1 // Copyright 2011 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
21 // ignoreCN disables interpreting Common Name as a hostname. See issue 24151.
22 var ignoreCN = strings.Contains(os.Getenv("GODEBUG"), "x509ignoreCN=1")
24 type InvalidReason int
27 // NotAuthorizedToSign results when a certificate is signed by another
28 // which isn't marked as a CA certificate.
29 NotAuthorizedToSign InvalidReason = iota
30 // Expired results when a certificate has expired, based on the time
31 // given in the VerifyOptions.
33 // CANotAuthorizedForThisName results when an intermediate or root
34 // certificate has a name constraint which doesn't permit a DNS or
35 // other name (including IP address) in the leaf certificate.
36 CANotAuthorizedForThisName
37 // TooManyIntermediates results when a path length constraint is
40 // IncompatibleUsage results when the certificate's key usage indicates
41 // that it may only be used for a different purpose.
43 // NameMismatch results when the subject name of a parent certificate
44 // does not match the issuer name in the child.
46 // NameConstraintsWithoutSANs results when a leaf certificate doesn't
47 // contain a Subject Alternative Name extension, but a CA certificate
48 // contains name constraints, and the Common Name can be interpreted as
51 // You can avoid this error by setting the experimental GODEBUG environment
52 // variable to "x509ignoreCN=1", disabling Common Name matching entirely.
53 // This behavior might become the default in the future.
54 NameConstraintsWithoutSANs
55 // UnconstrainedName results when a CA certificate contains permitted
56 // name constraints, but leaf certificate contains a name of an
57 // unsupported or unconstrained type.
59 // TooManyConstraints results when the number of comparison operations
60 // needed to check a certificate exceeds the limit set by
61 // VerifyOptions.MaxConstraintComparisions. This limit exists to
62 // prevent pathological certificates can consuming excessive amounts of
63 // CPU time to verify.
65 // CANotAuthorizedForExtKeyUsage results when an intermediate or root
66 // certificate does not permit a requested extended key usage.
67 CANotAuthorizedForExtKeyUsage
70 // CertificateInvalidError results when an odd error occurs. Users of this
71 // library probably want to handle all these errors uniformly.
72 type CertificateInvalidError struct {
78 func (e CertificateInvalidError) Error() string {
80 case NotAuthorizedToSign:
81 return "x509: certificate is not authorized to sign other certificates"
83 return "x509: certificate has expired or is not yet valid: " + e.Detail
84 case CANotAuthorizedForThisName:
85 return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail
86 case CANotAuthorizedForExtKeyUsage:
87 return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
88 case TooManyIntermediates:
89 return "x509: too many intermediates for path length constraint"
90 case IncompatibleUsage:
91 return "x509: certificate specifies an incompatible key usage"
93 return "x509: issuer name does not match subject from issuing certificate"
94 case NameConstraintsWithoutSANs:
95 return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
96 case UnconstrainedName:
97 return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
99 return "x509: unknown error"
102 // HostnameError results when the set of authorized names doesn't match the
104 type HostnameError struct {
105 Certificate *Certificate
109 func (h HostnameError) Error() string {
112 if !c.hasSANExtension() && !validHostname(c.Subject.CommonName) &&
113 matchHostnames(toLowerCaseASCII(c.Subject.CommonName), toLowerCaseASCII(h.Host)) {
114 // This would have validated, if it weren't for the validHostname check on Common Name.
115 return "x509: Common Name is not a valid hostname: " + c.Subject.CommonName
119 if ip := net.ParseIP(h.Host); ip != nil {
120 // Trying to validate an IP
121 if len(c.IPAddresses) == 0 {
122 return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
124 for _, san := range c.IPAddresses {
128 valid += san.String()
131 if c.commonNameAsHostname() {
132 valid = c.Subject.CommonName
134 valid = strings.Join(c.DNSNames, ", ")
139 return "x509: certificate is not valid for any names, but wanted to match " + h.Host
141 return "x509: certificate is valid for " + valid + ", not " + h.Host
144 // UnknownAuthorityError results when the certificate issuer is unknown
145 type UnknownAuthorityError struct {
147 // hintErr contains an error that may be helpful in determining why an
148 // authority wasn't found.
