[refactor] More post-NSS WebCrypto cleanups (utility functions).

components/webcrypto/algorithms/aes_gcm.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/evp.h>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "components/webcrypto/algorithms/aes.h"
@@ skipping 22 matching lines @@
 }
 
 Status AesGcmEncryptDecrypt(EncryptOrDecrypt mode,
                             const blink::WebCryptoAlgorithm& algorithm,
                             const blink::WebCryptoKey& key,
                             const CryptoData& data,
                             std::vector<uint8_t>* buffer) {
   const std::vector<uint8_t>& raw_key = GetSymmetricKeyData(key);
   const blink::WebCryptoAesGcmParams* params = algorithm.aesGcmParams();
 
-  unsigned int tag_length_bits;
-  Status status = GetAesGcmTagLengthInBits(params, &tag_length_bits);
-  if (status.IsError())
-    return status;
+  // The WebCrypto spec defines the default value for the tag length, as well as
+  // the allowed values for tag length.
+  unsigned int tag_length_bits = 128;
+  if (params->hasTagLengthBits()) {
+    tag_length_bits = params->optionalTagLengthBits();
+    if (tag_length_bits != 32 && tag_length_bits != 64 &&
+        tag_length_bits != 96 && tag_length_bits != 104 &&
+        tag_length_bits != 112 && tag_length_bits != 120 &&
+        tag_length_bits != 128) {
+      return Status::ErrorInvalidAesGcmTagLength();
+    }
+  }
 
   return AeadEncryptDecrypt(
       mode, raw_key, data, tag_length_bits / 8, CryptoData(params->iv()),
       CryptoData(params->optionalAdditionalData()),
       GetAesGcmAlgorithmFromKeySize(raw_key.size()), buffer);
 }
 
 class AesGcmImplementation : public AesAlgorithm {
  public:
   AesGcmImplementation() : AesAlgorithm("GCM") {}
@@ skipping 13 matching lines @@
   }
 };
 
 }  // namespace
 
 scoped_ptr<AlgorithmImplementation> CreateAesGcmImplementation() {
   return make_scoped_ptr(new AesGcmImplementation);
 }
 
 }  // namespace webcrypto