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.
20 type InvalidReason int
23 // NotAuthorizedToSign results when a certificate is signed by another
24 // which isn't marked as a CA certificate.
25 NotAuthorizedToSign InvalidReason = iota
26 // Expired results when a certificate has expired, based on the time
27 // given in the VerifyOptions.
29 // CANotAuthorizedForThisName results when an intermediate or root
30 // certificate has a name constraint which doesn't permit a DNS or
31 // other name (including IP address) in the leaf certificate.
32 CANotAuthorizedForThisName
33 // TooManyIntermediates results when a path length constraint is
36 // IncompatibleUsage results when the certificate's key usage indicates
37 // that it may only be used for a different purpose.
39 // NameMismatch results when the subject name of a parent certificate
40 // does not match the issuer name in the child.
42 // NameConstraintsWithoutSANs is a legacy error and is no longer returned.
43 NameConstraintsWithoutSANs
44 // UnconstrainedName results when a CA certificate contains permitted
45 // name constraints, but leaf certificate contains a name of an
46 // unsupported or unconstrained type.
48 // TooManyConstraints results when the number of comparison operations
49 // needed to check a certificate exceeds the limit set by
50 // VerifyOptions.MaxConstraintComparisions. This limit exists to
51 // prevent pathological certificates can consuming excessive amounts of
52 // CPU time to verify.
54 // CANotAuthorizedForExtKeyUsage results when an intermediate or root
55 // certificate does not permit a requested extended key usage.
56 CANotAuthorizedForExtKeyUsage
59 // CertificateInvalidError results when an odd error occurs. Users of this
60 // library probably want to handle all these errors uniformly.
61 type CertificateInvalidError struct {
67 func (e CertificateInvalidError) Error() string {
69 case NotAuthorizedToSign:
70 return "x509: certificate is not authorized to sign other certificates"
72 return "x509: certificate has expired or is not yet valid: " + e.Detail
73 case CANotAuthorizedForThisName:
74 return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail
75 case CANotAuthorizedForExtKeyUsage:
76 return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
77 case TooManyIntermediates:
78 return "x509: too many intermediates for path length constraint"
79 case IncompatibleUsage:
80 return "x509: certificate specifies an incompatible key usage"
82 return "x509: issuer name does not match subject from issuing certificate"
83 case NameConstraintsWithoutSANs:
84 return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
85 case UnconstrainedName:
86 return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
88 return "x509: unknown error"
91 // HostnameError results when the set of authorized names doesn't match the
93 type HostnameError struct {
94 Certificate *Certificate
98 func (h HostnameError) Error() string {
101 if !c.hasSANExtension() && matchHostnames(c.Subject.CommonName, h.Host) {
102 return "x509: certificate relies on legacy Common Name field, use SANs instead"
106 if ip := net.ParseIP(h.Host); ip != nil {
107 // Trying to validate an IP
108 if len(c.IPAddresses) == 0 {
109 return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
111 for _, san := range c.IPAddresses {
115 valid += san.String()
118 valid = strings.Join(c.DNSNames, ", ")
122 return "x509: certificate is not valid for any names, but wanted to match " + h.Host
124 return "x509: certificate is valid for " + valid + ", not " + h.Host
127 // UnknownAuthorityError results when the certificate issuer is unknown
128 type UnknownAuthorityError struct {
130 // hintErr contains an error that may be helpful in determining why an
131 // authority wasn't found.
133 // hintCert contains a possible authority certificate that was rejected
134 // because of the error in hintErr.
135 hintCert *Certificate
138 func (e UnknownAuthorityError) Error() string {
139 s := "x509: certificate signed by unknown authority"
140 if e.hintErr != nil {
141 certName := e.hintCert.Subject.CommonName
142 if len(certName) == 0 {
143 if len(e.hintCert.Subject.Organization) > 0 {
144 certName = e.hintCert.Subject.Organization[0]
146 certName = "serial:" + e.hintCert.SerialNumber.String()
149 s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
154 // SystemRootsError results when we fail to load the system root certificates.
155 type SystemRootsError struct {
159 func (se SystemRootsError) Error() string {
160 msg := "x509: failed to load system roots and no roots provided"
162 return msg + "; " + se.Err.Error()
167 func (se SystemRootsError) Unwrap() error { return se.Err }
169 // errNotParsed is returned when a certificate without ASN.1 contents is
170 // verified. Platform-specific verification needs the ASN.1 contents.
