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matcher.go
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matcher.go
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// Copyright 2014 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 scanner
import (
"context"
"log"
"math/big"
"regexp"
"time"
ct "github.com/google/certificate-transparency-go"
"github.com/google/certificate-transparency-go/asn1"
"github.com/google/certificate-transparency-go/client"
"github.com/google/certificate-transparency-go/x509"
)
// Matcher describes how to match certificates and precertificates, based solely on the parsed [pre-]certificate;
// clients should implement this interface to perform their own match criteria.
type Matcher interface {
// CertificateMatches is called by the scanner for each X509 Certificate found in the log.
// The implementation should return true if the passed Certificate is interesting, and false otherwise.
CertificateMatches(*x509.Certificate) bool
// PrecertificateMatches is called by the scanner for each CT Precertificate found in the log.
// The implementation should return true if the passed Precertificate is interesting, and false otherwise.
PrecertificateMatches(*ct.Precertificate) bool
}
// MatchAll is a Matcher which will match every possible Certificate and Precertificate.
type MatchAll struct{}
// CertificateMatches returns true if the given cert should match; in this case, always.
func (m MatchAll) CertificateMatches(_ *x509.Certificate) bool {
return true
}
// PrecertificateMatches returns true if the given precert should match, in this case, always.
func (m MatchAll) PrecertificateMatches(_ *ct.Precertificate) bool {
return true
}
// MatchNone is a Matcher which will never match any Certificate or Precertificate.
type MatchNone struct{}
// CertificateMatches returns true if the given cert should match; in this case, never.
func (m MatchNone) CertificateMatches(_ *x509.Certificate) bool {
return false
}
// PrecertificateMatches returns true if the given cert should match; in this case, never.
func (m MatchNone) PrecertificateMatches(_ *ct.Precertificate) bool {
return false
}
// MatchSerialNumber performs a match for a specific serial number.
type MatchSerialNumber struct {
SerialNumber big.Int
}
// CertificateMatches returns true if the given cert should match; in this
// case, only if the serial number matches.
func (m MatchSerialNumber) CertificateMatches(c *x509.Certificate) bool {
return c.SerialNumber.String() == m.SerialNumber.String()
}
// PrecertificateMatches returns true if the given cert should match; in this
// case, only if the serial number matches.
func (m MatchSerialNumber) PrecertificateMatches(p *ct.Precertificate) bool {
return p.TBSCertificate.SerialNumber.String() == m.SerialNumber.String()
}
// MatchSubjectRegex is a Matcher which will use CertificateSubjectRegex and PrecertificateSubjectRegex
// to determine whether Certificates and Precertificates are interesting.
// The two regexes are tested against Subject CN (Common Name) as well as all
// Subject Alternative Names
type MatchSubjectRegex struct {
CertificateSubjectRegex *regexp.Regexp
PrecertificateSubjectRegex *regexp.Regexp
}
// CertificateMatches returns true if either CN or any SAN of c matches m.CertificateSubjectRegex.
func (m MatchSubjectRegex) CertificateMatches(c *x509.Certificate) bool {
if m.CertificateSubjectRegex.FindStringIndex(c.Subject.CommonName) != nil {
return true
}
for _, alt := range c.DNSNames {
if m.CertificateSubjectRegex.FindStringIndex(alt) != nil {
return true
}
}
return false
}
// PrecertificateMatches returns true if either CN or any SAN of p matches m.PrecertificateSubjectRegex.
func (m MatchSubjectRegex) PrecertificateMatches(p *ct.Precertificate) bool {
if m.PrecertificateSubjectRegex.FindStringIndex(p.TBSCertificate.Subject.CommonName) != nil {
return true
}
for _, alt := range p.TBSCertificate.DNSNames {
if m.PrecertificateSubjectRegex.FindStringIndex(alt) != nil {
return true
}
}
return false
}
// MatchIssuerRegex matches on issuer CN (common name) by regex
type MatchIssuerRegex struct {
CertificateIssuerRegex *regexp.Regexp
PrecertificateIssuerRegex *regexp.Regexp
}
// CertificateMatches returns true if the given cert's CN matches.
func (m MatchIssuerRegex) CertificateMatches(c *x509.Certificate) bool {
return m.CertificateIssuerRegex.FindStringIndex(c.Issuer.CommonName) != nil
}
// PrecertificateMatches returns true if the given precert's CN matches.
func (m MatchIssuerRegex) PrecertificateMatches(p *ct.Precertificate) bool {
return m.PrecertificateIssuerRegex.FindStringIndex(p.TBSCertificate.Issuer.CommonName) != nil
}
// MatchSCTTimestamp is a matcher which matches leaf entries with the specified Timestamp.
type MatchSCTTimestamp struct {
Timestamp uint64
}
// Matches returns true if the timestamp embedded in the leaf matches the one
// specified by this matcher.
