Reserve proof

src/simplewallet/simplewallet.cpp

@@ -1690,6 +1690,16 @@ simple_wallet::simple_wallet()
                            boost::bind(&simple_wallet::check_spend_proof, this, _1),
                            tr("check_spend_proof <txid> <signature_file> [<message>]"),
                            tr("Check a signature proving that the signer generated <txid>, optionally with a challenge string <message>."));
+  m_cmd_binder.set_handler("get_reserve_proof",
+                           boost::bind(&simple_wallet::get_reserve_proof, this, _1),
+                           tr("get_reserve_proof (all|<amount>) [<message>]"),
+                           tr("Generate a signature proving that you own at least this much, optionally with a challenge string <message>.\n"
+                              "If 'all' is specified, you prove the entire sum of all of your existing accounts' balances.\n"
+                              "Otherwise, you prove the reserve of the smallest possible amount above <amount> available in your current account."));
+  m_cmd_binder.set_handler("check_reserve_proof",
+                           boost::bind(&simple_wallet::check_reserve_proof, this, _1),
+                           tr("check_reserve_proof <address> <signature_file> [<message>]"),
+                           tr("Check a signature proving that the owner of <address> holds at least this much, optionally with a challenge string <message>."));
   m_cmd_binder.set_handler("show_transfers",
                            boost::bind(&simple_wallet::show_transfers, this, _1),
                            tr("show_transfers [in|out|pending|failed|pool] [index=<N1>[,<N2>,...]] [<min_height> [<max_height>]]"),
@@ -5125,6 +5135,110 @@ bool simple_wallet::check_spend_proof(const std::vector<std::string> &args)
   return true;
 }
 //----------------------------------------------------------------------------------------------------
+bool simple_wallet::get_reserve_proof(const std::vector<std::string> &args)
+{
+  if(args.size() != 1 && args.size() != 2) {
+    fail_msg_writer() << tr("usage: get_reserve_proof (all|<amount>) [<message>]");
+    return true;
+  }
+
+  if (m_wallet->watch_only() || m_wallet->multisig())
+  {
+    fail_msg_writer() << tr("The reserve proof can be generated only by a full wallet");
+    return true;
+  }
+
+  boost::optional<std::pair<uint32_t, uint64_t>> account_minreserve;
+  if (args[0] != "all")
+  {
+    account_minreserve = std::pair<uint32_t, uint64_t>();
+    account_minreserve->first = m_current_subaddress_account;
+    if (!cryptonote::parse_amount(account_minreserve->second, args[0]))
+    {
+      fail_msg_writer() << tr("amount is wrong: ") << args[0];
+      return true;
+    }
+  }
+
+  if (!try_connect_to_daemon())
+  {
+    fail_msg_writer() << tr("failed to connect to the daemon");
+    return true;
+  }
+
+  if (m_wallet->ask_password() && !get_and_verify_password()) { return true; }
+
+  LOCK_IDLE_SCOPE();
+
+  try
+  {
+    const std::string sig_str = m_wallet->get_reserve_proof(account_minreserve, args.size() == 2 ? args[1] : "");
+    const std::string filename = "monero_reserve_proof";
+    if (epee::file_io_utils::save_string_to_file(filename, sig_str))
+      success_msg_writer() << tr("signature file saved to: ") << filename;
+    else
+      fail_msg_writer() << tr("failed to save signature file");
+  }
+  catch (const std::exception &e)
+  {
+    fail_msg_writer() << e.what();
+  }
+  return true;
+}
+//----------------------------------------------------------------------------------------------------
+bool simple_wallet::check_reserve_proof(const std::vector<std::string> &args)
+{
+  if(args.size() != 2 && args.size() != 3) {
+    fail_msg_writer() << tr("usage: check_reserve_proof <address> <signature_file> [<message>]");
+    return true;
+  }
+
+  if (!try_connect_to_daemon())
+  {
+    fail_msg_writer() << tr("failed to connect to the daemon");
+    return true;
+  }
+
+  cryptonote::address_parse_info info;
+  if(!cryptonote::get_account_address_from_str_or_url(info, m_wallet->testnet(), args[0], oa_prompter))
+  {
+    fail_msg_writer() << tr("failed to parse address");
+    return true;
+  }
+  if (info.is_subaddress)
+  {
+    fail_msg_writer() << tr("Address must not be a subaddress");
+    return true;
+  }
+
+  std::string sig_str;
+  if (!epee::file_io_utils::load_file_to_string(args[1], sig_str))
+  {
+    fail_msg_writer() << tr("failed to load signature file");
+    return true;
+  }
+
+  LOCK_IDLE_SCOPE();
+
+  try
+  {
+    uint64_t total, spent;
+    if (m_wallet->check_reserve_proof(info.address, args.size() == 3 ? args[2] : "", sig_str, total, spent))
+    {
+      success_msg_writer() << boost::format(tr("Good signature -- total: %s, spent: %s, unspent: %s")) % print_money(total) % print_money(spent) % print_money(total - spent);
+    }
+    else
+    {
+      fail_msg_writer() << tr("Bad signature");
+    }
+  }
+  catch (const std::exception& e)
+  {
+    fail_msg_writer() << e.what();
+  }
+  return true;
+}
+//----------------------------------------------------------------------------------------------------
 static std::string get_human_readable_timestamp(uint64_t ts)
 {
   char buffer[64];

