrypted state. When a user returns to the wallet
+  and decrypts the spend key, the wallet processes the background synced txs,
+  then the wallet picks up scanning normally right where the background sync
+  left off.
+*/
+void wallet2::start_background_sync()
+{
+  THROW_WALLET_EXCEPTION_IF(m_background_sync_type == BackgroundSyncOff, error::wallet_internal_error,
+      "must setup background sync first before using background sync");
+  THROW_WALLET_EXCEPTION_IF(m_is_background_wallet, error::wallet_internal_error,
+      "Can't start background syncing from a background wallet (it is always background syncing)");
+
+  MDEBUG("Starting background sync");
+
+  if (m_background_syncing)
+  {
+    MDEBUG("Already background syncing");
+    return;
+  }
+
+  if (m_background_sync_type == BackgroundSyncCustomPassword && !m_wallet_file.empty())
+  {
+    // Save the current state of the wallet cache. Only necessary when using a
+    // custom background password which uses distinct background wallet to sync.
+    // When reusing wallet password to sync we reuse the main wallet cache.
+    store();
+
+    // Wipe user data from the background wallet cache not needed to sync.
+    // Only wipe user data from background cache if wallet cache is stored
+    // on disk; otherwise we could lose the data.
+    clear_user_data();
+
+    // Wipe m_cache_key since it can be used to decrypt main wallet cache
+    m_cache_key.scrub();
+  }
+
+  reset_background_sync_data(m_background_sync_data);
+  m_background_syncing = true;
+
+  // Wipe the spend key from memory
+  m_account.forget_spend_key();
+
+  MDEBUG("Background sync started at height " << m_background_sync_data.start_height);
+}
+//----------------------------------------------------------------------------------------------------
+void wallet2::stop_background_sync(const epee::wipeable_string &wallet_password, const crypto::secret_key &spend_secret_key)
+{
+  MDEBUG("Stopping background sync");
+
+  // Verify provided password and spend secret key. If no spend secret key is
+  // provided, recover it from the wallet keys file
+  crypto::secret_key recovered_spend_key = crypto::null_skey;
+  if (!m_wallet_file.empty())
+  {
+    THROW_WALLET_EXCEPTION_IF(!verify_password(wallet_password, recovered_spend_key), error::invalid_password);
+  }
+  else
+  {
+    verify_password_with_cached_key(wallet_password);
+  }
+
+  if (spend_secret_key != crypto::null_skey)
+  {
+    THROW_WALLET_EXCEPTION_IF(!m_wallet_file.empty() && spend_secret_key != recovered_spend_key,
+        error::invalid_spend_key);
+    MDEBUG("Setting spend secret key with the provided key");
+    recovered_spend_key = spend_secret_key;
+  }
+
+  // Verify private spend key derives to wallet's public spend key
+  const auto verify_spend_key = [this](crypto::secret_key &recovered_spend_key) -> bool
+  {
+    crypto::public_key spend_public_key;
+    return recovered_spend_key != crypto::null_skey &&
+        crypto::secret_key_to_public_key(recovered_spend_key, spend_public_key) &&
+        m_account.get_keys().m_account_address.m_spend_public_key == spend_public_key;
+  };
+  THROW_WALLET_EXCEPTION_IF(!verify_spend_key(recovered_spend_key), error::invalid_spend_key);
+
+  THROW_WALLET_EXCEPTION_IF(m_background_sync_type == BackgroundSyncOff, error::wallet_internal_error,
+      "must setup background sync first before using background sync");
+  THROW_WALLET_EXCEPTION_IF(m_is_background_wallet, error::wallet_internal_error,
+      "Can't stop background syncing from a background wallet");
+
+  if (!m_background_syncing)
+    return;
+
+  // Copy background cache, we're about to overwrite it
+  const background_sync_data_t background_sync_data = m_background_sync_data;
+  const hashchain background_synced_chain = m_blockchain;
+  const uint64_t last_block_reward = m_last_block_reward;
+
+  if (m_background_sync_type == BackgroundSyncCustomPassword && !m_wallet_file.empty())
+  {
+    // Reload the wallet from disk
+    load(m_wallet_file, wallet_password);
+    THROW_WALLET_EXCEPTION_IF(!verify_spend_key(recovered_spend_key), error::invalid_spend_key);
+  }
+  m_background_syncing = false;
+
+  // Set the plaintext spend key
+  m_account.set_spend_key(recovered_spend_key);
+
+  // Encrypt the spend key when done if needed
+  epee::misc_utils::auto_scope_leave_caller keys_reencryptor;
+  if (m_ask_password == AskPasswordToDecrypt && !m_unattended && !m_watch_only)
+    keys_reencryptor = epee::misc_utils::create_scope_leave_handler([&, this]{encrypt_keys(wallet_password);});
+
+  // Now we can use the decrypted spend key to process background cache
+  process_background_cache(background_sync_data, background_synced_chain, last_block_reward);
+
+  // Reset the background cache after processing
+  reset_background_sync_data(m_background_sync_data);
+
+  MDEBUG("Background sync stopped");
+}
+//----------------------------------------------------------------------------------------------------
 wallet2::payment_container wallet2::export_payments() const
 {
   payment_container payments;
diff --git a/src/wallet/wallet2.h b/src/wallet/wallet2.h
index f3893c278..2f4ad52f1 100644
--- a/src/wallet/wallet2.h
+++ b/src/wallet/wallet2.h
@@ -256,6 +256,20 @@ private:
       BackgroundMiningNo = 2,
     };
 
