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. It's a structure
189 // because other PKIX verification APIs have ended up needing many options.
190 type VerifyOptions struct {
192 Intermediates *CertPool
193 Roots *CertPool // if nil, the system roots are used
194 CurrentTime time.Time // if zero, the current time is used
195 // KeyUsage specifies which Extended Key Usage values are acceptable. A leaf
196 // certificate is accepted if it contains any of the listed values. An empty
197 // list means ExtKeyUsageServerAuth. To accept any key usage, include
200 // Certificate chains are required to nest these extended key usage values.
201 // (This matches the Windows CryptoAPI behavior, but not the spec.)
202 KeyUsages []ExtKeyUsage
203 // MaxConstraintComparisions is the maximum number of comparisons to
204 // perform when checking a given certificate's name constraints. If
205 // zero, a sensible default is used. This limit prevents pathological
206 // certificates from consuming excessive amounts of CPU time when
208 MaxConstraintComparisions int
212 leafCertificate = iota
213 intermediateCertificate
217 // rfc2821Mailbox represents a “mailbox” (which is an email address to most
218 // people) by breaking it into the “local” (i.e. before the '@') and “domain”
220 type rfc2821Mailbox struct {
224 // parseRFC2821Mailbox parses an email address into local and domain parts,
225 // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
226 // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
227 // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
228 func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
230 return mailbox, false
233 localPartBytes := make([]byte, 0, len(in)/2)
236 // Quoted-string = DQUOTE *qcontent DQUOTE
237 // non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
238 // qcontent = qtext / quoted-pair
239 // qtext = non-whitespace-control /
240 // %d33 / %d35-91 / %d93-126
241 // quoted-pair = ("\" text) / obs-qp
242 // text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
244 // (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
245 // Section 4. Since it has been 16 years, we no longer accept that.)
250 return mailbox, false
262 return mailbox, false
266 (1 <= in[0] && in[0] <= 9) ||
267 (14 <= in[0] && in[0] <= 127) {
268 localPartBytes = append(localPartBytes, in[0])
271 return mailbox, false
276 // Space (char 32) is not allowed based on the
277 // BNF, but RFC 3696 gives an example that
278 // assumes that it is. Several “verified”
279 // errata continue to argue about this point.
280 // We choose to accept it.
284 (1 <= c && c <= 8) ||
285 (14 <= c && c <= 31) ||
286 (35 <= c && c <= 91) ||
287 (93 <= c && c <= 126):
289 localPartBytes = append(localPartBytes, c)
292 return mailbox, false
299 // atext from RFC 2822, Section 3.2.4
304 // Examples given in RFC 3696 suggest that
305 // escaped characters can appear outside of a
306 // quoted string. Several “verified” errata
307 // continue to argue the point. We choose to
311 return mailbox, false
315 case ('0' <= c && c <= '9') ||
316 ('a' <= c && c <= 'z') ||
317 ('A' <= c && c <= 'Z') ||
318 c == '!' || c == '#' || c == '$' || c == '%' ||
319 c == '&' || c == '\'' || c == '*' || c == '+' ||
320 c == '-' || c == '/' || c == '=' || c == '?' ||
321 c == '^' || c == '_' || c == '`' || c == '{' ||
322 c == '|' || c == '}' || c == '~' || c == '.':
323 localPartBytes = append(localPartBytes, in[0])
331 if len(localPartBytes) == 0 {
332 return mailbox, false
335 // From RFC 3696, Section 3:
336 // “period (".") may also appear, but may not be used to start
337 // or end the local part, nor may two or more consecutive
339 twoDots := []byte{'.', '.'}
340 if localPartBytes[0] == '.' ||
341 localPartBytes[len(localPartBytes)-1] == '.' ||
342 bytes.Contains(localPartBytes, twoDots) {
343 return mailbox, false
347 if len(in) == 0 || in[0] != '@' {
348 return mailbox, false
352 // The RFC species a format for domains, but that's known to be
353 // violated in practice so we accept that anything after an '@' is the
355 if _, ok := domainToReverseLabels(in); !ok {
356 return mailbox, false
359 mailbox.local = string(localPartBytes)
364 // domainToReverseLabels converts a textual domain name like foo.example.com to
365 // the list of labels in reverse order, e.g. ["com", "example", "foo"].
