net/quic/crypto/curve25519_key_exchange.cc

   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
  12 using base::StringPiece;
  13 using std::string;
  14
  15 namespace net {
  16
  17 Curve25519KeyExchange::Curve25519KeyExchange() {}
  18
  19 Curve25519KeyExchange::~Curve25519KeyExchange() {}
  20
  21 // static
  22 Curve25519KeyExchange* 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   static_assert(sizeof(ka->private_key_) == crypto::curve25519::kScalarBytes,
  29                 "header out of sync");
  30   static_assert(sizeof(ka->public_key_) == crypto::curve25519::kBytes,
  31                 "header out of sync");
  32
  33   if (private_key.size() != crypto::curve25519::kScalarBytes) {
  34     return nullptr;
  35   }
  36
  37   ka = new Curve25519KeyExchange();
  38   memcpy(ka->private_key_, private_key.data(),
  39          crypto::curve25519::kScalarBytes);
  40   crypto::curve25519::ScalarBaseMult(ka->private_key_, ka->public_key_);
  41   return ka;
  42 }
  43
  44 // static
  45 string Curve25519KeyExchange::NewPrivateKey(QuicRandom* rand) {
  46   uint8 private_key[crypto::curve25519::kScalarBytes];
  47   rand->RandBytes(private_key, sizeof(private_key));
  48
  49   // This makes |private_key| a valid scalar, as specified on
  50   // http://cr.yp.to/ecdh.html
  51   private_key[0] &= 248;
  52   private_key[31] &= 127;
  53   private_key[31] |= 64;
  54   return string(reinterpret_cast<char*>(private_key), sizeof(private_key));
  55 }
  56
  57 KeyExchange* Curve25519KeyExchange::NewKeyPair(QuicRandom* rand) const {
  58   const string private_value = NewPrivateKey(rand);
  59   return Curve25519KeyExchange::New(private_value);
  60 }
  61
  62 bool Curve25519KeyExchange::CalculateSharedKey(
  63     const StringPiece& peer_public_value,
  64     string* out_result) const {
  65   if (peer_public_value.size() != crypto::curve25519::kBytes) {
  66     return false;
  67   }
  68
  69   uint8 result[crypto::curve25519::kBytes];
  70   crypto::curve25519::ScalarMult(
  71       private_key_,
  72       reinterpret_cast<const uint8*>(peer_public_value.data()),
  73       result);
  74   out_result->assign(reinterpret_cast<char*>(result), sizeof(result));
  75
  76   return true;
  77 }
  78
  79 StringPiece Curve25519KeyExchange::public_value() const {
  80   return StringPiece(reinterpret_cast<const char*>(public_key_),
  81                      sizeof(public_key_));
  82 }
  83
  84 QuicTag Curve25519KeyExchange::tag() const { return kC255; }
  85
  86 }  // namespace net