src/simplewallet/simplewallet.h

@@ -170,6 +170,8 @@ namespace cryptonote
     bool check_tx_proof(const std::vector<std::string> &args);
     bool get_spend_proof(const std::vector<std::string> &args);
     bool check_spend_proof(const std::vector<std::string> &args);
+    bool get_reserve_proof(const std::vector<std::string> &args);
+    bool check_reserve_proof(const std::vector<std::string> &args);
     bool show_transfers(const std::vector<std::string> &args);
     bool unspent_outputs(const std::vector<std::string> &args);
     bool rescan_blockchain(const std::vector<std::string> &args);

src/wallet/api/wallet.cpp

@@ -1576,6 +1576,55 @@ 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 {
+    try
+    {
+        m_status = Status_Ok;
+        boost::optional<std::pair<uint32_t, uint64_t>> account_minreserve;
+        if (!all)
+        {
+            account_minreserve = std::make_pair(account_index, amount);
+        }
+        return m_wallet->get_reserve_proof(account_minreserve, message);
+    }
+    catch (const std::exception &e)
+    {
+        m_status = Status_Error;
+        m_errorString = e.what();
+        return "";
+    }
+}
+
+bool WalletImpl::checkReserveProof(const std::string &address, const std::string &message, const std::string &signature, bool &good, uint64_t &total, uint64_t &spent) const {
+    cryptonote::address_parse_info info;
+    if (!cryptonote::get_account_address_from_str(info, m_wallet->testnet(), address))
+    {
+        m_status = Status_Error;
+        m_errorString = tr("Failed to parse address");
+        return false;
+    }
+    if (info.is_subaddress)
+    {
+        m_status = Status_Error;
+        m_errorString = tr("Address must not be a subaddress");
+        return false;
+    }
+
+    good = false;
+    try
+    {
+        m_status = Status_Ok;
+        good = m_wallet->check_reserve_proof(info.address, message, signature, total, spent);
+        return true;
+    }
+    catch (const std::exception &e)
+    {
+        m_status = Status_Error;
+        m_errorString = e.what();
+        return false;
+    }
+}
+
 std::string WalletImpl::signMessage(const std::string &message)
 {
   return m_wallet->sign(message);

src/wallet/api/wallet.h

@@ -142,6 +142,8 @@ public:
     virtual bool checkTxProof(const std::string &txid, const std::string &address, const std::string &message, const std::string &signature, bool &good, uint64_t &received, bool &in_pool, uint64_t &confirmations);
     virtual std::string getSpendProof(const std::string &txid, const std::string &message) const;
     virtual bool checkSpendProof(const std::string &txid, const std::string &message, const std::string &signature, bool &good) const;
+    virtual std::string getReserveProof(bool all, uint32_t account_index, uint64_t amount, const std::string &message) const;
+    virtual bool checkReserveProof(const std::string &address, const std::string &message, const std::string &signature, bool &good, uint64_t &total, uint64_t &spent) const;
     virtual std::string signMessage(const std::string &message);
     virtual bool verifySignedMessage(const std::string &message, const std::string &address, const std::string &signature) const;
     virtual void startRefresh();

src/wallet/api/wallet2_api.h

@@ -706,6 +706,12 @@ struct Wallet
     virtual bool checkTxProof(const std::string &txid, const std::string &address, const std::string &message, const std::string &signature, bool &good, uint64_t &received, bool &in_pool, uint64_t &confirmations) = 0;
     virtual std::string getSpendProof(const std::string &txid, const std::string &message) const = 0;
     virtual bool checkSpendProof(const std::string &txid, const std::string &message, const std::string &signature, bool &good) const = 0;
+    /*!
+     * \brief getReserveProof - Generates a proof that proves the reserve of unspent funds
+     *                          Parameters `account_index` and `amount` are ignored when `all` is true
+     */
+    virtual std::string getReserveProof(bool all, uint32_t account_index, uint64_t amount, const std::string &message) const = 0;
+    virtual bool checkReserveProof(const std::string &address, const std::string &message, const std::string &signature, bool &good, uint64_t &total, uint64_t &spent) const = 0;
 
