[webcrypto] Implement AES-CTR using BoringSSL.

content/child/webcrypto/openssl/aes_ctr_openssl.cc

+// Copyright 2014 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 <openssl/aes.h>
+#include <openssl/evp.h>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/numerics/safe_math.h"
+#include "base/stl_util.h"
+#include "content/child/webcrypto/crypto_data.h"
+#include "content/child/webcrypto/openssl/aes_key_openssl.h"
+#include "content/child/webcrypto/openssl/key_openssl.h"
+#include "content/child/webcrypto/openssl/util_openssl.h"
+#include "content/child/webcrypto/status.h"
+#include "content/child/webcrypto/webcrypto_util.h"
+#include "crypto/openssl_util.h"
+#include "crypto/scoped_openssl_types.h"
+#include "third_party/WebKit/public/platform/WebCryptoAlgorithmParams.h"
+
+namespace content {
+
+namespace webcrypto {
+
+namespace {
+
+const EVP_CIPHER* GetAESCipherByKeyLength(unsigned int key_length_bytes) {
+  // BoringSSL does not support 192-bit AES keys.
+  switch (key_length_bytes) {
+    case 16:
+      return EVP_aes_128_ctr();
+    case 32:
+      return EVP_aes_256_ctr();
+    default:
+      return NULL;
+  }
+}
+
+// Encrypts/decrypts given a 128-bit counter.
+//
+// |output| must be a pointer to a buffer which has a length of at least
+// |input.byte_length()|.
+Status AesCtrEncrypt128BitCounter(const EVP_CIPHER* cipher,
+                                  const CryptoData& raw_key,
+                                  const CryptoData& input,
+                                  const CryptoData& counter,
+                                  uint8_t* output) {
+  DCHECK(cipher);
+  DCHECK_EQ(16u, counter.byte_length());
+
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+  crypto::ScopedOpenSSL<EVP_CIPHER_CTX, EVP_CIPHER_CTX_free>::Type context(
+      EVP_CIPHER_CTX_new());
+
+  if (!context.get())
+    return Status::OperationError();
+
+  if (!EVP_CipherInit_ex(context.get(),
+                         cipher,
+                         NULL,
+                         raw_key.bytes(),
+                         counter.bytes(),
+                         ENCRYPT)) {
+    return Status::OperationError();
+  }
+
+  int output_len = 0;
+  if (!EVP_CipherUpdate(context.get(),
+                        output,
+                        &output_len,
+                        input.bytes(),
+                        input.byte_length())) {
+    return Status::OperationError();
+  }
+  int final_output_chunk_len = 0;
+  if (!EVP_CipherFinal_ex(
+          context.get(), output + output_len, &final_output_chunk_len)) {
+    return Status::OperationError();
+  }
+
+  output_len += final_output_chunk_len;
+  if (static_cast<unsigned int>(output_len) != input.byte_length())
+    return Status::ErrorUnexpected();
+
+  return Status::Success();
+}
+
+// Returns ceil(a/b), where a and b are integers.
+template <typename T>
+T CeilDiv(T a, T b) {
+  return a == 0 ? 0 : 1 + (a - 1) / b;
+}
+
+// Extracts the counter as a BIGNUM. The counter is the rightmost
+// "counter_length_bits" of the block, interpreted as a big-endian number.
+crypto::ScopedBIGNUM GetCounter(const CryptoData& counter_block,
+                                unsigned int counter_length_bits) {
+  unsigned int counter_length_remainder_bits = (counter_length_bits % 8);
+
+  // If the counter is a multiple of 8 bits then can call BN_bin2bn() directly.
+  if (counter_length_remainder_bits == 0) {
+    unsigned int byte_length = counter_length_bits / 8;
+    return crypto::ScopedBIGNUM(BN_bin2bn(
+        counter_block.bytes() + counter_block.byte_length() - byte_length,
+        byte_length,
+        NULL));
+  }
+
+  // Otherwise make a copy of the counter and zero out the topmost bits so
+  // BN_bin2bn() can be called with a byte stream.