150 // hintCert contains a possible authority certificate that was rejected
151 // because of the error in hintErr.
152 hintCert *Certificate
155 func (e UnknownAuthorityError) Error() string {
156 s := "x509: certificate signed by unknown authority"
157 if e.hintErr != nil {
158 certName := e.hintCert.Subject.CommonName
159 if len(certName) == 0 {
160 if len(e.hintCert.Subject.Organization) > 0 {
161 certName = e.hintCert.Subject.Organization[0]
163 certName = "serial:" + e.hintCert.SerialNumber.String()
166 s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
171 // SystemRootsError results when we fail to load the system root certificates.
172 type SystemRootsError struct {
176 func (se SystemRootsError) Error() string {
177 msg := "x509: failed to load system roots and no roots provided"
179 return msg + "; " + se.Err.Error()
184 // errNotParsed is returned when a certificate without ASN.1 contents is
185 // verified. Platform-specific verification needs the ASN.1 contents.
186 var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
188 // VerifyOptions contains parameters for Certificate.Verify.
189 type VerifyOptions struct {
190 // IsBoring is a validity check for BoringCrypto.
191 // If not nil, it will be called to check whether a given certificate
192 // can be used for constructing verification chains.
193 IsBoring func(*Certificate) bool
195 // DNSName, if set, is checked against the leaf certificate with
196 // Certificate.VerifyHostname.
199 // Intermediates is an optional pool of certificates that are not trust
200 // anchors, but can be used to form a chain from the leaf certificate to a
202 Intermediates *CertPool
203 // Roots is the set of trusted root certificates the leaf certificate needs
204 // to chain up to. If nil, the system roots or the platform verifier are used.
207 // CurrentTime is used to check the validity of all certificates in the
208 // chain. If zero, the current time is used.
209 CurrentTime time.Time
211 // KeyUsage specifies which Extended Key Usage values are acceptable. A leaf
212 // certificate is accepted if it contains any of the listed values. An empty
213 // list means ExtKeyUsageServerAuth. To accept any key usage, include
216 // Certificate chains are required to nest these extended key usage values.
217 // (This matches the Windows CryptoAPI behavior, but not the spec.)
218 KeyUsages []ExtKeyUsage
220 // MaxConstraintComparisions is the maximum number of comparisons to
221 // perform when checking a given certificate's name constraints. If
222 // zero, a sensible default is used. This limit prevents pathological
223 // certificates from consuming excessive amounts of CPU time when
225 MaxConstraintComparisions int
229 leafCertificate = iota
230 intermediateCertificate
234 // rfc2821Mailbox represents a “mailbox” (which is an email address to most
235 // people) by breaking it into the “local” (i.e. before the '@') and “domain”
237 type rfc2821Mailbox struct {
241 // parseRFC2821Mailbox parses an email address into local and domain parts,
242 // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
243 // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
244 // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
245 func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
247 return mailbox, false
250 localPartBytes := make([]byte, 0, len(in)/2)
253 // Quoted-string = DQUOTE *qcontent DQUOTE
254 // non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
255 // qcontent = qtext / quoted-pair
256 // qtext = non-whitespace-control /
257 // %d33 / %d35-91 / %d93-126
258 // quoted-pair = ("\" text) / obs-qp
259 // text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
261 // (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
262 // Section 4. Since it has been 16 years, we no longer accept that.)
