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.
22 type InvalidReason int
25 // NotAuthorizedToSign results when a certificate is signed by another
26 // which isn't marked as a CA certificate.
27 NotAuthorizedToSign InvalidReason = iota
28 // Expired results when a certificate has expired, based on the time
29 // given in the VerifyOptions.
31 // CANotAuthorizedForThisName results when an intermediate or root
32 // certificate has a name constraint which doesn't permit a DNS or
33 // other name (including IP address) in the leaf certificate.
34 CANotAuthorizedForThisName
35 // TooManyIntermediates results when a path length constraint is
38 // IncompatibleUsage results when the certificate's key usage indicates
39 // that it may only be used for a different purpose.
41 // NameMismatch results when the subject name of a parent certificate
42 // does not match the issuer name in the child.
44 // NameConstraintsWithoutSANs is a legacy error and is no longer returned.
45 NameConstraintsWithoutSANs
46 // UnconstrainedName results when a CA certificate contains permitted
47 // name constraints, but leaf certificate contains a name of an
48 // unsupported or unconstrained type.
50 // TooManyConstraints results when the number of comparison operations
51 // needed to check a certificate exceeds the limit set by
52 // VerifyOptions.MaxConstraintComparisions. This limit exists to
53 // prevent pathological certificates can consuming excessive amounts of
54 // CPU time to verify.
56 // CANotAuthorizedForExtKeyUsage results when an intermediate or root
57 // certificate does not permit a requested extended key usage.
58 CANotAuthorizedForExtKeyUsage
61 // CertificateInvalidError results when an odd error occurs. Users of this
62 // library probably want to handle all these errors uniformly.
63 type CertificateInvalidError struct {
69 func (e CertificateInvalidError) Error() string {
71 case NotAuthorizedToSign:
72 return "x509: certificate is not authorized to sign other certificates"
74 return "x509: certificate has expired or is not yet valid: " + e.Detail
75 case CANotAuthorizedForThisName:
76 return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail
77 case CANotAuthorizedForExtKeyUsage:
78 return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
79 case TooManyIntermediates:
80 return "x509: too many intermediates for path length constraint"
81 case IncompatibleUsage:
82 return "x509: certificate specifies an incompatible key usage"
84 return "x509: issuer name does not match subject from issuing certificate"
85 case NameConstraintsWithoutSANs:
86 return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
87 case UnconstrainedName:
88 return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
90 return "x509: unknown error"
93 // HostnameError results when the set of authorized names doesn't match the
95 type HostnameError struct {
96 Certificate *Certificate
100 func (h HostnameError) Error() string {
103 if !c.hasSANExtension() && matchHostnames(c.Subject.CommonName, h.Host) {
104 return "x509: certificate relies on legacy Common Name field, use SANs instead"
108 if ip := net.ParseIP(h.Host); ip != nil {
109 // Trying to validate an IP
110 if len(c.IPAddresses) == 0 {
111 return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
113 for _, san := range c.IPAddresses {
117 valid += san.String()
120 valid = strings.Join(c.DNSNames, ", ")
124 return "x509: certificate is not valid for any names, but wanted to match " + h.Host
126 return "x509: certificate is valid for " + valid + ", not " + h.Host
129 // UnknownAuthorityError results when the certificate issuer is unknown
130 type UnknownAuthorityError struct {
132 // hintErr contains an error that may be helpful in determining why an
133 // authority wasn't found.
135 // hintCert contains a possible authority certificate that was rejected
136 // because of the error in hintErr.
137 hintCert *Certificate
140 func (e UnknownAuthorityError) Error() string {
141 s := "x509: certificate signed by unknown authority"
142 if e.hintErr != nil {
143 certName := e.hintCert.Subject.CommonName
144 if len(certName) == 0 {
145 if len(e.hintCert.Subject.Organization) > 0 {
146 certName = e.hintCert.Subject.Organization[0]
148 certName = "serial:" + e.hintCert.SerialNumber.String()
151 s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
156 // SystemRootsError results when we fail to load the system root certificates.
