Source file src/crypto/x509/verify.go

     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.
     4  
     5  package x509
     6  
     7  import (
     8  	"bytes"
     9  	"crypto"
    10  	"crypto/x509/pkix"
    11  	"errors"
    12  	"fmt"
    13  	"net"
    14  	"net/url"
    15  	"reflect"
    16  	"runtime"
    17  	"strings"
    18  	"time"
    19  	"unicode/utf8"
    20  )
    21  
    22  type InvalidReason int
    23  
    24  const (
    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.
    30  	Expired
    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
    36  	// violated.
    37  	TooManyIntermediates
    38  	// IncompatibleUsage results when the certificate's key usage indicates
    39  	// that it may only be used for a different purpose.
    40  	IncompatibleUsage
    41  	// NameMismatch results when the subject name of a parent certificate
    42  	// does not match the issuer name in the child.
    43  	NameMismatch
    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.
    49  	UnconstrainedName
    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.
    55  	TooManyConstraints
    56  	// CANotAuthorizedForExtKeyUsage results when an intermediate or root
    57  	// certificate does not permit a requested extended key usage.
    58  	CANotAuthorizedForExtKeyUsage
    59  )
    60  
    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 {
    64  	Cert   *Certificate
    65  	Reason InvalidReason
    66  	Detail string
    67  }
    68  
    69  func (e CertificateInvalidError) Error() string {
    70  	switch e.Reason {
    71  	case NotAuthorizedToSign:
    72  		return "x509: certificate is not authorized to sign other certificates"
    73  	case Expired:
    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"
    83  	case NameMismatch:
    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
    89  	}
    90  	return "x509: unknown error"
    91  }
    92  
    93  // HostnameError results when the set of authorized names doesn't match the
    94  // requested name.
    95  type HostnameError struct {
    96  	Certificate *Certificate
    97  	Host        string
    98  }
    99  
   100  func (h HostnameError) Error() string {
   101  	c := h.Certificate
   102  
   103  	if !c.hasSANExtension() && matchHostnames(c.Subject.CommonName, h.Host) {
   104  		return "x509: certificate relies on legacy Common Name field, use SANs instead"
   105  	}
   106  
   107  	var valid string
   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"
   112  		}
   113  		for _, san := range c.IPAddresses {
   114  			if len(valid) > 0 {
   115  				valid += ", "
   116  			}
   117  			valid += san.String()
   118  		}
   119  	} else {
   120  		valid = strings.Join(c.DNSNames, ", ")
   121  	}
   122  
   123  	if len(valid) == 0 {
   124  		return "x509: certificate is not valid for any names, but wanted to match " + h.Host
   125  	}
   126  	return "x509: certificate is valid for " + valid + ", not " + h.Host
   127  }
   128  
   129  // UnknownAuthorityError results when the certificate issuer is unknown
   130  type UnknownAuthorityError struct {
   131  	Cert *Certificate
   132  	// hintErr contains an error that may be helpful in determining why an
   133  	// authority wasn't found.
   134  	hintErr error
   135  	// hintCert contains a possible authority certificate that was rejected
   136  	// because of the error in hintErr.
   137  	hintCert *Certificate
   138  }
   139  
   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]
   147  			} else {
   148  				certName = "serial:" + e.hintCert.SerialNumber.String()
   149  			}
   150  		}
   151  		s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
   152  	}
   153  	return s
   154  }
   155  
   156  // SystemRootsError results when we fail to load the system root certificates.
   157  type SystemRootsError struct {
   158  	Err error
   159  }
   160  
   161  func (se SystemRootsError) Error() string {
   162  	msg := "x509: failed to load system roots and no roots provided"
   163  	if se.Err != nil {
   164  		return msg + "; " + se.Err.Error()
   165  	}
   166  	return msg
   167  }
   168  
   169  func (se SystemRootsError) Unwrap() error { return se.Err }
   170  
   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")
   174  
   175  // VerifyOptions contains parameters for Certificate.Verify.
   176  type VerifyOptions struct {
   177  	// DNSName, if set, is checked against the leaf certificate with
   178  	// Certificate.VerifyHostname or the platform verifier.
   179  	DNSName string
   180  
   181  	// Intermediates is an optional pool of certificates that are not trust
   182  	// anchors, but can be used to form a chain from the leaf certificate to a
   183  	// root certificate.
   184  	Intermediates *CertPool
   185  	// Roots is the set of trusted root certificates the leaf certificate needs
   186  	// to chain up to. If nil, the system roots or the platform verifier are used.
