1// Copyright (c) 2013 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "net/quic/crypto/curve25519_key_exchange.h"
6
7#include "base/basictypes.h"
8#include "base/logging.h"
9#include "crypto/curve25519.h"
10#include "net/quic/crypto/quic_random.h"
11
12using base::StringPiece;
13using std::string;
14
15namespace net {
16
17Curve25519KeyExchange::Curve25519KeyExchange() {}
18
19Curve25519KeyExchange::~Curve25519KeyExchange() {}
20
21// static
22Curve25519KeyExchange* Curve25519KeyExchange::New(
23    const StringPiece& private_key) {
24  Curve25519KeyExchange* ka;
25  // We don't want to #include the NaCl headers in the public header file, so
26  // we use literals for the sizes of private_key_ and public_key_. Here we
27  // assert that those values are equal to the values from the NaCl header.
28  COMPILE_ASSERT(
29      sizeof(ka->private_key_) == crypto::curve25519::kScalarBytes,
30      header_out_of_sync);
31  COMPILE_ASSERT(sizeof(ka->public_key_) == crypto::curve25519::kBytes,
32                 header_out_of_sync);
33
34  if (private_key.size() != crypto::curve25519::kScalarBytes) {
35    return NULL;
36  }
37
38  ka = new Curve25519KeyExchange();
39  memcpy(ka->private_key_, private_key.data(),
40         crypto::curve25519::kScalarBytes);
41  crypto::curve25519::ScalarBaseMult(ka->private_key_, ka->public_key_);
42  return ka;
43}
44
45// static
46string Curve25519KeyExchange::NewPrivateKey(QuicRandom* rand) {
47  uint8 private_key[crypto::curve25519::kScalarBytes];
48  rand->RandBytes(private_key, sizeof(private_key));
49
50  // This makes |private_key| a valid scalar, as specified on
51  // http://cr.yp.to/ecdh.html
52  private_key[0] &= 248;
53  private_key[31] &= 127;
54  private_key[31] |= 64;
55  return string(reinterpret_cast<char*>(private_key), sizeof(private_key));
56}
57
58KeyExchange* Curve25519KeyExchange::NewKeyPair(QuicRandom* rand) const {
59  const string private_value = NewPrivateKey(rand);
60  return Curve25519KeyExchange::New(private_value);
61}
62
63bool Curve25519KeyExchange::CalculateSharedKey(
64    const StringPiece& peer_public_value,
65    string* out_result) const {
66  if (peer_public_value.size() != crypto::curve25519::kBytes) {
67    return false;
68  }
69
70  uint8 result[crypto::curve25519::kBytes];
71  crypto::curve25519::ScalarMult(
72      private_key_,
73      reinterpret_cast<const uint8*>(peer_public_value.data()),
74      result);
75  out_result->assign(reinterpret_cast<char*>(result), sizeof(result));
76
77  return true;
78}
79
80StringPiece Curve25519KeyExchange::public_value() const {
81  return StringPiece(reinterpret_cast<const char*>(public_key_),
82                     sizeof(public_key_));
83}
84
85QuicTag Curve25519KeyExchange::tag() const { return kC255; }
86
87}  // namespace net
88