267 return mailbox, false
279 return mailbox, false
283 (1 <= in[0] && in[0] <= 9) ||
284 (14 <= in[0] && in[0] <= 127) {
285 localPartBytes = append(localPartBytes, in[0])
288 return mailbox, false
293 // Space (char 32) is not allowed based on the
294 // BNF, but RFC 3696 gives an example that
295 // assumes that it is. Several “verified”
296 // errata continue to argue about this point.
297 // We choose to accept it.
301 (1 <= c && c <= 8) ||
302 (14 <= c && c <= 31) ||
303 (35 <= c && c <= 91) ||
304 (93 <= c && c <= 126):
306 localPartBytes = append(localPartBytes, c)
309 return mailbox, false
316 // atext from RFC 2822, Section 3.2.4
321 // Examples given in RFC 3696 suggest that
322 // escaped characters can appear outside of a
323 // quoted string. Several “verified” errata
324 // continue to argue the point. We choose to
328 return mailbox, false
332 case ('0' <= c && c <= '9') ||
333 ('a' <= c && c <= 'z') ||
334 ('A' <= c && c <= 'Z') ||
335 c == '!' || c == '#' || c == '$' || c == '%' ||
336 c == '&' || c == '\'' || c == '*' || c == '+' ||
337 c == '-' || c == '/' || c == '=' || c == '?' ||
338 c == '^' || c == '_' || c == '`' || c == '{' ||
339 c == '|' || c == '}' || c == '~' || c == '.':
340 localPartBytes = append(localPartBytes, in[0])
348 if len(localPartBytes) == 0 {
349 return mailbox, false
352 // From RFC 3696, Section 3:
353 // “period (".") may also appear, but may not be used to start
354 // or end the local part, nor may two or more consecutive
356 twoDots := []byte{'.', '.'}
357 if localPartBytes[0] == '.' ||
358 localPartBytes[len(localPartBytes)-1] == '.' ||
359 bytes.Contains(localPartBytes, twoDots) {
360 return mailbox, false
364 if len(in) == 0 || in[0] != '@' {
365 return mailbox, false
369 // The RFC species a format for domains, but that's known to be
370 // violated in practice so we accept that anything after an '@' is the
372 if _, ok := domainToReverseLabels(in); !ok {
373 return mailbox, false
376 mailbox.local = string(localPartBytes)
381 // domainToReverseLabels converts a textual domain name like foo.example.com to
382 // the list of labels in reverse order, e.g. ["com", "example", "foo"].
383 func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
384 for len(domain) > 0 {
385 if i := strings.LastIndexByte(domain, '.'); i == -1 {
386 reverseLabels = append(reverseLabels, domain)
389 reverseLabels = append(reverseLabels, domain[i+1:])
394 if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
395 // An empty label at the end indicates an absolute value.
399 for _, label := range reverseLabels {
401 // Empty labels are otherwise invalid.
405 for _, c := range label {
406 if c < 33 || c > 126 {
407 // Invalid character.
413 return reverseLabels, true
416 func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
417 // If the constraint contains an @, then it specifies an exact mailbox
419 if strings.Contains(constraint, "@") {
420 constraintMailbox, ok := parseRFC2821Mailbox(constraint)
422 return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
424 return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
427 // Otherwise the constraint is like a DNS constraint of the domain part
429 return matchDomainConstraint(mailbox.domain, constraint)
432 func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
433 // From RFC 5280, Section 4.2.1.10:
434 // “a uniformResourceIdentifier that does not include an authority
435 // component with a host name specified as a fully qualified domain
436 // name (e.g., if the URI either does not include an authority
437 // component or includes an authority component in which the host name
438 // is specified as an IP address), then the application MUST reject the
443 return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
446 if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
448 host, _, err = net.SplitHostPort(uri.Host)
454 if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
455 net.ParseIP(host) != nil {
456 return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
459 return matchDomainConstraint(host, constraint)
462 func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
463 if len(ip) != len(constraint.IP) {
468 if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
476 func matchDomainConstraint(domain, constraint string) (bool, error) {
477 // The meaning of zero length constraints is not specified, but this
478 // code follows NSS and accepts them as matching everything.
