content/child/webcrypto/openssl/aes_ctr_openssl.cc

   1 // Copyright 2014 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 <openssl/aes.h>
   6 #include <openssl/evp.h>
   7
   8 #include "base/logging.h"
   9 #include "base/macros.h"
  10 #include "base/numerics/safe_math.h"
  11 #include "base/stl_util.h"
  12 #include "content/child/webcrypto/crypto_data.h"
  13 #include "content/child/webcrypto/openssl/aes_algorithm_openssl.h"
  14 #include "content/child/webcrypto/openssl/key_openssl.h"
  15 #include "content/child/webcrypto/openssl/util_openssl.h"
  16 #include "content/child/webcrypto/status.h"
  17 #include "content/child/webcrypto/webcrypto_util.h"
  18 #include "crypto/openssl_util.h"
  19 #include "crypto/scoped_openssl_types.h"
  20 #include "third_party/WebKit/public/platform/WebCryptoAlgorithmParams.h"
  21
  22 namespace content {
  23
  24 namespace webcrypto {
  25
  26 namespace {
  27
  28 const EVP_CIPHER* GetAESCipherByKeyLength(unsigned int key_length_bytes) {
  29   // BoringSSL does not support 192-bit AES keys.
  30   switch (key_length_bytes) {
  31     case 16:
  32       return EVP_aes_128_ctr();
  33     case 32:
  34       return EVP_aes_256_ctr();
  35     default:
  36       return NULL;
  37   }
  38 }
  39
  40 // Encrypts/decrypts given a 128-bit counter.
  41 //
  42 // |output| must be a pointer to a buffer which has a length of at least
  43 // |input.byte_length()|.
  44 Status AesCtrEncrypt128BitCounter(const EVP_CIPHER* cipher,
  45                                   const CryptoData& raw_key,
  46                                   const CryptoData& input,
  47                                   const CryptoData& counter,
  48                                   uint8_t* output) {
  49   DCHECK(cipher);
  50   DCHECK_EQ(16u, counter.byte_length());
  51
  52   crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
  53   crypto::ScopedOpenSSL<EVP_CIPHER_CTX, EVP_CIPHER_CTX_free> context(
  54       EVP_CIPHER_CTX_new());
  55
  56   if (!context.get())
  57     return Status::OperationError();
  58
  59   if (!EVP_CipherInit_ex(context.get(), cipher, NULL, raw_key.bytes(),
  60                          counter.bytes(), ENCRYPT)) {
  61     return Status::OperationError();
  62   }
  63
  64   int output_len = 0;
  65   if (!EVP_CipherUpdate(context.get(), output, &output_len, input.bytes(),
  66                         input.byte_length())) {
  67     return Status::OperationError();
  68   }
  69   int final_output_chunk_len = 0;
  70   if (!EVP_CipherFinal_ex(context.get(), output + output_len,
  71                           &final_output_chunk_len)) {
  72     return Status::OperationError();
  73   }
  74
  75   output_len += final_output_chunk_len;
  76   if (static_cast<unsigned int>(output_len) != input.byte_length())
  77     return Status::ErrorUnexpected();
  78
  79   return Status::Success();
  80 }
  81
  82 // Returns ceil(a/b), where a and b are integers.
  83 template <typename T>
  84 T CeilDiv(T a, T b) {
  85   return a == 0 ? 0 : 1 + (a - 1) / b;
  86 }
  87
  88 // Extracts the counter as a BIGNUM. The counter is the rightmost
  89 // "counter_length_bits" of the block, interpreted as a big-endian number.
  90 crypto::ScopedBIGNUM GetCounter(const CryptoData& counter_block,
  91                                 unsigned int counter_length_bits) {
  92   unsigned int counter_length_remainder_bits = (counter_length_bits % 8);
  93
  94   // If the counter is a multiple of 8 bits then can call BN_bin2bn() directly.
  95   if (counter_length_remainder_bits == 0) {
  96     unsigned int byte_length = counter_length_bits / 8;
  97     return crypto::ScopedBIGNUM(BN_bin2bn(
  98         counter_block.bytes() + counter_block.byte_length() - byte_length,
  99         byte_length, NULL));
 100   }
 101
 102   // Otherwise make a copy of the counter and zero out the topmost bits so
 103   // BN_bin2bn() can be called with a byte stream.
