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serialize.go
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serialize.go
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// Copyright 2016 Google Inc. 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"
"fmt"
"sync"
ct "github.com/google/certificate-transparency-go"
"github.com/google/certificate-transparency-go/tls"
"github.com/google/trillian/crypto"
)
// Cache the last signature generated for an STH, to reduce re-signing and slightly
// reduce the chances of being able to fingerprint get-sth users by their STH signature
// value.
var (
lastSTHMu sync.RWMutex
lastSTHBytes []byte
lastSTHSignature ct.DigitallySigned
)
func setLastSTHSignature(sthBytes []byte, sig ct.DigitallySigned) {
lastSTHMu.Lock()
defer lastSTHMu.Unlock()
lastSTHBytes = sthBytes
lastSTHSignature = sig
}
func getLastSTHSignature(sthBytes []byte) (ct.DigitallySigned, bool) {
lastSTHMu.RLock()
defer lastSTHMu.RUnlock()
if !bytes.Equal(sthBytes, lastSTHBytes) {
return ct.DigitallySigned{}, false
}
return lastSTHSignature, true
}
// 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) error {
sthBytes, err := ct.SerializeSTHSignatureInput(*sth)
if err != nil {
return err
}
if sig, ok := getLastSTHSignature(sthBytes); ok {
sth.TreeHeadSignature = sig
return nil
}
signature, err := signer.Sign(sthBytes)
if err != nil {
return err
}
sth.TreeHeadSignature = ct.DigitallySigned{
Algorithm: tls.SignatureAndHashAlgorithm{
Hash: tls.SHA256,
// This relies on the protobuf enum values matching the TLS-defined values.
Signature: tls.SignatureAlgorithm(crypto.SignatureAlgorithm(signer.Public())),
},
Signature: signature.Signature,
}
setLastSTHSignature(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: ct.CTExtensions{},
}
data, err := ct.SerializeSCTSignatureInput(sctInput, ct.LogEntry{Leaf: *leaf})
if err != nil {
return nil, fmt.Errorf("failed to serialize SCT data: %v", err)
}
signature, err := signer.Sign(data)
if err != nil {
return nil, fmt.Errorf("failed to sign SCT data: %v", err)
}
digitallySigned := ct.DigitallySigned{
Algorithm: tls.SignatureAndHashAlgorithm{
Hash: tls.SHA256,
// This relies on the protobuf enum values matching the TLS-defined values.
Signature: tls.SignatureAlgorithm(crypto.SignatureAlgorithm(signer.Public())),
},
Signature: 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: ct.CTExtensions{},
Signature: digitallySigned,
}, nil
}