     /*
      * \brief signMessage - sign a message with the spend private key

src/wallet/wallet2.cpp

@@ -7947,6 +7947,251 @@ bool wallet2::check_tx_proof(const crypto::hash &txid, const cryptonote::account
   return false;
 }
 
+std::string wallet2::get_reserve_proof(const boost::optional<std::pair<uint32_t, uint64_t>> &account_minreserve, const std::string &message)
+{
+  THROW_WALLET_EXCEPTION_IF(m_watch_only || m_multisig, error::wallet_internal_error, "Reserve proof can only be generated by a full wallet");
+  THROW_WALLET_EXCEPTION_IF(balance_all() == 0, error::wallet_internal_error, "Zero balance");
+  THROW_WALLET_EXCEPTION_IF(account_minreserve && balance(account_minreserve->first) < account_minreserve->second, error::wallet_internal_error,
+    "Not enough balance in this account for the requested minimum reserve amount");
+
+  // determine which outputs to include in the proof
+  std::vector<size_t> selected_transfers;
+  for (size_t i = 0; i < m_transfers.size(); ++i)
+  {
+    const transfer_details &td = m_transfers[i];
+    if (!td.m_spent && (!account_minreserve || account_minreserve->first == td.m_subaddr_index.major))
+      selected_transfers.push_back(i);
+  }
+
+  if (account_minreserve)
+  {
+    // minimize the number of outputs included in the proof, by only picking the N largest outputs that can cover the requested min reserve amount
+    std::sort(selected_transfers.begin(), selected_transfers.end(), [&](const size_t a, const size_t b)
+      { return m_transfers[a].amount() > m_transfers[b].amount(); });
+    while (selected_transfers.size() >= 2 && m_transfers[selected_transfers[1]].amount() >= account_minreserve->second)
+      selected_transfers.erase(selected_transfers.begin());
+    size_t sz = 0;
+    uint64_t total = 0;
+    while (total < account_minreserve->second)
+    {
+      total += m_transfers[selected_transfers[sz]].amount();
+      ++sz;
+    }
+    selected_transfers.resize(sz);
+  }
+
+  // compute signature prefix hash
+  std::string prefix_data = message;
+  prefix_data.append((const char*)&m_account.get_keys().m_account_address, sizeof(cryptonote::account_public_address));
+  for (size_t i = 0; i < selected_transfers.size(); ++i)
+  {
+    prefix_data.append((const char*)&m_transfers[selected_transfers[i]].m_key_image, sizeof(crypto::key_image));
+  }
+  crypto::hash prefix_hash;
+  crypto::cn_fast_hash(prefix_data.data(), prefix_data.size(), prefix_hash);
+
+  // generate proof entries
+  std::vector<reserve_proof_entry> proofs(selected_transfers.size());
+  std::unordered_set<cryptonote::subaddress_index> subaddr_indices = { {0,0} };
+  for (size_t i = 0; i < selected_transfers.size(); ++i)
+  {
+    const transfer_details &td = m_transfers[selected_transfers[i]];
+    reserve_proof_entry& proof = proofs[i];
+    proof.txid = td.m_txid;
+    proof.index_in_tx = td.m_internal_output_index;
+    proof.key_image = td.m_key_image;
+    subaddr_indices.insert(td.m_subaddr_index);
+
+    // get tx pub key 
+    const crypto::public_key tx_pub_key = get_tx_pub_key_from_extra(td.m_tx, td.m_pk_index);
+    THROW_WALLET_EXCEPTION_IF(tx_pub_key == crypto::null_pkey, error::wallet_internal_error, "The tx public key isn't found");
+    const std::vector<crypto::public_key> additional_tx_pub_keys = get_additional_tx_pub_keys_from_extra(td.m_tx);
+
+    // determine which tx pub key was used for deriving the output key