366 func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
367 for len(domain) > 0 {
368 if i := strings.LastIndexByte(domain, '.'); i == -1 {
369 reverseLabels = append(reverseLabels, domain)
372 reverseLabels = append(reverseLabels, domain[i+1:])
377 if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
378 // An empty label at the end indicates an absolute value.
382 for _, label := range reverseLabels {
384 // Empty labels are otherwise invalid.
388 for _, c := range label {
389 if c < 33 || c > 126 {
390 // Invalid character.
396 return reverseLabels, true
399 func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
400 // If the constraint contains an @, then it specifies an exact mailbox
402 if strings.Contains(constraint, "@") {
403 constraintMailbox, ok := parseRFC2821Mailbox(constraint)
405 return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
407 return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
410 // Otherwise the constraint is like a DNS constraint of the domain part
412 return matchDomainConstraint(mailbox.domain, constraint)
415 func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
416 // From RFC 5280, Section 4.2.1.10:
417 // “a uniformResourceIdentifier that does not include an authority
418 // component with a host name specified as a fully qualified domain
419 // name (e.g., if the URI either does not include an authority
420 // component or includes an authority component in which the host name
421 // is specified as an IP address), then the application MUST reject the
426 return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
429 if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
431 host, _, err = net.SplitHostPort(uri.Host)
437 if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
438 net.ParseIP(host) != nil {
439 return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
442 return matchDomainConstraint(host, constraint)
445 func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
446 if len(ip) != len(constraint.IP) {
451 if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
459 func matchDomainConstraint(domain, constraint string) (bool, error) {
460 // The meaning of zero length constraints is not specified, but this
461 // code follows NSS and accepts them as matching everything.
462 if len(constraint) == 0 {
466 domainLabels, ok := domainToReverseLabels(domain)
468 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
471 // RFC 5280 says that a leading period in a domain name means that at
472 // least one label must be prepended, but only for URI and email
473 // constraints, not DNS constraints. The code also supports that
474 // behaviour for DNS constraints.
476 mustHaveSubdomains := false
477 if constraint[0] == '.' {
478 mustHaveSubdomains = true
479 constraint = constraint[1:]
482 constraintLabels, ok := domainToReverseLabels(constraint)
484 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
487 if len(domainLabels) < len(constraintLabels) ||
488 (mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
492 for i, constraintLabel := range constraintLabels {
493 if !strings.EqualFold(constraintLabel, domainLabels[i]) {
501 // checkNameConstraints checks that c permits a child certificate to claim the
502 // given name, of type nameType. The argument parsedName contains the parsed
503 // form of name, suitable for passing to the match function. The total number
504 // of comparisons is tracked in the given count and should not exceed the given
506 func (c *Certificate) checkNameConstraints(count *int,
507 maxConstraintComparisons int,
510 parsedName interface{},
511 match func(parsedName, constraint interface{}) (match bool, err error),
512 permitted, excluded interface{}) error {
514 excludedValue := reflect.ValueOf(excluded)
516 *count += excludedValue.Len()
517 if *count > maxConstraintComparisons {
518 return CertificateInvalidError{c, TooManyConstraints, ""}
521 for i := 0; i < excludedValue.Len(); i++ {
522 constraint := excludedValue.Index(i).Interface()
523 match, err := match(parsedName, constraint)
525 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
529 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
533 permittedValue := reflect.ValueOf(permitted)
535 *count += permittedValue.Len()
536 if *count > maxConstraintComparisons {
537 return CertificateInvalidError{c, TooManyConstraints, ""}
541 for i := 0; i < permittedValue.Len(); i++ {
542 constraint := permittedValue.Index(i).Interface()
545 if ok, err = match(parsedName, constraint); err != nil {
546 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
555 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
561 // isValid performs validity checks on c given that it is a candidate to append
562 // to the chain in currentChain.