   187  	Roots *CertPool
   188  
   189  	// CurrentTime is used to check the validity of all certificates in the
   190  	// chain. If zero, the current time is used.
   191  	CurrentTime time.Time
   192  
   193  	// KeyUsages specifies which Extended Key Usage values are acceptable. A
   194  	// chain is accepted if it allows any of the listed values. An empty list
   195  	// means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
   196  	KeyUsages []ExtKeyUsage
   197  
   198  	// MaxConstraintComparisions is the maximum number of comparisons to
   199  	// perform when checking a given certificate's name constraints. If
   200  	// zero, a sensible default is used. This limit prevents pathological
   201  	// certificates from consuming excessive amounts of CPU time when
   202  	// validating. It does not apply to the platform verifier.
   203  	MaxConstraintComparisions int
   204  }
   205  
   206  const (
   207  	leafCertificate = iota
   208  	intermediateCertificate
   209  	rootCertificate
   210  )
   211  
   212  // rfc2821Mailbox represents a “mailbox” (which is an email address to most
   213  // people) by breaking it into the “local” (i.e. before the '@') and “domain”
   214  // parts.
   215  type rfc2821Mailbox struct {
   216  	local, domain string
   217  }
   218  
   219  // parseRFC2821Mailbox parses an email address into local and domain parts,
   220  // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
   221  // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
   222  // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
   223  func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
   224  	if len(in) == 0 {
   225  		return mailbox, false
   226  	}
   227  
   228  	localPartBytes := make([]byte, 0, len(in)/2)
   229  
   230  	if in[0] == '"' {
   231  		// Quoted-string = DQUOTE *qcontent DQUOTE
   232  		// non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
   233  		// qcontent = qtext / quoted-pair
   234  		// qtext = non-whitespace-control /
   235  		//         %d33 / %d35-91 / %d93-126
   236  		// quoted-pair = ("\" text) / obs-qp
   237  		// text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
   238  		//
   239  		// (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
   240  		// Section 4. Since it has been 16 years, we no longer accept that.)
   241  		in = in[1:]
   242  	QuotedString:
   243  		for {
   244  			if len(in) == 0 {
   245  				return mailbox, false
   246  			}
   247  			c := in[0]
   248  			in = in[1:]
   249  
   250  			switch {
   251  			case c == '"':
   252  				break QuotedString
   253  
   254  			case c == '\\':
   255  				// quoted-pair
   256  				if len(in) == 0 {
   257  					return mailbox, false
   258  				}
   259  				if in[0] == 11 ||
   260  					in[0] == 12 ||
   261  					(1 <= in[0] && in[0] <= 9) ||
   262  					(14 <= in[0] && in[0] <= 127) {
   263  					localPartBytes = append(localPartBytes, in[0])
   264  					in = in[1:]
   265  				} else {
   266  					return mailbox, false
   267  				}
   268  
   269  			case c == 11 ||
   270  				c == 12 ||
   271  				// Space (char 32) is not allowed based on the
   272  				// BNF, but RFC 3696 gives an example that
   273  				// assumes that it is. Several “verified”
   274  				// errata continue to argue about this point.
   275  				// We choose to accept it.
   276  				c == 32 ||
   277  				c == 33 ||
   278  				c == 127 ||
   279  				(1 <= c && c <= 8) ||
   280  				(14 <= c && c <= 31) ||
   281  				(35 <= c && c <= 91) ||
   282  				(93 <= c && c <= 126):
   283  				// qtext
   284  				localPartBytes = append(localPartBytes, c)
   285  
   286  			default:
   287  				return mailbox, false
   288  			}
   289  		}
   290  	} else {
   291  		// Atom ("." Atom)*
   292  	NextChar:
   293  		for len(in) > 0 {
   294  			// atext from RFC 2822, Section 3.2.4
   295  			c := in[0]
   296  
   297  			switch {
   298  			case c == '\\':
   299  				// Examples given in RFC 3696 suggest that
   300  				// escaped characters can appear outside of a
   301  				// quoted string. Several “verified” errata
   302  				// continue to argue the point. We choose to
   303  				// accept it.