+    const crypto::public_key *tx_pub_key_used = &tx_pub_key;
+    for (int i = 0; i < 2; ++i)
+    {
+      proof.shared_secret = rct::rct2pk(rct::scalarmultKey(rct::pk2rct(*tx_pub_key_used), rct::sk2rct(m_account.get_keys().m_view_secret_key)));
+      crypto::key_derivation derivation;
+      THROW_WALLET_EXCEPTION_IF(!crypto::generate_key_derivation(proof.shared_secret, rct::rct2sk(rct::I), derivation),
+        error::wallet_internal_error, "Failed to generate key derivation");
+      crypto::public_key subaddress_spendkey;
+      THROW_WALLET_EXCEPTION_IF(!derive_subaddress_public_key(td.get_public_key(), derivation, proof.index_in_tx, subaddress_spendkey),
+        error::wallet_internal_error, "Failed to derive subaddress public key");
+      if (m_subaddresses.count(subaddress_spendkey) == 1)
+        break;
+      THROW_WALLET_EXCEPTION_IF(additional_tx_pub_keys.empty(), error::wallet_internal_error,
+        "Normal tx pub key doesn't derive the expected output, while the additional tx pub keys are empty");
+      THROW_WALLET_EXCEPTION_IF(i == 1, error::wallet_internal_error,
+        "Neither normal tx pub key nor additional tx pub key derive the expected output key");
+      tx_pub_key_used = &additional_tx_pub_keys[proof.index_in_tx];
+    }
+
+    // generate signature for shared secret
+    crypto::generate_tx_proof(prefix_hash, m_account.get_keys().m_account_address.m_view_public_key, *tx_pub_key_used, boost::none, proof.shared_secret, m_account.get_keys().m_view_secret_key, proof.shared_secret_sig);
+
+    // derive ephemeral secret key
+    crypto::key_image ki;
+    cryptonote::keypair ephemeral;
+    const bool r = cryptonote::generate_key_image_helper(m_account.get_keys(), m_subaddresses, td.get_public_key(), tx_pub_key,  additional_tx_pub_keys, td.m_internal_output_index, ephemeral, ki);
+    THROW_WALLET_EXCEPTION_IF(!r, error::wallet_internal_error, "Failed to generate key image");
+    THROW_WALLET_EXCEPTION_IF(ephemeral.pub != td.get_public_key(), error::wallet_internal_error, "Derived public key doesn't agree with the stored one");
+
+    // generate signature for key image
+    const std::vector<const crypto::public_key*> pubs = { &ephemeral.pub };
+    crypto::generate_ring_signature(prefix_hash, td.m_key_image, &pubs[0], 1, ephemeral.sec, 0, &proof.key_image_sig);
+  }
+
+  // collect all subaddress spend keys that received those outputs and generate their signatures
+  std::unordered_map<crypto::public_key, crypto::signature> subaddr_spendkeys;
+  for (const cryptonote::subaddress_index &index : subaddr_indices)
+  {
+    crypto::secret_key subaddr_spend_skey = m_account.get_keys().m_spend_secret_key;
+    if (!index.is_zero())
+    {
+      crypto::secret_key m = cryptonote::get_subaddress_secret_key(m_account.get_keys().m_view_secret_key, index);
+      crypto::secret_key tmp = subaddr_spend_skey;
+      sc_add((unsigned char*)&subaddr_spend_skey, (unsigned char*)&m, (unsigned char*)&tmp);
+    }
+    crypto::public_key subaddr_spend_pkey;
+    secret_key_to_public_key(subaddr_spend_skey, subaddr_spend_pkey);
+    crypto::generate_signature(prefix_hash, subaddr_spend_pkey, subaddr_spend_skey, subaddr_spendkeys[subaddr_spend_pkey]);
+  }
+
+  // serialize & encode
+  std::ostringstream oss;
+  boost::archive::portable_binary_oarchive ar(oss);
+  ar << proofs << subaddr_spendkeys;