+  unsigned int byte_length = CeilDiv(counter_length_bits, 8u);
+  std::vector<uint8_t> counter(
+      counter_block.bytes() + counter_block.byte_length() - byte_length,
+      counter_block.bytes() + counter_block.byte_length());
+  counter[0] &= ~(0xFF << counter_length_remainder_bits);
+
+  return crypto::ScopedBIGNUM(
+      BN_bin2bn(&counter.front(), counter.size(), NULL));
+}
+
+// Returns a counter block with the counter bits all set all zero.
+std::vector<uint8_t> BlockWithZeroedCounter(const CryptoData& counter_block,
+                                            unsigned int counter_length_bits) {
+  unsigned int counter_length_bytes = counter_length_bits / 8;
+  unsigned int counter_length_bits_remainder = counter_length_bits % 8;
+
+  std::vector<uint8_t> new_counter_block(
+      counter_block.bytes(),
+      counter_block.bytes() + counter_block.byte_length());
+
+  unsigned int index = new_counter_block.size() - counter_length_bytes;
+  memset(&new_counter_block.front() + index, 0, counter_length_bytes);
+
+  if (counter_length_bits_remainder) {
+    new_counter_block[index - 1] &= 0xFF << counter_length_bits_remainder;
+  }
+
+  return new_counter_block;
+}
+
+// This function does encryption/decryption for AES-CTR (encryption and
+// decryption are the same).
+//
+// BoringSSL's interface for AES-CTR differs from that of WebCrypto. In
+// WebCrypto the caller specifies a 16-byte counter block and designates how
+// many of the right-most X bits to use as a big-endian counter. Whereas in
+// BoringSSL the entire counter block is interpreted as a 128-bit counter.
+//
+// In AES-CTR, the counter block MUST be unique across all messages that are
+// encrypted/decrypted. WebCrypto expects that the counter can start at any
+// value, and is therefore permitted to wrap around to zero on overflow.
+//
+// Some care is taken to fail if the counter wraps back to an earlier value.
+// However this protection is only enforced during a *single* call to
+// encrypt/decrypt.
+Status AesCtrEncryptDecrypt(const blink::WebCryptoAlgorithm& algorithm,
+                            const blink::WebCryptoKey& key,
+                            const CryptoData& data,
+                            std::vector<uint8_t>* buffer) {
+  const blink::WebCryptoAesCtrParams* params = algorithm.aesCtrParams();
+  const std::vector<uint8_t>& raw_key =
+      SymKeyOpenSsl::Cast(key)->raw_key_data();
+
+  if (params->counter().size() != 16)
+    return Status::ErrorIncorrectSizeAesCtrCounter();
+
+  unsigned int counter_length_bits = params->lengthBits();
+  if (counter_length_bits < 1 || counter_length_bits > 128)
+    return Status::ErrorInvalidAesCtrCounterLength();
+
+  // The output of AES-CTR is the same size as the input. However BoringSSL
+  // expects buffer sizes as an "int".
+  base::CheckedNumeric<int> output_max_len = data.byte_length();
+  if (!output_max_len.IsValid())
+    return Status::ErrorDataTooLarge();
+
+  const EVP_CIPHER* const cipher = GetAESCipherByKeyLength(raw_key.size());
+  if (!cipher)
+    return Status::ErrorUnexpected();
+
+  const CryptoData counter_block(params->counter());
+  buffer->resize(output_max_len.ValueOrDie());
+
+  // The total number of possible counter values is pow(2, counter_length_bits)
+  crypto::ScopedBIGNUM num_counter_values(BN_new());
+  if (!BN_lshift(num_counter_values.get(), BN_value_one(), counter_length_bits))
+    return Status::ErrorUnexpected();
+
+  crypto::ScopedBIGNUM current_counter =
+      GetCounter(counter_block, counter_length_bits);
+
+  // The number of AES blocks needed for encryption/decryption. The counter is
+  // incremented this many times.
