crypto/encryptor.cc

   1 // Copyright (c) 2011 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 "crypto/encryptor.h"
   6
   7 #include "base/logging.h"
   8 #include "base/sys_byteorder.h"
   9
  10 namespace crypto {
  11
  12 /////////////////////////////////////////////////////////////////////////////
  13 // Encyptor::Counter Implementation.
  14 Encryptor::Counter::Counter(const base::StringPiece& counter) {
  15   CHECK(sizeof(counter_) == counter.length());
  16
  17   memcpy(&counter_, counter.data(), sizeof(counter_));
  18 }
  19
  20 Encryptor::Counter::~Counter() {
  21 }
  22
  23 bool Encryptor::Counter::Increment() {
  24   uint64 low_num = base::ntohll(counter_.components64[1]);
  25   uint64 new_low_num = low_num + 1;
  26   counter_.components64[1] = base::htonll(new_low_num);
  27
  28   // If overflow occured then increment the most significant component.
  29   if (new_low_num < low_num) {
  30     counter_.components64[0] =
  31         base::htonll(base::ntohll(counter_.components64[0]) + 1);
  32   }
  33
  34   // TODO(hclam): Return false if counter value overflows.
  35   return true;
  36 }
  37
  38 void Encryptor::Counter::Write(void* buf) {
  39   uint8* buf_ptr = reinterpret_cast<uint8*>(buf);
  40   memcpy(buf_ptr, &counter_, sizeof(counter_));
  41 }
  42
  43 size_t Encryptor::Counter::GetLengthInBytes() const {
  44   return sizeof(counter_);
  45 }
  46
  47 /////////////////////////////////////////////////////////////////////////////
  48 // Partial Encryptor Implementation.
  49
  50 bool Encryptor::SetCounter(const base::StringPiece& counter) {
  51   if (mode_ != CTR)
  52     return false;
  53   if (counter.length() != 16u)
  54     return false;
  55
  56   counter_.reset(new Counter(counter));
  57   return true;
  58 }
  59
  60 bool Encryptor::GenerateCounterMask(size_t plaintext_len,
  61                                     uint8* mask,
  62                                     size_t* mask_len) {
  63   DCHECK_EQ(CTR, mode_);
  64   CHECK(mask);
  65   CHECK(mask_len);
  66
  67   const size_t kBlockLength = counter_->GetLengthInBytes();
  68   size_t blocks = (plaintext_len + kBlockLength - 1) / kBlockLength;
  69   CHECK(blocks);
  70
  71   *mask_len = blocks * kBlockLength;
  72
  73   for (size_t i = 0; i < blocks; ++i) {
  74     counter_->Write(mask);
  75     mask += kBlockLength;
  76
  77     bool ret = counter_->Increment();
  78     if (!ret)
  79       return false;
  80   }
  81   return true;
  82 }
  83
  84 void Encryptor::MaskMessage(const void* plaintext,
  85                             size_t plaintext_len,
  86                             const void* mask,
  87                             void* ciphertext) const {
  88   DCHECK_EQ(CTR, mode_);
  89   const uint8* plaintext_ptr = reinterpret_cast<const uint8*>(plaintext);
  90   const uint8* mask_ptr = reinterpret_cast<const uint8*>(mask);
  91   uint8* ciphertext_ptr = reinterpret_cast<uint8*>(ciphertext);
  92
  93   for (size_t i = 0; i < plaintext_len; ++i)
  94     ciphertext_ptr[i] = plaintext_ptr[i] ^ mask_ptr[i];
  95 }
  96
  97 }  // namespace crypto