479 if len(constraint) == 0 {
483 domainLabels, ok := domainToReverseLabels(domain)
485 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
488 // RFC 5280 says that a leading period in a domain name means that at
489 // least one label must be prepended, but only for URI and email
490 // constraints, not DNS constraints. The code also supports that
491 // behaviour for DNS constraints.
493 mustHaveSubdomains := false
494 if constraint[0] == '.' {
495 mustHaveSubdomains = true
496 constraint = constraint[1:]
499 constraintLabels, ok := domainToReverseLabels(constraint)
501 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
504 if len(domainLabels) < len(constraintLabels) ||
505 (mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
509 for i, constraintLabel := range constraintLabels {
510 if !strings.EqualFold(constraintLabel, domainLabels[i]) {
518 // checkNameConstraints checks that c permits a child certificate to claim the
519 // given name, of type nameType. The argument parsedName contains the parsed
520 // form of name, suitable for passing to the match function. The total number
521 // of comparisons is tracked in the given count and should not exceed the given
523 func (c *Certificate) checkNameConstraints(count *int,
524 maxConstraintComparisons int,
527 parsedName interface{},
528 match func(parsedName, constraint interface{}) (match bool, err error),
529 permitted, excluded interface{}) error {
531 excludedValue := reflect.ValueOf(excluded)
533 *count += excludedValue.Len()
534 if *count > maxConstraintComparisons {
535 return CertificateInvalidError{c, TooManyConstraints, ""}
538 for i := 0; i < excludedValue.Len(); i++ {
539 constraint := excludedValue.Index(i).Interface()
540 match, err := match(parsedName, constraint)
542 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
546 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
550 permittedValue := reflect.ValueOf(permitted)
552 *count += permittedValue.Len()
553 if *count > maxConstraintComparisons {
554 return CertificateInvalidError{c, TooManyConstraints, ""}
558 for i := 0; i < permittedValue.Len(); i++ {
559 constraint := permittedValue.Index(i).Interface()
562 if ok, err = match(parsedName, constraint); err != nil {
563 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
572 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
578 // isValid performs validity checks on c given that it is a candidate to append
579 // to the chain in currentChain.
580 func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
581 if len(c.UnhandledCriticalExtensions) > 0 {
582 return UnhandledCriticalExtension{}
585 if len(currentChain) > 0 {
586 child := currentChain[len(currentChain)-1]
587 if !bytes.Equal(child.RawIssuer, c.RawSubject) {
588 return CertificateInvalidError{c, NameMismatch, ""}
592 now := opts.CurrentTime
596 if now.Before(c.NotBefore) {
597 return CertificateInvalidError{
600 Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
602 } else if now.After(c.NotAfter) {
603 return CertificateInvalidError{
606 Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
610 maxConstraintComparisons := opts.MaxConstraintComparisions
611 if maxConstraintComparisons == 0 {
612 maxConstraintComparisons = 250000
616 var leaf *Certificate
617 if certType == intermediateCertificate || certType == rootCertificate {
618 if len(currentChain) == 0 {
619 return errors.New("x509: internal error: empty chain when appending CA cert")
621 leaf = currentChain[0]
624 checkNameConstraints := (certType == intermediateCertificate || certType == rootCertificate) && c.hasNameConstraints()
625 if checkNameConstraints && leaf.commonNameAsHostname() {
626 // This is the deprecated, legacy case of depending on the commonName as
627 // a hostname. We don't enforce name constraints against the CN, but
628 // VerifyHostname will look for hostnames in there if there are no SANs.
629 // In order to ensure VerifyHostname will not accept an unchecked name,
630 // return an error here.