563 func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
564 if len(c.UnhandledCriticalExtensions) > 0 {
565 return UnhandledCriticalExtension{}
568 if len(currentChain) > 0 {
569 child := currentChain[len(currentChain)-1]
570 if !bytes.Equal(child.RawIssuer, c.RawSubject) {
571 return CertificateInvalidError{c, NameMismatch, ""}
575 now := opts.CurrentTime
579 if now.Before(c.NotBefore) {
580 return CertificateInvalidError{
583 Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
585 } else if now.After(c.NotAfter) {
586 return CertificateInvalidError{
589 Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
593 maxConstraintComparisons := opts.MaxConstraintComparisions
594 if maxConstraintComparisons == 0 {
595 maxConstraintComparisons = 250000
599 var leaf *Certificate
600 if certType == intermediateCertificate || certType == rootCertificate {
601 if len(currentChain) == 0 {
602 return errors.New("x509: internal error: empty chain when appending CA cert")
604 leaf = currentChain[0]
607 checkNameConstraints := (certType == intermediateCertificate || certType == rootCertificate) && c.hasNameConstraints()
608 if checkNameConstraints && leaf.commonNameAsHostname() {
609 // This is the deprecated, legacy case of depending on the commonName as
610 // a hostname. We don't enforce name constraints against the CN, but
611 // VerifyHostname will look for hostnames in there if there are no SANs.
612 // In order to ensure VerifyHostname will not accept an unchecked name,
613 // return an error here.
614 return CertificateInvalidError{c, NameConstraintsWithoutSANs, ""}
615 } else if checkNameConstraints && leaf.hasSANExtension() {
616 err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
620 mailbox, ok := parseRFC2821Mailbox(name)
622 return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
625 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
626 func(parsedName, constraint interface{}) (bool, error) {
627 return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
628 }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
634 if _, ok := domainToReverseLabels(name); !ok {
635 return fmt.Errorf("x509: cannot parse dnsName %q", name)
638 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
639 func(parsedName, constraint interface{}) (bool, error) {
640 return matchDomainConstraint(parsedName.(string), constraint.(string))
641 }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
647 uri, err := url.Parse(name)
649 return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
652 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
653 func(parsedName, constraint interface{}) (bool, error) {
654 return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
655 }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
661 if l := len(ip); l != net.IPv4len && l != net.IPv6len {
662 return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
665 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
666 func(parsedName, constraint interface{}) (bool, error) {
667 return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
668 }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
673 // Unknown SAN types are ignored.
684 // KeyUsage status flags are ignored. From Engineering Security, Peter
685 // Gutmann: A European government CA marked its signing certificates as
686 // being valid for encryption only, but no-one noticed. Another
687 // European CA marked its signature keys as not being valid for
688 // signatures. A different CA marked its own trusted root certificate
689 // as being invalid for certificate signing. Another national CA
690 // distributed a certificate to be used to encrypt data for the
691 // country’s tax authority that was marked as only being usable for
692 // digital signatures but not for encryption. Yet another CA reversed
693 // the order of the bit flags in the keyUsage due to confusion over
694 // encoding endianness, essentially setting a random keyUsage in
695 // certificates that it issued. Another CA created a self-invalidating
696 // certificate by adding a certificate policy statement stipulating
697 // that the certificate had to be used strictly as specified in the
698 // keyUsage, and a keyUsage containing a flag indicating that the RSA
699 // encryption key could only be used for Diffie-Hellman key agreement.
701 if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
702 return CertificateInvalidError{c, NotAuthorizedToSign, ""}
705 if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
706 numIntermediates := len(currentChain) - 1
707 if numIntermediates > c.MaxPathLen {
708 return CertificateInvalidError{c, TooManyIntermediates, ""}
715 // Verify attempts to verify c by building one or more chains from c to a
716 // certificate in opts.Roots, using certificates in opts.Intermediates if
717 // needed. If successful, it returns one or more chains where the first
718 // element of the chain is c and the last element is from opts.Roots.
720 // If opts.Roots is nil and system roots are unavailable the returned error
721 // will be of type SystemRootsError.
