Refactor WebCrypto code

content/child/webcrypto/nss/aes_kw_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 <secerr.h>
+
+#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/sym_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 "crypto/scoped_nss_types.h"
+#include "third_party/WebKit/public/platform/WebCryptoAlgorithmParams.h"
+#include "third_party/WebKit/public/platform/WebCryptoKeyAlgorithm.h"
+
+namespace content {
+
+namespace webcrypto {
+
+namespace {
+
+// The Default IV for AES-KW. See http://www.ietf.org/rfc/rfc3394.txt
+// Section 2.2.3.1.
+const unsigned char kAesIv[] = {0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6, 0xA6};
+
+Status DoUnwrapSymKeyAesKw(const CryptoData& wrapped_key_data,

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

Document why this exists as working on a SymKey (141-142 notes it, but I should
be able to read the function, rather than its use, to determine its
purpose/design choices)

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

Done. Documented as:

// The result of unwrapping is a SymKey rather than a buffer. This is a
// consequence of how NSS exposes AES-KW. Subsequent code can extract the value
// of the sym key to interpret it as key bytes in another format.

+                           PK11SymKey* wrapping_key,
+                           CK_MECHANISM_TYPE mechanism,
+                           CK_FLAGS flags,
+                           crypto::ScopedPK11SymKey* unwrapped_key) {
+  DCHECK_GE(wrapped_key_data.byte_length(), 24u);
+  DCHECK_EQ(wrapped_key_data.byte_length() % 8, 0u);
+
+  SECItem iv_item = MakeSECItemForBuffer(CryptoData(kAesIv, sizeof(kAesIv)));
+  crypto::ScopedSECItem param_item(
+      PK11_ParamFromIV(CKM_NSS_AES_KEY_WRAP, &iv_item));
+  if (!param_item)
+    return Status::ErrorUnexpected();
+
+  SECItem cipher_text = MakeSECItemForBuffer(wrapped_key_data);
+
+  // The plaintext length is always 64 bits less than the data size.
+  const unsigned int plaintext_length = wrapped_key_data.byte_length() - 8;
+
+#if defined(USE_NSS)
+  // Part of workaround for
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=981170. See the explanation
+  // later in this function.
+  PORT_SetError(0);
+#endif
+
+  crypto::ScopedPK11SymKey new_key(
+      PK11_UnwrapSymKeyWithFlags(wrapping_key,
+                                 CKM_NSS_AES_KEY_WRAP,
+                                 param_item.get(),
+                                 &cipher_text,
+                                 mechanism,
+                                 CKA_FLAGS_ONLY,
+                                 plaintext_length,
+                                 flags));
+
+  // TODO(padolph): Use NSS PORT_GetError() and friends to report a more
+  // accurate error, providing if doesn't leak any information to web pages
+  // about other web crypto users, key details, etc.
+  if (!new_key)
+    return Status::OperationError();
+
+#if defined(USE_NSS)
+  // Workaround for https://bugzilla.mozilla.org/show_bug.cgi?id=981170
+  // which was fixed in NSS 3.16.0.
+  // If unwrap fails, NSS nevertheless returns a valid-looking PK11SymKey,
+  // with a reasonable length but with key data pointing to uninitialized
+  // memory.
+  // To understand this workaround see the fix for 981170:
+  // https://hg.mozilla.org/projects/nss/rev/753bb69e543c
+  if (!NSS_VersionCheck("3.16") && PORT_GetError() == SEC_ERROR_BAD_DATA)
+    return Status::OperationError();
+#endif
+
+  *unwrapped_key = new_key.Pass();
+  return Status::Success();
+}
+
+Status WrapSymKeyAesKw(PK11SymKey* key,
+                       PK11SymKey* wrapping_key,
+                       std::vector<uint8>* buffer) {
+  // The data size must be at least 16 bytes and a multiple of 8 bytes.
+  // RFC 3394 does not specify a maximum allowed data length, but since only
+  // keys are being wrapped in this application (which are small), a reasonable
+  // max limit is whatever will fit into an unsigned. For the max size test,
+  // note that AES Key Wrap always adds 8 bytes to the input data size.