   304  				in = in[1:]
   305  				if len(in) == 0 {
   306  					return mailbox, false
   307  				}
   308  				fallthrough
   309  
   310  			case ('0' <= c && c <= '9') ||
   311  				('a' <= c && c <= 'z') ||
   312  				('A' <= c && c <= 'Z') ||
   313  				c == '!' || c == '#' || c == '$' || c == '%' ||
   314  				c == '&' || c == '\'' || c == '*' || c == '+' ||
   315  				c == '-' || c == '/' || c == '=' || c == '?' ||
   316  				c == '^' || c == '_' || c == '`' || c == '{' ||
   317  				c == '|' || c == '}' || c == '~' || c == '.':
   318  				localPartBytes = append(localPartBytes, in[0])
   319  				in = in[1:]
   320  
   321  			default:
   322  				break NextChar
   323  			}
   324  		}
   325  
   326  		if len(localPartBytes) == 0 {
   327  			return mailbox, false
   328  		}
   329  
   330  		// From RFC 3696, Section 3:
   331  		// “period (".") may also appear, but may not be used to start
   332  		// or end the local part, nor may two or more consecutive
   333  		// periods appear.”
   334  		twoDots := []byte{'.', '.'}
   335  		if localPartBytes[0] == '.' ||
   336  			localPartBytes[len(localPartBytes)-1] == '.' ||
   337  			bytes.Contains(localPartBytes, twoDots) {
   338  			return mailbox, false
   339  		}
   340  	}
   341  
   342  	if len(in) == 0 || in[0] != '@' {
   343  		return mailbox, false
   344  	}
   345  	in = in[1:]
   346  
   347  	// The RFC species a format for domains, but that's known to be
   348  	// violated in practice so we accept that anything after an '@' is the
   349  	// domain part.
   350  	if _, ok := domainToReverseLabels(in); !ok {
   351  		return mailbox, false
   352  	}
   353  
   354  	mailbox.local = string(localPartBytes)
   355  	mailbox.domain = in
   356  	return mailbox, true
   357  }
   358  
   359  // domainToReverseLabels converts a textual domain name like foo.example.com to
   360  // the list of labels in reverse order, e.g. ["com", "example", "foo"].
   361  func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
   362  	for len(domain) > 0 {
   363  		if i := strings.LastIndexByte(domain, '.'); i == -1 {
   364  			reverseLabels = append(reverseLabels, domain)
   365  			domain = ""
   366  		} else {
   367  			reverseLabels = append(reverseLabels, domain[i+1:])
   368  			domain = domain[:i]
   369  		}
   370  	}
   371  
   372  	if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
   373  		// An empty label at the end indicates an absolute value.
   374  		return nil, false
   375  	}
   376  
   377  	for _, label := range reverseLabels {
   378  		if len(label) == 0 {
   379  			// Empty labels are otherwise invalid.
   380  			return nil, false
   381  		}
   382  
   383  		for _, c := range label {
   384  			if c < 33 || c > 126 {
   385  				// Invalid character.
   386  				return nil, false
   387  			}
   388  		}
   389  	}
   390  
   391  	return reverseLabels, true
   392  }
   393  
   394  func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
   395  	// If the constraint contains an @, then it specifies an exact mailbox
   396  	// name.
   397  	if strings.Contains(constraint, "@") {
   398  		constraintMailbox, ok := parseRFC2821Mailbox(constraint)
   399  		if !ok {
   400  			return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
   401  		}
   402  		return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
   403  	}
   404  
   405  	// Otherwise the constraint is like a DNS constraint of the domain part
   406  	// of the mailbox.
   407  	return matchDomainConstraint(mailbox.domain, constraint)
   408  }
   409  
   410  func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
   411  	// From RFC 5280, Section 4.2.1.10:
   412  	// “a uniformResourceIdentifier that does not include an authority
   413  	// component with a host name specified as a fully qualified domain
   414  	// name (e.g., if the URI either does not include an authority
   415  	// component or includes an authority component in which the host name
   416  	// is specified as an IP address), then the application MUST reject the
   417  	// certificate.”
   418  
   419  	host := uri.Host
   420  	if len(host) == 0 {
   421  		return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
   422  	}
   423  
   424  	if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
   425  		var err error
   426  		host, _, err = net.SplitHostPort(uri.Host)
   427  		if err != nil {
   428  			return false, err
   429  		}
   430  	}
   431  
   432  	if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
   433  		net.ParseIP(host) != nil {
   434  		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
   435  	}
   436  
   437  	return matchDomainConstraint(host, constraint)
   438  }
   439  
   440  func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
   441  	if len(ip) != len(constraint.IP) {
   442  		return false, nil
   443  	}
   444  
   445  	for i := range ip {
   446  		if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
   447  			return false, nil
   448  		}
   449  	}
   450  
   451  	return true, nil
   452  }
   453  
   454  func matchDomainConstraint(domain, constraint string) (bool, error) {
   455  	// The meaning of zero length constraints is not specified, but this
   456  	// code follows NSS and accepts them as matching everything.