171 var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
173 // VerifyOptions contains parameters for Certificate.Verify.
174 type VerifyOptions struct {
175 // DNSName, if set, is checked against the leaf certificate with
176 // Certificate.VerifyHostname or the platform verifier.
179 // Intermediates is an optional pool of certificates that are not trust
180 // anchors, but can be used to form a chain from the leaf certificate to a
182 Intermediates *CertPool
183 // Roots is the set of trusted root certificates the leaf certificate needs
184 // to chain up to. If nil, the system roots or the platform verifier are used.
187 // CurrentTime is used to check the validity of all certificates in the
188 // chain. If zero, the current time is used.
189 CurrentTime time.Time
191 // KeyUsages specifies which Extended Key Usage values are acceptable. A
192 // chain is accepted if it allows any of the listed values. An empty list
193 // means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
194 KeyUsages []ExtKeyUsage
196 // MaxConstraintComparisions is the maximum number of comparisons to
197 // perform when checking a given certificate's name constraints. If
198 // zero, a sensible default is used. This limit prevents pathological
199 // certificates from consuming excessive amounts of CPU time when
200 // validating. It does not apply to the platform verifier.
201 MaxConstraintComparisions int
205 leafCertificate = iota
206 intermediateCertificate
210 // rfc2821Mailbox represents a “mailbox” (which is an email address to most
211 // people) by breaking it into the “local” (i.e. before the '@') and “domain”
213 type rfc2821Mailbox struct {
217 // parseRFC2821Mailbox parses an email address into local and domain parts,
218 // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
219 // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
220 // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
221 func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
223 return mailbox, false
226 localPartBytes := make([]byte, 0, len(in)/2)
229 // Quoted-string = DQUOTE *qcontent DQUOTE
230 // non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
231 // qcontent = qtext / quoted-pair
232 // qtext = non-whitespace-control /
233 // %d33 / %d35-91 / %d93-126
234 // quoted-pair = ("\" text) / obs-qp
235 // text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
237 // (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
238 // Section 4. Since it has been 16 years, we no longer accept that.)
243 return mailbox, false
255 return mailbox, false
259 (1 <= in[0] && in[0] <= 9) ||
260 (14 <= in[0] && in[0] <= 127) {
261 localPartBytes = append(localPartBytes, in[0])
264 return mailbox, false
269 // Space (char 32) is not allowed based on the
270 // BNF, but RFC 3696 gives an example that
271 // assumes that it is. Several “verified”
272 // errata continue to argue about this point.
273 // We choose to accept it.
277 (1 <= c && c <= 8) ||
278 (14 <= c && c <= 31) ||
279 (35 <= c && c <= 91) ||
280 (93 <= c && c <= 126):
282 localPartBytes = append(localPartBytes, c)
285 return mailbox, false
292 // atext from RFC 2822, Section 3.2.4
297 // Examples given in RFC 3696 suggest that
298 // escaped characters can appear outside of a
299 // quoted string. Several “verified” errata
300 // continue to argue the point. We choose to
304 return mailbox, false
308 case ('0' <= c && c <= '9') ||
309 ('a' <= c && c <= 'z') ||
310 ('A' <= c && c <= 'Z') ||
311 c == '!' || c == '#' || c == '$' || c == '%' ||
312 c == '&' || c == '\'' || c == '*' || c == '+' ||
313 c == '-' || c == '/' || c == '=' || c == '?' ||
314 c == '^' || c == '_' || c == '`' || c == '{' ||
315 c == '|' || c == '}' || c == '~' || c == '.':
316 localPartBytes = append(localPartBytes, in[0])
324 if len(localPartBytes) == 0 {
325 return mailbox, false
328 // From RFC 3696, Section 3:
329 // “period (".") may also appear, but may not be used to start
330 // or end the local part, nor may two or more consecutive
332 twoDots := []byte{'.', '.'}
333 if localPartBytes[0] == '.' ||
334 localPartBytes[len(localPartBytes)-1] == '.' ||
335 bytes.Contains(localPartBytes, twoDots) {
336 return mailbox, false
340 if len(in) == 0 || in[0] != '@' {
341 return mailbox, false
345 // The RFC species a format for domains, but that's known to be
346 // violated in practice so we accept that anything after an '@' is the
348 if _, ok := domainToReverseLabels(in); !ok {
349 return mailbox, false
352 mailbox.local = string(localPartBytes)
357 // domainToReverseLabels converts a textual domain name like foo.example.com to
358 // the list of labels in reverse order, e.g. ["com", "example", "foo"].
