wallet-rpc: restore from multisig seed (and fix generation)

contrib/epee/include/span.h

@@ -147,6 +147,16 @@ namespace epee
     return {reinterpret_cast<const std::uint8_t*>(src.data()), src.size_bytes()}; 
   }
 
+  //! \return `span<std::uint8_t>` from a STL compatible `src`.
+  template<typename T>
+  constexpr span<std::uint8_t> to_mut_byte_span(T& src)
+  {
+    using value_type = typename T::value_type;
+    static_assert(!std::is_empty<value_type>(), "empty value types will not work -> sizeof == 1");
+    static_assert(!has_padding<value_type>(), "source value type may have padding");
+    return {reinterpret_cast<std::uint8_t*>(src.data()), src.size() * sizeof(value_type)};
+  }
+
   //! \return `span<const std::uint8_t>` which represents the bytes at `&src`.
   template<typename T>
   span<const std::uint8_t> as_byte_span(const T& src) noexcept

src/wallet/wallet2.cpp

@@ -986,6 +986,21 @@ bool get_pruned_tx(const cryptonote::COMMAND_RPC_GET_TRANSACTIONS::entry &entry,
   return false;
 }
 
+// Given M (threshold) and N (total), calculate the number of private multisig keys each
+// signer should have. This value is equal to (N - 1) choose (N - M)
+// Prereq: M >= 1 && N >= M && N <= 16
+uint64_t num_priv_multisig_keys_post_setup(uint64_t threshold, uint64_t total)
+{
+  THROW_WALLET_EXCEPTION_IF(threshold < 1 || total < threshold || threshold > 16,
+    tools::error::wallet_internal_error, "Invalid arguments to num_priv_multisig_keys_post_setup");
+
+  uint64_t n_multisig_keys = 1;
+  for (uint64_t i = 2; i <= total - 1; ++i) n_multisig_keys *= i; // multiply by (N - 1)!
+  for (uint64_t i = 2; i <= total - threshold; ++i) n_multisig_keys /= i; // divide by (N - M)!
+  for (uint64_t i = 2; i <= threshold - 1; ++i) n_multisig_keys /= i; // divide by ((N - 1) - (N - M))!
+  return n_multisig_keys;
+}
+
   //-----------------------------------------------------------------
 } //namespace
 
@@ -1394,7 +1409,7 @@ bool wallet2::get_seed(epee::wipeable_string& electrum_words, const epee::wipeab
   return true;
 }
 //----------------------------------------------------------------------------------------------------
-bool wallet2::get_multisig_seed(epee::wipeable_string& seed, const epee::wipeable_string &passphrase, bool raw) const
+bool wallet2::get_multisig_seed(epee::wipeable_string& seed, const epee::wipeable_string &passphrase) const
 {
   bool ready;
   uint32_t threshold, total;
@@ -1408,15 +1423,14 @@ bool wallet2::get_multisig_seed(epee::wipeable_string& seed, const epee::wipeabl
     std::cout << "This multisig wallet is not yet finalized" << std::endl;
     return false;
   }
-  if (!raw && seed_language.empty())
-  {
-    std::cout << "seed_language not set" << std::endl;
-    return false;
-  }
+
+  const uint64_t num_expected_ms_keys = num_priv_multisig_keys_post_setup(threshold, total);
 
   crypto::secret_key skey;
   crypto::public_key pkey;
   const account_keys &keys = get_account().get_keys();
+  THROW_WALLET_EXCEPTION_IF(num_expected_ms_keys != keys.m_multisig_keys.size(),
+    error::wallet_internal_error, "Unexpected number of private multisig keys")
   epee::wipeable_string data;
   data.append((const char*)&threshold, sizeof(uint32_t));
   data.append((const char*)&total, sizeof(uint32_t));
@@ -1441,18 +1455,7 @@ bool wallet2::get_multisig_seed(epee::wipeable_string& seed, const epee::wipeabl
     data = encrypt(data, key, true);
   }
 
-  if (raw)
-  {
-    seed = epee::to_hex::wipeable_string({(const unsigned char*)data.data(), data.size()});
-  }
-  else
-  {
-    if (!crypto::ElectrumWords::bytes_to_words(data.data(), data.size(), seed, seed_language))
-    {
-      std::cout << "Failed to encode seed";
-      return false;
-    }
-  }
+  seed = epee::to_hex::wipeable_string({(const unsigned char*)data.data(), data.size()});
 