+    enum BackgroundSyncType {
+      BackgroundSyncOff = 0,
+      BackgroundSyncReusePassword = 1,
+      BackgroundSyncCustomPassword = 2,
+    };
+
+    static BackgroundSyncType background_sync_type_from_str(const std::string &background_sync_type_str)
+    {
+      if (background_sync_type_str == "off") return BackgroundSyncOff;
+      if (background_sync_type_str == "reuse-wallet-password") return BackgroundSyncReusePassword;
+      if (background_sync_type_str == "custom-background-password") return BackgroundSyncCustomPassword;
+      throw std::logic_error("Unknown background sync type");
+    };
+
     enum ExportFormat {
       Binary = 0,
       Ascii,
@@ -282,7 +296,12 @@ private:
     //! Just parses variables.
     static std::unique_ptr<wallet2> make_dummy(const boost::program_options::variables_map& vm, bool unattended, const std::function<boost::optional<password_container>(const char *, bool)> &password_prompter);
 
-    static bool verify_password(const std::string& keys_file_name, const epee::wipeable_string& password, bool no_spend_key, hw::device &hwdev, uint64_t kdf_rounds);
+    static bool verify_password(const std::string& keys_file_name, const epee::wipeable_string& password, bool no_spend_key, hw::device &hwdev, uint64_t kdf_rounds)
+    {
+      crypto::secret_key spend_key = crypto::null_skey;
+      return verify_password(keys_file_name, password, no_spend_key, hwdev, kdf_rounds, spend_key);
+    };
+    static bool verify_password(const std::string& keys_file_name, const epee::wipeable_string& password, bool no_spend_key, hw::device &hwdev, uint64_t kdf_rounds, crypto::secret_key &spend_key_out);
     static bool query_device(hw::device::device_type& device_type, const std::string& keys_file_name, const epee::wipeable_string& password, uint64_t kdf_rounds = 1);
 
     wallet2(cryptonote::network_type nettype = cryptonote::MAINNET, uint64_t kdf_rounds = 1, bool unattended = false, std::unique_ptr<epee::net_utils::http::http_client_factory> http_client_factory = std::unique_ptr<epee::net_utils::http::http_client_factory>(new net::http::client_factory()));
@@ -792,6 +811,54 @@ private:
       END_SERIALIZE()
     };
 
+    struct background_synced_tx_t
+    {
+      uint64_t index_in_background_sync_data;
+      cryptonote::transaction tx;
+      std::vector<uint64_t> output_indices;
+      uint64_t height;
+      uint64_t block_timestamp;
+      bool double_spend_seen;
+
+      BEGIN_SERIALIZE_OBJECT()
+        VERSION_FIELD(0)
+        VARINT_FIELD(index_in_background_sync_data)
+
+        // prune tx; don't need to keep signature data
+        if (!tx.serialize_base(ar))
+          return false;
+
+        FIELD(output_indices)
+        VARINT_FIELD(height)
+        VARINT_FIELD(block_timestamp)
+        FIELD(double_spend_seen)
+      END_SERIALIZE()
+    };
+
+    struct background_sync_data_t
+    {
+      bool first_refresh_done = false;
+      uint64_t start_height = 0;
+      serializable_unordered_map<crypto::hash, background_synced_tx_t> txs;
+
+      // Relevant wallet settings
+      uint64_t wallet_refresh_from_block_height;
+      size_t subaddress_lookahead_major;
+      size_t subaddress_lookahead_minor;
+      RefreshType wallet_refresh_type;
+
+      BEGIN_SERIALIZE_OBJECT()
+        VERSION_FIELD(0)
+        FIELD(first_refresh_done)
+        FIELD(start_height)
+        FIELD(txs)
+        FIELD(wallet_refresh_from_block_height)
+        VARINT_FIELD(subaddress_lookahead_major)
+        VARINT_FIELD(subaddress_lookahead_minor)
+        VARINT_FIELD(wallet_refresh_type)
+      END_SERIALIZE()
+    };
+
     typedef std::tuple<uint64_t, crypto::public_key, rct::key> get_outs_entry;
 
     struct parsed_block
@@ -980,7 +1047,8 @@ private:
     /*!
      * \brief verifies given password is correct for default wallet keys file
      */
-    bool verify_password(const epee::wipeable_string& password);
+    bool verify_password(const epee::wipeable_string& password) {crypto::secret_key key = crypto::null_skey; return verify_password(password, key);};
+    bool verify_password(const epee::wipeable_string& password, crypto::secret_key &spend_key_out);
     cryptonote::account_base& get_account(){return m_account;}
     const cryptonote::account_base& get_account()const{return m_account;}
 
@@ -1076,6 +1144,7 @@ private:
     cryptonote::network_type nettype() const { return m_nettype; }
     bool watch_only() const { return m_watch_only; }
     bool multisig(bool *ready = NULL, uint32_t *threshold = NULL, uint32_t *total = NULL) const;
+    bool is_background_wallet() const { return m_is_background_wallet; }
     bool has_multisig_partial_key_images() const;
     bool has_unknown_key_images() const;
     bool get_multisig_seed(epee::wipeable_string& seed, const epee::wipeable_string &passphrase = std::string()) const;
@@ -1283,11 +1352,17 @@ private:
         return;
       }
       a & m_has_ever_refreshed_from_node;
+      if(ver < 31)
+      {
+        m_background_sync_data = background_sync_data_t{};
+        return;
+      }
+      a & m_background_sync_data;
     }
 
     BEGIN_SERIALIZE_OBJECT()
       MAGIC_FIELD("monero wallet cache")
-      VERSION_FIELD(1)
+      VERSION_FIELD(2)
       FIELD(m_blockchain)
       FIELD(m_transfers)
       FIELD(m_account_public_address)
@@ -1319,6 +1394,12 @@ private:
         return true;
       }
       FIELD(m_has_ever_refreshed_from_node)
+      if (version < 2)
+      {
+        m_background_sync_data = background_sync_data_t{};
+        return true;
+      }
+      FIELD(m_background_sync_data)
     END_SERIALIZE()
 
