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 // errNotParsed is returned when a certificate without ASN.1 contents is
191 // verified. Platform-specific verification needs the ASN.1 contents.
192 var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
194 // VerifyOptions contains parameters for Certificate.Verify.
195 type VerifyOptions struct {
196 // DNSName, if set, is checked against the leaf certificate with
197 // Certificate.VerifyHostname.
200 // Intermediates is an optional pool of certificates that are not trust
201 // anchors, but can be used to form a chain from the leaf certificate to a
203 Intermediates *CertPool
204 // Roots is the set of trusted root certificates the leaf certificate needs
205 // to chain up to. If nil, the system roots or the platform verifier are used.
208 // CurrentTime is used to check the validity of all certificates in the
209 // chain. If zero, the current time is used.
210 CurrentTime time.Time
212 // KeyUsage specifies which Extended Key Usage values are acceptable. A leaf
213 // certificate is accepted if it contains any of the listed values. An empty
214 // list means ExtKeyUsageServerAuth. To accept any key usage, include
217 // Certificate chains are required to nest these extended key usage values.
218 // (This matches the Windows CryptoAPI behavior, but not the spec.)
219 KeyUsages []ExtKeyUsage
221 // MaxConstraintComparisions is the maximum number of comparisons to
222 // perform when checking a given certificate's name constraints. If
223 // zero, a sensible default is used. This limit prevents pathological
224 // certificates from consuming excessive amounts of CPU time when
226 MaxConstraintComparisions int
230 leafCertificate = iota
231 intermediateCertificate
235 // rfc2821Mailbox represents a “mailbox” (which is an email address to most
236 // people) by breaking it into the “local” (i.e. before the '@') and “domain”
238 type rfc2821Mailbox struct {
242 // parseRFC2821Mailbox parses an email address into local and domain parts,
243 // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
244 // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
245 // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
246 func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
248 return mailbox, false
251 localPartBytes := make([]byte, 0, len(in)/2)
254 // Quoted-string = DQUOTE *qcontent DQUOTE
255 // non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
256 // qcontent = qtext / quoted-pair
257 // qtext = non-whitespace-control /
258 // %d33 / %d35-91 / %d93-126
259 // quoted-pair = ("\" text) / obs-qp
260 // text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
262 // (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
263 // Section 4. Since it has been 16 years, we no longer accept that.)
268 return mailbox, false
280 return mailbox, false
284 (1 <= in[0] && in[0] <= 9) ||
285 (14 <= in[0] && in[0] <= 127) {
286 localPartBytes = append(localPartBytes, in[0])
289 return mailbox, false
294 // Space (char 32) is not allowed based on the
295 // BNF, but RFC 3696 gives an example that
296 // assumes that it is. Several “verified”
297 // errata continue to argue about this point.
298 // We choose to accept it.
302 (1 <= c && c <= 8) ||
303 (14 <= c && c <= 31) ||
304 (35 <= c && c <= 91) ||
305 (93 <= c && c <= 126):
307 localPartBytes = append(localPartBytes, c)
310 return mailbox, false
317 // atext from RFC 2822, Section 3.2.4
322 // Examples given in RFC 3696 suggest that
323 // escaped characters can appear outside of a
324 // quoted string. Several “verified” errata
325 // continue to argue the point. We choose to
329 return mailbox, false
333 case ('0' <= c && c <= '9') ||
334 ('a' <= c && c <= 'z') ||
335 ('A' <= c && c <= 'Z') ||
336 c == '!' || c == '#' || c == '$' || c == '%' ||
337 c == '&' || c == '\'' || c == '*' || c == '+' ||
338 c == '-' || c == '/' || c == '=' || c == '?' ||
339 c == '^' || c == '_' || c == '`' || c == '{' ||
340 c == '|' || c == '}' || c == '~' || c == '.':
341 localPartBytes = append(localPartBytes, in[0])
349 if len(localPartBytes) == 0 {
350 return mailbox, false
353 // From RFC 3696, Section 3:
354 // “period (".") may also appear, but may not be used to start
355 // or end the local part, nor may two or more consecutive
357 twoDots := []byte{'.', '.'}
358 if localPartBytes[0] == '.' ||
359 localPartBytes[len(localPartBytes)-1] == '.' ||
360 bytes.Contains(localPartBytes, twoDots) {
361 return mailbox, false
365 if len(in) == 0 || in[0] != '@' {
366 return mailbox, false
370 // The RFC species a format for domains, but that's known to be
371 // violated in practice so we accept that anything after an '@' is the
373 if _, ok := domainToReverseLabels(in); !ok {
374 return mailbox, false
377 mailbox.local = string(localPartBytes)
382 // domainToReverseLabels converts a textual domain name like foo.example.com to
383 // the list of labels in reverse order, e.g. ["com", "example", "foo"].