   return true;
 }
@@ -4905,9 +4908,11 @@ void wallet2::generate(const std::string& wallet_, const epee::wipeable_string&
   offset += sizeof(uint32_t);
   uint32_t total = *(uint32_t*)(multisig_data.data() + offset);
   offset += sizeof(uint32_t);
-  THROW_WALLET_EXCEPTION_IF(threshold < 2, error::invalid_multisig_seed);
-  THROW_WALLET_EXCEPTION_IF(total != threshold && total != threshold + 1, error::invalid_multisig_seed);
-  const size_t n_multisig_keys =  total == threshold ? 1 : threshold;
+
+  THROW_WALLET_EXCEPTION_IF(threshold < 1, error::invalid_multisig_seed);
+  THROW_WALLET_EXCEPTION_IF(total < threshold, error::invalid_multisig_seed);
+  THROW_WALLET_EXCEPTION_IF(threshold > 16, error::invalid_multisig_seed); // doing N choose (N - M + 1) might overflow
+  const uint64_t n_multisig_keys = num_priv_multisig_keys_post_setup(threshold, total);
   THROW_WALLET_EXCEPTION_IF(multisig_data.size() != 8 + 32 * (4 + n_multisig_keys + total), error::invalid_multisig_seed);
 
   std::vector<crypto::secret_key> multisig_keys;

src/wallet/wallet2.h

@@ -1020,7 +1020,7 @@ namespace tools
     bool multisig(bool *ready = NULL, uint32_t *threshold = NULL, uint32_t *total = NULL) const;
     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(), bool raw = true) const;
+    bool get_multisig_seed(epee::wipeable_string& seed, const epee::wipeable_string &passphrase = std::string()) const;
     bool key_on_device() const { return get_device_type() != hw::device::device_type::SOFTWARE; }
     hw::device::device_type get_device_type() const { return m_key_device_type; }
     bool reconnect_device();

src/wallet/wallet_rpc_server.cpp

@@ -3807,7 +3807,7 @@ namespace tools
     std::string old_language;
 
     // check the given seed
-    {
+    if (!req.enable_multisig_experimental) {
       if (!crypto::ElectrumWords::words_to_bytes(req.seed, recovery_key, old_language))
       {
         er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
@@ -3830,6 +3830,13 @@ namespace tools
 
     // process seed_offset if given
     {
+      if (req.enable_multisig_experimental && !req.seed_offset.empty())
+      {
+        er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+        er.message = "Multisig seeds are not compatible with seed offsets";
+        return false;
+      }
+
       if (!req.seed_offset.empty())
       {
         recovery_key = cryptonote::decrypt_key(recovery_key, req.seed_offset);
@@ -3893,7 +3900,27 @@ namespace tools
     crypto::secret_key recovery_val;
     try
     {
-      recovery_val = wal->generate(wallet_file, std::move(rc.second).password(), recovery_key, true, false, false);
+      if (req.enable_multisig_experimental)
+      {
+        // Parse multisig seed into raw multisig data
+        epee::wipeable_string multisig_data;
+        multisig_data.resize(req.seed.size() / 2);
+        if (!epee::from_hex::to_buffer(epee::to_mut_byte_span(multisig_data), req.seed))
+        {
+          er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+          er.message = "Multisig seed not represented as hexadecimal string";
+          return false;
+        }
+
+        // Generate multisig wallet
+        wal->generate(wallet_file, std::move(rc.second).password(), multisig_data, false);
+        wal->enable_multisig(true);
+      }
+      else
+      {
+        // Generate normal wallet
+        recovery_val = wal->generate(wallet_file, std::move(rc.second).password(), recovery_key, true, false, false);
+      }
       MINFO("Wallet has been restored.\n");
     }
     catch (const std::exception &e)
@@ -3904,7 +3931,7 @@ namespace tools
 
     // // Convert the secret key back to seed
     epee::wipeable_string electrum_words;
-    if (!crypto::ElectrumWords::bytes_to_words(recovery_val, electrum_words, mnemonic_language))
+    if (!req.enable_multisig_experimental && !crypto::ElectrumWords::bytes_to_words(recovery_val, electrum_words, mnemonic_language))
     {
       er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
       er.message = "Failed to encode seed";

src/wallet/wallet_rpc_server_commands_defs.h

@@ -2360,6 +2360,7 @@ namespace wallet_rpc
       std::string password;
       std::string language;
       bool autosave_current;
+      bool enable_multisig_experimental;
 
       BEGIN_KV_SERIALIZE_MAP()
       KV_SERIALIZE_OPT(restore_height, (uint64_t)0)
@@ -2369,6 +2370,7 @@ namespace wallet_rpc
       KV_SERIALIZE(password)
       KV_SERIALIZE(language)
       KV_SERIALIZE_OPT(autosave_current, true)
+      KV_SERIALIZE_OPT(enable_multisig_experimental, false)
       END_KV_SERIALIZE_MAP()
     };
     typedef epee::misc_utils::struct_init<request_t> request;