359 func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
360 for len(domain) > 0 {
361 if i := strings.LastIndexByte(domain, '.'); i == -1 {
362 reverseLabels = append(reverseLabels, domain)
365 reverseLabels = append(reverseLabels, domain[i+1:])
370 if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
371 // An empty label at the end indicates an absolute value.
375 for _, label := range reverseLabels {
377 // Empty labels are otherwise invalid.
381 for _, c := range label {
382 if c < 33 || c > 126 {
383 // Invalid character.
389 return reverseLabels, true
392 func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
393 // If the constraint contains an @, then it specifies an exact mailbox
395 if strings.Contains(constraint, "@") {
396 constraintMailbox, ok := parseRFC2821Mailbox(constraint)
398 return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
400 return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
403 // Otherwise the constraint is like a DNS constraint of the domain part
405 return matchDomainConstraint(mailbox.domain, constraint)
408 func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
409 // From RFC 5280, Section 4.2.1.10:
410 // “a uniformResourceIdentifier that does not include an authority
411 // component with a host name specified as a fully qualified domain
412 // name (e.g., if the URI either does not include an authority
413 // component or includes an authority component in which the host name
414 // is specified as an IP address), then the application MUST reject the
419 return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
422 if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
424 host, _, err = net.SplitHostPort(uri.Host)
430 if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
431 net.ParseIP(host) != nil {
432 return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
435 return matchDomainConstraint(host, constraint)
438 func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
439 if len(ip) != len(constraint.IP) {
444 if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
452 func matchDomainConstraint(domain, constraint string) (bool, error) {
453 // The meaning of zero length constraints is not specified, but this
454 // code follows NSS and accepts them as matching everything.
455 if len(constraint) == 0 {
459 domainLabels, ok := domainToReverseLabels(domain)
461 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
464 // RFC 5280 says that a leading period in a domain name means that at
465 // least one label must be prepended, but only for URI and email
466 // constraints, not DNS constraints. The code also supports that
467 // behaviour for DNS constraints.
469 mustHaveSubdomains := false
470 if constraint[0] == '.' {
471 mustHaveSubdomains = true
472 constraint = constraint[1:]
475 constraintLabels, ok := domainToReverseLabels(constraint)
477 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
480 if len(domainLabels) < len(constraintLabels) ||
481 (mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
485 for i, constraintLabel := range constraintLabels {
486 if !strings.EqualFold(constraintLabel, domainLabels[i]) {
494 // checkNameConstraints checks that c permits a child certificate to claim the
495 // given name, of type nameType. The argument parsedName contains the parsed
496 // form of name, suitable for passing to the match function. The total number
497 // of comparisons is tracked in the given count and should not exceed the given
499 func (c *Certificate) checkNameConstraints(count *int,
500 maxConstraintComparisons int,
504 match func(parsedName, constraint any) (match bool, err error),
505 permitted, excluded any) error {
507 excludedValue := reflect.ValueOf(excluded)
509 *count += excludedValue.Len()
510 if *count > maxConstraintComparisons {
511 return CertificateInvalidError{c, TooManyConstraints, ""}
514 for i := 0; i < excludedValue.Len(); i++ {
515 constraint := excludedValue.Index(i).Interface()
516 match, err := match(parsedName, constraint)
518 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
522 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
526 permittedValue := reflect.ValueOf(permitted)
528 *count += permittedValue.Len()
529 if *count > maxConstraintComparisons {
530 return CertificateInvalidError{c, TooManyConstraints, ""}
534 for i := 0; i < permittedValue.Len(); i++ {
535 constraint := permittedValue.Index(i).Interface()
538 if ok, err = match(parsedName, constraint); err != nil {
539 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
548 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
554 // isValid performs validity checks on c given that it is a candidate to append
555 // to the chain in currentChain.