384 func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
385 for len(domain) > 0 {
386 if i := strings.LastIndexByte(domain, '.'); i == -1 {
387 reverseLabels = append(reverseLabels, domain)
390 reverseLabels = append(reverseLabels, domain[i+1:])
395 if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
396 // An empty label at the end indicates an absolute value.
400 for _, label := range reverseLabels {
402 // Empty labels are otherwise invalid.
406 for _, c := range label {
407 if c < 33 || c > 126 {
408 // Invalid character.
414 return reverseLabels, true
417 func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
418 // If the constraint contains an @, then it specifies an exact mailbox
420 if strings.Contains(constraint, "@") {
421 constraintMailbox, ok := parseRFC2821Mailbox(constraint)
423 return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
425 return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
428 // Otherwise the constraint is like a DNS constraint of the domain part
430 return matchDomainConstraint(mailbox.domain, constraint)
433 func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
434 // From RFC 5280, Section 4.2.1.10:
435 // “a uniformResourceIdentifier that does not include an authority
436 // component with a host name specified as a fully qualified domain
437 // name (e.g., if the URI either does not include an authority
438 // component or includes an authority component in which the host name
439 // is specified as an IP address), then the application MUST reject the
444 return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
447 if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
449 host, _, err = net.SplitHostPort(uri.Host)
455 if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
456 net.ParseIP(host) != nil {
457 return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
460 return matchDomainConstraint(host, constraint)
463 func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
464 if len(ip) != len(constraint.IP) {
469 if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
477 func matchDomainConstraint(domain, constraint string) (bool, error) {
478 // The meaning of zero length constraints is not specified, but this
479 // code follows NSS and accepts them as matching everything.
480 if len(constraint) == 0 {
484 domainLabels, ok := domainToReverseLabels(domain)
486 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
489 // RFC 5280 says that a leading period in a domain name means that at
490 // least one label must be prepended, but only for URI and email
491 // constraints, not DNS constraints. The code also supports that
492 // behaviour for DNS constraints.
494 mustHaveSubdomains := false
495 if constraint[0] == '.' {
496 mustHaveSubdomains = true
497 constraint = constraint[1:]
500 constraintLabels, ok := domainToReverseLabels(constraint)
502 return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
505 if len(domainLabels) < len(constraintLabels) ||
506 (mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
510 for i, constraintLabel := range constraintLabels {
511 if !strings.EqualFold(constraintLabel, domainLabels[i]) {
519 // checkNameConstraints checks that c permits a child certificate to claim the
520 // given name, of type nameType. The argument parsedName contains the parsed
521 // form of name, suitable for passing to the match function. The total number
522 // of comparisons is tracked in the given count and should not exceed the given
524 func (c *Certificate) checkNameConstraints(count *int,
525 maxConstraintComparisons int,
528 parsedName interface{},
529 match func(parsedName, constraint interface{}) (match bool, err error),
530 permitted, excluded interface{}) error {
532 excludedValue := reflect.ValueOf(excluded)
534 *count += excludedValue.Len()
535 if *count > maxConstraintComparisons {
536 return CertificateInvalidError{c, TooManyConstraints, ""}
539 for i := 0; i < excludedValue.Len(); i++ {
540 constraint := excludedValue.Index(i).Interface()
541 match, err := match(parsedName, constraint)
543 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
547 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
551 permittedValue := reflect.ValueOf(permitted)
553 *count += permittedValue.Len()
554 if *count > maxConstraintComparisons {
555 return CertificateInvalidError{c, TooManyConstraints, ""}
559 for i := 0; i < permittedValue.Len(); i++ {
560 constraint := permittedValue.Index(i).Interface()
563 if ok, err = match(parsedName, constraint); err != nil {
564 return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
573 return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
579 // isValid performs validity checks on c given that it is a candidate to append
580 // to the chain in currentChain.