     /*!
@@ -1334,6 +1415,8 @@ private:
      * \return                Whether path is valid format
      */
     static bool wallet_valid_path_format(const std::string& file_path);
+    static std::string make_background_wallet_file_name(const std::string &wallet_file);
+    static std::string make_background_keys_file_name(const std::string &wallet_file);
     static bool parse_long_payment_id(const std::string& payment_id_str, crypto::hash& payment_id);
     static bool parse_short_payment_id(const std::string& payment_id_str, crypto::hash8& payment_id);
     static bool parse_payment_id(const std::string& payment_id_str, crypto::hash& payment_id);
@@ -1382,6 +1465,9 @@ private:
     void ignore_outputs_below(uint64_t value) { m_ignore_outputs_below = value; }
     bool track_uses() const { return m_track_uses; }
     void track_uses(bool value) { m_track_uses = value; }
+    BackgroundSyncType background_sync_type() const { return m_background_sync_type; }
+    void setup_background_sync(BackgroundSyncType background_sync_type, const epee::wipeable_string &wallet_password, const boost::optional<epee::wipeable_string> &background_cache_password);
+    bool is_background_syncing() const { return m_background_syncing; }
     bool show_wallet_name_when_locked() const { return m_show_wallet_name_when_locked; }
     void show_wallet_name_when_locked(bool value) { m_show_wallet_name_when_locked = value; }
     BackgroundMiningSetupType setup_background_mining() const { return m_setup_background_mining; }
@@ -1696,6 +1782,9 @@ private:
     uint64_t get_bytes_sent() const;
     uint64_t get_bytes_received() const;
 
+    void start_background_sync();
+    void stop_background_sync(const epee::wipeable_string &wallet_password, const crypto::secret_key &spend_secret_key = crypto::null_skey);
+
     // MMS -------------------------------------------------------------------------------------------------
     mms::message_store& get_message_store() { return m_message_store; };
     const mms::message_store& get_message_store() const { return m_message_store; };
@@ -1731,6 +1820,9 @@ private:
      * \return                Whether it was successful.
      */
     bool store_keys(const std::string& keys_file_name, const epee::wipeable_string& password, bool watch_only = false);
+    bool store_keys(const std::string& keys_file_name, const crypto::chacha_key& key, bool watch_only = false, bool background_keys_file = false);
+    boost::optional<wallet2::keys_file_data> get_keys_file_data(const crypto::chacha_key& key, bool watch_only = false, bool background_keys_file = false);
+    bool store_keys_file_data(const std::string& keys_file_name, wallet2::keys_file_data &keys_file_data, bool background_keys_file = false);
     /*!
      * \brief Load wallet keys information from wallet file.
      * \param keys_file_name Name of wallet file
@@ -1744,6 +1836,7 @@ private:
      */
     bool load_keys_buf(const std::string& keys_buf, const epee::wipeable_string& password);
     bool load_keys_buf(const std::string& keys_buf, const epee::wipeable_string& password, boost::optional<crypto::chacha_key>& keys_to_encrypt);
+    void load_wallet_cache(const bool use_fs, const std::string& cache_buf = "");
     void process_new_transaction(const crypto::hash &txid, const cryptonote::transaction& tx, const std::vector<uint64_t> &o_indices, uint64_t height, uint8_t block_version, uint64_t ts, bool miner_tx, bool pool, bool double_spend_seen, const tx_cache_data &tx_cache_data, std::map<std::pair<uint64_t, uint64_t>, size_t> *output_tracker_cache = NULL, bool ignore_callbacks = false);
     bool should_skip_block(const cryptonote::block &b, uint64_t height) const;
     void process_new_blockchain_entry(const cryptonote::block& b, const cryptonote::block_complete_entry& bche, const parsed_block &parsed_block, const crypto::hash& bl_id, uint64_t height, const std::vector<tx_cache_data> &tx_cache_data, size_t tx_cache_data_offset, std::map<std::pair<uint64_t, uint64_t>, size_t> *output_tracker_cache = NULL);
@@ -1752,6 +1845,15 @@ private:
     void get_short_chain_history(std::list<crypto::hash>& ids, uint64_t granularity = 1) const;
     bool clear();
     void clear_soft(bool keep_key_images=false);
+    /*
+     * clear_user_data clears data created by the user, which is mostly data
+     * that a view key cannot identify on chain. This function was initially
+     * added to ensure that a "background" wallet (a wallet that syncs with just
+     * a view key hot in memory) does not have any sensitive data loaded that it
+     * does not need in order to sync. Future devs should take care to ensure
+     * that this function deletes data that is not useful for background syncing
+     */
+    void clear_user_data();
     void pull_blocks(bool first, bool try_incremental, uint64_t start_height, uint64_t& blocks_start_height, const std::list<crypto::hash> &short_chain_history, std::vector<cryptonote::block_complete_entry> &blocks, std::vector<cryptonote::COMMAND_RPC_GET_BLOCKS_FAST::block_output_indices> &o_indices, uint64_t &current_height);
     void pull_hashes(uint64_t start_height, uint64_t& blocks_start_height, const std::list<crypto::hash> &short_chain_history, std::vector<crypto::hash> &hashes);
     void fast_refresh(uint64_t stop_height, uint64_t &blocks_start_height, std::list<crypto::hash> &short_chain_history, bool force = false);
@@ -1803,10 +1905,23 @@ private:
     bool get_ring(const crypto::chacha_key &key, const crypto::key_image &key_image, std::vector<uint64_t> &outs);
     crypto::chacha_key get_ringdb_key();
     void setup_keys(const epee::wipeable_string &password);
+    const crypto::chacha_key get_cache_key();
+    void verify_password_with_cached_key(const epee::wipeable_string &password);
+    void verify_password_with_cached_key(const crypto::chacha_key &key);
     size_t get_transfer_details(const crypto::key_image &ki) const;
     tx_entry_data get_tx_entries(const std::unordered_set<crypto::hash> &txids);
     void sort_scan_tx_entries(std::vector<process_tx_entry_t> &unsorted_tx_entries);
     void process_scan_txs(const tx_entry_data &txs_to_scan, const tx_entry_data &txs_to_reprocess, const std::unordered_set<crypto::hash> &tx_hashes_to_reprocess, detached_blockchain_data &dbd);
+    void write_background_sync_wallet(const epee::wipeable_string &wallet_password, const epee::wipeable_string &background_cache_password);
+    void process_background_cache_on_open();
+    void process_background_cache(const background_sync_data_t &background_sync_data, const hashchain &background_chain, uint64_t last_block_reward);
+    void reset_background_sync_data(background_sync_data_t &background_sync_data);
+    void store_background_cache(const crypto::chacha_key &custom_background_key, const bool do_reset_background_sync_data = true);
+    void store_background_keys(const crypto::chacha_key &custom_background_key);
+
+    bool lock_background_keys_file(const std::string &background_keys_file);
+    bool unlock_background_keys_file();
+    bool is_background_keys_file_locked() const;
 