631 return CertificateInvalidError{c, NameConstraintsWithoutSANs, ""}
632 } else if checkNameConstraints && leaf.hasSANExtension() {
633 err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
637 mailbox, ok := parseRFC2821Mailbox(name)
639 return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
642 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
643 func(parsedName, constraint interface{}) (bool, error) {
644 return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
645 }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
651 if _, ok := domainToReverseLabels(name); !ok {
652 return fmt.Errorf("x509: cannot parse dnsName %q", name)
655 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
656 func(parsedName, constraint interface{}) (bool, error) {
657 return matchDomainConstraint(parsedName.(string), constraint.(string))
658 }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
664 uri, err := url.Parse(name)
666 return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
669 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
670 func(parsedName, constraint interface{}) (bool, error) {
671 return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
672 }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
678 if l := len(ip); l != net.IPv4len && l != net.IPv6len {
679 return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
682 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
683 func(parsedName, constraint interface{}) (bool, error) {
684 return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
685 }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
690 // Unknown SAN types are ignored.
701 // KeyUsage status flags are ignored. From Engineering Security, Peter
702 // Gutmann: A European government CA marked its signing certificates as
703 // being valid for encryption only, but no-one noticed. Another
704 // European CA marked its signature keys as not being valid for
705 // signatures. A different CA marked its own trusted root certificate
706 // as being invalid for certificate signing. Another national CA
707 // distributed a certificate to be used to encrypt data for the
708 // country’s tax authority that was marked as only being usable for
709 // digital signatures but not for encryption. Yet another CA reversed
710 // the order of the bit flags in the keyUsage due to confusion over
711 // encoding endianness, essentially setting a random keyUsage in
712 // certificates that it issued. Another CA created a self-invalidating
713 // certificate by adding a certificate policy statement stipulating
714 // that the certificate had to be used strictly as specified in the
715 // keyUsage, and a keyUsage containing a flag indicating that the RSA
716 // encryption key could only be used for Diffie-Hellman key agreement.
718 if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
719 return CertificateInvalidError{c, NotAuthorizedToSign, ""}
722 if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
723 numIntermediates := len(currentChain) - 1
724 if numIntermediates > c.MaxPathLen {
725 return CertificateInvalidError{c, TooManyIntermediates, ""}
729 if opts.IsBoring != nil && !opts.IsBoring(c) {
730 // IncompatibleUsage is not quite right here,
731 // but it's also the "no chains found" error
732 // and is close enough.
733 return CertificateInvalidError{c, IncompatibleUsage, ""}
739 // Verify attempts to verify c by building one or more chains from c to a
740 // certificate in opts.Roots, using certificates in opts.Intermediates if
741 // needed. If successful, it returns one or more chains where the first
742 // element of the chain is c and the last element is from opts.Roots.
744 // If opts.Roots is nil and system roots are unavailable the returned error
745 // will be of type SystemRootsError.
747 // Name constraints in the intermediates will be applied to all names claimed
748 // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
749 // example.com if an intermediate doesn't permit it, even if example.com is not
750 // the name being validated. Note that DirectoryName constraints are not
753 // Extended Key Usage values are enforced down a chain, so an intermediate or
754 // root that enumerates EKUs prevents a leaf from asserting an EKU not in that
757 // WARNING: this function doesn't do any revocation checking.
758 func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
759 // Platform-specific verification needs the ASN.1 contents so
760 // this makes the behavior consistent across platforms.
762 return nil, errNotParsed
764 if opts.Intermediates != nil {
765 for _, intermediate := range opts.Intermediates.certs {
766 if len(intermediate.Raw) == 0 {
767 return nil, errNotParsed
772 // Use Windows's own verification and chain building.
773 if opts.Roots == nil && runtime.GOOS == "windows" {
774 return c.systemVerify(&opts)
777 if opts.Roots == nil {
778 opts.Roots = systemRootsPool()
779 if opts.Roots == nil {
780 return nil, SystemRootsError{systemRootsErr}
784 err = c.isValid(leafCertificate, nil, &opts)
789 if len(opts.DNSName) > 0 {
790 err = c.VerifyHostname(opts.DNSName)
796 var candidateChains [][]*Certificate
797 if opts.Roots.contains(c) {
798 candidateChains = append(candidateChains, []*Certificate{c})
800 if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
805 keyUsages := opts.KeyUsages
806 if len(keyUsages) == 0 {
807 keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
810 // If any key usage is acceptable then we're done.