+  return "ReserveProofV1" + tools::base58::encode(oss.str());
+}
+
+bool wallet2::check_reserve_proof(const cryptonote::account_public_address &address, const std::string &message, const std::string &sig_str, uint64_t &total, uint64_t &spent)
+{
+  uint32_t rpc_version;
+  THROW_WALLET_EXCEPTION_IF(!check_connection(&rpc_version), error::wallet_internal_error, "Failed to connect to daemon: " + get_daemon_address());
+  THROW_WALLET_EXCEPTION_IF(rpc_version < MAKE_CORE_RPC_VERSION(1, 0), error::wallet_internal_error, "Daemon RPC version is too old");
+
+  static constexpr char header[] = "ReserveProofV1";
+  THROW_WALLET_EXCEPTION_IF(!boost::string_ref{sig_str}.starts_with(header), error::wallet_internal_error,
+    "Signature header check error");
+
+  std::string sig_decoded;
+  THROW_WALLET_EXCEPTION_IF(!tools::base58::decode(sig_str.substr(std::strlen(header)), sig_decoded), error::wallet_internal_error,
+    "Signature decoding error");
+
+  std::istringstream iss(sig_decoded);
+  boost::archive::portable_binary_iarchive ar(iss);
+  std::vector<reserve_proof_entry> proofs;
+  std::unordered_map<crypto::public_key, crypto::signature> subaddr_spendkeys;
+  ar >> proofs >> subaddr_spendkeys;
+
+  THROW_WALLET_EXCEPTION_IF(subaddr_spendkeys.count(address.m_spend_public_key) == 0, error::wallet_internal_error,
+    "The given address isn't found in the proof");
+
+  // compute signature prefix hash
+  std::string prefix_data = message;
+  prefix_data.append((const char*)&address, sizeof(cryptonote::account_public_address));
+  for (size_t i = 0; i < proofs.size(); ++i)
+  {
+    prefix_data.append((const char*)&proofs[i].key_image, sizeof(crypto::key_image));
+  }
+  crypto::hash prefix_hash;
+  crypto::cn_fast_hash(prefix_data.data(), prefix_data.size(), prefix_hash);
+
+  // fetch txes from daemon
+  COMMAND_RPC_GET_TRANSACTIONS::request gettx_req;
+  COMMAND_RPC_GET_TRANSACTIONS::response gettx_res;
+  for (size_t i = 0; i < proofs.size(); ++i)
+    gettx_req.txs_hashes.push_back(epee::string_tools::pod_to_hex(proofs[i].txid));
+  m_daemon_rpc_mutex.lock();
+  bool ok = net_utils::invoke_http_json("/gettransactions", gettx_req, gettx_res, m_http_client);
+  m_daemon_rpc_mutex.unlock();
+  THROW_WALLET_EXCEPTION_IF(!ok || gettx_res.txs.size() != proofs.size(),
+    error::wallet_internal_error, "Failed to get transaction from daemon");
+
+  // check spent status
+  COMMAND_RPC_IS_KEY_IMAGE_SPENT::request kispent_req;
+  COMMAND_RPC_IS_KEY_IMAGE_SPENT::response kispent_res;
+  for (size_t i = 0; i < proofs.size(); ++i)
+    kispent_req.key_images.push_back(epee::string_tools::pod_to_hex(proofs[i].key_image));
+  m_daemon_rpc_mutex.lock();
+  ok = epee::net_utils::invoke_http_json("/is_key_image_spent", kispent_req, kispent_res, m_http_client, rpc_timeout);
+  m_daemon_rpc_mutex.unlock();
+  THROW_WALLET_EXCEPTION_IF(!ok || kispent_res.spent_status.size() != proofs.size(),
+    error::wallet_internal_error, "Failed to get key image spent status from daemon");
+
+  total = spent = 0;
+  for (size_t i = 0; i < proofs.size(); ++i)
+  {
+    const reserve_proof_entry& proof = proofs[i];
+    THROW_WALLET_EXCEPTION_IF(gettx_res.txs[i].in_pool, error::wallet_internal_error, "Tx is unconfirmed");
+
+    cryptonote::blobdata tx_data;
+    ok = string_tools::parse_hexstr_to_binbuff(gettx_res.txs[i].as_hex, tx_data);