     void register_devices();
     hw::device& lookup_device(const std::string & device_descriptor);
@@ -1922,6 +2037,8 @@ private:
     uint64_t m_ignore_outputs_above;
     uint64_t m_ignore_outputs_below;
     bool m_track_uses;
+    bool m_is_background_wallet;
+    BackgroundSyncType m_background_sync_type;
     bool m_show_wallet_name_when_locked;
     uint32_t m_inactivity_lock_timeout;
     BackgroundMiningSetupType m_setup_background_mining;
@@ -1967,6 +2084,7 @@ private:
 
     uint64_t m_last_block_reward;
     std::unique_ptr<tools::file_locker> m_keys_file_locker;
+    std::unique_ptr<tools::file_locker> m_background_keys_file_locker;
     
     mms::message_store m_message_store;
     bool m_original_keys_available;
@@ -1974,6 +2092,7 @@ private:
     crypto::secret_key m_original_view_secret_key;
 
     crypto::chacha_key m_cache_key;
+    boost::optional<crypto::chacha_key> m_custom_background_key = boost::none;
     std::shared_ptr<wallet_keys_unlocker> m_encrypt_keys_after_refresh;
 
     bool m_unattended;
@@ -1989,9 +2108,13 @@ private:
 
     static boost::mutex default_daemon_address_lock;
     static std::string default_daemon_address;
+
+    bool m_background_syncing;
+    bool m_processing_background_cache;
+    background_sync_data_t m_background_sync_data;
   };
 }
-BOOST_CLASS_VERSION(tools::wallet2, 30)
+BOOST_CLASS_VERSION(tools::wallet2, 31)
 BOOST_CLASS_VERSION(tools::wallet2::transfer_details, 12)
 BOOST_CLASS_VERSION(tools::wallet2::multisig_info, 1)
 BOOST_CLASS_VERSION(tools::wallet2::multisig_info::LR, 0)
@@ -2007,6 +2130,8 @@ BOOST_CLASS_VERSION(tools::wallet2::signed_tx_set, 1)
 BOOST_CLASS_VERSION(tools::wallet2::tx_construction_data, 4)
 BOOST_CLASS_VERSION(tools::wallet2::pending_tx, 3)
 BOOST_CLASS_VERSION(tools::wallet2::multisig_sig, 1)
+BOOST_CLASS_VERSION(tools::wallet2::background_synced_tx_t, 0)
+BOOST_CLASS_VERSION(tools::wallet2::background_sync_data_t, 0)
 
 namespace boost
 {
@@ -2505,6 +2630,29 @@ namespace boost
         return;
       a & x.multisig_sigs;
     }
+
+    template <class Archive>
+    inline void serialize(Archive& a, tools::wallet2::background_synced_tx_t &x, const boost::serialization::version_type ver)
+    {
+      a & x.index_in_background_sync_data;
+      a & x.tx;
+      a & x.output_indices;
+      a & x.height;
+      a & x.block_timestamp;
+      a & x.double_spend_seen;
+    }
+
+    template <class Archive>
+    inline void serialize(Archive& a, tools::wallet2::background_sync_data_t &x, const boost::serialization::version_type ver)
+    {
+      a & x.first_refresh_done;
+      a & x.start_height;
+      a & x.txs.parent();
+      a & x.wallet_refresh_from_block_height;
+      a & x.subaddress_lookahead_major;
+      a & x.subaddress_lookahead_minor;
+      a & x.wallet_refresh_type;
+    }
   }
 }
 
diff --git a/src/wallet/wallet_errors.h b/src/wallet/wallet_errors.h
index c077313d4..c54cd3499 100644
--- a/src/wallet/wallet_errors.h
+++ b/src/wallet/wallet_errors.h
@@ -63,6 +63,7 @@ namespace tools
     //       invalid_password
     //       invalid_priority
     //       invalid_multisig_seed
+    //       invalid_spend_key
     //       refresh_error *
     //         acc_outs_lookup_error
     //         block_parse_error
@@ -97,6 +98,9 @@ namespace tools
     //       wallet_files_doesnt_correspond
     //       scan_tx_error *
     //         wont_reprocess_recent_txs_via_untrusted_daemon
+    //       background_sync_error *
+    //         background_wallet_already_open
+    //         background_custom_password_same_as_wallet_password
     //
     // * - class with protected ctor
 
@@ -304,6 +308,16 @@ namespace tools
       std::string to_string() const { return wallet_logic_error::to_string(); }
     };
 
