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// Copyright 2016 Google LLC. All Rights Reserved.
//
// 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 ctfe
import (
"bytes"
"crypto"
"crypto/rand"
"crypto/sha256"
"fmt"
"sync"
"github.com/google/certificate-transparency-go/tls"
ct "github.com/google/certificate-transparency-go"
)
// SignatureCache is a one-entry cache that stores the last generated signature
// for a given bytes input. It helps to reduce the number of signing
// operations, and the number of distinct signatures produced for the same
// input (some signing methods are non-deterministic).
type SignatureCache struct {
mu sync.RWMutex
input []byte
sig ct.DigitallySigned
}
// GetSignature returns the latest signature for the given bytes input. If the
// input is not in the cache, it returns (_, false).
func (sc *SignatureCache) GetSignature(input []byte) (ct.DigitallySigned, bool) {
sc.mu.RLock()
defer sc.mu.RUnlock()
if !bytes.Equal(input, sc.input) {
return ct.DigitallySigned{}, false
}
return sc.sig, true
}
// SetSignature associates the signature with the given bytes input.
func (sc *SignatureCache) SetSignature(input []byte, sig ct.DigitallySigned) {
sc.mu.Lock()
defer sc.mu.Unlock()
sc.input, sc.sig = input, sig
}
// signV1TreeHead signs a tree head for CT. The input STH should have been
// built from a backend response and already checked for validity.
func signV1TreeHead(signer crypto.Signer, sth *ct.SignedTreeHead, cache *SignatureCache) error {
sthBytes, err := ct.SerializeSTHSignatureInput(*sth)
if err != nil {
return err
}
if sig, ok := cache.GetSignature(sthBytes); ok {
sth.TreeHeadSignature = sig
return nil
}
h := sha256.New()
h.Write(sthBytes)
signature, err := signer.Sign(rand.Reader, h.Sum(nil), crypto.SHA256)
if err != nil {
return err
}
sth.TreeHeadSignature = ct.DigitallySigned{
Algorithm: tls.SignatureAndHashAlgorithm{
Hash: tls.SHA256,
Signature: tls.SignatureAlgorithmFromPubKey(signer.Public()),
},
Signature: signature,
}
cache.SetSignature(sthBytes, sth.TreeHeadSignature)
return nil
}
func buildV1SCT(signer crypto.Signer, leaf *ct.MerkleTreeLeaf) (*ct.SignedCertificateTimestamp, error) {
// Serialize SCT signature input to get the bytes that need to be signed
sctInput := ct.SignedCertificateTimestamp{
SCTVersion: ct.V1,
Timestamp: leaf.TimestampedEntry.Timestamp,
Extensions: leaf.TimestampedEntry.Extensions,
}
data, err := ct.SerializeSCTSignatureInput(sctInput, ct.LogEntry{Leaf: *leaf})
if err != nil {
return nil, fmt.Errorf("failed to serialize SCT data: %v", err)
}
h := sha256.Sum256(data)
signature, err := signer.Sign(rand.Reader, h[:], crypto.SHA256)
if err != nil {
return nil, fmt.Errorf("failed to sign SCT data: %v", err)
}
digitallySigned := ct.DigitallySigned{
Algorithm: tls.SignatureAndHashAlgorithm{
Hash: tls.SHA256,
Signature: tls.SignatureAlgorithmFromPubKey(signer.Public()),
},
Signature: signature,
}
logID, err := GetCTLogID(signer.Public())
if err != nil {
return nil, fmt.Errorf("failed to get logID for signing: %v", err)
}
return &ct.SignedCertificateTimestamp{
SCTVersion: ct.V1,
LogID: ct.LogID{KeyID: logID},
Timestamp: sctInput.Timestamp,
Extensions: sctInput.Extensions,
Signature: digitallySigned,
}, nil
}
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