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=0")
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 // This error is only returned when legacy Common Name matching is enabled
52 // by setting the GODEBUG environment variable to "x509ignoreCN=1". This
53 // setting might be removed 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() && matchHostnames(c.Subject.CommonName, h.Host) {
113 if !ignoreCN && !validHostnamePattern(c.Subject.CommonName) {
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
117 if ignoreCN && validHostnamePattern(c.Subject.CommonName) {
118 // This would have validated if x509ignoreCN=0 were set.
119 return "x509: certificate relies on legacy Common Name field, " +
120 "use SANs or temporarily enable Common Name matching with GODEBUG=x509ignoreCN=0"
125 if ip := net.ParseIP(h.Host); ip != nil {
126 // Trying to validate an IP
127 if len(c.IPAddresses) == 0 {
128 return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
130 for _, san := range c.IPAddresses {
134 valid += san.String()
137 if c.commonNameAsHostname() {
138 valid = c.Subject.CommonName
140 valid = strings.Join(c.DNSNames, ", ")
145 return "x509: certificate is not valid for any names, but wanted to match " + h.Host
147 return "x509: certificate is valid for " + valid + ", not " + h.Host
150 // UnknownAuthorityError results when the certificate issuer is unknown
151 type UnknownAuthorityError struct {
153 // hintErr contains an error that may be helpful in determining why an
154 // authority wasn't found.
156 // hintCert contains a possible authority certificate that was rejected
157 // because of the error in hintErr.
158 hintCert *Certificate
161 func (e UnknownAuthorityError) Error() string {
162 s := "x509: certificate signed by unknown authority"
163 if e.hintErr != nil {
164 certName := e.hintCert.Subject.CommonName
165 if len(certName) == 0 {
166 if len(e.hintCert.Subject.Organization) > 0 {
167 certName = e.hintCert.Subject.Organization[0]
169 certName = "serial:" + e.hintCert.SerialNumber.String()
172 s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
177 // SystemRootsError results when we fail to load the system root certificates.
178 type SystemRootsError struct {
182 func (se SystemRootsError) Error() string {
183 msg := "x509: failed to load system roots and no roots provided"
185 return msg + "; " + se.Err.Error()
190 func (se SystemRootsError) Unwrap() error { return se.Err }
192 // errNotParsed is returned when a certificate without ASN.1 contents is
193 // verified. Platform-specific verification needs the ASN.1 contents.
194 var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
196 // VerifyOptions contains parameters for Certificate.Verify.
197 type VerifyOptions struct {
198 // DNSName, if set, is checked against the leaf certificate with
199 // Certificate.VerifyHostname or the platform verifier.
202 // Intermediates is an optional pool of certificates that are not trust
203 // anchors, but can be used to form a chain from the leaf certificate to a
205 Intermediates *CertPool
206 // Roots is the set of trusted root certificates the leaf certificate needs
207 // to chain up to. If nil, the system roots or the platform verifier are used.
210 // CurrentTime is used to check the validity of all certificates in the
211 // chain. If zero, the current time is used.
212 CurrentTime time.Time
214 // KeyUsages specifies which Extended Key Usage values are acceptable. A
215 // chain is accepted if it allows any of the listed values. An empty list
216 // means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
217 KeyUsages []ExtKeyUsage
219 // MaxConstraintComparisions is the maximum number of comparisons to
220 // perform when checking a given certificate's name constraints. If
221 // zero, a sensible default is used. This limit prevents pathological
222 // certificates from consuming excessive amounts of CPU time when
223 // validating. It does not apply to the platform verifier.
224 MaxConstraintComparisions int
228 leafCertificate = iota
229 intermediateCertificate
233 // rfc2821Mailbox represents a “mailbox” (which is an email address to most
234 // people) by breaking it into the “local” (i.e. before the '@') and “domain”
236 type rfc2821Mailbox struct {
240 // parseRFC2821Mailbox parses an email address into local and domain parts,
241 // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
242 // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
243 // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
244 func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
246 return mailbox, false
249 localPartBytes := make([]byte, 0, len(in)/2)
252 // Quoted-string = DQUOTE *qcontent DQUOTE
253 // non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
254 // qcontent = qtext / quoted-pair
255 // qtext = non-whitespace-control /
256 // %d33 / %d35-91 / %d93-126
257 // quoted-pair = ("\" text) / obs-qp
258 // text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
260 // (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
261 // Section 4. Since it has been 16 years, we no longer accept that.)