+    THROW_WALLET_EXCEPTION_IF(!ok, error::wallet_internal_error, "Failed to parse transaction from daemon");
+
+    crypto::hash tx_hash, tx_prefix_hash;
+    cryptonote::transaction tx;
+    THROW_WALLET_EXCEPTION_IF(!cryptonote::parse_and_validate_tx_from_blob(tx_data, tx, tx_hash, tx_prefix_hash), error::wallet_internal_error,
+      "Failed to validate transaction from daemon");
+    THROW_WALLET_EXCEPTION_IF(tx_hash != proof.txid, error::wallet_internal_error, "Failed to get the right transaction from daemon");
+
+    THROW_WALLET_EXCEPTION_IF(proof.index_in_tx >= tx.vout.size(), error::wallet_internal_error, "index_in_tx is out of bound");
+
+    const cryptonote::txout_to_key* const out_key = boost::get<cryptonote::txout_to_key>(std::addressof(tx.vout[proof.index_in_tx].target));
+    THROW_WALLET_EXCEPTION_IF(!out_key, error::wallet_internal_error, "Output key wasn't found")
+
+    // get tx pub key
+    const crypto::public_key tx_pub_key = get_tx_pub_key_from_extra(tx);
+    THROW_WALLET_EXCEPTION_IF(tx_pub_key == crypto::null_pkey, error::wallet_internal_error, "The tx public key isn't found");
+    const std::vector<crypto::public_key> additional_tx_pub_keys = get_additional_tx_pub_keys_from_extra(tx);
+
+    // check singature for shared secret
+    ok = crypto::check_tx_proof(prefix_hash, address.m_view_public_key, tx_pub_key, boost::none, proof.shared_secret, proof.shared_secret_sig);
+    if (!ok && additional_tx_pub_keys.size() == tx.vout.size())
+      ok = crypto::check_tx_proof(prefix_hash, address.m_view_public_key, additional_tx_pub_keys[proof.index_in_tx], boost::none, proof.shared_secret, proof.shared_secret_sig);
+    if (!ok)
+      return false;
+
+    // check signature for key image
+    const std::vector<const crypto::public_key*> pubs = { &out_key->key };
+    ok = crypto::check_ring_signature(prefix_hash, proof.key_image, &pubs[0], 1, &proof.key_image_sig);
+    if (!ok)
+      return false;
+
+    // check if the address really received the fund
+    crypto::key_derivation derivation;
+    THROW_WALLET_EXCEPTION_IF(!crypto::generate_key_derivation(proof.shared_secret, rct::rct2sk(rct::I), derivation), error::wallet_internal_error, "Failed to generate key derivation");
+    crypto::public_key subaddr_spendkey;
+    crypto::derive_subaddress_public_key(out_key->key, derivation, proof.index_in_tx, subaddr_spendkey);
+    THROW_WALLET_EXCEPTION_IF(subaddr_spendkeys.count(subaddr_spendkey) == 0, error::wallet_internal_error,
+      "The address doesn't seem to have received the fund");
+
+    // check amount
+    uint64_t amount = tx.vout[proof.index_in_tx].amount;
+    if (amount == 0)
+    {
+      // decode rct
+      crypto::secret_key shared_secret;
+      crypto::derivation_to_scalar(derivation, proof.index_in_tx, shared_secret);
+      rct::ecdhTuple ecdh_info = tx.rct_signatures.ecdhInfo[proof.index_in_tx];
+      rct::ecdhDecode(ecdh_info, rct::sk2rct(shared_secret));
+      amount = rct::h2d(ecdh_info.amount);
+    }
+    total += amount;
+    if (kispent_res.spent_status[i])
+      spent += amount;
+  }
+
+  // check signatures for all subaddress spend keys
+  for (const auto &i : subaddr_spendkeys)
+  {
+    if (!crypto::check_signature(prefix_hash, i.first, i.second))
+      return false;
+  }
+  return true;
+}
+
 std::string wallet2::get_wallet_file() const
 {
   return m_wallet_file;