func (m MatchSCTTimestamp) Matches(leaf *ct.LeafEntry) bool {
entry, _ := ct.LogEntryFromLeaf(1, leaf)
if entry == nil {
// Can't validate if we can't parse
return false
}
return entry.Leaf.TimestampedEntry.Timestamp == m.Timestamp
}
// LeafMatcher describes how to match log entries, based on the Log LeafEntry
// (which includes the unparsed [pre-]certificate; clients should implement this
// interface to perform their own match criteria.
type LeafMatcher interface {
Matches(*ct.LeafEntry) bool
}
// CertParseFailMatcher is a LeafMatcher which will match any Certificate or Precertificate that
// triggered an error on parsing.
type CertParseFailMatcher struct {
MatchNonFatalErrs bool
}
// Matches returns true for parse errors.
func (m CertParseFailMatcher) Matches(leaf *ct.LeafEntry) bool {
_, err := ct.LogEntryFromLeaf(1, leaf)
if err != nil {
if x509.IsFatal(err) {
return true
}
return m.MatchNonFatalErrs
}
return false
}
// CertVerifyFailMatcher is a LeafMatcher which will match any Certificate or Precertificate that fails
// validation. The PopulateRoots() method should be called before use.
type CertVerifyFailMatcher struct {
roots *x509.CertPool
}
// PopulateRoots adds the accepted roots for the log to the pool for validation.
func (m *CertVerifyFailMatcher) PopulateRoots(ctx context.Context, logClient *client.LogClient) {
if m.roots != nil {
return
}
m.roots = x509.NewCertPool()
roots, err := logClient.GetAcceptedRoots(ctx)
if err != nil {
log.Fatal(err)
}
for _, root := range roots {
cert, _ := x509.ParseCertificate(root.Data)
if cert != nil {
m.roots.AddCert(cert)
} else {
log.Fatal(err)
}
}
}
// Matches returns true for validation errors.
func (m CertVerifyFailMatcher) Matches(leaf *ct.LeafEntry) bool {
entry, _ := ct.LogEntryFromLeaf(1, leaf)
if entry == nil {
// Can't validate if we can't parse
return false
}
// Validate the [pre-]certificate as of just before its expiry.
var notBefore time.Time
if entry.X509Cert != nil {
notBefore = entry.X509Cert.NotAfter
} else {
notBefore = entry.Precert.TBSCertificate.NotAfter
}
when := notBefore.Add(-1 * time.Second)
opts := x509.VerifyOptions{
KeyUsages: []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
Roots: m.roots,
Intermediates: x509.NewCertPool(),
CurrentTime: when,
}
chain := make([]*x509.Certificate, len(entry.Chain))
for ii, cert := range entry.Chain {
intermediate, err := x509.ParseCertificate(cert.Data)
if intermediate == nil {
log.Printf("Intermediate %d fails to parse: %v", ii, err)
return true
}
chain[ii] = intermediate
opts.Intermediates.AddCert(intermediate)
}
if entry.X509Cert != nil {
if _, err := entry.X509Cert.Verify(opts); err != nil {
log.Printf("Cert fails to validate as of %v: %v", opts.CurrentTime, err)
return true
}
return false
}
if entry.Precert != nil {
precert, err := x509.ParseCertificate(entry.Precert.Submitted.Data)
if err != nil {
log.Printf("Precert fails to parse as of %v: %v", opts.CurrentTime, err)
return true
}
// Ignore unhandled poison extension.
dropUnhandledExtension(precert, x509.OIDExtensionCTPoison)
for i := 1; i < len(chain); i++ {
// PolicyConstraints is legal (and critical) but unparsed.
dropUnhandledExtension(chain[i], x509.OIDExtensionPolicyConstraints)
}
// Drop CT EKU from preissuer if present.
if len(chain) > 0 {
for i, eku := range chain[0].ExtKeyUsage {
if eku == x509.ExtKeyUsageCertificateTransparency {
chain[0].ExtKeyUsage = append(chain[0].ExtKeyUsage[:i], chain[0].ExtKeyUsage[i+1:]...)
break
}
}
}
if _, err := precert.Verify(opts); err != nil {
log.Printf("Precert fails to validate as of %v: %v", opts.CurrentTime, err)
return true
}
return false
}
log.Printf("Neither cert nor precert present!")
return true
}
func dropUnhandledExtension(cert *x509.Certificate, oid asn1.ObjectIdentifier) {
for j, extOID := range cert.UnhandledCriticalExtensions {
if extOID.Equal(oid) {
cert.UnhandledCriticalExtensions = append(cert.UnhandledCriticalExtensions[:j], cert.UnhandledCriticalExtensions[j+1:]...)
return
}
}
}