webcrypto: Add ECDSA algorithm (chromium-side)

content/child/webcrypto/openssl/ecdsa_openssl.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/ec.h>
+#include <openssl/ec_key.h>
+#include <openssl/evp.h>
+
+#include "base/logging.h"
+#include "content/child/webcrypto/algorithm_implementation.h"
+#include "content/child/webcrypto/crypto_data.h"
+#include "content/child/webcrypto/generate_key_result.h"
+#include "content/child/webcrypto/openssl/ec_key_openssl.h"
+#include "content/child/webcrypto/openssl/key_openssl.h"
+#include "content/child/webcrypto/openssl/util_openssl.h"
+#include "content/child/webcrypto/status.h"
+#include "content/child/webcrypto/webcrypto_util.h"
+#include "crypto/openssl_util.h"
+#include "crypto/scoped_openssl_types.h"
+#include "crypto/secure_util.h"
+#include "third_party/WebKit/public/platform/WebCryptoAlgorithmParams.h"
+#include "third_party/WebKit/public/platform/WebCryptoKey.h"
+#include "third_party/WebKit/public/platform/WebCryptoKeyAlgorithm.h"
+
+namespace content {
+
+namespace webcrypto {
+
+namespace {
+
+// Extracts the OpenSSL key and digest from a WebCrypto key + algorithm. The
+// returned pkey pointer will remain valid as long as |key| is alive.
+Status GetPKeyAndDigest(const blink::WebCryptoAlgorithm& algorithm,
+                        const blink::WebCryptoKey& key,
+                        EVP_PKEY** pkey,
+                        const EVP_MD** digest) {
+  *pkey = AsymKeyOpenSsl::Cast(key)->key();
+  *digest = GetDigest(algorithm.ecdsaParams()->hash().id());
+  if (!*digest)
+    return Status::ErrorUnsupported();
+  return Status::Success();
+}
+
+// Gets the EC key's group degree in bytes.
+Status GetEcGroupDegreeInBytes(EVP_PKEY* pkey, size_t* degree_bytes) {
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+
+  crypto::ScopedEC_KEY ec(EVP_PKEY_get1_EC_KEY(pkey));
+  if (!ec.get())
+    return Status::ErrorUnexpected();
+
+  const EC_GROUP* group = EC_KEY_get0_group(ec.get());
+  *degree_bytes = (EC_GROUP_get_degree(group) + 7) / 8;
+  return Status::Success();
+}
+
+// Formats a DER-encoded signature (ECDSA-Sig-Value as specified in RFC 3279) to
+// the signature format expected by WebCrypto (raw concatenated "r" and "s").
+//
+// TODO(eroman): Where is the specification for WebCrypto's signature format?
+Status ConvertDerSignatureToWebCryptoSignature(
+    EVP_PKEY* key,
+    std::vector<uint8_t>* signature) {
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+
+  const unsigned char* der_data = &signature->front();
+  crypto::ScopedECDSA_SIG ecdsa_sig(
+      d2i_ECDSA_SIG(NULL, &der_data, static_cast<long>(signature->size())));
+  if (!ecdsa_sig.get())
+    return Status::OperationError();
+
+  // Note that |der_data| is updated to point to past the end of the DER
+  // structure. It is possible there are unconsumed bytes at the end, and
+  // this is OK. (Since the ECDSA signature appears to be padded up to
+  // ECDSA_size()).
+
+  // Determine the maximum length of r and s.
+  size_t degree_bytes;
+  Status status = GetEcGroupDegreeInBytes(key, &degree_bytes);

[davidben, 2014/11/10 20:24:00]

I don't think these are quiiiite the same, are they? One's the number of bits to
represent an element of the underlying field (so for P-*, the number of bits in
the prime) while the order of the group is the order of (the subgroup generated
by) the base point.

I believe the order is the one you want since an ECDSA signature is a pair of
numbers to multiply points on the curve by, not a point on the curve itself.
(And so they're taken modulo the order.) Looks like the order and degree are the
same size in bits in the NIST P-* curves, but I don't think this is necessarily
true in general?

I dunno. Math. :-)

[eroman, 2014/11/10 20:55:52]

Thanks David. I thought it was the size of the order too, but simplified it to
using the degree after seeing this code in BoringSSL which was doing the same
thing:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/boring...