   457  	if len(constraint) == 0 {
   458  		return true, nil
   459  	}
   460  
   461  	domainLabels, ok := domainToReverseLabels(domain)
   462  	if !ok {
   463  		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
   464  	}
   465  
   466  	// RFC 5280 says that a leading period in a domain name means that at
   467  	// least one label must be prepended, but only for URI and email
   468  	// constraints, not DNS constraints. The code also supports that
   469  	// behaviour for DNS constraints.
   470  
   471  	mustHaveSubdomains := false
   472  	if constraint[0] == '.' {
   473  		mustHaveSubdomains = true
   474  		constraint = constraint[1:]
   475  	}
   476  
   477  	constraintLabels, ok := domainToReverseLabels(constraint)
   478  	if !ok {
   479  		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
   480  	}
   481  
   482  	if len(domainLabels) < len(constraintLabels) ||
   483  		(mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
   484  		return false, nil
   485  	}
   486  
   487  	for i, constraintLabel := range constraintLabels {
   488  		if !strings.EqualFold(constraintLabel, domainLabels[i]) {
   489  			return false, nil
   490  		}
   491  	}
   492  
   493  	return true, nil
   494  }
   495  
   496  // checkNameConstraints checks that c permits a child certificate to claim the
   497  // given name, of type nameType. The argument parsedName contains the parsed
   498  // form of name, suitable for passing to the match function. The total number
   499  // of comparisons is tracked in the given count and should not exceed the given
   500  // limit.
   501  func (c *Certificate) checkNameConstraints(count *int,
   502  	maxConstraintComparisons int,
   503  	nameType string,
   504  	name string,
   505  	parsedName any,
   506  	match func(parsedName, constraint any) (match bool, err error),
   507  	permitted, excluded any) error {
   508  
   509  	excludedValue := reflect.ValueOf(excluded)
   510  
   511  	*count += excludedValue.Len()
   512  	if *count > maxConstraintComparisons {
   513  		return CertificateInvalidError{c, TooManyConstraints, ""}
   514  	}
   515  
   516  	for i := 0; i < excludedValue.Len(); i++ {
   517  		constraint := excludedValue.Index(i).Interface()
   518  		match, err := match(parsedName, constraint)
   519  		if err != nil {
   520  			return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
   521  		}
   522  
   523  		if match {
   524  			return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
   525  		}
   526  	}
   527  
   528  	permittedValue := reflect.ValueOf(permitted)
   529  
   530  	*count += permittedValue.Len()
   531  	if *count > maxConstraintComparisons {
   532  		return CertificateInvalidError{c, TooManyConstraints, ""}
   533  	}
   534  
   535  	ok := true
   536  	for i := 0; i < permittedValue.Len(); i++ {
   537  		constraint := permittedValue.Index(i).Interface()
   538  
   539  		var err error
   540  		if ok, err = match(parsedName, constraint); err != nil {
   541  			return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
   542  		}
   543  
   544  		if ok {
   545  			break
   546  		}
   547  	}
   548  
   549  	if !ok {
   550  		return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
   551  	}
   552  
   553  	return nil
   554  }
   555  
   556  // isValid performs validity checks on c given that it is a candidate to append
   557  // to the chain in currentChain.