src/wallet/wallet2.h

@@ -433,6 +433,16 @@ namespace tools
       bool m_is_subaddress;
     };
 
+    struct reserve_proof_entry
+    {
+      crypto::hash txid;
+      uint64_t index_in_tx;
+      crypto::public_key shared_secret;
+      crypto::key_image key_image;
+      crypto::signature shared_secret_sig;
+      crypto::signature key_image_sig;
+    };
+
     typedef std::tuple<uint64_t, crypto::public_key, rct::key> get_outs_entry;
 
     /*!
@@ -836,6 +846,26 @@ namespace tools
 
     std::string get_spend_proof(const crypto::hash &txid, const std::string &message);
     bool check_spend_proof(const crypto::hash &txid, const std::string &message, const std::string &sig_str);
+
+    /*!
+     * \brief  Generates a proof that proves the reserve of unspent funds
+     * \param  account_minreserve       When specified, collect outputs only belonging to the given account and prove the smallest reserve above the given amount
+     *                                  When unspecified, proves for all unspent outputs across all accounts
+     * \param  message                  Arbitrary challenge message to be signed together
+     * \return                          Signature string
+     */
+    std::string get_reserve_proof(const boost::optional<std::pair<uint32_t, uint64_t>> &account_minreserve, const std::string &message);
+    /*!
+     * \brief  Verifies a proof of reserve
+     * \param  address                  The signer's address
+     * \param  message                  Challenge message used for signing
+     * \param  sig_str                  Signature string
+     * \param  total                    [OUT] the sum of funds included in the signature
+     * \param  spent                    [OUT] the sum of spent funds included in the signature
+     * \return                          true if the signature verifies correctly
+     */
+    bool check_reserve_proof(const cryptonote::account_public_address &address, const std::string &message, const std::string &sig_str, uint64_t &total, uint64_t &spent);
+
    /*!
     * \brief GUI Address book get/store
     */
@@ -1119,6 +1149,7 @@ BOOST_CLASS_VERSION(tools::wallet2::pool_payment_details, 1)
 BOOST_CLASS_VERSION(tools::wallet2::unconfirmed_transfer_details, 7)
 BOOST_CLASS_VERSION(tools::wallet2::confirmed_transfer_details, 5)
 BOOST_CLASS_VERSION(tools::wallet2::address_book_row, 17)
+BOOST_CLASS_VERSION(tools::wallet2::reserve_proof_entry, 0)
 BOOST_CLASS_VERSION(tools::wallet2::unsigned_tx_set, 0)
 BOOST_CLASS_VERSION(tools::wallet2::signed_tx_set, 0)
 BOOST_CLASS_VERSION(tools::wallet2::tx_construction_data, 2)
@@ -1401,6 +1432,17 @@ namespace boost
       a & x.m_is_subaddress;
     }
 
+    template <class Archive>
+    inline void serialize(Archive& a, tools::wallet2::reserve_proof_entry& x, const boost::serialization::version_type ver)
+    {
+      a & x.txid;
+      a & x.index_in_tx;
+      a & x.shared_secret;
+      a & x.key_image;
+      a & x.shared_secret_sig;
+      a & x.key_image_sig;
+    }
+
     template <class Archive>
     inline void serialize(Archive &a, tools::wallet2::unsigned_tx_set &x, const boost::serialization::version_type ver)
     {

src/wallet/wallet_rpc_server.cpp

@@ -1721,6 +1721,66 @@ namespace tools
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------------
+  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)
+  {
+    if (!m_wallet) return not_open(er);
+
+    boost::optional<std::pair<uint32_t, uint64_t>> account_minreserve;
+    if (!req.all)
+    {
+      if (req.account_index >= m_wallet->get_num_subaddress_accounts())
+      {
+        er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+        er.message = "Account index is out of bound";
+        return false;
+      }
+      account_minreserve = std::make_pair(req.account_index, req.amount);
+    }
+
+    try
+    {
+      res.signature = m_wallet->get_reserve_proof(account_minreserve, req.message);
+    }
+    catch (const std::exception &e)
+    {
+      er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+      er.message = e.what();
+      return false;
+    }
+    return true;
+  }
+  //------------------------------------------------------------------------------------------------------------------------------
+  bool wallet_rpc_server::on_check_reserve_proof(const wallet_rpc::COMMAND_RPC_CHECK_RESERVE_PROOF::request& req, wallet_rpc::COMMAND_RPC_CHECK_RESERVE_PROOF::response& res, epee::json_rpc::error& er)
+  {
+    if (!m_wallet) return not_open(er);
+
+    cryptonote::address_parse_info info;
+    if (!get_account_address_from_str(info, m_wallet->testnet(), req.address))
+    {
+      er.code = WALLET_RPC_ERROR_CODE_WRONG_ADDRESS;
+      er.message = "Invalid address";
+      return false;
+    }
+    if (info.is_subaddress)
+    {
+      er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+      er.message = "Address must not be a subaddress";
+      return false;
+    }
+
+    try
+    {
+      res.good = m_wallet->check_reserve_proof(info.address, req.message, req.signature, res.total, res.spent);
+    }
+    catch (const std::exception &e)
+    {
+      er.code = WALLET_RPC_ERROR_CODE_UNKNOWN_ERROR;
+      er.message = e.what();
+      return false;
+    }
+    return true;
+  }
+  //------------------------------------------------------------------------------------------------------------------------------
   bool wallet_rpc_server::on_get_transfers(const wallet_rpc::COMMAND_RPC_GET_TRANSFERS::request& req, wallet_rpc::COMMAND_RPC_GET_TRANSFERS::response& res, epee::json_rpc::error& er)
   {
     if (!m_wallet) return not_open(er);

