1// Copyright 2022 Google LLC 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14// 15//////////////////////////////////////////////////////////////////////////////// 16 17package signature 18 19import ( 20 "crypto" 21 "crypto/rand" 22 "crypto/rsa" 23 "fmt" 24 "hash" 25 26 "github.com/google/tink/go/subtle" 27 "github.com/google/tink/go/tink" 28) 29 30// RSA_SSA_PSS_Signer is an implementation of Signer for RSA-SSA-PSS. 31type RSA_SSA_PSS_Signer struct { 32 privateKey *rsa.PrivateKey 33 hashFunc func() hash.Hash 34 hashID crypto.Hash 35 saltLength int 36} 37 38var _ tink.Signer = (*RSA_SSA_PSS_Signer)(nil) 39 40// New_RSA_SSA_PSS_Signer creates a new instance of RSA_SSA_PSS_Signer. 41func New_RSA_SSA_PSS_Signer(hashAlg string, saltLength int, privKey *rsa.PrivateKey) (*RSA_SSA_PSS_Signer, error) { 42 if err := validRSAPublicKey(&privKey.PublicKey); err != nil { 43 return nil, err 44 } 45 hashFunc, hashID, err := rsaHashFunc(hashAlg) 46 if err != nil { 47 return nil, err 48 } 49 if saltLength < 0 { 50 return nil, fmt.Errorf("invalid salt length") 51 } 52 return &RSA_SSA_PSS_Signer{ 53 privateKey: privKey, 54 hashFunc: hashFunc, 55 hashID: hashID, 56 saltLength: saltLength, 57 }, nil 58} 59 60// Sign computes a signature for the given data. 61func (s *RSA_SSA_PSS_Signer) Sign(data []byte) ([]byte, error) { 62 digest, err := subtle.ComputeHash(s.hashFunc, data) 63 if err != nil { 64 return nil, err 65 } 66 return rsa.SignPSS(rand.Reader, s.privateKey, s.hashID, digest, &rsa.PSSOptions{SaltLength: s.saltLength}) 67 68} 69