Updating D2D protocol to v1 to support separate sequence numbers.

components/cryptauth/session_keys.cc

Index: components/cryptauth/session_keys.cc
diff --git a/components/cryptauth/session_keys.cc b/components/cryptauth/session_keys.cc
new file mode 100644
index 0000000000000000000000000000000000000000..74783a2d30bd8ae8bc9cbedbd0d264844add8659
--- /dev/null
+++ b/components/cryptauth/session_keys.cc
@@ -0,0 +1,56 @@
+// Copyright 2017 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.
+
+#include "components/cryptauth/session_keys.h"
+
+#include "base/strings/string_piece.h"
+#include "crypto/hkdf.h"
+
+namespace cryptauth {
+namespace {
+
+// The salt used to compute the devired keys. SHA256 of "D2D".
+const uint8_t kSalt[] = {0x82, 0xAA, 0x55, 0xA0, 0xD3, 0x97, 0xF8, 0x83,
+                         0x46, 0xCA, 0x1C, 0xEE, 0x8D, 0x39, 0x09, 0xB9,
+                         0x5F, 0x13, 0xFA, 0x7D, 0xEB, 0x1D, 0x4A, 0xB3,
+                         0x83, 0x76, 0xB8, 0x25, 0x6D, 0xA8, 0x55, 0x10};
+
+// The number of bytes in the derived keys.
+const int kKeySize = 32;
+
+// String used in the derivation of the inititor encoding key.
+const char kInitiatorPurpose[] = "initiator";
+
+// String used in the derivation of the responder encoding key.
+const char kResponderPurpose[] = "responder";
+
+}  // namespace
+
+SessionKeys::SessionKeys(const std::string& master_symmetric_key) {
+  std::string salt(reinterpret_cast<const char*>(&kSalt[0]), sizeof(kSalt));
+
+  // We set the key_length to the length of the expected output and then take
+  // the result from the first key, which is the client write key.
+  crypto::HKDF initiator_encode(master_symmetric_key, salt, kInitiatorPurpose,
+                                kKeySize, 0, 0);
+  initiator_encode_key_ = initiator_encode.client_write_key().as_string();
+
+  crypto::HKDF responder_encode(master_symmetric_key, salt, kResponderPurpose,
+                                kKeySize, 0, 0);
+  responder_encode_key_ = responder_encode.client_write_key().as_string();
+}
+
+SessionKeys::SessionKeys() {}
+
+SessionKeys::~SessionKeys() {}
+
+std::string SessionKeys::initiator_encode_key() const {
+  return initiator_encode_key_;
+}
+
+std::string SessionKeys::responder_encode_key() const {
+  return responder_encode_key_;
+}
+
+}  // namespace cryptauth