+  const unsigned int input_length = PK11_GetKeyLength(key);
+  DCHECK_GE(input_length, 16u);
+  DCHECK((input_length % 8) == 0);
+  if (input_length > UINT_MAX - 8)
+    return Status::ErrorDataTooLarge();
+
+  SECItem iv_item = MakeSECItemForBuffer(CryptoData(kAesIv, sizeof(kAesIv)));
+  crypto::ScopedSECItem param_item(
+      PK11_ParamFromIV(CKM_NSS_AES_KEY_WRAP, &iv_item));
+  if (!param_item)
+    return Status::ErrorUnexpected();
+
+  const unsigned int output_length = input_length + 8;
+  buffer->resize(output_length);
+  SECItem wrapped_key_item = MakeSECItemForBuffer(CryptoData(*buffer));
+
+  if (SECSuccess != PK11_WrapSymKey(CKM_NSS_AES_KEY_WRAP,
+                                    param_item.get(),
+                                    wrapping_key,
+                                    key,
+                                    &wrapped_key_item)) {
+    return Status::OperationError();
+  }
+  if (output_length != wrapped_key_item.len)
+    return Status::ErrorUnexpected();
+
+  return Status::Success();
+}
+
+class AesKwCryptoAlgorithmNss : public AesAlgorithm {
+ public:
+  AesKwCryptoAlgorithmNss()
+      : AesAlgorithm(
+            CKM_NSS_AES_KEY_WRAP,
+            CKF_WRAP | CKF_WRAP,
+            blink::WebCryptoKeyUsageWrapKey | blink::WebCryptoKeyUsageUnwrapKey,
+            "KW") {}
+
+  virtual Status Encrypt(const blink::WebCryptoAlgorithm& algorithm,
+                         const blink::WebCryptoKey& wrapping_key,
+                         const CryptoData& data,
+                         std::vector<uint8>* buffer) const OVERRIDE {
+    if (data.byte_length() < 16)
+      return Status::ErrorDataTooSmall();
+    if (data.byte_length() % 8)
+      return Status::ErrorInvalidAesKwDataLength();
+
+    // Due to limitations in the NSS API for the AES-KW algorithm, |data| must
+    // be temporarily viewed as a symmetric key to be wrapped (encrypted).
+    SECItem data_item = MakeSECItemForBuffer(data);
+    crypto::ScopedPK11Slot slot(PK11_GetInternalSlot());
+    crypto::ScopedPK11SymKey data_as_sym_key(
+        PK11_ImportSymKey(slot.get(),
+                          CKK_GENERIC_SECRET,
+                          PK11_OriginUnwrap,
+                          CKA_SIGN,
+                          &data_item,
+                          NULL));
+    if (!data_as_sym_key)
+      return Status::OperationError();
+
+    return WrapSymKeyAesKw(
+        data_as_sym_key.get(), SymKeyNss::Cast(wrapping_key)->key(), buffer);
+  }
+
+  virtual Status Decrypt(const blink::WebCryptoAlgorithm& algorithm,
+                         const blink::WebCryptoKey& wrapping_key,
+                         const CryptoData& data,
+                         std::vector<uint8>* buffer) const OVERRIDE {
+    if (data.byte_length() < 24)
+      return Status::ErrorDataTooSmall();
+    if (data.byte_length() % 8)
+      return Status::ErrorInvalidAesKwDataLength();
+
+    // Due to limitations in the NSS API for the AES-KW algorithm, |data| must
+    // be
+    // temporarily viewed as a symmetric key to be unwrapped (decrypted).
+    crypto::ScopedPK11SymKey decrypted;
+    Status status = DoUnwrapSymKeyAesKw(data,
+                                        SymKeyNss::Cast(wrapping_key)->key(),
+                                        CKK_GENERIC_SECRET,
+                                        0,
+                                        &decrypted);
+    if (status.IsError())
+      return status;
+
+    // Once the decrypt is complete, extract the resultant raw bytes from NSS
+    // and return them to the caller.
+    if (PK11_ExtractKeyValue(decrypted.get()) != SECSuccess)
+      return Status::OperationError();
+    const SECItem* const key_data = PK11_GetKeyData(decrypted.get());
+    if (!key_data)
+      return Status::OperationError();
+    buffer->assign(key_data->data, key_data->data + key_data->len);
+
+    return Status::Success();
+  }
+};
+
+}  // namespace
+
+AlgorithmImplementation* CreatePlatformAesKwImplementation() {
+  return new AesKwCryptoAlgorithmNss;
+}
+
+}  // namespace webcrypto
+
+}  // namespace content