   558  func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
   559  	if len(c.UnhandledCriticalExtensions) > 0 {
   560  		return UnhandledCriticalExtension{}
   561  	}
   562  
   563  	if len(currentChain) > 0 {
   564  		child := currentChain[len(currentChain)-1]
   565  		if !bytes.Equal(child.RawIssuer, c.RawSubject) {
   566  			return CertificateInvalidError{c, NameMismatch, ""}
   567  		}
   568  	}
   569  
   570  	now := opts.CurrentTime
   571  	if now.IsZero() {
   572  		now = time.Now()
   573  	}
   574  	if now.Before(c.NotBefore) {
   575  		return CertificateInvalidError{
   576  			Cert:   c,
   577  			Reason: Expired,
   578  			Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
   579  		}
   580  	} else if now.After(c.NotAfter) {
   581  		return CertificateInvalidError{
   582  			Cert:   c,
   583  			Reason: Expired,
   584  			Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
   585  		}
   586  	}
   587  
   588  	maxConstraintComparisons := opts.MaxConstraintComparisions
   589  	if maxConstraintComparisons == 0 {
   590  		maxConstraintComparisons = 250000
   591  	}
   592  	comparisonCount := 0
   593  
   594  	var leaf *Certificate
   595  	if certType == intermediateCertificate || certType == rootCertificate {
   596  		if len(currentChain) == 0 {
   597  			return errors.New("x509: internal error: empty chain when appending CA cert")
   598  		}
   599  		leaf = currentChain[0]
   600  	}
   601  
   602  	if (certType == intermediateCertificate || certType == rootCertificate) &&
   603  		c.hasNameConstraints() {
   604  		toCheck := []*Certificate{}
   605  		if leaf.hasSANExtension() {
   606  			toCheck = append(toCheck, leaf)
   607  		}
   608  		if c.hasSANExtension() {
   609  			toCheck = append(toCheck, c)
   610  		}
   611  		for _, sanCert := range toCheck {
   612  			err := forEachSAN(sanCert.getSANExtension(), func(tag int, data []byte) error {
   613  				switch tag {
   614  				case nameTypeEmail:
   615  					name := string(data)
   616  					mailbox, ok := parseRFC2821Mailbox(name)
   617  					if !ok {
   618  						return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
   619  					}
   620  
   621  					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
   622  						func(parsedName, constraint any) (bool, error) {
   623  							return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
   624  						}, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
   625  						return err
   626  					}
   627  
   628  				case nameTypeDNS:
   629  					name := string(data)
   630  					if _, ok := domainToReverseLabels(name); !ok {
   631  						return fmt.Errorf("x509: cannot parse dnsName %q", name)
   632  					}
   633  
   634  					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
   635  						func(parsedName, constraint any) (bool, error) {
   636  							return matchDomainConstraint(parsedName.(string), constraint.(string))
   637  						}, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
   638  						return err
   639  					}
   640  
   641  				case nameTypeURI:
   642  					name := string(data)
   643  					uri, err := url.Parse(name)
   644  					if err != nil {
   645  						return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
   646  					}
   647  
   648  					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
   649  						func(parsedName, constraint any) (bool, error) {
   650  							return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
   651  						}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
   652  						return err
   653  					}
   654  
   655  				case nameTypeIP:
   656  					ip := net.IP(data)
   657  					if l := len(ip); l != net.IPv4len && l != net.IPv6len {
   658  						return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
   659  					}
   660  
   661  					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
   662  						func(parsedName, constraint any) (bool, error) {
   663  							return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
   664  						}, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
   665  						return err
   666  					}
   667  
   668  				default:
   669  					// Unknown SAN types are ignored.
   670  				}
   671  
   672  				return nil
   673  			})
   674  
   675  			if err != nil {
   676  				return err
   677  			}
   678  		}
   679  	}
   680  
   681  	// KeyUsage status flags are ignored. From Engineering Security, Peter
   682  	// Gutmann: A European government CA marked its signing certificates as
   683  	// being valid for encryption only, but no-one noticed. Another
   684  	// European CA marked its signature keys as not being valid for
   685  	// signatures. A different CA marked its own trusted root certificate
   686  	// as being invalid for certificate signing. Another national CA
   687  	// distributed a certificate to be used to encrypt data for the
   688  	// country’s tax authority that was marked as only being usable for
   689  	// digital signatures but not for encryption. Yet another CA reversed
   690  	// the order of the bit flags in the keyUsage due to confusion over
   691  	// encoding endianness, essentially setting a random keyUsage in
   692  	// certificates that it issued. Another CA created a self-invalidating
   693  	// certificate by adding a certificate policy statement stipulating
   694  	// that the certificate had to be used strictly as specified in the
   695  	// keyUsage, and a keyUsage containing a flag indicating that the RSA
   696  	// encryption key could only be used for Diffie-Hellman key agreement.
   697  
   698  	if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
   699  		return CertificateInvalidError{c, NotAuthorizedToSign, ""}
   700  	}
   701  
   702  	if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
   703  		numIntermediates := len(currentChain) - 1
   704  		if numIntermediates > c.MaxPathLen {
   705  			return CertificateInvalidError{c, TooManyIntermediates, ""}
   706  		}
   707  	}
   708  
   709  	if !boringAllowCert(c) {
   710  		// IncompatibleUsage is not quite right here,
   711  		// but it's also the "no chains found" error
   712  		// and is close enough.