811 for _, usage := range keyUsages {
812 if usage == ExtKeyUsageAny {
813 return candidateChains, nil
817 for _, candidate := range candidateChains {
818 if checkChainForKeyUsage(candidate, keyUsages) {
819 chains = append(chains, candidate)
823 if len(chains) == 0 {
824 return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
830 func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
831 n := make([]*Certificate, len(chain)+1)
837 // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
838 // that an invocation of buildChains will (tranistively) make. Most chains are
839 // less than 15 certificates long, so this leaves space for multiple chains and
840 // for failed checks due to different intermediates having the same Subject.
841 const maxChainSignatureChecks = 100
843 func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
846 hintCert *Certificate
849 considerCandidate := func(certType int, candidate *Certificate) {
850 for _, cert := range currentChain {
851 if cert.Equal(candidate) {
856 if sigChecks == nil {
860 if *sigChecks > maxChainSignatureChecks {
861 err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
865 if err := c.CheckSignatureFrom(candidate); err != nil {
873 err = candidate.isValid(certType, currentChain, opts)
879 case rootCertificate:
880 chains = append(chains, appendToFreshChain(currentChain, candidate))
881 case intermediateCertificate:
883 cache = make(map[*Certificate][][]*Certificate)
885 childChains, ok := cache[candidate]
887 childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
888 cache[candidate] = childChains
890 chains = append(chains, childChains...)
894 for _, rootNum := range opts.Roots.findPotentialParents(c) {
895 considerCandidate(rootCertificate, opts.Roots.certs[rootNum])
897 for _, intermediateNum := range opts.Intermediates.findPotentialParents(c) {
898 considerCandidate(intermediateCertificate, opts.Intermediates.certs[intermediateNum])
904 if len(chains) == 0 && err == nil {
905 err = UnknownAuthorityError{c, hintErr, hintCert}
911 // validHostname reports whether host is a valid hostname that can be matched or
912 // matched against according to RFC 6125 2.2, with some leniency to accommodate
914 func validHostname(host string) bool {
915 host = strings.TrimSuffix(host, ".")
921 for i, part := range strings.Split(host, ".") {
926 if i == 0 && part == "*" {
927 // Only allow full left-most wildcards, as those are the only ones
928 // we match, and matching literal '*' characters is probably never
929 // the expected behavior.
932 for j, c := range part {
933 if 'a' <= c && c <= 'z' {
936 if '0' <= c && c <= '9' {
939 if 'A' <= c && c <= 'Z' {
942 if c == '-' && j != 0 {
945 if c == '_' || c == ':' {
946 // Not valid characters in hostnames, but commonly
947 // found in deployments outside the WebPKI.
957 // commonNameAsHostname reports whether the Common Name field should be
958 // considered the hostname that the certificate is valid for. This is a legacy
959 // behavior, disabled if the Subject Alt Name extension is present.
961 // It applies the strict validHostname check to the Common Name field, so that
962 // certificates without SANs can still be validated against CAs with name
963 // constraints if there is no risk the CN would be matched as a hostname.
964 // See NameConstraintsWithoutSANs and issue 24151.
965 func (c *Certificate) commonNameAsHostname() bool {
966 return !ignoreCN && !c.hasSANExtension() && validHostname(c.Subject.CommonName)
969 func matchHostnames(pattern, host string) bool {
970 host = strings.TrimSuffix(host, ".")
971 pattern = strings.TrimSuffix(pattern, ".")
973 if len(pattern) == 0 || len(host) == 0 {
977 patternParts := strings.Split(pattern, ".")
