wallet: encrypt outputs and key images files with the view key

This key is available to both cold and hot wallet.
Authenticated encryption will guard against interception and/or
modification of the file.

src/simplewallet/simplewallet.cpp

@@ -77,8 +77,8 @@ typedef cryptonote::simple_wallet sw;
 
 #define DEFAULT_MIX 4
 
-#define KEY_IMAGE_EXPORT_FILE_MAGIC "Monero key image export\001"
+#define KEY_IMAGE_EXPORT_FILE_MAGIC "Monero key image export\002"
-#define OUTPUT_EXPORT_FILE_MAGIC "Monero output export\001"
+#define OUTPUT_EXPORT_FILE_MAGIC "Monero output export\002"
 
 // workaround for a suspected bug in pthread/kernel on MacOS X
 #ifdef __APPLE__
@@ -4018,8 +4018,10 @@ bool simple_wallet::export_key_images(const std::vector<std::string> &args)
   try
   {
     std::vector<std::pair<crypto::key_image, crypto::signature>> ski = m_wallet->export_key_images();
-    std::string data(KEY_IMAGE_EXPORT_FILE_MAGIC, strlen(KEY_IMAGE_EXPORT_FILE_MAGIC));
+    std::string magic(KEY_IMAGE_EXPORT_FILE_MAGIC, strlen(KEY_IMAGE_EXPORT_FILE_MAGIC));
     const cryptonote::account_public_address &keys = m_wallet->get_account().get_keys().m_account_address;
+
+    std::string data;
     data += std::string((const char *)&keys.m_spend_public_key, sizeof(crypto::public_key));
     data += std::string((const char *)&keys.m_view_public_key, sizeof(crypto::public_key));
     for (const auto &i: ski)
@@ -4027,7 +4029,10 @@ bool simple_wallet::export_key_images(const std::vector<std::string> &args)
       data += std::string((const char *)&i.first, sizeof(crypto::key_image));
       data += std::string((const char *)&i.second, sizeof(crypto::signature));
     }
-    bool r = epee::file_io_utils::save_string_to_file(filename, data);
+
+    // encrypt data, keep magic plaintext
+    std::string ciphertext = m_wallet->encrypt_with_view_secret_key(data);
+    bool r = epee::file_io_utils::save_string_to_file(filename, magic + ciphertext);
     if (!r)
     {
       fail_msg_writer() << tr("failed to save file ") << filename;
@@ -4067,14 +4072,25 @@ bool simple_wallet::import_key_images(const std::vector<std::string> &args)
     fail_msg_writer() << "Bad key image export file magic in " << filename;
     return true;
   }
-  const size_t headerlen = magiclen + 2 * sizeof(crypto::public_key);
+
+  try
+  {
+    data = m_wallet->decrypt_with_view_secret_key(std::string(data, magiclen));
+  }
+  catch (const std::exception &e)
+  {
+    fail_msg_writer() << "Failed to decrypt " << filename << ": " << e.what();
+    return true;
+  }
+
+  const size_t headerlen = 2 * sizeof(crypto::public_key);
   if (data.size() < headerlen)
   {
     fail_msg_writer() << "Bad data size from file " << filename;
     return true;
   }
-  const crypto::public_key &public_spend_key = *(const crypto::public_key*)&data[magiclen];
+  const crypto::public_key &public_spend_key = *(const crypto::public_key*)&data[0];
-  const crypto::public_key &public_view_key = *(const crypto::public_key*)&data[magiclen + sizeof(crypto::public_key)];
+  const crypto::public_key &public_view_key = *(const crypto::public_key*)&data[sizeof(crypto::public_key)];
   const cryptonote::account_public_address &keys = m_wallet->get_account().get_keys().m_account_address;
   if (public_spend_key != keys.m_spend_public_key || public_view_key != keys.m_view_public_key)
   {
@@ -4133,11 +4149,13 @@ bool simple_wallet::export_outputs(const std::vector<std::string> &args)
     boost::archive::binary_oarchive ar(oss);
     ar << outs;
 
-    std::string data(OUTPUT_EXPORT_FILE_MAGIC, strlen(OUTPUT_EXPORT_FILE_MAGIC));
+    std::string magic(OUTPUT_EXPORT_FILE_MAGIC, strlen(OUTPUT_EXPORT_FILE_MAGIC));
     const cryptonote::account_public_address &keys = m_wallet->get_account().get_keys().m_account_address;
-    data += std::string((const char *)&keys.m_spend_public_key, sizeof(crypto::public_key));
+    std::string header;
-    data += std::string((const char *)&keys.m_view_public_key, sizeof(crypto::public_key));
+    header += std::string((const char *)&keys.m_spend_public_key, sizeof(crypto::public_key));
-    bool r = epee::file_io_utils::save_string_to_file(filename, data + oss.str());
+    header += std::string((const char *)&keys.m_view_public_key, sizeof(crypto::public_key));
+    std::string ciphertext = m_wallet->encrypt_with_view_secret_key(header + oss.str());
+    bool r = epee::file_io_utils::save_string_to_file(filename, magic + ciphertext);
     if (!r)
     {
       fail_msg_writer() << tr("failed to save file ") << filename;
@@ -4177,14 +4195,25 @@ bool simple_wallet::import_outputs(const std::vector<std::string> &args)
     fail_msg_writer() << "Bad output export file magic in " << filename;
     return true;
   }
-  const size_t headerlen = magiclen + 2 * sizeof(crypto::public_key);
+
+  try
+  {
+    data = m_wallet->decrypt_with_view_secret_key(std::string(data, magiclen));
+  }
+  catch (const std::exception &e)
+  {
+    fail_msg_writer() << "Failed to decrypt " << filename << ": " << e.what();
+    return true;
+  }
+
+  const size_t headerlen = 2 * sizeof(crypto::public_key);
   if (data.size() < headerlen)
   {
     fail_msg_writer() << "Bad data size from file " << filename;
     return true;
   }
-  const crypto::public_key &public_spend_key = *(const crypto::public_key*)&data[magiclen];
+  const crypto::public_key &public_spend_key = *(const crypto::public_key*)&data[0];
-  const crypto::public_key &public_view_key = *(const crypto::public_key*)&data[magiclen + sizeof(crypto::public_key)];
+  const crypto::public_key &public_view_key = *(const crypto::public_key*)&data[sizeof(crypto::public_key)];
   const cryptonote::account_public_address &keys = m_wallet->get_account().get_keys().m_account_address;
   if (public_spend_key != keys.m_spend_public_key || public_view_key != keys.m_view_public_key)
   {