157 type SystemRootsError struct {
161 func (se SystemRootsError) Error() string {
162 msg := "x509: failed to load system roots and no roots provided"
164 return msg + "; " + se.Err.Error()
169 func (se SystemRootsError) Unwrap() error { return se.Err }
171 // errNotParsed is returned when a certificate without ASN.1 contents is
172 // verified. Platform-specific verification needs the ASN.1 contents.
173 var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
175 // VerifyOptions contains parameters for Certificate.Verify.
176 type VerifyOptions struct {
177 // IsBoring is a validity check for BoringCrypto.
178 // If not nil, it will be called to check whether a given certificate
179 // can be used for constructing verification chains.
180 IsBoring func(*Certificate) bool
182 // DNSName, if set, is checked against the leaf certificate with
183 // Certificate.VerifyHostname or the platform verifier.
186 // Intermediates is an optional pool of certificates that are not trust
187 // anchors, but can be used to form a chain from the leaf certificate to a
189 Intermediates *CertPool
190 // Roots is the set of trusted root certificates the leaf certificate needs
191 // to chain up to. If nil, the system roots or the platform verifier are used.
194 // CurrentTime is used to check the validity of all certificates in the
195 // chain. If zero, the current time is used.
196 CurrentTime time.Time
198 // KeyUsages specifies which Extended Key Usage values are acceptable. A
199 // chain is accepted if it allows any of the listed values. An empty list
200 // means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
201 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
207 // validating. It does not apply to the platform verifier.
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,
511 match func(parsedName, constraint any) (match bool, err error),
512 permitted, excluded any) 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 if (len(c.ExtKeyUsage) > 0 || len(c.UnknownExtKeyUsage) > 0) && len(opts.KeyUsages) > 0 {
608 acceptableUsage := false
609 um := make(map[ExtKeyUsage]bool, len(opts.KeyUsages))
610 for _, u := range opts.KeyUsages {
613 if !um[ExtKeyUsageAny] {
614 for _, u := range c.ExtKeyUsage {
615 if u == ExtKeyUsageAny || um[u] {
616 acceptableUsage = true
620 if !acceptableUsage {
621 return CertificateInvalidError{c, IncompatibleUsage, ""}
626 if (certType == intermediateCertificate || certType == rootCertificate) &&
627 c.hasNameConstraints() {
628 toCheck := []*Certificate{}
629 if leaf.hasSANExtension() {
630 toCheck = append(toCheck, leaf)
632 if c.hasSANExtension() {
633 toCheck = append(toCheck, c)
635 for _, sanCert := range toCheck {
636 err := forEachSAN(sanCert.getSANExtension(), func(tag int, data []byte) error {
640 mailbox, ok := parseRFC2821Mailbox(name)
642 return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
645 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
646 func(parsedName, constraint any) (bool, error) {
647 return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
648 }, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
654 if _, ok := domainToReverseLabels(name); !ok {
655 return fmt.Errorf("x509: cannot parse dnsName %q", name)
658 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
659 func(parsedName, constraint any) (bool, error) {
660 return matchDomainConstraint(parsedName.(string), constraint.(string))
661 }, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
667 uri, err := url.Parse(name)
669 return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
672 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
673 func(parsedName, constraint any) (bool, error) {
674 return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
675 }, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
681 if l := len(ip); l != net.IPv4len && l != net.IPv6len {
682 return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
685 if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
686 func(parsedName, constraint any) (bool, error) {
687 return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
688 }, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
693 // Unknown SAN types are ignored.