I will change it back to the order size so it is more general and won't break if
support for other curves is added.

[davidben, 2014/11/10 21:00:58]

Joy. We get that code from OpenSSL, so I will wave hands in their direction.

+agl. Is my understanding of ECC correct here, that degree and order sizes are
not necessarily interchangeable? (And thus we should probably go fix that
file...)

[agl, 2014/11/10 21:42:27]

Right, r and s are both scalars. So it's the group order that's pertinent here.

While the group order is bounded by Hasse's theorem
(http://en.wikipedia.org/wiki/Hasse's_theorem_on_elliptic_curves), that bound
isn't sufficiently tight to ensure that the order is always the same length as
the field, even with cofactor=1. (Even though they are for P-{224|256|384|521}
curves.)

[eroman, 2014/11/10 22:02:59]

Done -- using the order size.

+  if (status.IsError())
+    return status;
+
+  signature->resize(degree_bytes * 2);
+
+  if (!BN_bn2bin_padded(&signature->front(), degree_bytes, ecdsa_sig.get()->r))
+    return Status::ErrorUnexpected();
+
+  if (!BN_bn2bin_padded(&(*signature)[degree_bytes], degree_bytes,
+                        ecdsa_sig.get()->s))
+    return Status::ErrorUnexpected();

[davidben, 2014/11/10 20:24:00]

Nit: I think if the condition stretched over two lines, we also put in braces
usually?

[eroman, 2014/11/10 22:02:59]

Done.

+
+  return Status::Success();
+}
+
+// Formats a WebCrypto ECDSA signature to a DER-encoded signature
+// (ECDSA-Sig-Value as specified in RFC 3279).
+//
+// TODO(eroman): What is the specification for WebCrypto's signature format?
+//
+// If the signature length is incorrect (not 2 * degree), then
+// Status::Success() is returned and |*incorrect_length| is set to true;
+//
+// Otherwise on success, der_signature is filled with a ASN.1 encoded
+// ECDSA-Sig-Value.
+Status ConvertWebCryptoSignatureToDerSignature(
+    EVP_PKEY* key,
+    const CryptoData& signature,
+    std::vector<uint8_t>* der_signature,
+    bool* incorrect_length) {
+  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+
+  // Determine the length of r and s.
+  size_t degree_bytes;
+  Status status = GetEcGroupDegreeInBytes(key, &degree_bytes);
+  if (status.IsError())
+    return status;
+
+  // If the size of the signature is incorrect, verification must fail. Success
+  // is returned here rather than an error, so that the caller can fail
+  // verification with a boolean, rather than reject the promise with an
+  // exception.
+  if (signature.byte_length() != 2 * degree_bytes) {
+    *incorrect_length = true;
+    return Status::Success();
+  }
+
+  *incorrect_length = false;
+
+  // Construct an ECDSA_SIG from |signature|.
+  crypto::ScopedECDSA_SIG ecdsa_sig(ECDSA_SIG_new());
+  if (!ecdsa_sig)
+    return Status::OperationError();
+
+  ecdsa_sig->r = BN_bin2bn(signature.bytes(), degree_bytes, NULL);
+  ecdsa_sig->s =
+      BN_bin2bn(signature.bytes() + degree_bytes, degree_bytes, NULL);
+
+  if (!ecdsa_sig->r || !ecdsa_sig->s)
+    return Status::ErrorUnexpected();
+
+  // Determine the size of the DER-encoded signature.
+  int der_encoding_size = i2d_ECDSA_SIG(ecdsa_sig.get(), NULL);
+  if (der_encoding_size < 0)
+    return Status::OperationError();
+
+  // DER-encode the signature.
+  der_signature->resize(der_encoding_size);
+  uint8_t* result = &der_signature->front();
+  if (0 > i2d_ECDSA_SIG(ecdsa_sig.get(), &result))
+    return Status::OperationError();
+
+  return Status::Success();
+}
+
+class EcdsaImplementation : public EcAlgorithm {
+ public:
+  EcdsaImplementation()
+      : EcAlgorithm(blink::WebCryptoKeyUsageVerify,
+                    blink::WebCryptoKeyUsageSign) {}
+
+  const char* GetJwkAlgorithm(
+      const blink::WebCryptoNamedCurve curve) const override {
+    switch (curve) {
+      case blink::WebCryptoNamedCurveP256:
+        return "ES256";
+      case blink::WebCryptoNamedCurveP384:
+        return "ES384";
+      case blink::WebCryptoNamedCurveP521:
+        // This is not a typo! ES512 means P-521 with SHA-512.
+        return "ES512";
+      default:
+        return NULL;
+    }
+  }
+
+  Status Sign(const blink::WebCryptoAlgorithm& algorithm,
+              const blink::WebCryptoKey& key,
+              const CryptoData& data,
+              std::vector<uint8_t>* buffer) const override {
+    if (key.type() != blink::WebCryptoKeyTypePrivate)
+      return Status::ErrorUnexpectedKeyType();
+
+    crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+    crypto::ScopedEVP_MD_CTX ctx(EVP_MD_CTX_create());
+
+    EVP_PKEY* private_key = NULL;
+    const EVP_MD* digest = NULL;
+    Status status = GetPKeyAndDigest(algorithm, key, &private_key, &digest);
+    if (status.IsError())
+      return status;
+
+    // NOTE: A call to EVP_DigestSignFinal() with a NULL second parameter
+    // returns a maximum allocation size, while the call without a NULL returns
+    // the real one, which may be smaller.
+    size_t sig_len = 0;
+    if (!ctx.get() ||
+        !EVP_DigestSignInit(ctx.get(), NULL, digest, NULL, private_key) ||
+        !EVP_DigestSignUpdate(ctx.get(), data.bytes(), data.byte_length()) ||
+        !EVP_DigestSignFinal(ctx.get(), NULL, &sig_len)) {
+      return Status::OperationError();
+    }
+
+    buffer->resize(sig_len);
+    if (!EVP_DigestSignFinal(ctx.get(), &buffer->front(), &sig_len))
+      return Status::OperationError();
+    buffer->resize(sig_len);
+
+    // ECDSA signing in BoringSSL outputs a DER-encoded (r,s). WebCrypto however
+    // expects a padded bitstring that is r concatenated to s. Convert to the
+    // expected format.
+    return ConvertDerSignatureToWebCryptoSignature(private_key, buffer);
+  }
+
+  Status Verify(const blink::WebCryptoAlgorithm& algorithm,
+                const blink::WebCryptoKey& key,
+                const CryptoData& signature,
+                const CryptoData& data,
+                bool* signature_match) const override {
+    if (key.type() != blink::WebCryptoKeyTypePublic)
+      return Status::ErrorUnexpectedKeyType();
+
+    *signature_match = false;