src/wallet/wallet2.cpp

@@ -4410,6 +4410,61 @@ size_t wallet2::import_outputs(const std::vector<tools::wallet2::transfer_detail
   return m_transfers.size();
 }
 //----------------------------------------------------------------------------------------------------
+std::string wallet2::encrypt(const std::string &plaintext, const crypto::secret_key &skey, bool authenticated) const
+{
+  crypto::chacha8_key key;
+  crypto::generate_chacha8_key(&skey, sizeof(skey), key);
+  std::string ciphertext;
+  crypto::chacha8_iv iv = crypto::rand<crypto::chacha8_iv>();
+  ciphertext.resize(plaintext.size() + sizeof(iv) + (authenticated ? sizeof(crypto::signature) : 0));
+  crypto::chacha8(plaintext.data(), plaintext.size(), key, iv, &ciphertext[sizeof(iv)]);
+  memcpy(&ciphertext[0], &iv, sizeof(iv));
+  if (authenticated)
+  {
+    crypto::hash hash;
+    crypto::cn_fast_hash(ciphertext.data(), ciphertext.size() - sizeof(signature), hash);
+    crypto::public_key pkey;
+    crypto::secret_key_to_public_key(skey, pkey);
+    crypto::signature &signature = *(crypto::signature*)&ciphertext[ciphertext.size() - sizeof(crypto::signature)];
+    crypto::generate_signature(hash, pkey, skey, signature);
+  }
+  return std::move(ciphertext);
+}
+//----------------------------------------------------------------------------------------------------
+std::string wallet2::encrypt_with_view_secret_key(const std::string &plaintext, bool authenticated) const
+{
+  return encrypt(plaintext, get_account().get_keys().m_view_secret_key, authenticated);
+}
+//----------------------------------------------------------------------------------------------------
+std::string wallet2::decrypt(const std::string &ciphertext, const crypto::secret_key &skey, bool authenticated) const
+{
+  THROW_WALLET_EXCEPTION_IF(ciphertext.size() < sizeof(chacha8_iv),
+    error::wallet_internal_error, "key_image generated ephemeral public key not matched with output_key");
+
+  crypto::chacha8_key key;
+  crypto::generate_chacha8_key(&skey, sizeof(skey), key);
+  const crypto::chacha8_iv &iv = *(const crypto::chacha8_iv*)&ciphertext[0];
+  std::string plaintext;
+  plaintext.resize(ciphertext.size() - sizeof(iv) - (authenticated ? sizeof(crypto::signature) : 0));
+  if (authenticated)
+  {
+    crypto::hash hash;
+    crypto::cn_fast_hash(ciphertext.data(), ciphertext.size() - sizeof(signature), hash);
+    crypto::public_key pkey;
+    crypto::secret_key_to_public_key(skey, pkey);
+    const crypto::signature &signature = *(const crypto::signature*)&ciphertext[ciphertext.size() - sizeof(crypto::signature)];
+    THROW_WALLET_EXCEPTION_IF(!crypto::check_signature(hash, pkey, signature),
+      error::wallet_internal_error, "Failed to authenticate criphertext");
+  }
+  crypto::chacha8(ciphertext.data() + sizeof(iv), ciphertext.size() - sizeof(iv), key, iv, &plaintext[0]);
+  return std::move(plaintext);
+}
+//----------------------------------------------------------------------------------------------------
+std::string wallet2::decrypt_with_view_secret_key(const std::string &ciphertext, bool authenticated) const
+{
+  return decrypt(ciphertext, get_account().get_keys().m_view_secret_key, authenticated);
+}
+//----------------------------------------------------------------------------------------------------
 void wallet2::generate_genesis(cryptonote::block& b) {
   if (m_testnet)
   {

src/wallet/wallet2.h

@@ -480,6 +480,12 @@ namespace tools
     uint64_t import_key_images(const std::vector<std::pair<crypto::key_image, crypto::signature>> &signed_key_images, uint64_t &spent, uint64_t &unspent);
 
     void update_pool_state();
+
+    std::string encrypt(const std::string &plaintext, const crypto::secret_key &skey, bool authenticated = true) const;
+    std::string encrypt_with_view_secret_key(const std::string &plaintext, bool authenticated = true) const;
+    std::string decrypt(const std::string &ciphertext, const crypto::secret_key &skey, bool authenticated = true) const;
+    std::string decrypt_with_view_secret_key(const std::string &ciphertext, bool authenticated = true) const;
+
   private:
     /*!
      * \brief  Stores wallet information to wallet file.