705 // KeyUsage status flags are ignored. From Engineering Security, Peter
706 // Gutmann: A European government CA marked its signing certificates as
707 // being valid for encryption only, but no-one noticed. Another
708 // European CA marked its signature keys as not being valid for
709 // signatures. A different CA marked its own trusted root certificate
710 // as being invalid for certificate signing. Another national CA
711 // distributed a certificate to be used to encrypt data for the
712 // country’s tax authority that was marked as only being usable for
713 // digital signatures but not for encryption. Yet another CA reversed
714 // the order of the bit flags in the keyUsage due to confusion over
715 // encoding endianness, essentially setting a random keyUsage in
716 // certificates that it issued. Another CA created a self-invalidating
717 // certificate by adding a certificate policy statement stipulating
718 // that the certificate had to be used strictly as specified in the
719 // keyUsage, and a keyUsage containing a flag indicating that the RSA
720 // encryption key could only be used for Diffie-Hellman key agreement.
722 if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
723 return CertificateInvalidError{c, NotAuthorizedToSign, ""}
726 if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
727 numIntermediates := len(currentChain) - 1
728 if numIntermediates > c.MaxPathLen {
729 return CertificateInvalidError{c, TooManyIntermediates, ""}
733 if opts.IsBoring != nil && !opts.IsBoring(c) {
734 // IncompatibleUsage is not quite right here,
735 // but it's also the "no chains found" error
736 // and is close enough.
737 return CertificateInvalidError{c, IncompatibleUsage, ""}
743 // Verify attempts to verify c by building one or more chains from c to a
744 // certificate in opts.Roots, using certificates in opts.Intermediates if
745 // needed. If successful, it returns one or more chains where the first
746 // element of the chain is c and the last element is from opts.Roots.
748 // If opts.Roots is nil, the platform verifier might be used, and
749 // verification details might differ from what is described below. If system
750 // roots are unavailable the returned error will be of type SystemRootsError.
752 // Name constraints in the intermediates will be applied to all names claimed
753 // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
754 // example.com if an intermediate doesn't permit it, even if example.com is not
755 // the name being validated. Note that DirectoryName constraints are not
758 // Name constraint validation follows the rules from RFC 5280, with the
759 // addition that DNS name constraints may use the leading period format
760 // defined for emails and URIs. When a constraint has a leading period
761 // it indicates that at least one additional label must be prepended to
762 // the constrained name to be considered valid.
764 // Extended Key Usage values are enforced nested down a chain, so an intermediate
765 // or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
766 // list. (While this is not specified, it is common practice in order to limit
767 // the types of certificates a CA can issue.)
769 // Certificates that use SHA1WithRSA and ECDSAWithSHA1 signatures are not supported,
770 // and will not be used to build chains.
772 // WARNING: this function doesn't do any revocation checking.
773 func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
774 // Platform-specific verification needs the ASN.1 contents so
775 // this makes the behavior consistent across platforms.
777 return nil, errNotParsed
779 for i := 0; i < opts.Intermediates.len(); i++ {
780 c, err := opts.Intermediates.cert(i)
782 return nil, fmt.Errorf("crypto/x509: error fetching intermediate: %w", err)
785 return nil, errNotParsed
789 // Use platform verifiers, where available, if Roots is from SystemCertPool.
790 if runtime.GOOS == "windows" || runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
791 if opts.Roots == nil {
792 return c.systemVerify(&opts)
794 if opts.Roots != nil && opts.Roots.systemPool {
795 platformChains, err := c.systemVerify(&opts)
796 // If the platform verifier succeeded, or there are no additional
797 // roots, return the platform verifier result. Otherwise, continue
798 // with the Go verifier.
799 if err == nil || opts.Roots.len() == 0 {
800 return platformChains, err
805 if opts.Roots == nil {
806 opts.Roots = systemRootsPool()
807 if opts.Roots == nil {
808 return nil, SystemRootsError{systemRootsErr}
812 if len(opts.KeyUsages) == 0 {
813 opts.KeyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
816 err = c.isValid(leafCertificate, nil, &opts)
821 if len(opts.DNSName) > 0 {
822 err = c.VerifyHostname(opts.DNSName)
828 if opts.Roots.contains(c) {
829 return [][]*Certificate{{c}}, nil
831 return c.buildChains([]*Certificate{c}, nil, &opts)
834 func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
835 n := make([]*Certificate, len(chain)+1)
841 // alreadyInChain checks whether a candidate certificate is present in a chain.