266 return mailbox, false
278 return mailbox, false
282 (1 <= in[0] && in[0] <= 9) ||
283 (14 <= in[0] && in[0] <= 127) {
284 localPartBytes = append(localPartBytes, in[0])
287 return mailbox, false
292 // Space (char 32) is not allowed based on the
293 // BNF, but RFC 3696 gives an example that
294 // assumes that it is. Several “verified”
295 // errata continue to argue about this point.
296 // We choose to accept it.
300 (1 <= c && c <= 8) ||
301 (14 <= c && c <= 31) ||
302 (35 <= c && c <= 91) ||
303 (93 <= c && c <= 126):
305 localPartBytes = append(localPartBytes, c)
308 return mailbox, false
315 // atext from RFC 2822, Section 3.2.4
320 // Examples given in RFC 3696 suggest that
321 // escaped characters can appear outside of a
322 // quoted string. Several “verified” errata
323 // continue to argue the point. We choose to
327 return mailbox, false
331 case ('0' <= c && c <= '9') ||
332 ('a' <= c && c <= 'z') ||
333 ('A' <= c && c <= 'Z') ||
334 c == '!' || c == '#' || c == '$' || c == '%' ||
335 c == '&' || c == '\'' || c == '*' || c == '+' ||
336 c == '-' || c == '/' || c == '=' || c == '?' ||
337 c == '^' || c == '_' || c == '`' || c == '{' ||
338 c == '|' || c == '}' || c == '~' || c == '.':
339 localPartBytes = append(localPartBytes, in[0])
347 if len(localPartBytes) == 0 {
348 return mailbox, false
351 // From RFC 3696, Section 3:
352 // “period (".") may also appear, but may not be used to start
353 // or end the local part, nor may two or more consecutive
355 twoDots := []byte{'.', '.'}
356 if localPartBytes[0] == '.' ||
357 localPartBytes[len(localPartBytes)-1] == '.' ||
358 bytes.Contains(localPartBytes, twoDots) {
359 return mailbox, false
363 if len(in) == 0 || in[0] != '@' {
364 return mailbox, false
368 // The RFC species a format for domains, but that's known to be
369 // violated in practice so we accept that anything after an '@' is the
371 if _, ok := domainToReverseLabels(in); !ok {
372 return mailbox, false
375 mailbox.local = string(localPartBytes)
380 // domainToReverseLabels converts a textual domain name like foo.example.com to
381 // the list of labels in reverse order, e.g. ["com", "example", "foo"].
382 func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
383 for len(domain) > 0 {
384 if i := strings.LastIndexByte(domain, '.'); i == -1 {
385 reverseLabels = append(reverseLabels, domain)
388 reverseLabels = append(reverseLabels, domain[i+1:])
393 if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
394 // An empty label at the end indicates an absolute value.
398 for _, label := range reverseLabels {
400 // Empty labels are otherwise invalid.
404 for _, c := range label {
405 if c < 33 || c > 126 {
406 // Invalid character.
412 return reverseLabels, true
415 func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
416 // If the constraint contains an @, then it specifies an exact mailbox
418 if strings.Contains(constraint, "@") {
419 constraintMailbox, ok := parseRFC2821Mailbox(constraint)
421 return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
423 return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
426 // Otherwise the constraint is like a DNS constraint of the domain part
428 return matchDomainConstraint(mailbox.domain, constraint)
431 func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
432 // From RFC 5280, Section 4.2.1.10:
433 // “a uniformResourceIdentifier that does not include an authority
434 // component with a host name specified as a fully qualified domain
435 // name (e.g., if the URI either does not include an authority
436 // component or includes an authority component in which the host name
437 // is specified as an IP address), then the application MUST reject the
442 return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
445 if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
447 host, _, err = net.SplitHostPort(uri.Host)
453 if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
454 net.ParseIP(host) != nil {
455 return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
458 return matchDomainConstraint(host, constraint)
461 func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
462 if len(ip) != len(constraint.IP) {
467 if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
475 func matchDomainConstraint(domain, constraint string) (bool, error) {
476 // The meaning of zero length constraints is not specified, but this
477 // code follows NSS and accepts them as matching everything.