   713  		return CertificateInvalidError{c, IncompatibleUsage, ""}
   714  	}
   715  
   716  	return nil
   717  }
   718  
   719  // Verify attempts to verify c by building one or more chains from c to a
   720  // certificate in opts.Roots, using certificates in opts.Intermediates if
   721  // needed. If successful, it returns one or more chains where the first
   722  // element of the chain is c and the last element is from opts.Roots.
   723  //
   724  // If opts.Roots is nil, the platform verifier might be used, and
   725  // verification details might differ from what is described below. If system
   726  // roots are unavailable the returned error will be of type SystemRootsError.
   727  //
   728  // Name constraints in the intermediates will be applied to all names claimed
   729  // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
   730  // example.com if an intermediate doesn't permit it, even if example.com is not
   731  // the name being validated. Note that DirectoryName constraints are not
   732  // supported.
   733  //
   734  // Name constraint validation follows the rules from RFC 5280, with the
   735  // addition that DNS name constraints may use the leading period format
   736  // defined for emails and URIs. When a constraint has a leading period
   737  // it indicates that at least one additional label must be prepended to
   738  // the constrained name to be considered valid.
   739  //
   740  // Extended Key Usage values are enforced nested down a chain, so an intermediate
   741  // or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
   742  // list. (While this is not specified, it is common practice in order to limit
   743  // the types of certificates a CA can issue.)
   744  //
   745  // Certificates that use SHA1WithRSA and ECDSAWithSHA1 signatures are not supported,
   746  // and will not be used to build chains.
   747  //
   748  // WARNING: this function doesn't do any revocation checking.
   749  func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
   750  	// Platform-specific verification needs the ASN.1 contents so
   751  	// this makes the behavior consistent across platforms.
   752  	if len(c.Raw) == 0 {
   753  		return nil, errNotParsed
   754  	}
   755  	for i := 0; i < opts.Intermediates.len(); i++ {
   756  		c, err := opts.Intermediates.cert(i)
   757  		if err != nil {
   758  			return nil, fmt.Errorf("crypto/x509: error fetching intermediate: %w", err)
   759  		}
   760  		if len(c.Raw) == 0 {
   761  			return nil, errNotParsed
   762  		}
   763  	}
   764  
   765  	// Use platform verifiers, where available, if Roots is from SystemCertPool.
   766  	if runtime.GOOS == "windows" || runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
   767  		if opts.Roots == nil {
   768  			return c.systemVerify(&opts)
   769  		}
   770  		if opts.Roots != nil && opts.Roots.systemPool {
   771  			platformChains, err := c.systemVerify(&opts)
   772  			// If the platform verifier succeeded, or there are no additional
   773  			// roots, return the platform verifier result. Otherwise, continue
   774  			// with the Go verifier.
   775  			if err == nil || opts.Roots.len() == 0 {
   776  				return platformChains, err
   777  			}
   778  		}
   779  	}
   780  
   781  	if opts.Roots == nil {
   782  		opts.Roots = systemRootsPool()
   783  		if opts.Roots == nil {
   784  			return nil, SystemRootsError{systemRootsErr}
   785  		}
   786  	}
   787  
   788  	err = c.isValid(leafCertificate, nil, &opts)
   789  	if err != nil {
   790  		return
   791  	}
   792  
   793  	if len(opts.DNSName) > 0 {
   794  		err = c.VerifyHostname(opts.DNSName)
   795  		if err != nil {
   796  			return
   797  		}
   798  	}
   799  
   800  	var candidateChains [][]*Certificate
   801  	if opts.Roots.contains(c) {
   802  		candidateChains = [][]*Certificate{{c}}
   803  	} else {
   804  		candidateChains, err = c.buildChains([]*Certificate{c}, nil, &opts)
   805  		if err != nil {
   806  			return nil, err
   807  		}
   808  	}
   809  
   810  	if len(opts.KeyUsages) == 0 {
   811  		opts.KeyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
   812  	}
   813  
   814  	for _, eku := range opts.KeyUsages {
   815  		if eku == ExtKeyUsageAny {
   816  			// If any key usage is acceptable, no need to check the chain for
   817  			// key usages.
   818  			return candidateChains, nil
   819  		}
   820  	}
   821  
   822  	chains = make([][]*Certificate, 0, len(candidateChains))
   823  	for _, candidate := range candidateChains {
   824  		if checkChainForKeyUsage(candidate, opts.KeyUsages) {
   825  			chains = append(chains, candidate)
   826  		}
   827  	}
   828  
   829  	if len(chains) == 0 {
   830  		return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
   831  	}
   832  
   833  	return chains, nil
   834  }
   835  
   836  func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
   837  	n := make([]*Certificate, len(chain)+1)
   838  	copy(n, chain)
   839  	n[len(chain)] = cert
   840  	return n
   841  }
   842  
   843  // alreadyInChain checks whether a candidate certificate is present in a chain.
