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// Copyright 2024 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 ecdsa
import (
"bytes"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/sha256"
"crypto/sha512"
"fmt"
"hash"
"math/big"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
internalecdsa "github.com/tink-crypto/tink-go/v2/internal/signature/ecdsa"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/tink"
)
// verifier implements the [tink.Verifier] interface for ECDSA (RFC6979).
//
// It accepts signature in both ASN.1 and IEEE_P1363 encoding.
type verifier struct {
key *ecdsa.PublicKey
prefix []byte
parameters *Parameters
hashFunc func() hash.Hash
}
var _ tink.Verifier = (*verifier)(nil)
func curveFromTinkECDSACurveType(curveType CurveType) (elliptic.Curve, error) {
switch curveType {
case NistP256:
return elliptic.P256(), nil
case NistP384:
return elliptic.P384(), nil
case NistP521:
return elliptic.P521(), nil
default:
// Should never happen.
return nil, fmt.Errorf("unsupported curve: %v", curveType)
}
}
func hashFunctionFromEnum(hash HashType) (func() hash.Hash, error) {
switch hash {
case SHA256:
return sha256.New, nil
case SHA384:
return sha512.New384, nil
case SHA512:
return sha512.New, nil
default:
return nil, fmt.Errorf("invalid hash type: %s", hash)
}
}
// NewVerifier creates a new ECDSA Verifier.
//
// This is an internal API.
func NewVerifier(publicKey *PublicKey, _ internalapi.Token) (tink.Verifier, error) {
hashFunc, err := hashFunctionFromEnum(publicKey.parameters.HashType())
if err != nil {
return nil, err
}
curve, err := curveFromTinkECDSACurveType(publicKey.parameters.CurveType())
if err != nil {
return nil, err
}
publicPoint := publicKey.PublicPoint()
xy := publicPoint[1:]
ecdsaPublicKey := &ecdsa.PublicKey{
Curve: curve,
X: new(big.Int).SetBytes(xy[:len(xy)/2]),
Y: new(big.Int).SetBytes(xy[len(xy)/2:]),
}
return &verifier{
key: ecdsaPublicKey,
prefix: publicKey.OutputPrefix(),
parameters: publicKey.parameters,
hashFunc: hashFunc,
}, nil
}
// Verify verifies whether the given signature is valid for the given data.
//
// The signature is expected to be of the form: prefix || signature, where
// prefix is the key's output prefix and can be empty, and signature is the
// signature in the encoding specified by the key's parameters.
func (e *verifier) Verify(signatureBytes, data []byte) error {
if !bytes.HasPrefix(signatureBytes, e.prefix) {
return fmt.Errorf("ecdsa_verifier: invalid signature prefix")
}
rawSignature := signatureBytes[len(e.prefix):]
h := e.hashFunc()
h.Write(data)
if e.parameters.Variant() == VariantLegacy {
h.Write([]byte{0})
}
hashed := h.Sum(nil)
var asn1Signature []byte
switch encoding := e.parameters.SignatureEncoding(); encoding {
case DER:
asn1Signature = rawSignature
case IEEEP1363:
decodedSig, err := internalecdsa.IEEEP1363Decode(rawSignature)
if err != nil {
return err
}
asn1Signature, err = internalecdsa.ASN1Encode(decodedSig)
if err != nil {
return err
}
default:
return fmt.Errorf("ecdsa_verifier: unsupported encoding: %s", encoding)
}
if ok := ecdsa.VerifyASN1(e.key, hashed, asn1Signature); !ok {
return fmt.Errorf("ecdsa_verifier: invalid signature")
}
return nil
}
func verifierConstructor(key key.Key) (any, error) {
that, ok := key.(*PublicKey)
if !ok {
return nil, fmt.Errorf("key is not a *ecdsa.PublicKey")
}
return NewVerifier(that, internalapi.Token{})
}
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