842 // Rather than doing a direct byte for byte equivalency check, we check if the
843 // subject, public key, and SAN, if present, are equal. This prevents loops that
844 // are created by mutual cross-signatures, or other cross-signature bridge
846 func alreadyInChain(candidate *Certificate, chain []*Certificate) bool {
847 type pubKeyEqual interface {
848 Equal(crypto.PublicKey) bool
851 var candidateSAN *pkix.Extension
852 for _, ext := range candidate.Extensions {
853 if ext.Id.Equal(oidExtensionSubjectAltName) {
859 for _, cert := range chain {
860 if !bytes.Equal(candidate.RawSubject, cert.RawSubject) {
863 if !candidate.PublicKey.(pubKeyEqual).Equal(cert.PublicKey) {
866 var certSAN *pkix.Extension
867 for _, ext := range cert.Extensions {
868 if ext.Id.Equal(oidExtensionSubjectAltName) {
873 if candidateSAN == nil && certSAN == nil {
875 } else if candidateSAN == nil || certSAN == nil {
878 if bytes.Equal(candidateSAN.Value, certSAN.Value) {
885 // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
886 // that an invocation of buildChains will (transitively) make. Most chains are
887 // less than 15 certificates long, so this leaves space for multiple chains and
888 // for failed checks due to different intermediates having the same Subject.
889 const maxChainSignatureChecks = 100
891 func (c *Certificate) buildChains(currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
894 hintCert *Certificate
897 considerCandidate := func(certType int, candidate *Certificate) {
898 if alreadyInChain(candidate, currentChain) {
902 if sigChecks == nil {
906 if *sigChecks > maxChainSignatureChecks {
907 err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
911 if err := c.CheckSignatureFrom(candidate); err != nil {
919 err = candidate.isValid(certType, currentChain, opts)
925 case rootCertificate:
926 chains = append(chains, appendToFreshChain(currentChain, candidate))
927 case intermediateCertificate:
928 var childChains [][]*Certificate
929 childChains, err = candidate.buildChains(appendToFreshChain(currentChain, candidate), sigChecks, opts)
930 chains = append(chains, childChains...)
934 for _, root := range opts.Roots.findPotentialParents(c) {
935 considerCandidate(rootCertificate, root)
937 for _, intermediate := range opts.Intermediates.findPotentialParents(c) {
938 considerCandidate(intermediateCertificate, intermediate)
944 if len(chains) == 0 && err == nil {
945 err = UnknownAuthorityError{c, hintErr, hintCert}
951 func validHostnamePattern(host string) bool { return validHostname(host, true) }
952 func validHostnameInput(host string) bool { return validHostname(host, false) }
954 // validHostname reports whether host is a valid hostname that can be matched or
955 // matched against according to RFC 6125 2.2, with some leniency to accommodate
957 func validHostname(host string, isPattern bool) bool {
959 host = strings.TrimSuffix(host, ".")
965 for i, part := range strings.Split(host, ".") {
970 if isPattern && i == 0 && part == "*" {
971 // Only allow full left-most wildcards, as those are the only ones
972 // we match, and matching literal '*' characters is probably never
973 // the expected behavior.
976 for j, c := range part {
977 if 'a' <= c && c <= 'z' {
980 if '0' <= c && c <= '9' {
983 if 'A' <= c && c <= 'Z' {
986 if c == '-' && j != 0 {
990 // Not a valid character in hostnames, but commonly
991 // found in deployments outside the WebPKI.
