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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "content/browser/webid/jwt_signer.h"
#include <map>
#include "base/base64.h"
#include "base/base64url.h"
#include "base/containers/span.h"
#include "base/functional/bind.h"
#include "base/functional/callback.h"
#include "base/json/json_reader.h"
#include "base/json/json_writer.h"
#include "base/logging.h"
#include "base/values.h"
#include "content/browser/webid/sd_jwt.h"
#include "crypto/openssl_util.h"
#include "crypto/random.h"
#include "crypto/sign.h"
#include "third_party/boringssl/src/include/openssl/base.h"
#include "third_party/boringssl/src/include/openssl/bn.h"
#include "third_party/boringssl/src/include/openssl/bytestring.h"
#include "third_party/boringssl/src/include/openssl/ec.h"
#include "third_party/boringssl/src/include/openssl/ec_key.h"
#include "third_party/boringssl/src/include/openssl/ecdsa.h"
#include "third_party/boringssl/src/include/openssl/evp.h"
#include "third_party/boringssl/src/include/openssl/mem.h"
#include "third_party/boringssl/src/include/openssl/nid.h"
#include "url/gurl.h"
#include "url/origin.h"
namespace content::sdjwt {
namespace {
// Rounds a bit count (up) to the nearest byte count.
//
// This is mathematically equivalent to (x + 7) / 8, however has no
// possibility of integer overflow.
template <typename T>
T NumBitsToBytes(T x) {
return (x / 8) + (7 + (x % 8)) / 8;
}
int GetGroupDegreeInBytes(EC_KEY* ec) {
const EC_GROUP* group = EC_KEY_get0_group(ec);
return NumBitsToBytes(EC_GROUP_get_degree(group));
}
bool IsEcdsaP256(EVP_PKEY* evp_key) {
if (EVP_PKEY_base_id(evp_key) != EVP_PKEY_EC) {
return false;
}
EC_KEY* ec_key = EVP_PKEY_get0_EC_KEY(evp_key);
CHECK(ec_key);
return EC_KEY_get0_group(ec_key) == EC_group_p256();
}
std::optional<std::string> BIGNUMToPadded(const BIGNUM* value,
size_t padded_length) {
std::vector<uint8_t> padded_bytes(padded_length);
if (!BN_bn2bin_padded(padded_bytes.data(), padded_bytes.size(), value)) {
return std::nullopt;
}
std::string base64;
base::Base64UrlEncode(base::as_byte_span(padded_bytes),
base::Base64UrlEncodePolicy::OMIT_PADDING, &base64);
return base64;
}
// Given a DER-encoded ECDSA-Sig-Value, unpack it into a raw ECDSA signature:
// (r, s) represented as two big-endian, zero-padded 256-bit integers. This
// function requires that the input be a valid ECDSA signature and that both r
// and s are <= 256 bits.
std::vector<uint8_t> UnpackDERSignature(base::span<const uint8_t> der_sig) {
crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
// Create ECDSA_SIG object from DER-encoded data.
bssl::UniquePtr<ECDSA_SIG> ecdsa_sig(
ECDSA_SIG_from_bytes(der_sig.data(), der_sig.size()));
CHECK(ecdsa_sig.get());
// The result is made of two 32-byte vectors.
const size_t kMaxBytesPerBN = 32;
std::vector<uint8_t> result(2 * kMaxBytesPerBN);
CHECK(BN_bn2bin_padded(&result[0], kMaxBytesPerBN, ecdsa_sig->r));
CHECK(
BN_bn2bin_padded(&result[kMaxBytesPerBN], kMaxBytesPerBN, ecdsa_sig->s));
return result;
}
std::optional<std::vector<uint8_t>> SignJwt(
crypto::keypair::PrivateKey private_key,
const std::string_view& message) {
// The signature unpacking step won't work if the key uses a curve other than
// P-256.
if (!IsEcdsaP256(private_key.key())) {
return std::nullopt;
}
const auto sig = crypto::sign::Sign(crypto::sign::SignatureKind::ECDSA_SHA256,
private_key, base::as_byte_span(message));
return UnpackDERSignature(sig);
}
} // namespace
std::optional<Jwk> ExportPublicKey(
const crypto::keypair::PrivateKey& private_pkey) {
EC_KEY* ec = EVP_PKEY_get0_EC_KEY(private_pkey.key());
if (!ec) {
return std::nullopt;
}
Jwk jwk;
jwk.kty = "EC";
jwk.crv = "P-256";
// Get public key
bssl::UniquePtr<BIGNUM> x(BN_new());
bssl::UniquePtr<BIGNUM> y(BN_new());
const EC_GROUP* group = EC_KEY_get0_group(ec);
const EC_POINT* point = EC_KEY_get0_public_key(ec);
if (!EC_POINT_get_affine_coordinates_GFp(group, point, x.get(), y.get(),
nullptr)) {
return std::nullopt;
}
int degree_bytes = GetGroupDegreeInBytes(ec);
auto x_base64 = BIGNUMToPadded(x.get(), degree_bytes);
if (!x_base64) {
return std::nullopt;
}
jwk.x = *x_base64;
auto y_base64 = BIGNUMToPadded(y.get(), degree_bytes);
if (!y_base64) {
return std::nullopt;
}
jwk.y = *y_base64;
return jwk;
}
Signer CreateJwtSigner(crypto::keypair::PrivateKey private_key) {
return base::BindOnce(SignJwt, std::move(private_key));
}
} // namespace content::sdjwt
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