+    struct invalid_spend_key : public wallet_logic_error
+    {
+      explicit invalid_spend_key(std::string&& loc)
+        : wallet_logic_error(std::move(loc), "invalid spend key")
+      {
+      }
+
+      std::string to_string() const { return wallet_logic_error::to_string(); }
+    };
+
     //----------------------------------------------------------------------------------------------------
     struct invalid_pregenerated_random : public wallet_logic_error
     {
@@ -947,6 +961,31 @@ namespace tools
       }
     };
     //----------------------------------------------------------------------------------------------------
+    struct background_sync_error : public wallet_logic_error
+    {
+    protected:
+      explicit background_sync_error(std::string&& loc, const std::string& message)
+        : wallet_logic_error(std::move(loc), message)
+      {
+      }
+    };
+    //----------------------------------------------------------------------------------------------------
+    struct background_wallet_already_open : public background_sync_error
+    {
+      explicit background_wallet_already_open(std::string&& loc, const std::string& background_wallet_file)
+        : background_sync_error(std::move(loc), "background wallet " + background_wallet_file + " is already opened by another wallet program")
+      {
+      }
+    };
+    //----------------------------------------------------------------------------------------------------
+    struct background_custom_password_same_as_wallet_password : public background_sync_error
+    {
+      explicit background_custom_password_same_as_wallet_password(std::string&& loc)
+        : background_sync_error(std::move(loc), "custom background password must be different than wallet password")
+      {
+      }
+    };
+    //----------------------------------------------------------------------------------------------------
 
 #if !defined(_MSC_VER)
 
diff --git a/src/wallet/wallet_rpc_server.cpp b/src/wallet/wallet_rpc_server.cpp
index bab558b82..14c66c5f5 100644
--- a/src/wallet/wallet_rpc_server.cpp
+++ b/src/wallet/wallet_rpc_server.cpp
@@ -73,6 +73,54 @@ using namespace epee;
     } \
   } while(0)
 
+#define CHECK_IF_BACKGROUND_SYNCING() \
+  do \
+  { \
+    if (!m_wallet) { return not_open(er); } \
+    if (m_wallet->is_background_wallet()) \
+    { \
+      er.code = WALLET_RPC_ERROR_CODE_IS_BACKGROUND_WALLET; \
+      er.message = "This command is disabled for background wallets."; \
+      return false; \
+    } \
+    if (m_wallet->is_background_syncing()) \
+    { \
+      er.code = WALLET_RPC_ERROR_CODE_IS_BACKGROUND_SYNCING; \
+      er.message = "This command is disabled while background syncing. Stop background syncing to use this command."; \
+      return false; \
+    } \
+  } while(0)
+
+#define PRE_VALIDATE_BACKGROUND_SYNC() \
+  do \
+  { \
+    if (!m_wallet) { return not_open(er); } \
+    if (m_restricted) \
+    { \
+      er.code = WALLET_RPC_ERROR_CODE_DENIED; \
+      er.message = "Command unavailable in restricted mode."; \
+      return false; \
+    } \
+    if (m_wallet->key_on_device()) \
+    { \
+      er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR; \
+      er.message = "Command not supported by HW wallet"; \
+      return false; \
+    } \
+    if (m_wallet->multisig()) \
+    { \
+      er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR; \
+      er.message = "Multisig wallet cannot enable background sync"; \
+      return false; \
+    } \
+    if (m_wallet->watch_only()) \
+    { \
+      er.code = WALLET_RPC_ERROR_CODE_WATCH_ONLY; \
+      er.message = "Watch-only wallet cannot enable background sync"; \
+      return false; \
+    } \
+  } while (0)
+
 namespace
 {
   const command_line::arg_descriptor<std::string, true> arg_rpc_bind_port = {"rpc-bind-port", "Sets bind port for server"};
@@ -291,6 +339,9 @@ namespace tools
   {
     if (!m_wallet)
       return;
+    // Background mining can be toggled from the main wallet
+    if (m_wallet->is_background_wallet() || m_wallet->is_background_syncing())
+      return;
 
     tools::wallet2::BackgroundMiningSetupType setup = m_wallet->setup_background_mining();
     if (setup == tools::wallet2::BackgroundMiningNo)
@@ -582,6 +633,7 @@ namespace tools
   bool wallet_rpc_server::on_create_address(const wallet_rpc::COMMAND_RPC_CREATE_ADDRESS::request& req, wallet_rpc::COMMAND_RPC_CREATE_ADDRESS::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       if (req.count < 1 || req.count > 64) {
@@ -619,6 +671,7 @@ namespace tools
   bool wallet_rpc_server::on_label_address(const wallet_rpc::COMMAND_RPC_LABEL_ADDRESS::request& req, wallet_rpc::COMMAND_RPC_LABEL_ADDRESS::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->set_subaddress_label(req.index, req.label);
@@ -681,6 +734,7 @@ namespace tools
   bool wallet_rpc_server::on_create_account(const wallet_rpc::COMMAND_RPC_CREATE_ACCOUNT::request& req, wallet_rpc::COMMAND_RPC_CREATE_ACCOUNT::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->add_subaddress_account(req.label);
@@ -698,6 +752,7 @@ namespace tools
   bool wallet_rpc_server::on_label_account(const wallet_rpc::COMMAND_RPC_LABEL_ACCOUNT::request& req, wallet_rpc::COMMAND_RPC_LABEL_ACCOUNT::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->set_subaddress_label({req.account_index, 0}, req.label);
@@ -713,6 +768,7 @@ namespace tools
   bool wallet_rpc_server::on_get_account_tags(const wallet_rpc::COMMAND_RPC_GET_ACCOUNT_TAGS::request& req, wallet_rpc::COMMAND_RPC_GET_ACCOUNT_TAGS::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     const std::pair<std::map<std::string, std::string>, std::vector<std::string>> account_tags = m_wallet->get_account_tags();
     for (const std::pair<const std::string, std::string>& p : account_tags.first)
     {
@@ -732,6 +788,7 @@ namespace tools
   bool wallet_rpc_server::on_tag_accounts(const wallet_rpc::COMMAND_RPC_TAG_ACCOUNTS::request& req, wallet_rpc::COMMAND_RPC_TAG_ACCOUNTS::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->set_account_tag(req.accounts, req.tag);
@@ -747,6 +804,7 @@ namespace tools
   bool wallet_rpc_server::on_untag_accounts(const wallet_rpc::COMMAND_RPC_UNTAG_ACCOUNTS::request& req, wallet_rpc::COMMAND_RPC_UNTAG_ACCOUNTS::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->set_account_tag(req.accounts, "");
@@ -762,6 +820,7 @@ namespace tools
   bool wallet_rpc_server::on_set_account_tag_description(const wallet_rpc::COMMAND_RPC_SET_ACCOUNT_TAG_DESCRIPTION::request& req, wallet_rpc::COMMAND_RPC_SET_ACCOUNT_TAG_DESCRIPTION::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->set_account_tag_description(req.tag, req.description);
@@ -792,6 +851,7 @@ namespace tools
   bool wallet_rpc_server::on_freeze(const wallet_rpc::COMMAND_RPC_FREEZE::request& req, wallet_rpc::COMMAND_RPC_FREEZE::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       if (req.key_image.empty())
@@ -820,6 +880,7 @@ namespace tools
   bool wallet_rpc_server::on_thaw(const wallet_rpc::COMMAND_RPC_THAW::request& req, wallet_rpc::COMMAND_RPC_THAW::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       if (req.key_image.empty())
@@ -848,6 +909,7 @@ namespace tools
   bool wallet_rpc_server::on_frozen(const wallet_rpc::COMMAND_RPC_FROZEN::request& req, wallet_rpc::COMMAND_RPC_FROZEN::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       if (req.key_image.empty())
@@ -875,6 +937,8 @@ namespace tools
   //------------------------------------------------------------------------------------------------------------------------------
   bool wallet_rpc_server::validate_transfer(const std::list<wallet_rpc::transfer_destination>& destinations, const std::string& payment_id, std::vector<cryptonote::tx_destination_entry>& dsts, std::vector<uint8_t>& extra, bool at_least_one_destination, epee::json_rpc::error& er)
   {
+    CHECK_IF_BACKGROUND_SYNCING();
+
     crypto::hash8 integrated_payment_id = crypto::null_hash8;
     std::string extra_nonce;
     for (auto it = destinations.begin(); it != destinations.end(); it++)
@@ -1204,6 +1268,7 @@ namespace tools
     }
 