556 func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
557 if len(c.UnhandledCriticalExtensions) > 0 {
558 return UnhandledCriticalExtension{}
561 if len(currentChain) > 0 {
562 child := currentChain[len(currentChain)-1]
563 if !bytes.Equal(child.RawIssuer, c.RawSubject) {
564 return CertificateInvalidError{c, NameMismatch, ""}
568 now := opts.CurrentTime
572 if now.Before(c.NotBefore) {
573 return CertificateInvalidError{
576 Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
578 } else if now.After(c.NotAfter) {
579 return CertificateInvalidError{
582 Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
586 maxConstraintComparisons := opts.MaxConstraintComparisions
587 if maxConstraintComparisons == 0 {
588 maxConstraintComparisons = 250000
592 var leaf *Certificate
593 if certType == intermediateCertificate || certType == rootCertificate {
594 if len(currentChain) == 0 {
595 return errors.New("x509: internal error: empty chain when appending CA cert")
597 leaf = currentChain[0]
600 if (certType == intermediateCertificate || certType == rootCertificate) &&
601 c.hasNameConstraints() && leaf.hasSANExtension() {
602 err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
606 mailbox, ok := parseRFC2821Mailbox(name)
608 return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
611 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
612 func(parsedName, constraint any) (bool, error) {
613 return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
614 }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
620 if _, ok := domainToReverseLabels(name); !ok {
621 return fmt.Errorf("x509: cannot parse dnsName %q", name)
624 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
625 func(parsedName, constraint any) (bool, error) {
626 return matchDomainConstraint(parsedName.(string), constraint.(string))
627 }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
633 uri, err := url.Parse(name)
635 return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
638 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
639 func(parsedName, constraint any) (bool, error) {
640 return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
641 }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
647 if l := len(ip); l != net.IPv4len && l != net.IPv6len {
648 return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
651 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
652 func(parsedName, constraint any) (bool, error) {
653 return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
654 }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
659 // Unknown SAN types are ignored.
670 // KeyUsage status flags are ignored. From Engineering Security, Peter
671 // Gutmann: A European government CA marked its signing certificates as
672 // being valid for encryption only, but no-one noticed. Another
673 // European CA marked its signature keys as not being valid for
674 // signatures. A different CA marked its own trusted root certificate
675 // as being invalid for certificate signing. Another national CA
676 // distributed a certificate to be used to encrypt data for the
677 // country’s tax authority that was marked as only being usable for
678 // digital signatures but not for encryption. Yet another CA reversed
679 // the order of the bit flags in the keyUsage due to confusion over
680 // encoding endianness, essentially setting a random keyUsage in
681 // certificates that it issued. Another CA created a self-invalidating
682 // certificate by adding a certificate policy statement stipulating
683 // that the certificate had to be used strictly as specified in the
684 // keyUsage, and a keyUsage containing a flag indicating that the RSA
685 // encryption key could only be used for Diffie-Hellman key agreement.
687 if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
688 return CertificateInvalidError{c, NotAuthorizedToSign, ""}
691 if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
692 numIntermediates := len(currentChain) - 1
693 if numIntermediates > c.MaxPathLen {
694 return CertificateInvalidError{c, TooManyIntermediates, ""}
701 // Verify attempts to verify c by building one or more chains from c to a
702 // certificate in opts.Roots, using certificates in opts.Intermediates if
703 // needed. If successful, it returns one or more chains where the first
704 // element of the chain is c and the last element is from opts.Roots.
706 // If opts.Roots is nil, the platform verifier might be used, and
707 // verification details might differ from what is described below. If system
708 // roots are unavailable the returned error will be of type SystemRootsError.
710 // Name constraints in the intermediates will be applied to all names claimed
711 // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
712 // example.com if an intermediate doesn't permit it, even if example.com is not
713 // the name being validated. Note that DirectoryName constraints are not
716 // Name constraint validation follows the rules from RFC 5280, with the
717 // addition that DNS name constraints may use the leading period format
718 // defined for emails and URIs. When a constraint has a leading period
719 // it indicates that at least one additional label must be prepended to
720 // the constrained name to be considered valid.