 104   unsigned int byte_length = CeilDiv(counter_length_bits, 8u);
 105   std::vector<uint8_t> counter(
 106       counter_block.bytes() + counter_block.byte_length() - byte_length,
 107       counter_block.bytes() + counter_block.byte_length());
 108   counter[0] &= ~(0xFF << counter_length_remainder_bits);
 109
 110   return crypto::ScopedBIGNUM(
 111       BN_bin2bn(vector_as_array(&counter), counter.size(), NULL));
 112 }
 113
 114 // Returns a counter block with the counter bits all set all zero.
 115 std::vector<uint8_t> BlockWithZeroedCounter(const CryptoData& counter_block,
 116                                             unsigned int counter_length_bits) {
 117   unsigned int counter_length_bytes = counter_length_bits / 8;
 118   unsigned int counter_length_bits_remainder = counter_length_bits % 8;
 119
 120   std::vector<uint8_t> new_counter_block(
 121       counter_block.bytes(),
 122       counter_block.bytes() + counter_block.byte_length());
 123
 124   unsigned int index = new_counter_block.size() - counter_length_bytes;
 125   memset(&new_counter_block.front() + index, 0, counter_length_bytes);
 126
 127   if (counter_length_bits_remainder) {
 128     new_counter_block[index - 1] &= 0xFF << counter_length_bits_remainder;
 129   }
 130
 131   return new_counter_block;
 132 }
 133
 134 // This function does encryption/decryption for AES-CTR (encryption and
 135 // decryption are the same).
 136 //
 137 // BoringSSL's interface for AES-CTR differs from that of WebCrypto. In
 138 // WebCrypto the caller specifies a 16-byte counter block and designates how
 139 // many of the right-most X bits to use as a big-endian counter. Whereas in
 140 // BoringSSL the entire counter block is interpreted as a 128-bit counter.
 141 //
 142 // In AES-CTR, the counter block MUST be unique across all messages that are
 143 // encrypted/decrypted. WebCrypto expects that the counter can start at any
 144 // value, and is therefore permitted to wrap around to zero on overflow.
 145 //
 146 // Some care is taken to fail if the counter wraps back to an earlier value.
 147 // However this protection is only enforced during a *single* call to
 148 // encrypt/decrypt.
 149 Status AesCtrEncryptDecrypt(const blink::WebCryptoAlgorithm& algorithm,
 150                             const blink::WebCryptoKey& key,
 151                             const CryptoData& data,
 152                             std::vector<uint8_t>* buffer) {
 153   const blink::WebCryptoAesCtrParams* params = algorithm.aesCtrParams();
 154   const std::vector<uint8_t>& raw_key =
 155       SymKeyOpenSsl::Cast(key)->raw_key_data();
 156
 157   if (params->counter().size() != 16)
 158     return Status::ErrorIncorrectSizeAesCtrCounter();
 159
 160   unsigned int counter_length_bits = params->lengthBits();
 161   if (counter_length_bits < 1 || counter_length_bits > 128)
 162     return Status::ErrorInvalidAesCtrCounterLength();
 163
 164   // The output of AES-CTR is the same size as the input. However BoringSSL
 165   // expects buffer sizes as an "int".
 166   base::CheckedNumeric<int> output_max_len = data.byte_length();
 167   if (!output_max_len.IsValid())
 168     return Status::ErrorDataTooLarge();
 169
 170   const EVP_CIPHER* const cipher = GetAESCipherByKeyLength(raw_key.size());
 171   if (!cipher)
 172     return Status::ErrorUnexpected();
 173
 174   const CryptoData counter_block(params->counter());
 175   buffer->resize(output_max_len.ValueOrDie());
 176
 177   // The total number of possible counter values is pow(2, counter_length_bits)
 178   crypto::ScopedBIGNUM num_counter_values(BN_new());
 179   if (!BN_lshift(num_counter_values.get(), BN_value_one(), counter_length_bits))
 180     return Status::ErrorUnexpected();
 181
 182   crypto::ScopedBIGNUM current_counter =
 183       GetCounter(counter_block, counter_length_bits);
 184
 185   // The number of AES blocks needed for encryption/decryption. The counter is
 186   // incremented this many times.
