diff --git a/crypto/hmac.cc b/crypto/hmac.cc
new file mode 100644
index 0000000..c9a2b74
--- /dev/null
+++ b/crypto/hmac.cc
@@ -0,0 +1,57 @@
+// Copyright (c) 2012 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 "crypto/hmac.h"
+
+#include <algorithm>
+
+#include "base/logging.h"
+#include "crypto/secure_util.h"
+#include "crypto/symmetric_key.h"
+
+namespace crypto {
+
+bool HMAC::Init(SymmetricKey* key) {
+  std::string raw_key;
+  bool result = key->GetRawKey(&raw_key) && Init(raw_key);
+  // Zero out key copy.  This might get optimized away, but one can hope.
+  // Using std::string to store key info at all is a larger problem.
+  std::fill(raw_key.begin(), raw_key.end(), 0);
+  return result;
+}
+
+size_t HMAC::DigestLength() const {
+  switch (hash_alg_) {
+    case SHA1:
+      return 20;
+    case SHA256:
+      return 32;
+    default:
+      NOTREACHED();
+      return 0;
+  }
+}
+
+bool HMAC::Verify(const base::StringPiece& data,
+                  const base::StringPiece& digest) const {
+  if (digest.size() != DigestLength())
+    return false;
+  return VerifyTruncated(data, digest);
+}
+
+bool HMAC::VerifyTruncated(const base::StringPiece& data,
+                           const base::StringPiece& digest) const {
+  if (digest.empty())
+    return false;
+  size_t digest_length = DigestLength();
+  scoped_ptr<unsigned char[]> computed_digest(
+      new unsigned char[digest_length]);
+  if (!Sign(data, computed_digest.get(), digest_length))
+    return false;
+
+  return SecureMemEqual(digest.data(), computed_digest.get(),
+                        std::min(digest.size(), digest_length));
+}
+
+}  // namespace crypto