Teach the GCM Driver how to decrypt incoming messages.

components/gcm_driver/crypto/gcm_message_cryptographer.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_GCM_DRIVER_CRYPTO_GCM_MESSAGE_CRYPTOGRAPHER_H_
 #define COMPONENTS_GCM_DRIVER_CRYPTO_GCM_MESSAGE_CRYPTOGRAPHER_H_
 
 #include <stdint.h>
 #include <string>
 
@@ skipping 14 matching lines @@
 // draft-thomson-http-encryption-01:
 //
 // https://tools.ietf.org/html/draft-thomson-http-encryption-01
 //
 // Note that while this class is not responsible for creating or storing the
 // actual keys, it uses a key derivation function for the actual message
 // encryption/decryption, thus allowing for the safe re-use of keys in multiple
 // messages provided that a cryptographically-strong random salt is used.
 class GCMMessageCryptographer {
  public:
+  // Salt size, in bytes, that will be used together with the key to create a
+  // unique content encryption key for a given message.
+  static const size_t kSaltSize;
+
   GCMMessageCryptographer();
   ~GCMMessageCryptographer();
 
   // Encrypts |plaintext| using the |key| and the |salt|, both of which must be
   // 16 octets in length. The |plaintext| will be written to a single record,
   // and will include a 16 octet authentication tag. The encrypted result will
   // be written to |ciphertext|, the record size to |record_size|. This
   // implementation does not support prepending padding to the |plaintext|.
   bool Encrypt(const base::StringPiece& plaintext,
                const base::StringPiece& key,
@@ skipping 32 matching lines @@
                                          const base::StringPiece& salt) const;
 
   // Derives the nonce from |key| and |salt|.
   std::string DeriveNonce(const base::StringPiece& key,
                           const base::StringPiece& salt) const;
 };
 
 }  // namespace gcm
 
 #endif  // COMPONENTS_GCM_DRIVER_CRYPTO_GCM_MESSAGE_CRYPTOGRAPHER_H_