 187   crypto::ScopedBIGNUM num_output_blocks(BN_new());
 188   if (!BN_set_word(
 189           num_output_blocks.get(),
 190           CeilDiv(buffer->size(), static_cast<size_t>(AES_BLOCK_SIZE)))) {
 191     return Status::ErrorUnexpected();
 192   }
 193
 194   // If the counter is going to be incremented more times than there are counter
 195   // values, fail. (Repeating values of the counter block is bad).
 196   if (BN_cmp(num_output_blocks.get(), num_counter_values.get()) > 0)
 197     return Status::ErrorAesCtrInputTooLongCounterRepeated();
 198
 199   // This is the number of blocks that can be successfully encrypted without
 200   // overflowing the counter. Encrypting the subsequent block will need to
 201   // reset the counter to zero.
 202   crypto::ScopedBIGNUM num_blocks_until_reset(BN_new());
 203
 204   if (!BN_sub(num_blocks_until_reset.get(), num_counter_values.get(),
 205               current_counter.get())) {
 206     return Status::ErrorUnexpected();
 207   }
 208
 209   // If the counter can be incremented for the entire input without
 210   // wrapping-around, do it as a single call into BoringSSL.
 211   if (BN_cmp(num_blocks_until_reset.get(), num_output_blocks.get()) >= 0) {
 212     return AesCtrEncrypt128BitCounter(cipher, CryptoData(raw_key), data,
 213                                       counter_block, vector_as_array(buffer));
 214   }
 215
 216   // Otherwise the encryption needs to be done in 2 parts. The first part using
 217   // the current counter_block, and the next part resetting the counter portion
 218   // of the block to zero.
 219
 220   // This is guaranteed to fit in an "unsigned int" because input size in bytes
 221   // fits in an "unsigned int".
 222   BN_ULONG num_blocks_part1 = BN_get_word(num_blocks_until_reset.get());
 223   BN_ULONG input_size_part1 = num_blocks_part1 * AES_BLOCK_SIZE;
 224   DCHECK_LT(input_size_part1, data.byte_length());
 225
 226   // Encrypt the first part (before wrap-around).
 227   Status status = AesCtrEncrypt128BitCounter(
 228       cipher, CryptoData(raw_key), CryptoData(data.bytes(), input_size_part1),
 229       counter_block, vector_as_array(buffer));
 230   if (status.IsError())
 231     return status;
 232
 233   // Encrypt the second part (after wrap-around).
 234   std::vector<uint8_t> counter_block_part2 =
 235       BlockWithZeroedCounter(counter_block, counter_length_bits);
 236
 237   return AesCtrEncrypt128BitCounter(
 238       cipher, CryptoData(raw_key),
 239       CryptoData(data.bytes() + input_size_part1,
 240                  data.byte_length() - input_size_part1),
 241       CryptoData(counter_block_part2),
 242       vector_as_array(buffer) + input_size_part1);
 243 }
 244
 245 class AesCtrImplementation : public AesAlgorithm {
 246  public:
 247   AesCtrImplementation() : AesAlgorithm("CTR") {}
 248
 249   Status Encrypt(const blink::WebCryptoAlgorithm& algorithm,
 250                  const blink::WebCryptoKey& key,
 251                  const CryptoData& data,
 252                  std::vector<uint8_t>* buffer) const override {
 253     return AesCtrEncryptDecrypt(algorithm, key, data, buffer);
 254   }
 255
 256   Status Decrypt(const blink::WebCryptoAlgorithm& algorithm,
 257                  const blink::WebCryptoKey& key,
 258                  const CryptoData& data,
 259                  std::vector<uint8_t>* buffer) const override {
 260     return AesCtrEncryptDecrypt(algorithm, key, data, buffer);
 261   }
 262 };
 263
 264 }  // namespace
 265
 266 AlgorithmImplementation* CreatePlatformAesCtrImplementation() {
 267   return new AesCtrImplementation;
 268 }
 269
 270 }  // namespace webcrypto
 271
 272 }  // namespace content