722 // Extended Key Usage values are enforced nested down a chain, so an intermediate
723 // or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
724 // list. (While this is not specified, it is common practice in order to limit
725 // the types of certificates a CA can issue.)
727 // WARNING: this function doesn't do any revocation checking.
728 func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
729 // Platform-specific verification needs the ASN.1 contents so
730 // this makes the behavior consistent across platforms.
732 return nil, errNotParsed
734 for i := 0; i < opts.Intermediates.len(); i++ {
735 c, err := opts.Intermediates.cert(i)
737 return nil, fmt.Errorf("crypto/x509: error fetching intermediate: %w", err)
740 return nil, errNotParsed
744 // Use platform verifiers, where available, if Roots is from SystemCertPool.
745 if runtime.GOOS == "windows" || runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
746 if opts.Roots == nil {
747 return c.systemVerify(&opts)
749 if opts.Roots != nil && opts.Roots.systemPool {
750 platformChains, err := c.systemVerify(&opts)
751 // If the platform verifier succeeded, or there are no additional
752 // roots, return the platform verifier result. Otherwise, continue
753 // with the Go verifier.
754 if err == nil || opts.Roots.len() == 0 {
755 return platformChains, err
760 if opts.Roots == nil {
761 opts.Roots = systemRootsPool()
762 if opts.Roots == nil {
763 return nil, SystemRootsError{systemRootsErr}
767 err = c.isValid(leafCertificate, nil, &opts)
772 if len(opts.DNSName) > 0 {
773 err = c.VerifyHostname(opts.DNSName)
779 var candidateChains [][]*Certificate
780 if opts.Roots.contains(c) {
781 candidateChains = append(candidateChains, []*Certificate{c})
783 if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
788 keyUsages := opts.KeyUsages
789 if len(keyUsages) == 0 {
790 keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
793 // If any key usage is acceptable then we're done.
794 for _, usage := range keyUsages {
795 if usage == ExtKeyUsageAny {
796 return candidateChains, nil
800 for _, candidate := range candidateChains {
801 if checkChainForKeyUsage(candidate, keyUsages) {
802 chains = append(chains, candidate)
806 if len(chains) == 0 {
807 return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
813 func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
814 n := make([]*Certificate, len(chain)+1)
820 // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
821 // that an invocation of buildChains will (transitively) make. Most chains are
822 // less than 15 certificates long, so this leaves space for multiple chains and
823 // for failed checks due to different intermediates having the same Subject.
824 const maxChainSignatureChecks = 100
826 func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
829 hintCert *Certificate
832 considerCandidate := func(certType int, candidate *Certificate) {
833 for _, cert := range currentChain {
834 if cert.Equal(candidate) {
839 if sigChecks == nil {
843 if *sigChecks > maxChainSignatureChecks {
844 err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
848 if err := c.CheckSignatureFrom(candidate); err != nil {
856 err = candidate.isValid(certType, currentChain, opts)
862 case rootCertificate:
863 chains = append(chains, appendToFreshChain(currentChain, candidate))
864 case intermediateCertificate:
866 cache = make(map[*Certificate][][]*Certificate)
868 childChains, ok := cache[candidate]
870 childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
871 cache[candidate] = childChains
873 chains = append(chains, childChains...)
877 for _, root := range opts.Roots.findPotentialParents(c) {
878 considerCandidate(rootCertificate, root)
880 for _, intermediate := range opts.Intermediates.findPotentialParents(c) {
881 considerCandidate(intermediateCertificate, intermediate)
887 if len(chains) == 0 && err == nil {
888 err = UnknownAuthorityError{c, hintErr, hintCert}
894 func validHostnamePattern(host string) bool { return validHostname(host, true) }
895 func validHostnameInput(host string) bool { return validHostname(host, false) }
897 // validHostname reports whether host is a valid hostname that can be matched or
898 // matched against according to RFC 6125 2.2, with some leniency to accommodate
900 func validHostname(host string, isPattern bool) bool {
902 host = strings.TrimSuffix(host, ".")
908 for i, part := range strings.Split(host, ".") {
913 if isPattern && i == 0 && part == "*" {
914 // Only allow full left-most wildcards, as those are the only ones
915 // we match, and matching literal '*' characters is probably never
916 // the expected behavior.
