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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 rsassapkcs1
import (
"bytes"
"crypto/rsa"
"fmt"
"math/big"
"slices"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/internal/signature"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/tink"
)
// verifier is an implementation of [tink.Verifier] for RSA-SSA-PKCS1.
type verifier struct {
rawVerifier tink.Verifier
variant Variant
prefix []byte
}
var _ tink.Verifier = (*verifier)(nil)
// NewVerifier returns a new [tink.Verifier] that implements the primitive
// described by pubKey.
func NewVerifier(pubKey *PublicKey, _ internalapi.Token) (tink.Verifier, error) {
v, err := signature.New_RSA_SSA_PKCS1_Verifier(pubKey.parameters.HashType().String(), &rsa.PublicKey{
N: new(big.Int).SetBytes(pubKey.Modulus()),
E: pubKey.parameters.PublicExponent(),
})
if err != nil {
return nil, err
}
return &verifier{
rawVerifier: v,
prefix: pubKey.OutputPrefix(),
variant: pubKey.parameters.Variant(),
}, nil
}
// Verify verifies the signature on the given data.
func (v *verifier) Verify(sig, data []byte) error {
if !bytes.HasPrefix(sig, v.prefix) {
return fmt.Errorf("signature does not start with prefix")
}
toVerify := data
if v.variant == VariantLegacy {
toVerify = slices.Concat(data, []byte{0})
}
signatureWithoutPrefix := sig[len(v.prefix):]
return v.rawVerifier.Verify(signatureWithoutPrefix, toVerify)
}
func verifierConstructor(key key.Key) (any, error) {
that, ok := key.(*PublicKey)
if !ok {
return nil, fmt.Errorf("key is not a *rsassapkcs1.PublicKey")
}
return NewVerifier(that, internalapi.Token{})
}
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