581 func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
582 if len(c.UnhandledCriticalExtensions) > 0 {
583 return UnhandledCriticalExtension{}
586 if len(currentChain) > 0 {
587 child := currentChain[len(currentChain)-1]
588 if !bytes.Equal(child.RawIssuer, c.RawSubject) {
589 return CertificateInvalidError{c, NameMismatch, ""}
593 now := opts.CurrentTime
597 if now.Before(c.NotBefore) {
598 return CertificateInvalidError{
601 Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
603 } else if now.After(c.NotAfter) {
604 return CertificateInvalidError{
607 Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
611 maxConstraintComparisons := opts.MaxConstraintComparisions
612 if maxConstraintComparisons == 0 {
613 maxConstraintComparisons = 250000
617 var leaf *Certificate
618 if certType == intermediateCertificate || certType == rootCertificate {
619 if len(currentChain) == 0 {
620 return errors.New("x509: internal error: empty chain when appending CA cert")
622 leaf = currentChain[0]
625 checkNameConstraints := (certType == intermediateCertificate || certType == rootCertificate) && c.hasNameConstraints()
626 if checkNameConstraints && leaf.commonNameAsHostname() {
627 // This is the deprecated, legacy case of depending on the commonName as
628 // a hostname. We don't enforce name constraints against the CN, but
629 // VerifyHostname will look for hostnames in there if there are no SANs.
630 // In order to ensure VerifyHostname will not accept an unchecked name,
631 // return an error here.
632 return CertificateInvalidError{c, NameConstraintsWithoutSANs, ""}
633 } else if checkNameConstraints && leaf.hasSANExtension() {
634 err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
638 mailbox, ok := parseRFC2821Mailbox(name)
640 return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
643 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
644 func(parsedName, constraint interface{}) (bool, error) {
645 return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
646 }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
652 if _, ok := domainToReverseLabels(name); !ok {
653 return fmt.Errorf("x509: cannot parse dnsName %q", name)
656 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
657 func(parsedName, constraint interface{}) (bool, error) {
658 return matchDomainConstraint(parsedName.(string), constraint.(string))
659 }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
665 uri, err := url.Parse(name)
667 return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
670 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
671 func(parsedName, constraint interface{}) (bool, error) {
672 return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
673 }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
679 if l := len(ip); l != net.IPv4len && l != net.IPv6len {
680 return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
683 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
684 func(parsedName, constraint interface{}) (bool, error) {
685 return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
686 }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
691 // Unknown SAN types are ignored.
702 // KeyUsage status flags are ignored. From Engineering Security, Peter
703 // Gutmann: A European government CA marked its signing certificates as
704 // being valid for encryption only, but no-one noticed. Another
705 // European CA marked its signature keys as not being valid for
706 // signatures. A different CA marked its own trusted root certificate
707 // as being invalid for certificate signing. Another national CA
708 // distributed a certificate to be used to encrypt data for the
709 // country’s tax authority that was marked as only being usable for
710 // digital signatures but not for encryption. Yet another CA reversed
711 // the order of the bit flags in the keyUsage due to confusion over
712 // encoding endianness, essentially setting a random keyUsage in
713 // certificates that it issued. Another CA created a self-invalidating
714 // certificate by adding a certificate policy statement stipulating
715 // that the certificate had to be used strictly as specified in the
716 // keyUsage, and a keyUsage containing a flag indicating that the RSA
717 // encryption key could only be used for Diffie-Hellman key agreement.
719 if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
720 return CertificateInvalidError{c, NotAuthorizedToSign, ""}
723 if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
724 numIntermediates := len(currentChain) - 1
725 if numIntermediates > c.MaxPathLen {
726 return CertificateInvalidError{c, TooManyIntermediates, ""}
733 // Verify attempts to verify c by building one or more chains from c to a
734 // certificate in opts.Roots, using certificates in opts.Intermediates if
735 // needed. If successful, it returns one or more chains where the first
736 // element of the chain is c and the last element is from opts.Roots.
738 // If opts.Roots is nil and system roots are unavailable the returned error
739 // will be of type SystemRootsError.
741 // Name constraints in the intermediates will be applied to all names claimed
742 // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
743 // example.com if an intermediate doesn't permit it, even if example.com is not
744 // the name being validated. Note that DirectoryName constraints are not
747 // Extended Key Usage values are enforced down a chain, so an intermediate or
748 // root that enumerates EKUs prevents a leaf from asserting an EKU not in that
751 // WARNING: this function doesn't do any revocation checking.
752 func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
753 // Platform-specific verification needs the ASN.1 contents so
754 // this makes the behavior consistent across platforms.
756 return nil, errNotParsed
758 if opts.Intermediates != nil {
759 for _, intermediate := range opts.Intermediates.certs {
760 if len(intermediate.Raw) == 0 {
761 return nil, errNotParsed
766 // Use Windows's own verification and chain building.
