CT: Adding SCT verification functionality: A CTLogVerifier instance can verify SCTs signed by a sin…

net/cert/ct_log_verifier_openssl.cc

+// Copyright (c) 2013 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 "net/cert/ct_log_verifier.h"
+
+#include <openssl/evp.h>
+#include <openssl/x509.h>
+
+#include "base/logging.h"
+#include "crypto/openssl_util.h"
+#include "crypto/sha2.h"
+
+namespace net {
+
+namespace {
+
+const EVP_MD* GetEvpAlg(ct::DigitallySigned::HashAlgorithm alg) {
+  switch (alg) {
+    case ct::DigitallySigned::HASH_ALGO_MD5:
+      return EVP_md5();
+    case ct::DigitallySigned::HASH_ALGO_SHA1:
+      return EVP_sha1();
+    case ct::DigitallySigned::HASH_ALGO_SHA224:
+      return EVP_sha224();
+    case ct::DigitallySigned::HASH_ALGO_SHA256:
+      return EVP_sha256();
+    case ct::DigitallySigned::HASH_ALGO_SHA384:
+      return EVP_sha384();
+    case ct::DigitallySigned::HASH_ALGO_SHA512:
+      return EVP_sha512();
+    case ct::DigitallySigned::HASH_ALGO_NONE:

[wtc, 2013/11/08 21:04:00]

Nit: add a default case, unless you know it is impossible.

[Eran M. (Google), 2013/11/12 12:01:28]

Done.

+      NOTREACHED();
+      return NULL;
+  }
+}
+
+}  // namespace
+
+CTLogVerifier::~CTLogVerifier() {
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+
+  if (public_key_)
+    EVP_PKEY_free(public_key_);
+}
+
+CTLogVerifier::CTLogVerifier() : public_key_(NULL) {}

[wtc, 2013/11/08 21:04:00]

Should also initialize hash_algorithm_ and sig_algorithm_.

[Eran M. (Google), 2013/11/12 12:01:28]

Done.

+
+bool CTLogVerifier::Init(const base::StringPiece& public_key,
+                         const base::StringPiece& description) {
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+
+  crypto::ScopedOpenSSL<BIO, BIO_free_all> bio(
+      BIO_new_mem_buf(const_cast<char*>(public_key.data()), public_key.size()));
+  if (!bio.get())
+    return false;
+
+  public_key_ = d2i_PUBKEY_bio(bio.get(), NULL);
+  if (!public_key_)
+    return false;
+
+  key_id_ = crypto::SHA256HashString(public_key);
+  description_ = description.as_string();
+
+  switch (EVP_PKEY_type(public_key_->type)) {
+    case EVP_PKEY_RSA:
+      hash_algorithm_ = ct::DigitallySigned::HASH_ALGO_SHA256;
+      sig_algorithm_ = ct::DigitallySigned::SIG_ALGO_RSA;
+      break;
+    case EVP_PKEY_EC:
+      hash_algorithm_ = ct::DigitallySigned::HASH_ALGO_SHA256;
+      sig_algorithm_ = ct::DigitallySigned::SIG_ALGO_ECDSA;
+      break;
+    default:
+      DVLOG(1) << "Unsupported key type: " << EVP_PKEY_type(public_key_->type);
+      return false;
+  }
+
+  // EVP_PKEY_size returns the size in bytes. 256 = 2048-bit RSA key.
+  if (sig_algorithm_ == ct::DigitallySigned::SIG_ALGO_RSA &&
+      EVP_PKEY_size(public_key_) < 256) {
+    DVLOG(1) << "Too small a public key.";
+    return false;
+  }
+
+  return true;
+}
+
+bool CTLogVerifier::VerifySignature(const base::StringPiece& data_to_sign,
+                                    const base::StringPiece& signature) {
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+
+  const EVP_MD* hash_alg = GetEvpAlg(hash_algorithm_);
+  if (hash_alg == NULL)
+    return false;
+
+  EVP_MD_CTX ctx;
+  EVP_MD_CTX_init(&ctx);
+
+  bool ok =
+      (1 == EVP_VerifyInit(&ctx, hash_alg) &&

[wtc, 2013/11/08 21:04:00]

I am not familiar with OpenSSL. Would EVP_DigestVerify* be a better interface
than EVP_Verify*? Chromium's crypto/signature_verifier_openssl.cc uses the
EVP_DigestVerify* interface.

[Eran M. (Google), 2013/11/12 12:01:28]

Converted the code to using EVP_DigestVerify although I can't judge if it's
better - it's the same number of calls and same arguments.

[wtc, 2013/11/14 18:46:30]

I was hoping you could ask Ben Laurie :-)

The only external difference I can tell is that EVP_DigestVerifyInit has two
more arguments, but we are not using them. I am curious if there is an internal
difference.

[Eran M. (Google), 2013/11/16 22:59:16]

As mentioned in an offline email, I ended up asking the author of the API,
Steve. He explained the difference (it's not relevant here) and pointed out 
that EVP_DigestVerify is the newer API of the two. So I just migrated the code
to use the newer one.

+       1 == EVP_VerifyUpdate(&ctx, data_to_sign.data(), data_to_sign.size()) &&
+       1 == EVP_VerifyFinal(
+                &ctx,
+                reinterpret_cast<const unsigned char*>(signature.data()),
+                signature.size(),
+                public_key_));
+
+  EVP_MD_CTX_cleanup(&ctx);
+  return ok;
+}
+
+}  // namespace net