478 if len(constraint) == 0 {
482 domainLabels, ok := domainToReverseLabels(domain)
484 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
487 // RFC 5280 says that a leading period in a domain name means that at
488 // least one label must be prepended, but only for URI and email
489 // constraints, not DNS constraints. The code also supports that
490 // behaviour for DNS constraints.
492 mustHaveSubdomains := false
493 if constraint[0] == '.' {
494 mustHaveSubdomains = true
495 constraint = constraint[1:]
498 constraintLabels, ok := domainToReverseLabels(constraint)
500 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
503 if len(domainLabels) < len(constraintLabels) ||
504 (mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
508 for i, constraintLabel := range constraintLabels {
509 if !strings.EqualFold(constraintLabel, domainLabels[i]) {
517 // checkNameConstraints checks that c permits a child certificate to claim the
518 // given name, of type nameType. The argument parsedName contains the parsed
519 // form of name, suitable for passing to the match function. The total number
520 // of comparisons is tracked in the given count and should not exceed the given
522 func (c *Certificate) checkNameConstraints(count *int,
523 maxConstraintComparisons int,
526 parsedName interface{},
527 match func(parsedName, constraint interface{}) (match bool, err error),
528 permitted, excluded interface{}) error {
530 excludedValue := reflect.ValueOf(excluded)
532 *count += excludedValue.Len()
533 if *count > maxConstraintComparisons {
534 return CertificateInvalidError{c, TooManyConstraints, ""}
537 for i := 0; i < excludedValue.Len(); i++ {
538 constraint := excludedValue.Index(i).Interface()
539 match, err := match(parsedName, constraint)
541 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
545 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
549 permittedValue := reflect.ValueOf(permitted)
551 *count += permittedValue.Len()
552 if *count > maxConstraintComparisons {
553 return CertificateInvalidError{c, TooManyConstraints, ""}
557 for i := 0; i < permittedValue.Len(); i++ {
558 constraint := permittedValue.Index(i).Interface()
561 if ok, err = match(parsedName, constraint); err != nil {
562 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
571 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
577 // isValid performs validity checks on c given that it is a candidate to append
578 // to the chain in currentChain.
579 func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
580 if len(c.UnhandledCriticalExtensions) > 0 {
581 return UnhandledCriticalExtension{}
584 if len(currentChain) > 0 {
585 child := currentChain[len(currentChain)-1]
586 if !bytes.Equal(child.RawIssuer, c.RawSubject) {
587 return CertificateInvalidError{c, NameMismatch, ""}
591 now := opts.CurrentTime
595 if now.Before(c.NotBefore) {
596 return CertificateInvalidError{
599 Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
601 } else if now.After(c.NotAfter) {
602 return CertificateInvalidError{
605 Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
609 maxConstraintComparisons := opts.MaxConstraintComparisions
610 if maxConstraintComparisons == 0 {
611 maxConstraintComparisons = 250000
615 var leaf *Certificate
616 if certType == intermediateCertificate || certType == rootCertificate {
617 if len(currentChain) == 0 {
618 return errors.New("x509: internal error: empty chain when appending CA cert")
620 leaf = currentChain[0]
623 checkNameConstraints := (certType == intermediateCertificate || certType == rootCertificate) && c.hasNameConstraints()
624 if checkNameConstraints && leaf.commonNameAsHostname() {
625 // This is the deprecated, legacy case of depending on the commonName as
626 // a hostname. We don't enforce name constraints against the CN, but
627 // VerifyHostname will look for hostnames in there if there are no SANs.
628 // In order to ensure VerifyHostname will not accept an unchecked name,
629 // return an error here.
630 return CertificateInvalidError{c, NameConstraintsWithoutSANs, ""}
631 } else if checkNameConstraints && leaf.hasSANExtension() {
632 err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
636 mailbox, ok := parseRFC2821Mailbox(name)
638 return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
641 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
642 func(parsedName, constraint interface{}) (bool, error) {
643 return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
644 }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
650 if _, ok := domainToReverseLabels(name); !ok {
651 return fmt.Errorf("x509: cannot parse dnsName %q", name)
654 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
655 func(parsedName, constraint interface{}) (bool, error) {
656 return matchDomainConstraint(parsedName.(string), constraint.(string))
657 }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
663 uri, err := url.Parse(name)
665 return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
668 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
669 func(parsedName, constraint interface{}) (bool, error) {
670 return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
671 }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
677 if l := len(ip); l != net.IPv4len && l != net.IPv6len {
678 return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
681 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
682 func(parsedName, constraint interface{}) (bool, error) {
683 return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
684 }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
689 // Unknown SAN types are ignored.