     CHECK_MULTISIG_ENABLED();
+    CHECK_IF_BACKGROUND_SYNCING();
 
     cryptonote::blobdata blob;
     if (!epee::string_tools::parse_hexstr_to_binbuff(req.unsigned_txset, blob))
@@ -1285,6 +1350,7 @@ namespace tools
       er.message = "command not supported by watch-only wallet";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
     if(req.unsigned_txset.empty() && req.multisig_txset.empty())
     {
       er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
@@ -1554,6 +1620,7 @@ namespace tools
     }
 
     CHECK_MULTISIG_ENABLED();
+    CHECK_IF_BACKGROUND_SYNCING();
 
     try
     {
@@ -2115,6 +2182,7 @@ namespace tools
             er.message = "The wallet is watch-only. Cannot retrieve seed.";
             return false;
           }
+          CHECK_IF_BACKGROUND_SYNCING();
           if (!m_wallet->is_deterministic())
           {
             er.code = WALLET_RPC_ERROR_CODE_NON_DETERMINISTIC;
@@ -2143,6 +2211,7 @@ namespace tools
             er.message = "The wallet is watch-only. Cannot retrieve spend key.";
             return false;
           }
+          CHECK_IF_BACKGROUND_SYNCING();
           epee::wipeable_string key = epee::to_hex::wipeable_string(m_wallet->get_account().get_keys().m_spend_secret_key);
           res.key = std::string(key.data(), key.size());
       }
@@ -2164,6 +2233,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     try
     {
@@ -2177,6 +2247,79 @@ namespace tools
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------------
+  bool wallet_rpc_server::on_setup_background_sync(const wallet_rpc::COMMAND_RPC_SETUP_BACKGROUND_SYNC::request& req, wallet_rpc::COMMAND_RPC_SETUP_BACKGROUND_SYNC::response& res, epee::json_rpc::error& er, const connection_context *ctx)
+  {
+    try
+    {
+      PRE_VALIDATE_BACKGROUND_SYNC();
+      const tools::wallet2::BackgroundSyncType background_sync_type = tools::wallet2::background_sync_type_from_str(req.background_sync_type);
+      boost::optional<epee::wipeable_string> background_cache_password = boost::none;
+      if (background_sync_type == tools::wallet2::BackgroundSyncCustomPassword)
+        background_cache_password = boost::optional<epee::wipeable_string>(req.background_cache_password);
+      m_wallet->setup_background_sync(background_sync_type, req.wallet_password, background_cache_password);
+    }
+    catch (...)
+    {
+      handle_rpc_exception(std::current_exception(), er, WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR);
+      return false;
+    }
+    return true;
+  }
+  //------------------------------------------------------------------------------------------------------------------------------
+  bool wallet_rpc_server::on_start_background_sync(const wallet_rpc::COMMAND_RPC_START_BACKGROUND_SYNC::request& req, wallet_rpc::COMMAND_RPC_START_BACKGROUND_SYNC::response& res, epee::json_rpc::error& er, const connection_context *ctx)
+  {
+    try
+    {
+      PRE_VALIDATE_BACKGROUND_SYNC();
+      m_wallet->start_background_sync();
+    }
+    catch (...)
+    {
+      handle_rpc_exception(std::current_exception(), er, WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR);
+      return false;
+    }
+    return true;
+  }
+  //------------------------------------------------------------------------------------------------------------------------------
+  bool wallet_rpc_server::on_stop_background_sync(const wallet_rpc::COMMAND_RPC_STOP_BACKGROUND_SYNC::request& req, wallet_rpc::COMMAND_RPC_STOP_BACKGROUND_SYNC::response& res, epee::json_rpc::error& er, const connection_context *ctx)
+  {
+    try
+    {
+      PRE_VALIDATE_BACKGROUND_SYNC();
+      crypto::secret_key spend_secret_key = crypto::null_skey;
+
+      // Load the spend key from seed if seed is provided
+      if (!req.seed.empty())
+      {
+        crypto::secret_key recovery_key;
+        std::string language;
+
+        if (!crypto::ElectrumWords::words_to_bytes(req.seed, recovery_key, language))
+        {
+          er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+          er.message = "Electrum-style word list failed verification";
+          return false;
+        }
+
+        if (!req.seed_offset.empty())
+          recovery_key = cryptonote::decrypt_key(recovery_key, req.seed_offset);
+
+        // generate spend key
+        cryptonote::account_base account;
+        account.generate(recovery_key, true, false);
+        spend_secret_key = account.get_keys().m_spend_secret_key;
+      }
+
+      m_wallet->stop_background_sync(req.wallet_password, spend_secret_key);
+    }
+    catch (...)
+    {
+      handle_rpc_exception(std::current_exception(), er, WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR);
+      return false;
+    }
+    return true;
+  }
+  //------------------------------------------------------------------------------------------------------------------------------
   bool wallet_rpc_server::on_sign(const wallet_rpc::COMMAND_RPC_SIGN::request& req, wallet_rpc::COMMAND_RPC_SIGN::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
@@ -2186,6 +2329,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     tools::wallet2::message_signature_type_t signature_type = tools::wallet2::sign_with_spend_key;
     if (req.signature_type == "spend" || req.signature_type == "")
@@ -2278,6 +2422,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     if (req.txids.size() != req.notes.size())
     {
@@ -2350,6 +2495,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     m_wallet->set_attribute(req.key, req.value);
 