723 // Name constraints in the intermediates will be applied to all names claimed
724 // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
725 // example.com if an intermediate doesn't permit it, even if example.com is not
726 // the name being validated. Note that DirectoryName constraints are not
729 // Extended Key Usage values are enforced down a chain, so an intermediate or
730 // root that enumerates EKUs prevents a leaf from asserting an EKU not in that
733 // WARNING: this function doesn't do any revocation checking.
734 func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
735 // Platform-specific verification needs the ASN.1 contents so
736 // this makes the behavior consistent across platforms.
738 return nil, errNotParsed
740 if opts.Intermediates != nil {
741 for _, intermediate := range opts.Intermediates.certs {
742 if len(intermediate.Raw) == 0 {
743 return nil, errNotParsed
748 // Use Windows's own verification and chain building.
749 if opts.Roots == nil && runtime.GOOS == "windows" {
750 return c.systemVerify(&opts)
753 if opts.Roots == nil {
754 opts.Roots = systemRootsPool()
755 if opts.Roots == nil {
756 return nil, SystemRootsError{systemRootsErr}
760 err = c.isValid(leafCertificate, nil, &opts)
765 if len(opts.DNSName) > 0 {
766 err = c.VerifyHostname(opts.DNSName)
772 var candidateChains [][]*Certificate
773 if opts.Roots.contains(c) {
774 candidateChains = append(candidateChains, []*Certificate{c})
776 if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
781 keyUsages := opts.KeyUsages
782 if len(keyUsages) == 0 {
783 keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
786 // If any key usage is acceptable then we're done.
787 for _, usage := range keyUsages {
788 if usage == ExtKeyUsageAny {
789 return candidateChains, nil
793 for _, candidate := range candidateChains {
794 if checkChainForKeyUsage(candidate, keyUsages) {
795 chains = append(chains, candidate)
799 if len(chains) == 0 {
800 return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
806 func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
807 n := make([]*Certificate, len(chain)+1)
813 // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
814 // that an invocation of buildChains will (tranistively) make. Most chains are
815 // less than 15 certificates long, so this leaves space for multiple chains and
816 // for failed checks due to different intermediates having the same Subject.
817 const maxChainSignatureChecks = 100
819 func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
822 hintCert *Certificate
825 considerCandidate := func(certType int, candidate *Certificate) {
826 for _, cert := range currentChain {
827 if cert.Equal(candidate) {
832 if sigChecks == nil {
836 if *sigChecks > maxChainSignatureChecks {
837 err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
841 if err := c.CheckSignatureFrom(candidate); err != nil {
849 err = candidate.isValid(certType, currentChain, opts)
855 case rootCertificate:
856 chains = append(chains, appendToFreshChain(currentChain, candidate))
857 case intermediateCertificate:
859 cache = make(map[*Certificate][][]*Certificate)
861 childChains, ok := cache[candidate]
863 childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
864 cache[candidate] = childChains
866 chains = append(chains, childChains...)
870 for _, rootNum := range opts.Roots.findPotentialParents(c) {
871 considerCandidate(rootCertificate, opts.Roots.certs[rootNum])
873 for _, intermediateNum := range opts.Intermediates.findPotentialParents(c) {
874 considerCandidate(intermediateCertificate, opts.Intermediates.certs[intermediateNum])
880 if len(chains) == 0 && err == nil {
881 err = UnknownAuthorityError{c, hintErr, hintCert}
887 // validHostname reports whether host is a valid hostname that can be matched or
888 // matched against according to RFC 6125 2.2, with some leniency to accommodate
890 func validHostname(host string) bool {
891 host = strings.TrimSuffix(host, ".")
897 for i, part := range strings.Split(host, ".") {
902 if i == 0 && part == "*" {
903 // Only allow full left-most wildcards, as those are the only ones
904 // we match, and matching literal '*' characters is probably never
905 // the expected behavior.
908 for j, c := range part {
909 if 'a' <= c && c <= 'z' {
912 if '0' <= c && c <= '9' {
915 if 'A' <= c && c <= 'Z' {
918 if c == '-' && j != 0 {
921 if c == '_' || c == ':' {
922 // Not valid characters in hostnames, but commonly
923 // found in deployments outside the WebPKI.