919 for j, c := range part {
920 if 'a' <= c && c <= 'z' {
923 if '0' <= c && c <= '9' {
926 if 'A' <= c && c <= 'Z' {
929 if c == '-' && j != 0 {
933 // Not a valid character in hostnames, but commonly
934 // found in deployments outside the WebPKI.
944 func matchExactly(hostA, hostB string) bool {
945 if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
948 return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
951 func matchHostnames(pattern, host string) bool {
952 pattern = toLowerCaseASCII(pattern)
953 host = toLowerCaseASCII(strings.TrimSuffix(host, "."))
955 if len(pattern) == 0 || len(host) == 0 {
959 patternParts := strings.Split(pattern, ".")
960 hostParts := strings.Split(host, ".")
962 if len(patternParts) != len(hostParts) {
966 for i, patternPart := range patternParts {
967 if i == 0 && patternPart == "*" {
970 if patternPart != hostParts[i] {
978 // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
979 // an explicitly ASCII function to avoid any sharp corners resulting from
980 // performing Unicode operations on DNS labels.
981 func toLowerCaseASCII(in string) string {
982 // If the string is already lower-case then there's nothing to do.
983 isAlreadyLowerCase := true
984 for _, c := range in {
985 if c == utf8.RuneError {
986 // If we get a UTF-8 error then there might be
987 // upper-case ASCII bytes in the invalid sequence.
988 isAlreadyLowerCase = false
991 if 'A' <= c && c <= 'Z' {
992 isAlreadyLowerCase = false
997 if isAlreadyLowerCase {
1002 for i, c := range out {
1003 if 'A' <= c && c <= 'Z' {
1010 // VerifyHostname returns nil if c is a valid certificate for the named host.
1011 // Otherwise it returns an error describing the mismatch.
1013 // IP addresses can be optionally enclosed in square brackets and are checked
1014 // against the IPAddresses field. Other names are checked case insensitively
1015 // against the DNSNames field. If the names are valid hostnames, the certificate
1016 // fields can have a wildcard as the left-most label.
1018 // Note that the legacy Common Name field is ignored.
1019 func (c *Certificate) VerifyHostname(h string) error {
1020 // IP addresses may be written in [ ].
1022 if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
1023 candidateIP = h[1 : len(h)-1]
1025 if ip := net.ParseIP(candidateIP); ip != nil {
1026 // We only match IP addresses against IP SANs.
1027 // See RFC 6125, Appendix B.2.
1028 for _, candidate := range c.IPAddresses {
1029 if ip.Equal(candidate) {
1033 return HostnameError{c, candidateIP}
1036 candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
1037 validCandidateName := validHostnameInput(candidateName)
1039 for _, match := range c.DNSNames {
1040 // Ideally, we'd only match valid hostnames according to RFC 6125 like
1041 // browsers (more or less) do, but in practice Go is used in a wider
1042 // array of contexts and can't even assume DNS resolution. Instead,
1043 // always allow perfect matches, and only apply wildcard and trailing
1044 // dot processing to valid hostnames.
1045 if validCandidateName && validHostnamePattern(match) {
1046 if matchHostnames(match, candidateName) {
1050 if matchExactly(match, candidateName) {
1056 return HostnameError{c, h}
1059 func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
1060 usages := make([]ExtKeyUsage, len(keyUsages))
1061 copy(usages, keyUsages)
1063 if len(chain) == 0 {
1067 usagesRemaining := len(usages)
1069 // We walk down the list and cross out any usages that aren't supported
1070 // by each certificate. If we cross out all the usages, then the chain
1074 for i := len(chain) - 1; i >= 0; i-- {
1076 if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
1077 // The certificate doesn't have any extended key usage specified.
1081 for _, usage := range cert.ExtKeyUsage {
1082 if usage == ExtKeyUsageAny {
1083 // The certificate is explicitly good for any usage.
1088 const invalidUsage ExtKeyUsage = -1
1091 for i, requestedUsage := range usages {
1092 if requestedUsage == invalidUsage {
1096 for _, usage := range cert.ExtKeyUsage {
1097 if requestedUsage == usage {
1098 continue NextRequestedUsage
1102 usages[i] = invalidUsage
1104 if usagesRemaining == 0 {