Add wallet2::verify_password method

Allows wallet password to be verified without changing wallet state.

src/wallet/wallet2.cpp

@@ -570,6 +570,54 @@ void wallet2::load_keys(const std::string& keys_file_name, const std::string& pa
   THROW_WALLET_EXCEPTION_IF(!r, error::invalid_password);
 }
 
+/*!
+ * \brief verify password for default wallet keys file.
+ * \param password       Password to verify
+ *
+ * for verification only
+ * should not mutate state, unlike load_keys()
+ * can be used prior to rewriting wallet keys file, to ensure user has entered the correct password
+ *
+ */
+bool wallet2::verify_password(const std::string& password)
+{
+  const std::string keys_file_name = m_keys_file;
+  wallet2::keys_file_data keys_file_data;
+  std::string buf;
+  bool r = epee::file_io_utils::load_file_to_string(keys_file_name, buf);
+  THROW_WALLET_EXCEPTION_IF(!r, error::file_read_error, keys_file_name);
+
+  // Decrypt the contents
+  r = ::serialization::parse_binary(buf, keys_file_data);
+  THROW_WALLET_EXCEPTION_IF(!r, error::wallet_internal_error, "internal error: failed to deserialize \"" + keys_file_name + '\"');
+  crypto::chacha8_key key;
+  crypto::generate_chacha8_key(password, key);
+  std::string account_data;
+  account_data.resize(keys_file_data.account_data.size());
+  crypto::chacha8(keys_file_data.account_data.data(), keys_file_data.account_data.size(), key, keys_file_data.iv, &account_data[0]);
+
+  // The contents should be JSON if the wallet follows the new format.
+  rapidjson::Document json;
+  if (json.Parse(account_data.c_str(), keys_file_data.account_data.size()).HasParseError())
+  {
+    // old format before JSON wallet key file format
+  }
+  else
+  {
+    account_data = std::string(json["key_data"].GetString(), json["key_data"].GetString() +
+      json["key_data"].GetStringLength());
+  }
+
+  cryptonote::account_base account_data_check;
+
+  r = epee::serialization::load_t_from_binary(account_data_check, account_data);
+  const cryptonote::account_keys& keys = account_data_check.get_keys();
+
+  r = r && verify_keys(keys.m_view_secret_key,  keys.m_account_address.m_view_public_key);
+  r = r && verify_keys(keys.m_spend_secret_key, keys.m_account_address.m_spend_public_key);
+  return r;
+}
+
 /*!
  * \brief  Generates a wallet or restores one.
  * \param  wallet_        Name of wallet file

src/wallet/wallet2.h

@@ -153,6 +153,11 @@ namespace tools
     void rewrite(const std::string& wallet_name, const std::string& password);
     void load(const std::string& wallet, const std::string& password);
     void store();
+
+    /*!
+     * \brief verifies given password is correct for default wallet keys file
+     */
+    bool verify_password(const std::string& password);
     cryptonote::account_base& get_account(){return m_account;}
 
     // upper_transaction_size_limit as defined below is set to