933 // commonNameAsHostname reports whether the Common Name field should be
934 // considered the hostname that the certificate is valid for. This is a legacy
935 // behavior, disabled if the Subject Alt Name extension is present.
937 // It applies the strict validHostname check to the Common Name field, so that
938 // certificates without SANs can still be validated against CAs with name
939 // constraints if there is no risk the CN would be matched as a hostname.
940 // See NameConstraintsWithoutSANs and issue 24151.
941 func (c *Certificate) commonNameAsHostname() bool {
942 return !ignoreCN && !c.hasSANExtension() && validHostname(c.Subject.CommonName)
945 func matchHostnames(pattern, host string) bool {
946 host = strings.TrimSuffix(host, ".")
947 pattern = strings.TrimSuffix(pattern, ".")
949 if len(pattern) == 0 || len(host) == 0 {
953 patternParts := strings.Split(pattern, ".")
954 hostParts := strings.Split(host, ".")
956 if len(patternParts) != len(hostParts) {
960 for i, patternPart := range patternParts {
961 if i == 0 && patternPart == "*" {
964 if patternPart != hostParts[i] {
972 // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
973 // an explicitly ASCII function to avoid any sharp corners resulting from
974 // performing Unicode operations on DNS labels.
975 func toLowerCaseASCII(in string) string {
976 // If the string is already lower-case then there's nothing to do.
977 isAlreadyLowerCase := true
978 for _, c := range in {
979 if c == utf8.RuneError {
980 // If we get a UTF-8 error then there might be
981 // upper-case ASCII bytes in the invalid sequence.
982 isAlreadyLowerCase = false
985 if 'A' <= c && c <= 'Z' {
986 isAlreadyLowerCase = false
991 if isAlreadyLowerCase {
996 for i, c := range out {
997 if 'A' <= c && c <= 'Z' {
1004 // VerifyHostname returns nil if c is a valid certificate for the named host.
1005 // Otherwise it returns an error describing the mismatch.
1006 func (c *Certificate) VerifyHostname(h string) error {
1007 // IP addresses may be written in [ ].
1009 if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
1010 candidateIP = h[1 : len(h)-1]
1012 if ip := net.ParseIP(candidateIP); ip != nil {
1013 // We only match IP addresses against IP SANs.
1014 // See RFC 6125, Appendix B.2.
1015 for _, candidate := range c.IPAddresses {
1016 if ip.Equal(candidate) {
1020 return HostnameError{c, candidateIP}
1023 lowered := toLowerCaseASCII(h)
1025 if c.commonNameAsHostname() {
1026 if matchHostnames(toLowerCaseASCII(c.Subject.CommonName), lowered) {
1030 for _, match := range c.DNSNames {
1031 if matchHostnames(toLowerCaseASCII(match), lowered) {
1037 return HostnameError{c, h}
1040 func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
1041 usages := make([]ExtKeyUsage, len(keyUsages))
1042 copy(usages, keyUsages)
1044 if len(chain) == 0 {
1048 usagesRemaining := len(usages)
1050 // We walk down the list and cross out any usages that aren't supported
1051 // by each certificate. If we cross out all the usages, then the chain
1055 for i := len(chain) - 1; i >= 0; i-- {
1057 if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
1058 // The certificate doesn't have any extended key usage specified.
1062 for _, usage := range cert.ExtKeyUsage {
1063 if usage == ExtKeyUsageAny {
1064 // The certificate is explicitly good for any usage.
1069 const invalidUsage ExtKeyUsage = -1
1072 for i, requestedUsage := range usages {
1073 if requestedUsage == invalidUsage {
1077 for _, usage := range cert.ExtKeyUsage {
1078 if requestedUsage == usage {
1079 continue NextRequestedUsage
1080 } else if requestedUsage == ExtKeyUsageServerAuth &&
1081 (usage == ExtKeyUsageNetscapeServerGatedCrypto ||
1082 usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
1083 // In order to support COMODO
1084 // certificate chains, we have to
1085 // accept Netscape or Microsoft SGC
1086 // usages as equal to ServerAuth.
1087 continue NextRequestedUsage
1091 usages[i] = invalidUsage
1093 if usagesRemaining == 0 {