@@ -2377,6 +2523,7 @@ namespace tools
   bool wallet_rpc_server::on_get_tx_key(const wallet_rpc::COMMAND_RPC_GET_TX_KEY::request& req, wallet_rpc::COMMAND_RPC_GET_TX_KEY::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
 
     crypto::hash txid;
     if (!epee::string_tools::hex_to_pod(req.txid, txid))
@@ -2468,6 +2615,7 @@ namespace tools
   bool wallet_rpc_server::on_get_tx_proof(const wallet_rpc::COMMAND_RPC_GET_TX_PROOF::request& req, wallet_rpc::COMMAND_RPC_GET_TX_PROOF::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
 
     crypto::hash txid;
     if (!epee::string_tools::hex_to_pod(req.txid, txid))
@@ -2584,6 +2732,7 @@ namespace tools
   bool wallet_rpc_server::on_get_reserve_proof(const wallet_rpc::COMMAND_RPC_GET_RESERVE_PROOF::request& req, wallet_rpc::COMMAND_RPC_GET_RESERVE_PROOF::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
 
     boost::optional<std::pair<uint32_t, uint64_t>> account_minreserve;
     if (!req.all)
@@ -2826,6 +2975,7 @@ namespace tools
       er.message = "command not supported by HW wallet";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     try
     {
@@ -2855,6 +3005,7 @@ namespace tools
       er.message = "command not supported by HW wallet";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     cryptonote::blobdata blob;
     if (!epee::string_tools::parse_hexstr_to_binbuff(req.outputs_data_hex, blob))
@@ -2880,6 +3031,7 @@ namespace tools
   bool wallet_rpc_server::on_export_key_images(const wallet_rpc::COMMAND_RPC_EXPORT_KEY_IMAGES::request& req, wallet_rpc::COMMAND_RPC_EXPORT_KEY_IMAGES::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       std::pair<uint64_t, std::vector<std::pair<crypto::key_image, crypto::signature>>> ski = m_wallet->export_key_images(req.all);
@@ -2916,6 +3068,7 @@ namespace tools
       er.message = "This command requires a trusted daemon.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       std::vector<std::pair<crypto::key_image, crypto::signature>> ski;
@@ -2984,6 +3137,7 @@ namespace tools
   bool wallet_rpc_server::on_get_address_book(const wallet_rpc::COMMAND_RPC_GET_ADDRESS_BOOK_ENTRY::request& req, wallet_rpc::COMMAND_RPC_GET_ADDRESS_BOOK_ENTRY::response& res, epee::json_rpc::error& er, const connection_context *ctx)
   {
     if (!m_wallet) return not_open(er);
+    CHECK_IF_BACKGROUND_SYNCING();
     const auto ab = m_wallet->get_address_book();
     if (req.entries.empty())
     {
@@ -3029,6 +3183,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     cryptonote::address_parse_info info;
     er.message = "";
@@ -3071,6 +3226,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     const auto ab = m_wallet->get_address_book();
     if (req.index >= ab.size())
@@ -3133,6 +3289,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     const auto ab = m_wallet->get_address_book();
     if (req.index >= ab.size())
@@ -3203,6 +3360,7 @@ namespace tools
           er.message = "Command unavailable in restricted mode.";
           return false;
       }
+      CHECK_IF_BACKGROUND_SYNCING();
 
       std::unordered_set<crypto::hash> txids;
       std::list<std::string>::const_iterator i = req.txids.begin();
@@ -3242,6 +3400,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
     try
     {
       m_wallet->rescan_spent();
@@ -3506,6 +3665,7 @@ namespace tools
       er.message = "Command unavailable in restricted mode.";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
     if (m_wallet->verify_password(req.old_password))
     {
       try
@@ -4033,6 +4193,7 @@ namespace tools
       er.message = "wallet is watch-only and cannot be made multisig";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     res.multisig_info = m_wallet->get_multisig_first_kex_msg();
     return true;
@@ -4060,6 +4221,7 @@ namespace tools
       er.message = "wallet is watch-only and cannot be made multisig";
       return false;
     }
+    CHECK_IF_BACKGROUND_SYNCING();
 
