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// Copyright 2022 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 signature
import (
"crypto"
"crypto/rand"
"crypto/rsa"
"fmt"
"hash"
"github.com/tink-crypto/tink-go/v2/subtle"
"github.com/tink-crypto/tink-go/v2/tink"
)
// RSA_SSA_PSS_Signer is an implementation of Signer for RSA-SSA-PSS.
type RSA_SSA_PSS_Signer struct {
privateKey *rsa.PrivateKey
hashFunc func() hash.Hash
hashID crypto.Hash
saltLength int
}
var _ tink.Signer = (*RSA_SSA_PSS_Signer)(nil)
// New_RSA_SSA_PSS_Signer creates a new instance of RSA_SSA_PSS_Signer.
func New_RSA_SSA_PSS_Signer(hashAlg string, saltLength int, privKey *rsa.PrivateKey) (*RSA_SSA_PSS_Signer, error) {
if err := validRSAPublicKey(&privKey.PublicKey); err != nil {
return nil, err
}
hashFunc, hashID, err := rsaHashFunc(hashAlg)
if err != nil {
return nil, err
}
if saltLength < 0 {
return nil, fmt.Errorf("invalid salt length")
}
return &RSA_SSA_PSS_Signer{
privateKey: privKey,
hashFunc: hashFunc,
hashID: hashID,
saltLength: saltLength,
}, nil
}
// Sign computes a signature for the given data.
func (s *RSA_SSA_PSS_Signer) Sign(data []byte) ([]byte, error) {
digest, err := subtle.ComputeHash(s.hashFunc, data)
if err != nil {
return nil, err
}
return rsa.SignPSS(rand.Reader, s.privateKey, s.hashID, digest, &rsa.PSSOptions{SaltLength: s.saltLength})
}
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