+  crypto::ScopedBIGNUM num_output_blocks(BN_new());
+  if (!BN_set_word(
+          num_output_blocks.get(),
+          CeilDiv(buffer->size(), static_cast<size_t>(AES_BLOCK_SIZE)))) {
+    return Status::ErrorUnexpected();
+  }
+
+  // If the counter is going to be incremented more times than there are counter
+  // values, fail. (Repeating values of the counter block is bad).
+  if (BN_cmp(num_output_blocks.get(), num_counter_values.get()) > 0)
+    return Status::ErrorAesCtrInputTooLongCounterRepeated();
+
+  // This is the number of blocks that can be successfully encrypted without
+  // overflowing the counter. Encrypting the subsequent block will need to
+  // reset the counter to zero.
+  crypto::ScopedBIGNUM num_blocks_until_reset(BN_new());
+
+  if (!BN_sub(num_blocks_until_reset.get(),
+              num_counter_values.get(),
+              current_counter.get())) {
+    return Status::ErrorUnexpected();
+  }
+
+  // If the counter can be incremented for the entire input without
+  // wrapping-around, do it as a single call into BoringSSL.
+  if (BN_cmp(num_blocks_until_reset.get(), num_output_blocks.get()) >= 0) {
+    return AesCtrEncrypt128BitCounter(cipher,
+                                      CryptoData(raw_key),
+                                      data,
+                                      counter_block,
+                                      vector_as_array(buffer));
+  }
+
+  // Otherwise the encryption needs to be done in 2 parts. The first part using
+  // the current counter_block, and the next part resetting the counter portion
+  // of the block to zero.
+
+  // This is guaranteed to fit in an "unsigned int" because input size in bytes
+  // fits in an "unsigned int".
+  BN_ULONG num_blocks_part1 = BN_get_word(num_blocks_until_reset.get());
+  BN_ULONG input_size_part1 = num_blocks_part1 * AES_BLOCK_SIZE;
+  DCHECK_LT(input_size_part1, data.byte_length());
+
+  // Encrypt the first part (before wrap-around).
+  Status status =
+      AesCtrEncrypt128BitCounter(cipher,
+                                 CryptoData(raw_key),
+                                 CryptoData(data.bytes(), input_size_part1),
+                                 counter_block,
+                                 vector_as_array(buffer));
+  if (status.IsError())
+    return status;
+
+  // Encrypt the second part (after wrap-around).
+  std::vector<uint8_t> counter_block_part2 =
+      BlockWithZeroedCounter(counter_block, counter_length_bits);
+
+  return AesCtrEncrypt128BitCounter(
+      cipher,
+      CryptoData(raw_key),
+      CryptoData(data.bytes() + input_size_part1,
+                 data.byte_length() - input_size_part1),
+      CryptoData(counter_block_part2),
+      vector_as_array(buffer) + input_size_part1);
+}
+
+class AesCtrImplementation : public AesAlgorithm {
+ public:
+  AesCtrImplementation() : AesAlgorithm("CTR") {}
+
+  virtual Status Encrypt(const blink::WebCryptoAlgorithm& algorithm,
+                         const blink::WebCryptoKey& key,
+                         const CryptoData& data,
+                         std::vector<uint8_t>* buffer) const OVERRIDE {
+    return AesCtrEncryptDecrypt(algorithm, key, data, buffer);
+  }
+
+  virtual Status Decrypt(const blink::WebCryptoAlgorithm& algorithm,
+                         const blink::WebCryptoKey& key,
+                         const CryptoData& data,
+                         std::vector<uint8_t>* buffer) const OVERRIDE {
+    return AesCtrEncryptDecrypt(algorithm, key, data, buffer);
+  }
+};
+
+}  // namespace
+
+AlgorithmImplementation* CreatePlatformAesCtrImplementation() {
+  return new AesCtrImplementation;
+}
+
+}  // namespace webcrypto
+
+}  // namespace content