src/wallet/wallet_rpc_server.h

@@ -104,6 +104,8 @@ namespace tools
         MAP_JON_RPC_WE("check_tx_proof",     on_check_tx_proof,     wallet_rpc::COMMAND_RPC_CHECK_TX_PROOF)
         MAP_JON_RPC_WE("get_spend_proof",    on_get_spend_proof,    wallet_rpc::COMMAND_RPC_GET_SPEND_PROOF)
         MAP_JON_RPC_WE("check_spend_proof",  on_check_spend_proof,  wallet_rpc::COMMAND_RPC_CHECK_SPEND_PROOF)
+        MAP_JON_RPC_WE("get_reserve_proof",    on_get_reserve_proof,    wallet_rpc::COMMAND_RPC_GET_RESERVE_PROOF)
+        MAP_JON_RPC_WE("check_reserve_proof",  on_check_reserve_proof,  wallet_rpc::COMMAND_RPC_CHECK_RESERVE_PROOF)
         MAP_JON_RPC_WE("get_transfers",      on_get_transfers,      wallet_rpc::COMMAND_RPC_GET_TRANSFERS)
         MAP_JON_RPC_WE("get_transfer_by_txid", on_get_transfer_by_txid, wallet_rpc::COMMAND_RPC_GET_TRANSFER_BY_TXID)
         MAP_JON_RPC_WE("sign",               on_sign,               wallet_rpc::COMMAND_RPC_SIGN)
@@ -170,6 +172,8 @@ namespace tools
       bool on_check_tx_proof(const wallet_rpc::COMMAND_RPC_CHECK_TX_PROOF::request& req, wallet_rpc::COMMAND_RPC_CHECK_TX_PROOF::response& res, epee::json_rpc::error& er);
       bool on_get_spend_proof(const wallet_rpc::COMMAND_RPC_GET_SPEND_PROOF::request& req, wallet_rpc::COMMAND_RPC_GET_SPEND_PROOF::response& res, epee::json_rpc::error& er);
       bool on_check_spend_proof(const wallet_rpc::COMMAND_RPC_CHECK_SPEND_PROOF::request& req, wallet_rpc::COMMAND_RPC_CHECK_SPEND_PROOF::response& res, epee::json_rpc::error& er);
+      bool 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);
+      bool on_check_reserve_proof(const wallet_rpc::COMMAND_RPC_CHECK_RESERVE_PROOF::request& req, wallet_rpc::COMMAND_RPC_CHECK_RESERVE_PROOF::response& res, epee::json_rpc::error& er);
       bool on_get_transfers(const wallet_rpc::COMMAND_RPC_GET_TRANSFERS::request& req, wallet_rpc::COMMAND_RPC_GET_TRANSFERS::response& res, epee::json_rpc::error& er);
       bool on_get_transfer_by_txid(const wallet_rpc::COMMAND_RPC_GET_TRANSFER_BY_TXID::request& req, wallet_rpc::COMMAND_RPC_GET_TRANSFER_BY_TXID::response& res, epee::json_rpc::error& er);
       bool on_sign(const wallet_rpc::COMMAND_RPC_SIGN::request& req, wallet_rpc::COMMAND_RPC_SIGN::response& res, epee::json_rpc::error& er);

src/wallet/wallet_rpc_server_commands_defs.h

@@ -1180,6 +1180,62 @@ namespace wallet_rpc
     };
   };
 
+  struct COMMAND_RPC_GET_RESERVE_PROOF
+  {
+    struct request
+    {
+      bool all;
+      uint32_t account_index;     // ignored when `all` is true
+      uint64_t amount;            // ignored when `all` is true
+      std::string message;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(all)
+        KV_SERIALIZE(account_index)
+        KV_SERIALIZE(amount)
+        KV_SERIALIZE(message)
+      END_KV_SERIALIZE_MAP()
+    };
+
+    struct response
+    {
+      std::string signature;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(signature)
+      END_KV_SERIALIZE_MAP()
+    };
+  };
+
+  struct COMMAND_RPC_CHECK_RESERVE_PROOF
+  {
+    struct request
+    {
+      std::string address;
+      std::string message;
+      std::string signature;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(address)
+        KV_SERIALIZE(message)
+        KV_SERIALIZE(signature)
+      END_KV_SERIALIZE_MAP()
+    };
+
+    struct response
+    {
+      bool good;
+      uint64_t total;
+      uint64_t spent;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(good)
+        KV_SERIALIZE(total)
+        KV_SERIALIZE(spent)
+      END_KV_SERIALIZE_MAP()
+    };
+  };
+
   struct COMMAND_RPC_GET_TRANSFERS
   {
     struct request