Implement QUIC key extraction.

crypto/hkdf.h

 // Copyright (c) 2013 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 CRYPTO_HKDF_H_
 #define CRYPTO_HKDF_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/strings/string_piece.h"
-#include "build/build_config.h"
 #include "crypto/crypto_export.h"
 
 namespace crypto {
 
 // HKDF implements the key derivation function specified in RFC 5869 (using
 // SHA-256) and outputs key material, as needed by QUIC.
 // See https://tools.ietf.org/html/rfc5869 for details.
 class CRYPTO_EXPORT HKDF {
  public:
-  // |secret|: The input shared secret (or, from RFC 5869, the IKM).
+  // |secret|: the input shared secret (or, from RFC 5869, the IKM).
   // |salt|: an (optional) public salt / non-secret random value. While
   // optional, callers are strongly recommended to provide a salt. There is no
   // added security value in making this larger than the SHA-256 block size of
   // 64 bytes.
   // |info|: an (optional) label to distinguish different uses of HKDF. It is
   // optional context and application specific information (can be a zero-length
   // string).
-  // |key_bytes_to_generate|: the number of bytes of key material to generate.
-  // |iv_bytes_to_generate|: the number of bytes of IV to generate.
+  // |key_bytes_to_generate|: the number of bytes of key material to generate
+  // for both client and server.
+  // |iv_bytes_to_generate|: the number of bytes of IV to generate for both
+  // client and server.
+  // |subkey_secret_bytes_to_generate|: the number of bytes of subkey secret to
+  // generate, shared between client and server.
   HKDF(const base::StringPiece& secret,
        const base::StringPiece& salt,
        const base::StringPiece& info,
        size_t key_bytes_to_generate,
-       size_t iv_bytes_to_generate);
+       size_t iv_bytes_to_generate,
+       size_t subkey_secret_bytes_to_generate);

[wtc, 2014/07/30 18:16:52]

Adam: while porting this change to Chromium, I realized that the HKDF class has
become very QUIC-specific. In the internal QUIC source tree, this class is
inside the quic/crypto/base directory, so a QUIC-specific interface is
acceptable. In Chromium's crypto directory, a QUIC-specific interface seems bad,
although I just noticed the comment on line 17 that says this class generates
output "as needed by QUIC".

I am surprised that I didn't need to change any files outside net/quic. So this
means no other code is using the HKDF class right now.

   ~HKDF();
 
   base::StringPiece client_write_key() const {
     return client_write_key_;
   }
   base::StringPiece client_write_iv() const {
     return client_write_iv_;
   }
   base::StringPiece server_write_key() const {
     return server_write_key_;
   }
   base::StringPiece server_write_iv() const {
     return server_write_iv_;
   }
+  base::StringPiece subkey_secret() const {
+    return subkey_secret_;
+  }
 
  private:
   std::vector<uint8> output_;
 
   base::StringPiece client_write_key_;
   base::StringPiece server_write_key_;
   base::StringPiece client_write_iv_;
   base::StringPiece server_write_iv_;
+  base::StringPiece subkey_secret_;
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_HKDF_H_