Refactor WebCrypto code

content/child/webcrypto/nss/aes_gcm_nss.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 "content/child/webcrypto/crypto_data.h"
+#include "content/child/webcrypto/nss/aes_key_nss.h"
+#include "content/child/webcrypto/nss/key_nss.h"
+#include "content/child/webcrypto/nss/util_nss.h"
+#include "content/child/webcrypto/status.h"
+#include "content/child/webcrypto/webcrypto_util.h"
+#include "third_party/WebKit/public/platform/WebCryptoAlgorithmParams.h"
+
+// At the time of this writing:
+//   * Windows and Mac builds ship with their own copy of NSS (3.15+)
+//   * Linux builds use the system's libnss, which is 3.14 on Debian (but 3.15+
+//     on other distros).
+//
+// Since NSS provides AES-GCM support starting in version 3.15, it may be
+// unavailable for Linux Chrome users.
+//
+//  * !defined(CKM_AES_GCM)
+//
+//      This means that at build time, the NSS header pkcs11t.h is older than
+//      3.15. However at runtime support may be present.
+//
+//  * !defined(USE_NSS)
+//
+//      This means that Chrome is being built with an embedded copy of NSS,
+//      which can be assumed to be >= 3.15. On the other hand if USE_NSS is
+//      defined, it also implies running on Linux.
+//
+// TODO(eroman): Simplify this once 3.15+ is required by Linux builds.
+#if !defined(CKM_AES_GCM)
+#define CKM_AES_GCM 0x00001087
+
+struct CK_GCM_PARAMS {
+  CK_BYTE_PTR pIv;
+  CK_ULONG ulIvLen;
+  CK_BYTE_PTR pAAD;
+  CK_ULONG ulAADLen;
+  CK_ULONG ulTagBits;
+};
+#endif  // !defined(CKM_AES_GCM)
+
+namespace content {
+
+namespace webcrypto {
+
+namespace {
+
+Status NssSupportsAesGcm() {
+  if (NssRuntimeSupport::Get()->IsAesGcmSupported())
+    return Status::Success();
+  return Status::ErrorUnsupported(
+      "NSS version doesn't support AES-GCM. Try using version 3.15 or later");
+}
+
+// Helper to either encrypt or decrypt for AES-GCM. The result of encryption is
+// the concatenation of the ciphertext and the authentication tag. Similarly,
+// this is the expectation for the input to decryption.
+Status AesGcmEncryptDecrypt(EncryptOrDecrypt mode,
+                            const blink::WebCryptoAlgorithm& algorithm,
+                            const blink::WebCryptoKey& key,
+                            const CryptoData& data,
+                            std::vector<uint8>* buffer) {
+  Status status = NssSupportsAesGcm();
+  if (status.IsError())
+    return status;
+
+  PK11SymKey* sym_key = SymKeyNss::Cast(key)->key();
+  const blink::WebCryptoAesGcmParams* params = algorithm.aesGcmParams();
+  if (!params)
+    return Status::ErrorUnexpected();
+
+  unsigned int tag_length_bits;
+  status = GetAesGcmTagLength(params, &tag_length_bits);
+  if (status.IsError())
+    return status;
+  unsigned int tag_length_bytes = tag_length_bits / 8;
+
+  CryptoData iv(params->iv());
+  CryptoData additional_data(params->optionalAdditionalData());
+
+  CK_GCM_PARAMS gcm_params = {0};
+  gcm_params.pIv = const_cast<unsigned char*>(iv.bytes());
+  gcm_params.ulIvLen = iv.byte_length();
+
+  gcm_params.pAAD = const_cast<unsigned char*>(additional_data.bytes());
+  gcm_params.ulAADLen = additional_data.byte_length();
+
+  gcm_params.ulTagBits = tag_length_bits;
+
+  SECItem param;
+  param.type = siBuffer;
+  param.data = reinterpret_cast<unsigned char*>(&gcm_params);
+  param.len = sizeof(gcm_params);
+
+  unsigned int buffer_size = 0;
+
+  // Calculate the output buffer size.
+  if (mode == ENCRYPT) {
+    // TODO(eroman): This is ugly, abstract away the safe integer arithmetic.
+    if (data.byte_length() > (UINT_MAX - tag_length_bytes))
+      return Status::ErrorDataTooLarge();

[Ryan Sleevi, 2014/07/17 00:06:54]

base::CheckedNumeric<> for a follow-up if you want.