   844  // Rather than doing a direct byte for byte equivalency check, we check if the
   845  // subject, public key, and SAN, if present, are equal. This prevents loops that
   846  // are created by mutual cross-signatures, or other cross-signature bridge
   847  // oddities.
   848  func alreadyInChain(candidate *Certificate, chain []*Certificate) bool {
   849  	type pubKeyEqual interface {
   850  		Equal(crypto.PublicKey) bool
   851  	}
   852  
   853  	var candidateSAN *pkix.Extension
   854  	for _, ext := range candidate.Extensions {
   855  		if ext.Id.Equal(oidExtensionSubjectAltName) {
   856  			candidateSAN = &ext
   857  			break
   858  		}
   859  	}
   860  
   861  	for _, cert := range chain {
   862  		if !bytes.Equal(candidate.RawSubject, cert.RawSubject) {
   863  			continue
   864  		}
   865  		if !candidate.PublicKey.(pubKeyEqual).Equal(cert.PublicKey) {
   866  			continue
   867  		}
   868  		var certSAN *pkix.Extension
   869  		for _, ext := range cert.Extensions {
   870  			if ext.Id.Equal(oidExtensionSubjectAltName) {
   871  				certSAN = &ext
   872  				break
   873  			}
   874  		}
   875  		if candidateSAN == nil && certSAN == nil {
   876  			return true
   877  		} else if candidateSAN == nil || certSAN == nil {
   878  			return false
   879  		}
   880  		if bytes.Equal(candidateSAN.Value, certSAN.Value) {
   881  			return true
   882  		}
   883  	}
   884  	return false
   885  }
   886  
   887  // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
   888  // that an invocation of buildChains will (transitively) make. Most chains are
   889  // less than 15 certificates long, so this leaves space for multiple chains and
   890  // for failed checks due to different intermediates having the same Subject.
   891  const maxChainSignatureChecks = 100
   892  
   893  func (c *Certificate) buildChains(currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
   894  	var (
   895  		hintErr  error
   896  		hintCert *Certificate
   897  	)
   898  
   899  	considerCandidate := func(certType int, candidate *Certificate) {
   900  		if alreadyInChain(candidate, currentChain) {
   901  			return
   902  		}
   903  
   904  		if sigChecks == nil {
   905  			sigChecks = new(int)
   906  		}
   907  		*sigChecks++
   908  		if *sigChecks > maxChainSignatureChecks {
   909  			err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
   910  			return
   911  		}
   912  
   913  		if err := c.CheckSignatureFrom(candidate); err != nil {
   914  			if hintErr == nil {
   915  				hintErr = err
   916  				hintCert = candidate
   917  			}
   918  			return
   919  		}
   920  
   921  		err = candidate.isValid(certType, currentChain, opts)
   922  		if err != nil {
   923  			return
   924  		}
   925  
   926  		switch certType {
   927  		case rootCertificate:
   928  			chains = append(chains, appendToFreshChain(currentChain, candidate))
   929  		case intermediateCertificate:
   930  			var childChains [][]*Certificate
   931  			childChains, err = candidate.buildChains(appendToFreshChain(currentChain, candidate), sigChecks, opts)
   932  			chains = append(chains, childChains...)
   933  		}
   934  	}
   935  
   936  	for _, root := range opts.Roots.findPotentialParents(c) {
   937  		considerCandidate(rootCertificate, root)
   938  	}
   939  	for _, intermediate := range opts.Intermediates.findPotentialParents(c) {
   940  		considerCandidate(intermediateCertificate, intermediate)
   941  	}
   942  
   943  	if len(chains) > 0 {
   944  		err = nil
   945  	}
   946  	if len(chains) == 0 && err == nil {
   947  		err = UnknownAuthorityError{c, hintErr, hintCert}
   948  	}
   949  
   950  	return
   951  }
   952  
   953  func validHostnamePattern(host string) bool { return validHostname(host, true) }
   954  func validHostnameInput(host string) bool   { return validHostname(host, false) }
   955  
   956  // validHostname reports whether host is a valid hostname that can be matched or
   957  // matched against according to RFC 6125 2.2, with some leniency to accommodate
   958  // legacy values.
