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serialize.go
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serialize.go
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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 sctfe
import (
"crypto"
"crypto/rand"
"crypto/sha256"
"encoding/binary"
"fmt"
"math"
"github.com/google/certificate-transparency-go/tls"
"github.com/transparency-dev/formats/log"
"github.com/transparency-dev/static-ct/modules/dedup"
"golang.org/x/crypto/cryptobyte"
"golang.org/x/mod/sumdb/note"
ct "github.com/google/certificate-transparency-go"
)
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
}
type RFC6962NoteSignature struct {
timestamp uint64
signature ct.DigitallySigned
}
// buildCp builds a https://c2sp.org/static-ct-api checkpoint.
// TODO(phboneff): add tests
func buildCp(signer crypto.Signer, size uint64, timeMilli uint64, hash []byte) ([]byte, error) {
sth := ct.SignedTreeHead{
Version: ct.V1,
TreeSize: size,
Timestamp: timeMilli,
}
copy(sth.SHA256RootHash[:], hash)
sthBytes, err := ct.SerializeSTHSignatureInput(sth)
if err != nil {
return nil, fmt.Errorf("ct.SerializeSTHSignatureInput(): %v", err)
}
h := sha256.Sum256(sthBytes)
signature, err := signer.Sign(rand.Reader, h[:], crypto.SHA256)
if err != nil {
return nil, err
}
rfc6962Note := RFC6962NoteSignature{
timestamp: sth.Timestamp,
signature: ct.DigitallySigned{
Algorithm: tls.SignatureAndHashAlgorithm{
Hash: tls.SHA256,
Signature: tls.SignatureAlgorithmFromPubKey(signer.Public()),
},
Signature: signature,
},
}
sig, err := tls.Marshal(rfc6962Note)
if err != nil {
return nil, fmt.Errorf("couldn't encode RFC6962NoteSignature: %w", err)
}
return sig, nil
}
// CpSigner implements note.Signer. It can generate https://c2sp.org/static-ct-api checkpoints.
type CpSigner struct {
sthSigner crypto.Signer
origin string
keyHash uint32
timeSource TimeSource
}
// Sign takes an unsigned checkpoint, and signs it with a https://c2sp.org/static-ct-api signature.
// Returns an error if the message doesn't parse as a checkpoint, or if the
// checkpoint origin doesn't match with the Signer's origin.
// TODO(phboneff): add tests
func (cts *CpSigner) Sign(msg []byte) ([]byte, error) {
ckpt := &log.Checkpoint{}
rest, err := ckpt.Unmarshal(msg)
if len(rest) != 0 {
return nil, fmt.Errorf("checkpoint contains trailing data: %s", string(rest))
} else if err != nil {
return nil, fmt.Errorf("ckpt.Unmarshal: %v", err)
} else if ckpt.Origin != cts.origin {
return nil, fmt.Errorf("checkpoint's origin %s doesn't match signer's origin %s", ckpt.Origin, cts.origin)
}
// TODO(phboneff): make sure that it's ok to generate the timestamp here
t := uint64(cts.timeSource.Now().UnixMilli())
sig, err := buildCp(cts.sthSigner, ckpt.Size, t, ckpt.Hash[:])
if err != nil {
return nil, fmt.Errorf("coudn't sign CT checkpoint: %v", err)
}
return sig, nil
}
func (cts *CpSigner) Name() string {
return cts.origin
}
func (cts *CpSigner) KeyHash() uint32 {
return cts.keyHash
}
// NewCpSigner returns a new note signer that can sign https://c2sp.org/static-ct-api checkpoints.
// TODO(phboneff): add tests
func NewCpSigner(signer crypto.Signer, origin string, logID [32]byte, timeSource TimeSource) note.Signer {
h := sha256.New()
h.Write([]byte(origin))
h.Write([]byte{0x0A}) // newline
h.Write([]byte{0x05}) // signature type
h.Write(logID[:])
sum := h.Sum(nil)
ctSigner := &CpSigner{
sthSigner: signer,
origin: origin,
keyHash: binary.BigEndian.Uint32(sum),
timeSource: timeSource,
}
return ctSigner
}
// DedupFromBundle converts a bundle into an array of {leafID, idx}.
//
// The index of a leaf is computed from its position in the log, instead of parsing SCTs.
// Greatly inspired by https://github.com/FiloSottile/sunlight/blob/main/tile.go
func DedupFromBundle(bundle []byte, bundleIdx uint64) ([]dedup.LeafIdx, error) {
kvs := []dedup.LeafIdx{}
s := cryptobyte.String(bundle)
for len(s) > 0 {
var timestamp uint64
var entryType uint16
var extensions, fingerprints cryptobyte.String
if !s.ReadUint64(×tamp) || !s.ReadUint16(&entryType) || timestamp > math.MaxInt64 {
return nil, fmt.Errorf("invalid data tile")
}
crt := []byte{}
switch entryType {
case 0: // x509_entry
if !s.ReadUint24LengthPrefixed((*cryptobyte.String)(&crt)) ||
!s.ReadUint16LengthPrefixed(&extensions) ||
!s.ReadUint16LengthPrefixed(&fingerprints) {
return nil, fmt.Errorf("invalid data tile x509_entry")
}
case 1: // precert_entry
IssuerKeyHash := [32]byte{}
var defangedCrt, extensions cryptobyte.String
if !s.CopyBytes(IssuerKeyHash[:]) ||
!s.ReadUint24LengthPrefixed(&defangedCrt) ||
!s.ReadUint16LengthPrefixed(&extensions) ||
!s.ReadUint24LengthPrefixed((*cryptobyte.String)(&crt)) ||
!s.ReadUint16LengthPrefixed(&fingerprints) {
return nil, fmt.Errorf("invalid data tile precert_entry")
}
default:
return nil, fmt.Errorf("invalid data tile: unknown type %d", entryType)
}
k := sha256.Sum256(crt)
kvs = append(kvs, dedup.LeafIdx{LeafID: k[:], Idx: bundleIdx*256 + uint64(len(kvs))})
}
return kvs, nil
}