[eroman, 2014/07/17 20:37:25]

Will follow up through:
https://code.google.com/p/chromium/issues/detail?id=394821

+    buffer_size = data.byte_length() + tag_length_bytes;
+  } else {
+    // TODO(eroman): In theory the buffer allocated for the plain text should be
+    // sized as |data.byte_length() - tag_length_bytes|.
+    //
+    // However NSS has a bug whereby it will fail if the output buffer size is
+    // not at least as large as the ciphertext:
+    //
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=%20853674
+    //
+    // From the analysis of that bug it looks like it might be safe to pass a
+    // correctly sized buffer but lie about its size. Since resizing the
+    // WebCryptoArrayBuffer is expensive that hack may be worth looking into.
+    buffer_size = data.byte_length();
+  }
+
+  buffer->resize(buffer_size);
+  unsigned char* buffer_data = Uint8VectorStart(buffer);
+
+  PK11_EncryptDecryptFunction func =

[Ryan Sleevi, 2014/07/17 00:06:53]

pedantry: encrypt_or_decrypt_function?

[eroman, 2014/07/17 20:37:25]

Done.

+      (mode == ENCRYPT) ? NssRuntimeSupport::Get()->pk11_encrypt_func()
+                        : NssRuntimeSupport::Get()->pk11_decrypt_func();
+
+  unsigned int output_len = 0;
+  SECStatus result = func(sym_key,
+                          CKM_AES_GCM,
+                          &param,
+                          buffer_data,
+                          &output_len,
+                          buffer->size(),
+                          data.bytes(),
+                          data.byte_length());
+
+  if (result != SECSuccess)
+    return Status::OperationError();
+
+  // Unfortunately the buffer needs to be shrunk for decryption (see the NSS bug
+  // above).
+  buffer->resize(output_len);
+
+  return Status::Success();
+}
+
+class AesGcmImplementation : public AesAlgorithm {
+ public:
+  AesGcmImplementation() : AesAlgorithm(CKM_AES_GCM, "GCM") {}
+
+  virtual Status VerifyKeyUsagesBeforeImportKey(
+      blink::WebCryptoKeyFormat format,
+      blink::WebCryptoKeyUsageMask usage_mask) const OVERRIDE {
+    // Prevent importing AES-GCM keys if it is unavailable.
+    Status status = NssSupportsAesGcm();
+    if (status.IsError())
+      return status;
+    return AesAlgorithm::VerifyKeyUsagesBeforeImportKey(format, usage_mask);
+  }
+
+  virtual Status VerifyKeyUsagesBeforeGenerateKey(
+      blink::WebCryptoKeyUsageMask usage_mask) const OVERRIDE {
+    // Prevent generating AES-GCM keys if it is unavailable.
+    Status status = NssSupportsAesGcm();
+    if (status.IsError())
+      return status;
+    return AesAlgorithm::VerifyKeyUsagesBeforeGenerateKey(usage_mask);
+  }
+
+  virtual Status Encrypt(const blink::WebCryptoAlgorithm& algorithm,
+                         const blink::WebCryptoKey& key,
+                         const CryptoData& data,
+                         std::vector<uint8>* buffer) const OVERRIDE {
+    return AesGcmEncryptDecrypt(ENCRYPT, algorithm, key, data, buffer);
+  }
+
+  virtual Status Decrypt(const blink::WebCryptoAlgorithm& algorithm,
+                         const blink::WebCryptoKey& key,
+                         const CryptoData& data,
+                         std::vector<uint8>* buffer) const OVERRIDE {
+    return AesGcmEncryptDecrypt(DECRYPT, algorithm, key, data, buffer);
+  }
+};
+
+}  // namespace
+
+AlgorithmImplementation* CreatePlatformAesGcmImplementation() {
+  return new AesGcmImplementation;
+}
+
+}  // namespace webcrypto
+
+}  // namespace content