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// Copyright 2018 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.
// sctscan is a utility to scan a CT log and check embedded SCTs (Signed Certificate
// Timestamps) in certificates in the log.
package main
import (
"context"
"crypto/sha256"
"flag"
"net/http"
"time"
ct "github.com/google/certificate-transparency-go"
"github.com/google/certificate-transparency-go/client"
"github.com/google/certificate-transparency-go/ctutil"
"github.com/google/certificate-transparency-go/jsonclient"
"github.com/google/certificate-transparency-go/loglist3"
"github.com/google/certificate-transparency-go/scanner"
"github.com/google/certificate-transparency-go/x509"
"github.com/google/certificate-transparency-go/x509util"
"k8s.io/klog/v2"
)
var (
logURI = flag.String("log_uri", "https://ct.googleapis.com/pilot", "CT log base URI")
logList = flag.String("log_list", loglist3.AllLogListURL, "Location of master CT log list (URL or filename)")
inclusion = flag.Bool("inclusion", false, "Whether to do inclusion checking")
deadline = flag.Duration("deadline", 30*time.Second, "Timeout deadline for HTTP requests")
batchSize = flag.Int("batch_size", 1000, "Max number of entries to request at per call to get-entries")
numWorkers = flag.Int("num_workers", 2, "Number of concurrent matchers")
parallelFetch = flag.Int("parallel_fetch", 2, "Number of concurrent GetEntries fetches")
startIndex = flag.Int64("start_index", 0, "Log index to start scanning at")
)
func main() {
klog.InitFlags(nil)
flag.Parse()
ctx := context.Background()
klog.CopyStandardLogTo("WARNING")
hc := &http.Client{
Timeout: *deadline,
Transport: &http.Transport{
TLSHandshakeTimeout: 30 * time.Second,
ResponseHeaderTimeout: 30 * time.Second,
MaxIdleConnsPerHost: 10,
DisableKeepAlives: false,
MaxIdleConns: 100,
IdleConnTimeout: 90 * time.Second,
ExpectContinueTimeout: 1 * time.Second,
},
}
logClient, err := client.New(*logURI, hc, jsonclient.Options{UserAgent: "ct-go-sctscan/1.0"})
if err != nil {
klog.Exitf("Failed to create log client: %v", err)
}
llData, err := x509util.ReadFileOrURL(*logList, hc)
if err != nil {
klog.Exitf("Failed to read log list: %v", err)
}
ll, err := loglist3.NewFromJSON(llData)
if err != nil {
klog.Exitf("Failed to parse log list: %v", err)
}
klog.Warning("Performing validations via direct log queries")
logsByHash, err := ctutil.LogInfoByKeyHash(ll, hc)
if err != nil {
klog.Exitf("Failed to build log info map: %v", err)
}
scanOpts := scanner.ScannerOptions{
FetcherOptions: scanner.FetcherOptions{
BatchSize: *batchSize,
ParallelFetch: *parallelFetch,
StartIndex: *startIndex,
},
Matcher: EmbeddedSCTMatcher{},
NumWorkers: *numWorkers,
}
s := scanner.NewScanner(logClient, scanOpts)
if err := s.Scan(ctx,
func(entry *ct.RawLogEntry) {
checkCertWithEmbeddedSCT(ctx, logsByHash, *inclusion, entry)
},
func(entry *ct.RawLogEntry) {
klog.Errorf("Internal error: found pre-cert! %+v", entry)
}); err != nil {
klog.Exitf("Scan failed: %v", err)
}
}
// EmbeddedSCTMatcher implements the scanner.Matcher interface by matching just certificates
// that have embedded SCTs.
type EmbeddedSCTMatcher struct{}
// CertificateMatches identifies certificates in the log that have the SCTList extension.
func (e EmbeddedSCTMatcher) CertificateMatches(cert *x509.Certificate) bool {
return len(cert.SCTList.SCTList) > 0
}
// PrecertificateMatches identifies those precertificates in the log that are of
// interest: none.
func (e EmbeddedSCTMatcher) PrecertificateMatches(*ct.Precertificate) bool {
return false
}
// checkCertWithEmbeddedSCT is the callback that the scanner invokes for each cert found by the matcher.
// Here, we only expect to get certificates that have embedded SCT lists.
func checkCertWithEmbeddedSCT(ctx context.Context, logsByKey map[[sha256.Size]byte]*ctutil.LogInfo, checkInclusion bool, rawEntry *ct.RawLogEntry) {
entry, err := rawEntry.ToLogEntry()
if x509.IsFatal(err) {
klog.Errorf("[%d] Internal error: failed to parse cert in entry: %v", rawEntry.Index, err)
return
}
leaf := entry.X509Cert
if leaf == nil {
klog.Errorf("[%d] Internal error: no cert in entry", entry.Index)
return
}
if len(entry.Chain) == 0 {
klog.Errorf("[%d] No issuance chain found", entry.Index)
return
}
issuer, err := x509.ParseCertificate(entry.Chain[0].Data)
if err != nil {
klog.Errorf("[%d] Failed to parse issuer: %v", entry.Index, err)
}
// Build a Merkle leaf that corresponds to the embedded SCTs. We can use the same
// leaf for all of the SCTs, as long as the timestamp field gets updated.
merkleLeaf, err := ct.MerkleTreeLeafForEmbeddedSCT([]*x509.Certificate{leaf, issuer}, 0)
if err != nil {
klog.Errorf("[%d] Failed to build Merkle leaf: %v", entry.Index, err)
return
}
for i, sctData := range leaf.SCTList.SCTList {
sct, err := x509util.ExtractSCT(&sctData)
if err != nil {
klog.Errorf("[%d] Failed to deserialize SCT[%d] data: %v", entry.Index, i, err)
continue
}
logInfo := logsByKey[sct.LogID.KeyID]
if logInfo == nil {
klog.Infof("[%d] SCT[%d] for unknown logID: %x, cannot validate SCT", entry.Index, i, sct.LogID)
continue
}
if err := logInfo.VerifySCTSignature(*sct, *merkleLeaf); err != nil {
klog.Errorf("[%d] Failed to verify SCT[%d] signature from log %q: %v", entry.Index, i, logInfo.Description, err)
} else {
klog.V(1).Infof("[%d] Verified SCT[%d] against log %q", entry.Index, i, logInfo.Description)
}
if !checkInclusion {
continue
}
if index, err := logInfo.VerifyInclusionLatest(ctx, *merkleLeaf, sct.Timestamp); err != nil {
// Inclusion failure may be OK if the SCT is within the Log's MMD
sth := logInfo.LastSTH()
if sth != nil {
delta := time.Duration(sth.Timestamp-sct.Timestamp) * time.Millisecond
if delta < logInfo.MMD {
klog.Warningf("[%d] Failed to verify SCT[%d] inclusion proof (%v), but Log's MMD has not passed %d -> %d < %v", entry.Index, i, err, sct.Timestamp, sth.Timestamp, logInfo.MMD)
continue
}
}
klog.Errorf("[%d] Failed to verify SCT[%d] inclusion proof: %v", entry.Index, i, err)
} else {
klog.V(1).Infof("[%d] Checked SCT[%d] inclusion against log %q, at index %d", entry.Index, i, logInfo.Description, index)
}
}
}
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