978 hostParts := strings.Split(host, ".")
980 if len(patternParts) != len(hostParts) {
984 for i, patternPart := range patternParts {
985 if i == 0 && patternPart == "*" {
988 if patternPart != hostParts[i] {
996 // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
997 // an explicitly ASCII function to avoid any sharp corners resulting from
998 // performing Unicode operations on DNS labels.
999 func toLowerCaseASCII(in string) string {
1000 // If the string is already lower-case then there's nothing to do.
1001 isAlreadyLowerCase := true
1002 for _, c := range in {
1003 if c == utf8.RuneError {
1004 // If we get a UTF-8 error then there might be
1005 // upper-case ASCII bytes in the invalid sequence.
1006 isAlreadyLowerCase = false
1009 if 'A' <= c && c <= 'Z' {
1010 isAlreadyLowerCase = false
1015 if isAlreadyLowerCase {
1020 for i, c := range out {
1021 if 'A' <= c && c <= 'Z' {
1028 // VerifyHostname returns nil if c is a valid certificate for the named host.
1029 // Otherwise it returns an error describing the mismatch.
1031 // IP addresses can be optionally enclosed in square brackets and are checked
1032 // against the IPAddresses field. Other names are checked case insensitively
1033 // against the DNSNames field, with support for only one wildcard as the whole
1036 // If the Common Name field is a valid hostname, and the certificate doesn't
1037 // have any Subject Alternative Names, the name will also be checked against the
1038 // Common Name. This legacy behavior can be disabled by setting the GODEBUG
1039 // environment variable to "x509ignoreCN=1" and might be removed in the future.
1040 func (c *Certificate) VerifyHostname(h string) error {
1041 // IP addresses may be written in [ ].
1043 if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
1044 candidateIP = h[1 : len(h)-1]
1046 if ip := net.ParseIP(candidateIP); ip != nil {
1047 // We only match IP addresses against IP SANs.
1048 // See RFC 6125, Appendix B.2.
1049 for _, candidate := range c.IPAddresses {
1050 if ip.Equal(candidate) {
1054 return HostnameError{c, candidateIP}
1057 lowered := toLowerCaseASCII(h)
1059 if c.commonNameAsHostname() {
1060 if matchHostnames(toLowerCaseASCII(c.Subject.CommonName), lowered) {
1064 for _, match := range c.DNSNames {
1065 if matchHostnames(toLowerCaseASCII(match), lowered) {
1071 return HostnameError{c, h}
1074 func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
1075 usages := make([]ExtKeyUsage, len(keyUsages))
1076 copy(usages, keyUsages)
1078 if len(chain) == 0 {
1082 usagesRemaining := len(usages)
1084 // We walk down the list and cross out any usages that aren't supported
1085 // by each certificate. If we cross out all the usages, then the chain
1089 for i := len(chain) - 1; i >= 0; i-- {
1091 if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
1092 // The certificate doesn't have any extended key usage specified.
1096 for _, usage := range cert.ExtKeyUsage {
1097 if usage == ExtKeyUsageAny {
1098 // The certificate is explicitly good for any usage.
1103 const invalidUsage ExtKeyUsage = -1
1106 for i, requestedUsage := range usages {
1107 if requestedUsage == invalidUsage {
1111 for _, usage := range cert.ExtKeyUsage {
1112 if requestedUsage == usage {
1113 continue NextRequestedUsage
1114 } else if requestedUsage == ExtKeyUsageServerAuth &&
1115 (usage == ExtKeyUsageNetscapeServerGatedCrypto ||
1116 usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
1117 // In order to support COMODO
1118 // certificate chains, we have to
1119 // accept Netscape or Microsoft SGC
1120 // usages as equal to ServerAuth.
1121 continue NextRequestedUsage
1125 usages[i] = invalidUsage
1127 if usagesRemaining == 0 {