700 // KeyUsage status flags are ignored. From Engineering Security, Peter
701 // Gutmann: A European government CA marked its signing certificates as
702 // being valid for encryption only, but no-one noticed. Another
703 // European CA marked its signature keys as not being valid for
704 // signatures. A different CA marked its own trusted root certificate
705 // as being invalid for certificate signing. Another national CA
706 // distributed a certificate to be used to encrypt data for the
707 // country’s tax authority that was marked as only being usable for
708 // digital signatures but not for encryption. Yet another CA reversed
709 // the order of the bit flags in the keyUsage due to confusion over
710 // encoding endianness, essentially setting a random keyUsage in
711 // certificates that it issued. Another CA created a self-invalidating
712 // certificate by adding a certificate policy statement stipulating
713 // that the certificate had to be used strictly as specified in the
714 // keyUsage, and a keyUsage containing a flag indicating that the RSA
715 // encryption key could only be used for Diffie-Hellman key agreement.
717 if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
718 return CertificateInvalidError{c, NotAuthorizedToSign, ""}
721 if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
722 numIntermediates := len(currentChain) - 1
723 if numIntermediates > c.MaxPathLen {
724 return CertificateInvalidError{c, TooManyIntermediates, ""}
731 // Verify attempts to verify c by building one or more chains from c to a
732 // certificate in opts.Roots, using certificates in opts.Intermediates if
733 // needed. If successful, it returns one or more chains where the first
734 // element of the chain is c and the last element is from opts.Roots.
736 // If opts.Roots is nil, the platform verifier might be used, and
737 // verification details might differ from what is described below. If system
738 // roots are unavailable the returned error will be of type SystemRootsError.
740 // Name constraints in the intermediates will be applied to all names claimed
741 // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
742 // example.com if an intermediate doesn't permit it, even if example.com is not
743 // the name being validated. Note that DirectoryName constraints are not
746 // Name constraint validation follows the rules from RFC 5280, with the
747 // addition that DNS name constraints may use the leading period format
748 // defined for emails and URIs. When a constraint has a leading period
749 // it indicates that at least one additional label must be prepended to
750 // the constrained name to be considered valid.
752 // Extended Key Usage values are enforced nested down a chain, so an intermediate
753 // or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
754 // list. (While this is not specified, it is common practice in order to limit
755 // the types of certificates a CA can issue.)
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 func validHostnamePattern(host string) bool { return validHostname(host, true) }
912 func validHostnameInput(host string) bool { return validHostname(host, false) }
914 // validHostname reports whether host is a valid hostname that can be matched or
915 // matched against according to RFC 6125 2.2, with some leniency to accommodate
917 func validHostname(host string, isPattern bool) bool {
919 host = strings.TrimSuffix(host, ".")
925 for i, part := range strings.Split(host, ".") {
930 if isPattern && i == 0 && part == "*" {
931 // Only allow full left-most wildcards, as those are the only ones
932 // we match, and matching literal '*' characters is probably never
933 // the expected behavior.
936 for j, c := range part {
937 if 'a' <= c && c <= 'z' {
940 if '0' <= c && c <= '9' {
943 if 'A' <= c && c <= 'Z' {
946 if c == '-' && j != 0 {
950 // Not a valid character in hostnames, but commonly
951 // found in deployments outside the WebPKI.
961 // commonNameAsHostname reports whether the Common Name field should be
962 // considered the hostname that the certificate is valid for. This is a legacy
963 // behavior, disabled by default or if the Subject Alt Name extension is present.
965 // It applies the strict validHostname check to the Common Name field, so that
966 // certificates without SANs can still be validated against CAs with name
967 // constraints if there is no risk the CN would be matched as a hostname.
968 // See NameConstraintsWithoutSANs and issue 24151.
969 func (c *Certificate) commonNameAsHostname() bool {
970 return !ignoreCN && !c.hasSANExtension() && validHostnamePattern(c.Subject.CommonName)
973 func matchExactly(hostA, hostB string) bool {
974 if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
977 return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
980 func matchHostnames(pattern, host string) bool {
981 pattern = toLowerCaseASCII(pattern)
982 host = toLowerCaseASCII(strings.TrimSuffix(host, "."))