767 if opts.Roots == nil && runtime.GOOS == "windows" {
768 return c.systemVerify(&opts)
771 if opts.Roots == nil {
772 opts.Roots = systemRootsPool()
773 if opts.Roots == nil {
774 return nil, SystemRootsError{systemRootsErr}
778 err = c.isValid(leafCertificate, nil, &opts)
783 if len(opts.DNSName) > 0 {
784 err = c.VerifyHostname(opts.DNSName)
790 var candidateChains [][]*Certificate
791 if opts.Roots.contains(c) {
792 candidateChains = append(candidateChains, []*Certificate{c})
794 if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
799 keyUsages := opts.KeyUsages
800 if len(keyUsages) == 0 {
801 keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
804 // If any key usage is acceptable then we're done.
805 for _, usage := range keyUsages {
806 if usage == ExtKeyUsageAny {
807 return candidateChains, nil
811 for _, candidate := range candidateChains {
812 if checkChainForKeyUsage(candidate, keyUsages) {
813 chains = append(chains, candidate)
817 if len(chains) == 0 {
818 return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
824 func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
825 n := make([]*Certificate, len(chain)+1)
831 // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
832 // that an invocation of buildChains will (tranistively) make. Most chains are
833 // less than 15 certificates long, so this leaves space for multiple chains and
834 // for failed checks due to different intermediates having the same Subject.
835 const maxChainSignatureChecks = 100
837 func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
840 hintCert *Certificate
843 considerCandidate := func(certType int, candidate *Certificate) {
844 for _, cert := range currentChain {
845 if cert.Equal(candidate) {
850 if sigChecks == nil {
854 if *sigChecks > maxChainSignatureChecks {
855 err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
859 if err := c.CheckSignatureFrom(candidate); err != nil {
867 err = candidate.isValid(certType, currentChain, opts)
873 case rootCertificate:
874 chains = append(chains, appendToFreshChain(currentChain, candidate))
875 case intermediateCertificate:
877 cache = make(map[*Certificate][][]*Certificate)
879 childChains, ok := cache[candidate]
881 childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
882 cache[candidate] = childChains
884 chains = append(chains, childChains...)
888 for _, rootNum := range opts.Roots.findPotentialParents(c) {
889 considerCandidate(rootCertificate, opts.Roots.certs[rootNum])
891 for _, intermediateNum := range opts.Intermediates.findPotentialParents(c) {
892 considerCandidate(intermediateCertificate, opts.Intermediates.certs[intermediateNum])
898 if len(chains) == 0 && err == nil {
899 err = UnknownAuthorityError{c, hintErr, hintCert}
905 func validHostnamePattern(host string) bool { return validHostname(host, true) }
906 func validHostnameInput(host string) bool { return validHostname(host, false) }
908 // validHostname reports whether host is a valid hostname that can be matched or
909 // matched against according to RFC 6125 2.2, with some leniency to accommodate
911 func validHostname(host string, isPattern bool) bool {
913 host = strings.TrimSuffix(host, ".")
919 for i, part := range strings.Split(host, ".") {
924 if isPattern && i == 0 && part == "*" {
925 // Only allow full left-most wildcards, as those are the only ones
926 // we match, and matching literal '*' characters is probably never
927 // the expected behavior.
930 for j, c := range part {
931 if 'a' <= c && c <= 'z' {
934 if '0' <= c && c <= '9' {
937 if 'A' <= c && c <= 'Z' {
940 if c == '-' && j != 0 {
944 // Not a valid character in hostnames, but commonly
945 // found in deployments outside the WebPKI.
955 // commonNameAsHostname reports whether the Common Name field should be
956 // considered the hostname that the certificate is valid for. This is a legacy
957 // behavior, disabled by default or if the Subject Alt Name extension is present.
959 // It applies the strict validHostname check to the Common Name field, so that
960 // certificates without SANs can still be validated against CAs with name
961 // constraints if there is no risk the CN would be matched as a hostname.
962 // See NameConstraintsWithoutSANs and issue 24151.
963 func (c *Certificate) commonNameAsHostname() bool {
964 return !ignoreCN && !c.hasSANExtension() && validHostnamePattern(c.Subject.CommonName)
967 func matchExactly(hostA, hostB string) bool {
968 if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
971 return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
974 func matchHostnames(pattern, host string) bool {
975 pattern = toLowerCaseASCII(pattern)
976 host = toLowerCaseASCII(strings.TrimSuffix(host, "."))