     try
     {
diff --git a/src/wallet/wallet_rpc_server.h b/src/wallet/wallet_rpc_server.h
index 3308d1751..c2329aafe 100644
--- a/src/wallet/wallet_rpc_server.h
+++ b/src/wallet/wallet_rpc_server.h
@@ -160,6 +160,9 @@ namespace tools
         MAP_JON_RPC_WE("set_log_categories", on_set_log_categories, wallet_rpc::COMMAND_RPC_SET_LOG_CATEGORIES)
         MAP_JON_RPC_WE("estimate_tx_size_and_weight", on_estimate_tx_size_and_weight, wallet_rpc::COMMAND_RPC_ESTIMATE_TX_SIZE_AND_WEIGHT)
         MAP_JON_RPC_WE("get_version",        on_get_version,        wallet_rpc::COMMAND_RPC_GET_VERSION)
+        MAP_JON_RPC_WE("setup_background_sync", on_setup_background_sync, wallet_rpc::COMMAND_RPC_SETUP_BACKGROUND_SYNC)
+        MAP_JON_RPC_WE("start_background_sync", on_start_background_sync, wallet_rpc::COMMAND_RPC_START_BACKGROUND_SYNC)
+        MAP_JON_RPC_WE("stop_background_sync", on_stop_background_sync, wallet_rpc::COMMAND_RPC_STOP_BACKGROUND_SYNC)
       END_JSON_RPC_MAP()
     END_URI_MAP2()
 
@@ -251,6 +254,9 @@ namespace tools
       bool on_set_log_categories(const wallet_rpc::COMMAND_RPC_SET_LOG_CATEGORIES::request& req, wallet_rpc::COMMAND_RPC_SET_LOG_CATEGORIES::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
       bool on_estimate_tx_size_and_weight(const wallet_rpc::COMMAND_RPC_ESTIMATE_TX_SIZE_AND_WEIGHT::request& req, wallet_rpc::COMMAND_RPC_ESTIMATE_TX_SIZE_AND_WEIGHT::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
       bool on_get_version(const wallet_rpc::COMMAND_RPC_GET_VERSION::request& req, wallet_rpc::COMMAND_RPC_GET_VERSION::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
+      bool on_setup_background_sync(const wallet_rpc::COMMAND_RPC_SETUP_BACKGROUND_SYNC::request& req, wallet_rpc::COMMAND_RPC_SETUP_BACKGROUND_SYNC::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
+      bool on_start_background_sync(const wallet_rpc::COMMAND_RPC_START_BACKGROUND_SYNC::request& req, wallet_rpc::COMMAND_RPC_START_BACKGROUND_SYNC::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
+      bool on_stop_background_sync(const wallet_rpc::COMMAND_RPC_STOP_BACKGROUND_SYNC::request& req, wallet_rpc::COMMAND_RPC_STOP_BACKGROUND_SYNC::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
 
       //json rpc v2
       bool on_query_key(const wallet_rpc::COMMAND_RPC_QUERY_KEY::request& req, wallet_rpc::COMMAND_RPC_QUERY_KEY::response& res, epee::json_rpc::error& er, const connection_context *ctx = NULL);
diff --git a/src/wallet/wallet_rpc_server_commands_defs.h b/src/wallet/wallet_rpc_server_commands_defs.h
index 2ce39f667..72a35eb73 100644
--- a/src/wallet/wallet_rpc_server_commands_defs.h
+++ b/src/wallet/wallet_rpc_server_commands_defs.h
@@ -2698,5 +2698,69 @@ namespace wallet_rpc
     typedef epee::misc_utils::struct_init<response_t> response;
   };
 
+  struct COMMAND_RPC_SETUP_BACKGROUND_SYNC
+  {
+    struct request_t
+    {
+      std::string background_sync_type;
+      std::string wallet_password;
+      std::string background_cache_password;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(background_sync_type)
+        KV_SERIALIZE(wallet_password)
+        KV_SERIALIZE_OPT(background_cache_password, (std::string)"")
+      END_KV_SERIALIZE_MAP()
+    };
+    typedef epee::misc_utils::struct_init<request_t> request;
+
+    struct response_t
+    {
+      BEGIN_KV_SERIALIZE_MAP()
+      END_KV_SERIALIZE_MAP()
+    };
+    typedef epee::misc_utils::struct_init<response_t> response;
+  };
+
+  struct COMMAND_RPC_START_BACKGROUND_SYNC
+  {
+    struct request_t
+    {
+      BEGIN_KV_SERIALIZE_MAP()
+      END_KV_SERIALIZE_MAP()
+    };
+    typedef epee::misc_utils::struct_init<request_t> request;
+
+    struct response_t
+    {
+      BEGIN_KV_SERIALIZE_MAP()
+      END_KV_SERIALIZE_MAP()
+    };
+    typedef epee::misc_utils::struct_init<response_t> response;
+  };
+
+  struct COMMAND_RPC_STOP_BACKGROUND_SYNC
+  {
+    struct request_t
+    {
+      std::string wallet_password;
+      std::string seed;
+      std::string seed_offset;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(wallet_password)
+        KV_SERIALIZE_OPT(seed, (std::string)"")
+        KV_SERIALIZE_OPT(seed_offset, (std::string)"")
+      END_KV_SERIALIZE_MAP()
+    };
+    typedef epee::misc_utils::struct_init<request_t> request;
+
+    struct response_t
+    {
+      BEGIN_KV_SERIALIZE_MAP()
+      END_KV_SERIALIZE_MAP()
+    };
+    typedef epee::misc_utils::struct_init<response_t> response;
+  };
 }
 }
diff --git a/src/wallet/wallet_rpc_server_error_codes.h b/src/wallet/wallet_rpc_server_error_codes.h
index 541d29f86..4756c191c 100644
--- a/src/wallet/wallet_rpc_server_error_codes.h
+++ b/src/wallet/wallet_rpc_server_error_codes.h
@@ -81,3 +81,5 @@
 #define WALLET_RPC_ERROR_CODE_DISABLED               -48
 #define WALLET_RPC_ERROR_CODE_PROXY_ALREADY_DEFINED  -49
 #define WALLET_RPC_ERROR_CODE_NONZERO_UNLOCK_TIME    -50
+#define WALLET_RPC_ERROR_CODE_IS_BACKGROUND_WALLET   -51
+#define WALLET_RPC_ERROR_CODE_IS_BACKGROUND_SYNCING  -52