984 if len(pattern) == 0 || len(host) == 0 {
988 patternParts := strings.Split(pattern, ".")
989 hostParts := strings.Split(host, ".")
991 if len(patternParts) != len(hostParts) {
995 for i, patternPart := range patternParts {
996 if i == 0 && patternPart == "*" {
999 if patternPart != hostParts[i] {
1007 // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
1008 // an explicitly ASCII function to avoid any sharp corners resulting from
1009 // performing Unicode operations on DNS labels.
1010 func toLowerCaseASCII(in string) string {
1011 // If the string is already lower-case then there's nothing to do.
1012 isAlreadyLowerCase := true
1013 for _, c := range in {
1014 if c == utf8.RuneError {
1015 // If we get a UTF-8 error then there might be
1016 // upper-case ASCII bytes in the invalid sequence.
1017 isAlreadyLowerCase = false
1020 if 'A' <= c && c <= 'Z' {
1021 isAlreadyLowerCase = false
1026 if isAlreadyLowerCase {
1031 for i, c := range out {
1032 if 'A' <= c && c <= 'Z' {
1039 // VerifyHostname returns nil if c is a valid certificate for the named host.
1040 // Otherwise it returns an error describing the mismatch.
1042 // IP addresses can be optionally enclosed in square brackets and are checked
1043 // against the IPAddresses field. Other names are checked case insensitively
1044 // against the DNSNames field. If the names are valid hostnames, the certificate
1045 // fields can have a wildcard as the left-most label.
1047 // The legacy Common Name field is ignored unless it's a valid hostname, the
1048 // certificate doesn't have any Subject Alternative Names, and the GODEBUG
1049 // environment variable is set to "x509ignoreCN=0". Support for Common Name is
1050 // deprecated will be entirely removed in the future.
1051 func (c *Certificate) VerifyHostname(h string) error {
1052 // IP addresses may be written in [ ].
1054 if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
1055 candidateIP = h[1 : len(h)-1]
1057 if ip := net.ParseIP(candidateIP); ip != nil {
1058 // We only match IP addresses against IP SANs.
1059 // See RFC 6125, Appendix B.2.
1060 for _, candidate := range c.IPAddresses {
1061 if ip.Equal(candidate) {
1065 return HostnameError{c, candidateIP}
1069 if c.commonNameAsHostname() {
1070 names = []string{c.Subject.CommonName}
1073 candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
1074 validCandidateName := validHostnameInput(candidateName)
1076 for _, match := range names {
1077 // Ideally, we'd only match valid hostnames according to RFC 6125 like
1078 // browsers (more or less) do, but in practice Go is used in a wider
1079 // array of contexts and can't even assume DNS resolution. Instead,
1080 // always allow perfect matches, and only apply wildcard and trailing
1081 // dot processing to valid hostnames.
1082 if validCandidateName && validHostnamePattern(match) {
1083 if matchHostnames(match, candidateName) {
1087 if matchExactly(match, candidateName) {
1093 return HostnameError{c, h}
1096 func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
1097 usages := make([]ExtKeyUsage, len(keyUsages))
1098 copy(usages, keyUsages)
1100 if len(chain) == 0 {
1104 usagesRemaining := len(usages)
1106 // We walk down the list and cross out any usages that aren't supported
1107 // by each certificate. If we cross out all the usages, then the chain
1111 for i := len(chain) - 1; i >= 0; i-- {
1113 if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
1114 // The certificate doesn't have any extended key usage specified.
1118 for _, usage := range cert.ExtKeyUsage {
1119 if usage == ExtKeyUsageAny {
1120 // The certificate is explicitly good for any usage.
1125 const invalidUsage ExtKeyUsage = -1
1128 for i, requestedUsage := range usages {
1129 if requestedUsage == invalidUsage {
1133 for _, usage := range cert.ExtKeyUsage {
1134 if requestedUsage == usage {
1135 continue NextRequestedUsage
1136 } else if requestedUsage == ExtKeyUsageServerAuth &&
1137 (usage == ExtKeyUsageNetscapeServerGatedCrypto ||
1138 usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
1139 // In order to support COMODO
1140 // certificate chains, we have to
1141 // accept Netscape or Microsoft SGC
1142 // usages as equal to ServerAuth.
1143 continue NextRequestedUsage
1147 usages[i] = invalidUsage
1149 if usagesRemaining == 0 {