978 if len(pattern) == 0 || len(host) == 0 {
982 patternParts := strings.Split(pattern, ".")
983 hostParts := strings.Split(host, ".")
985 if len(patternParts) != len(hostParts) {
989 for i, patternPart := range patternParts {
990 if i == 0 && patternPart == "*" {
993 if patternPart != hostParts[i] {
1001 // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
1002 // an explicitly ASCII function to avoid any sharp corners resulting from
1003 // performing Unicode operations on DNS labels.
1004 func toLowerCaseASCII(in string) string {
1005 // If the string is already lower-case then there's nothing to do.
1006 isAlreadyLowerCase := true
1007 for _, c := range in {
1008 if c == utf8.RuneError {
1009 // If we get a UTF-8 error then there might be
1010 // upper-case ASCII bytes in the invalid sequence.
1011 isAlreadyLowerCase = false
1014 if 'A' <= c && c <= 'Z' {
1015 isAlreadyLowerCase = false
1020 if isAlreadyLowerCase {
1025 for i, c := range out {
1026 if 'A' <= c && c <= 'Z' {
1033 // VerifyHostname returns nil if c is a valid certificate for the named host.
1034 // Otherwise it returns an error describing the mismatch.
1036 // IP addresses can be optionally enclosed in square brackets and are checked
1037 // against the IPAddresses field. Other names are checked case insensitively
1038 // against the DNSNames field. If the names are valid hostnames, the certificate
1039 // fields can have a wildcard as the left-most label.
1041 // The legacy Common Name field is ignored unless it's a valid hostname, the
1042 // certificate doesn't have any Subject Alternative Names, and the GODEBUG
1043 // environment variable is set to "x509ignoreCN=0". Support for Common Name is
1044 // deprecated will be entirely removed in the future.
1045 func (c *Certificate) VerifyHostname(h string) error {
1046 // IP addresses may be written in [ ].
1048 if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
1049 candidateIP = h[1 : len(h)-1]
1051 if ip := net.ParseIP(candidateIP); ip != nil {
1052 // We only match IP addresses against IP SANs.
1053 // See RFC 6125, Appendix B.2.
1054 for _, candidate := range c.IPAddresses {
1055 if ip.Equal(candidate) {
1059 return HostnameError{c, candidateIP}
1063 if c.commonNameAsHostname() {
1064 names = []string{c.Subject.CommonName}
1067 candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
1068 validCandidateName := validHostnameInput(candidateName)
1070 for _, match := range names {
1071 // Ideally, we'd only match valid hostnames according to RFC 6125 like
1072 // browsers (more or less) do, but in practice Go is used in a wider
1073 // array of contexts and can't even assume DNS resolution. Instead,
1074 // always allow perfect matches, and only apply wildcard and trailing
1075 // dot processing to valid hostnames.
1076 if validCandidateName && validHostnamePattern(match) {
1077 if matchHostnames(match, candidateName) {
1081 if matchExactly(match, candidateName) {
1087 return HostnameError{c, h}
1090 func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
1091 usages := make([]ExtKeyUsage, len(keyUsages))
1092 copy(usages, keyUsages)
1094 if len(chain) == 0 {
1098 usagesRemaining := len(usages)
1100 // We walk down the list and cross out any usages that aren't supported
1101 // by each certificate. If we cross out all the usages, then the chain
1105 for i := len(chain) - 1; i >= 0; i-- {
1107 if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
1108 // The certificate doesn't have any extended key usage specified.
1112 for _, usage := range cert.ExtKeyUsage {
1113 if usage == ExtKeyUsageAny {
1114 // The certificate is explicitly good for any usage.
1119 const invalidUsage ExtKeyUsage = -1
1122 for i, requestedUsage := range usages {
1123 if requestedUsage == invalidUsage {
1127 for _, usage := range cert.ExtKeyUsage {
1128 if requestedUsage == usage {
1129 continue NextRequestedUsage
1130 } else if requestedUsage == ExtKeyUsageServerAuth &&
1131 (usage == ExtKeyUsageNetscapeServerGatedCrypto ||
1132 usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
1133 // In order to support COMODO
1134 // certificate chains, we have to
1135 // accept Netscape or Microsoft SGC
1136 // usages as equal to ServerAuth.
1137 continue NextRequestedUsage
1141 usages[i] = invalidUsage
1143 if usagesRemaining == 0 {