[webcrypto] Implement AES-CTR using BoringSSL.

content/child/webcrypto/openssl/util_openssl.h

 // 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.
 
 #ifndef CONTENT_CHILD_WEBCRYPTO_OPENSSL_UTIL_OPENSSL_H_
 #define CONTENT_CHILD_WEBCRYPTO_OPENSSL_UTIL_OPENSSL_H_
 
 #include <vector>
 
 #include <openssl/ossl_typ.h>
 
 #include "third_party/WebKit/public/platform/WebCryptoAlgorithm.h"
 #include "third_party/WebKit/public/platform/WebCryptoKey.h"
 
 namespace content {
 
 namespace webcrypto {
 
 class CryptoData;
 class Status;
 
-enum EncryptOrDecrypt { ENCRYPT, DECRYPT };
+// The values of these constants correspond with the "enc" parameter of
+// EVP_CipherInit_ex(), do not change.
+enum EncryptOrDecrypt { DECRYPT=0, ENCRYPT=1 };
 
 const EVP_MD* GetDigest(blink::WebCryptoAlgorithmId id);
 
 // Does either encryption or decryption for an AEAD algorithm.
 //   * |mode| controls whether encryption or decryption is done
 //   * |aead_alg| the algorithm (for instance AES-GCM)
 //   * |buffer| where the ciphertext or plaintext is written to.
 Status AeadEncryptDecrypt(EncryptOrDecrypt mode,
                           const std::vector<uint8_t>& raw_key,
                           const CryptoData& data,
                           unsigned int tag_length_bytes,
                           const CryptoData& iv,
                           const CryptoData& additional_data,
                           const EVP_AEAD* aead_alg,
                           std::vector<uint8_t>* buffer);
 
 }  // namespace webcrypto
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_WEBCRYPTO_OPENSSL_UTIL_OPENSSL_H_