[davidben, 2014/11/10 20:24:00]

Nit: If this is getting set on errors too, may as well lift it above
ErrorUnexpectedKeyType() too.

[eroman, 2014/11/10 22:02:59]

I moved this to the end, for consistent style with
https://codereview.chromium.org/688983004/

+
+    crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
+    crypto::ScopedEVP_MD_CTX ctx(EVP_MD_CTX_create());
+
+    EVP_PKEY* public_key = NULL;
+    const EVP_MD* digest = NULL;
+    Status status = GetPKeyAndDigest(algorithm, key, &public_key, &digest);
+    if (status.IsError())
+      return status;
+
+    std::vector<uint8_t> der_signature;
+    bool incorrect_length_signature;
+    status = ConvertWebCryptoSignatureToDerSignature(
+        public_key, signature, &der_signature, &incorrect_length_signature);
+    if (status.IsError())
+      return status;
+
+    if (incorrect_length_signature) {
+      *signature_match = false;
+      return Status::Success();
+    }
+
+    if (!EVP_DigestVerifyInit(ctx.get(), NULL, digest, NULL, public_key) ||
+        !EVP_DigestVerifyUpdate(ctx.get(), data.bytes(), data.byte_length())) {
+      return Status::OperationError();
+    }
+
+    if (EVP_DigestVerifyFinal(ctx.get(), &der_signature.front(),
+                              der_signature.size())) {
+      *signature_match = true;
+    }
+
+    return Status::Success();
+  }
+};
+
+}  // namespace
+
+AlgorithmImplementation* CreatePlatformEcdsaImplementation() {
+  return new EcdsaImplementation;
+}
+
+}  // namespace webcrypto
+
+}  // namespace content