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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package subtle
import (
"crypto/ecdsa"
"errors"
"fmt"
"hash"
"math/big"
internalecdsa "github.com/tink-crypto/tink-go/v2/internal/signature/ecdsa"
"github.com/tink-crypto/tink-go/v2/subtle"
)
// ECDSAVerifier is an implementation of Verifier for ECDSA.
// At the moment, the implementation only accepts signatures with strict DER encoding.
type ECDSAVerifier struct {
publicKey *ecdsa.PublicKey
hashFunc func() hash.Hash
encoding string
}
// NewECDSAVerifier creates a new instance of ECDSAVerifier.
func NewECDSAVerifier(hashAlg string, curve string, encoding string, x []byte, y []byte) (*ECDSAVerifier, error) {
publicKey := &ecdsa.PublicKey{
Curve: subtle.GetCurve(curve),
X: new(big.Int).SetBytes(x),
Y: new(big.Int).SetBytes(y),
}
return NewECDSAVerifierFromPublicKey(hashAlg, encoding, publicKey)
}
// NewECDSAVerifierFromPublicKey creates a new instance of ECDSAVerifier.
func NewECDSAVerifierFromPublicKey(hashAlg string, encoding string, publicKey *ecdsa.PublicKey) (*ECDSAVerifier, error) {
if publicKey.Curve == nil {
return nil, errors.New("ecdsa_verifier: invalid curve")
}
if !publicKey.Curve.IsOnCurve(publicKey.X, publicKey.Y) {
return nil, fmt.Errorf("ecdsa_verifier: invalid public key")
}
curve := subtle.ConvertCurveName(publicKey.Curve.Params().Name)
if err := ValidateECDSAParams(hashAlg, curve, encoding); err != nil {
return nil, fmt.Errorf("ecdsa_verifier: %s", err)
}
hashFunc := subtle.GetHashFunc(hashAlg)
return &ECDSAVerifier{
publicKey: publicKey,
hashFunc: hashFunc,
encoding: encoding,
}, nil
}
// Verify verifies whether the given signature is valid for the given data.
// It returns an error if the signature is not valid; nil otherwise.
func (e *ECDSAVerifier) Verify(signatureBytes, data []byte) error {
hashed, err := subtle.ComputeHash(e.hashFunc, data)
if err != nil {
return err
}
var asn1Signature []byte
switch e.encoding {
case "DER":
asn1Signature = signatureBytes
case "IEEE_P1363":
decodedSig, err := internalecdsa.IEEEP1363Decode(signatureBytes)
if err != nil {
return err
}
asn1Signature, err = internalecdsa.ASN1Encode(decodedSig)
if err != nil {
return err
}
default:
return fmt.Errorf("ecdsa: unsupported encoding: %s", e.encoding)
}
if ok := ecdsa.VerifyASN1(e.publicKey, hashed, asn1Signature); !ok {
return fmt.Errorf("ecdsa_verifier: invalid signature")
}
return nil
}
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