106 lines
4.1 KiB
C++
106 lines
4.1 KiB
C++
// Copyright 2021 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#define PW_LOG_MODULE_NAME "ECDSA-UECC"
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#define PW_LOG_LEVEL PW_LOG_LEVEL_WARN
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#include <cstring>
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#include "pw_crypto/ecdsa.h"
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#include "pw_log/log.h"
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#include "uECC.h"
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namespace pw::crypto::ecdsa {
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constexpr size_t kP256CurveOrderBytes = 32;
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constexpr size_t kP256PublicKeySize = 2 * kP256CurveOrderBytes + 1;
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constexpr size_t kP256SignatureSize = kP256CurveOrderBytes * 2;
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Status VerifyP256Signature(ConstByteSpan public_key,
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ConstByteSpan digest,
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ConstByteSpan signature) {
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// Signature expected in raw format (r||s)
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if (signature.size() != kP256SignatureSize) {
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PW_LOG_DEBUG("Bad signature format");
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return Status::InvalidArgument();
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}
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// Supports SEC 1 uncompressed form (04||X||Y) only.
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if (public_key.size() != kP256PublicKeySize ||
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std::to_integer<uint8_t>(public_key.data()[0]) != 0x04) {
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PW_LOG_DEBUG("Bad public key format");
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return Status::InvalidArgument();
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}
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#if defined(uECC_VLI_NATIVE_LITTLE_ENDIAN) && uECC_VLI_NATIVE_LITTLE_ENDIAN
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// uECC_VLI_NATIVE_LITTLE_ENDIAN is defined with a non-zero value when
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// pw_crypto_ECDSA_BACKEND is set to "//pw_crypto:ecdsa_uecc_little_endian".
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//
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// Since pw_crypto APIs are big endian only (standard practice), here we
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// need to convert input parameters to little endian.
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//
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// Additionally uECC requires these little endian buffers to be word aligned
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// in case unaligned accesses are not supported by the hardware. We choose
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// the maximum 8-byte alignment to avoid referrencing internal uECC headers.
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alignas(8) uint8_t signature_bytes[kP256SignatureSize];
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memcpy(signature_bytes, signature.data(), sizeof(signature_bytes));
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std::reverse(signature_bytes, signature_bytes + kP256CurveOrderBytes); // r
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std::reverse(signature_bytes + kP256CurveOrderBytes,
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signature_bytes + sizeof(signature_bytes)); // s
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alignas(8) uint8_t public_key_bytes[kP256PublicKeySize - 1];
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memcpy(public_key_bytes, public_key.data() + 1, sizeof(public_key_bytes));
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std::reverse(public_key_bytes, public_key_bytes + kP256CurveOrderBytes); // X
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std::reverse(public_key_bytes + kP256CurveOrderBytes,
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public_key_bytes + sizeof(public_key_bytes)); // Y
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alignas(8) uint8_t digest_bytes[kP256CurveOrderBytes];
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memcpy(digest_bytes, digest.data(), sizeof(digest_bytes));
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std::reverse(digest_bytes, digest_bytes + sizeof(digest_bytes));
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#else
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const uint8_t* public_key_bytes =
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reinterpret_cast<const uint8_t*>(public_key.data()) + 1;
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const uint8_t* digest_bytes = reinterpret_cast<const uint8_t*>(digest.data());
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const uint8_t* signature_bytes =
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reinterpret_cast<const uint8_t*>(signature.data());
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#endif // uECC_VLI_NATIVE_LITTLE_ENDIAN
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uECC_Curve curve = uECC_secp256r1();
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// Make sure the public key is on the curve.
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if (!uECC_valid_public_key(public_key_bytes, curve)) {
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PW_LOG_DEBUG("Bad public key curve");
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return Status::InvalidArgument();
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}
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// Digests must be at least 32 bytes. Digests longer than 32
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// bytes are truncated to 32 bytes.
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if (digest.size() < kP256CurveOrderBytes) {
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PW_LOG_DEBUG("Digest is too short");
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return Status::InvalidArgument();
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}
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// Verify the signature.
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if (!uECC_verify(public_key_bytes,
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digest_bytes,
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digest.size(),
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signature_bytes,
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curve)) {
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PW_LOG_DEBUG("Signature verification failed");
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return Status::Unauthenticated();
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}
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return OkStatus();
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}
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} // namespace pw::crypto::ecdsa
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