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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 ed25519
import (
"bytes"
"crypto/ed25519"
"fmt"
"slices"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/tink"
)
// verifier is an implementation of [tink.Verifier] for ED25519.
type verifier struct {
publicKey ed25519.PublicKey
prefix []byte
variant Variant
}
var _ tink.Verifier = (*verifier)(nil)
// NewVerifier creates a new [tink.Verifier] for ED25519.
//
// This is an internal API.
func NewVerifier(publicKey *PublicKey, _ internalapi.Token) (tink.Verifier, error) {
return &verifier{
publicKey: publicKey.KeyBytes(),
variant: publicKey.params.Variant(),
prefix: publicKey.OutputPrefix(),
}, nil
}
// Verify verifies whether the given signature is valid for the given data.
//
// It returns an error if the prefix is not valid or the signature is not
// valid.
func (e *verifier) Verify(signature, data []byte) error {
if !bytes.HasPrefix(signature, e.prefix) {
return fmt.Errorf("ed25519: the signature doesn't have the expected prefix")
}
signatureNoPrefix := signature[len(e.prefix):]
if len(signatureNoPrefix) != ed25519.SignatureSize {
return fmt.Errorf("ed25519: the length of the signature is not %d", ed25519.SignatureSize)
}
signedMessage := data
if e.variant == VariantLegacy {
signedMessage = slices.Concat(data, []byte{0})
}
if !ed25519.Verify(e.publicKey, signedMessage, signatureNoPrefix) {
return fmt.Errorf("ed25519: 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 *ed25519.PublicKey")
}
return NewVerifier(that, internalapi.Token{})
}
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