1001 func matchExactly(hostA, hostB string) bool {
1002 if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
1005 return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
1008 func matchHostnames(pattern, host string) bool {
1009 pattern = toLowerCaseASCII(pattern)
1010 host = toLowerCaseASCII(strings.TrimSuffix(host, "."))
1012 if len(pattern) == 0 || len(host) == 0 {
1016 patternParts := strings.Split(pattern, ".")
1017 hostParts := strings.Split(host, ".")
1019 if len(patternParts) != len(hostParts) {
1023 for i, patternPart := range patternParts {
1024 if i == 0 && patternPart == "*" {
1027 if patternPart != hostParts[i] {
1035 // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
1036 // an explicitly ASCII function to avoid any sharp corners resulting from
1037 // performing Unicode operations on DNS labels.
1038 func toLowerCaseASCII(in string) string {
1039 // If the string is already lower-case then there's nothing to do.
1040 isAlreadyLowerCase := true
1041 for _, c := range in {
1042 if c == utf8.RuneError {
1043 // If we get a UTF-8 error then there might be
1044 // upper-case ASCII bytes in the invalid sequence.
1045 isAlreadyLowerCase = false
1048 if 'A' <= c && c <= 'Z' {
1049 isAlreadyLowerCase = false
1054 if isAlreadyLowerCase {
1059 for i, c := range out {
1060 if 'A' <= c && c <= 'Z' {
1067 // VerifyHostname returns nil if c is a valid certificate for the named host.
1068 // Otherwise it returns an error describing the mismatch.
1070 // IP addresses can be optionally enclosed in square brackets and are checked
1071 // against the IPAddresses field. Other names are checked case insensitively
1072 // against the DNSNames field. If the names are valid hostnames, the certificate
1073 // fields can have a wildcard as the left-most label.
1075 // Note that the legacy Common Name field is ignored.
1076 func (c *Certificate) VerifyHostname(h string) error {
1077 // IP addresses may be written in [ ].
1079 if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
1080 candidateIP = h[1 : len(h)-1]
1082 if ip := net.ParseIP(candidateIP); ip != nil {
1083 // We only match IP addresses against IP SANs.
1084 // See RFC 6125, Appendix B.2.
1085 for _, candidate := range c.IPAddresses {
1086 if ip.Equal(candidate) {
1090 return HostnameError{c, candidateIP}
1093 candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
1094 validCandidateName := validHostnameInput(candidateName)
1096 for _, match := range c.DNSNames {
1097 // Ideally, we'd only match valid hostnames according to RFC 6125 like
1098 // browsers (more or less) do, but in practice Go is used in a wider
1099 // array of contexts and can't even assume DNS resolution. Instead,
1100 // always allow perfect matches, and only apply wildcard and trailing
1101 // dot processing to valid hostnames.
1102 if validCandidateName && validHostnamePattern(match) {
1103 if matchHostnames(match, candidateName) {
1107 if matchExactly(match, candidateName) {
1113 return HostnameError{c, h}
1116 func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
1117 usages := make([]ExtKeyUsage, len(keyUsages))
1118 copy(usages, keyUsages)
1120 if len(chain) == 0 {
1124 usagesRemaining := len(usages)
1126 // We walk down the list and cross out any usages that aren't supported
1127 // by each certificate. If we cross out all the usages, then the chain
1131 for i := len(chain) - 1; i >= 0; i-- {
1133 if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
1134 // The certificate doesn't have any extended key usage specified.
1138 for _, usage := range cert.ExtKeyUsage {
1139 if usage == ExtKeyUsageAny {
1140 // The certificate is explicitly good for any usage.
1145 const invalidUsage ExtKeyUsage = -1
1148 for i, requestedUsage := range usages {
1149 if requestedUsage == invalidUsage {
1153 for _, usage := range cert.ExtKeyUsage {
1154 if requestedUsage == usage {
1155 continue NextRequestedUsage
1159 usages[i] = invalidUsage
1161 if usagesRemaining == 0 {