   959  func validHostname(host string, isPattern bool) bool {
   960  	if !isPattern {
   961  		host = strings.TrimSuffix(host, ".")
   962  	}
   963  	if len(host) == 0 {
   964  		return false
   965  	}
   966  
   967  	for i, part := range strings.Split(host, ".") {
   968  		if part == "" {
   969  			// Empty label.
   970  			return false
   971  		}
   972  		if isPattern && i == 0 && part == "*" {
   973  			// Only allow full left-most wildcards, as those are the only ones
   974  			// we match, and matching literal '*' characters is probably never
   975  			// the expected behavior.
   976  			continue
   977  		}
   978  		for j, c := range part {
   979  			if 'a' <= c && c <= 'z' {
   980  				continue
   981  			}
   982  			if '0' <= c && c <= '9' {
   983  				continue
   984  			}
   985  			if 'A' <= c && c <= 'Z' {
   986  				continue
   987  			}
   988  			if c == '-' && j != 0 {
   989  				continue
   990  			}
   991  			if c == '_' {
   992  				// Not a valid character in hostnames, but commonly
   993  				// found in deployments outside the WebPKI.
   994  				continue
   995  			}
   996  			return false
   997  		}
   998  	}
   999  
  1000  	return true
  1001  }
  1002  
  1003  func matchExactly(hostA, hostB string) bool {
  1004  	if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
  1005  		return false
  1006  	}
  1007  	return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
  1008  }
  1009  
  1010  func matchHostnames(pattern, host string) bool {
  1011  	pattern = toLowerCaseASCII(pattern)
  1012  	host = toLowerCaseASCII(strings.TrimSuffix(host, "."))
  1013  
  1014  	if len(pattern) == 0 || len(host) == 0 {
  1015  		return false
  1016  	}
  1017  
  1018  	patternParts := strings.Split(pattern, ".")
  1019  	hostParts := strings.Split(host, ".")
  1020  
  1021  	if len(patternParts) != len(hostParts) {
  1022  		return false
  1023  	}
  1024  
  1025  	for i, patternPart := range patternParts {
  1026  		if i == 0 && patternPart == "*" {
  1027  			continue
  1028  		}
  1029  		if patternPart != hostParts[i] {
  1030  			return false
  1031  		}
  1032  	}
  1033  
  1034  	return true
  1035  }
  1036  
  1037  // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
  1038  // an explicitly ASCII function to avoid any sharp corners resulting from
  1039  // performing Unicode operations on DNS labels.
  1040  func toLowerCaseASCII(in string) string {
  1041  	// If the string is already lower-case then there's nothing to do.
  1042  	isAlreadyLowerCase := true
  1043  	for _, c := range in {
  1044  		if c == utf8.RuneError {
  1045  			// If we get a UTF-8 error then there might be
  1046  			// upper-case ASCII bytes in the invalid sequence.
  1047  			isAlreadyLowerCase = false
  1048  			break
  1049  		}
  1050  		if 'A' <= c && c <= 'Z' {
  1051  			isAlreadyLowerCase = false
  1052  			break
  1053  		}
  1054  	}
  1055  
  1056  	if isAlreadyLowerCase {
  1057  		return in
  1058  	}
  1059  
  1060  	out := []byte(in)
  1061  	for i, c := range out {
  1062  		if 'A' <= c && c <= 'Z' {
  1063  			out[i] += 'a' - 'A'
  1064  		}
  1065  	}
  1066  	return string(out)
  1067  }
  1068  
  1069  // VerifyHostname returns nil if c is a valid certificate for the named host.
  1070  // Otherwise it returns an error describing the mismatch.
  1071  //
  1072  // IP addresses can be optionally enclosed in square brackets and are checked
  1073  // against the IPAddresses field. Other names are checked case insensitively
  1074  // against the DNSNames field. If the names are valid hostnames, the certificate
  1075  // fields can have a wildcard as the left-most label.
  1076  //
  1077  // Note that the legacy Common Name field is ignored.
  1078  func (c *Certificate) VerifyHostname(h string) error {
  1079  	// IP addresses may be written in [ ].
  1080  	candidateIP := h
  1081  	if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
  1082  		candidateIP = h[1 : len(h)-1]
  1083  	}
  1084  	if ip := net.ParseIP(candidateIP); ip != nil {
  1085  		// We only match IP addresses against IP SANs.
  1086  		// See RFC 6125, Appendix B.2.
  1087  		for _, candidate := range c.IPAddresses {
  1088  			if ip.Equal(candidate) {
  1089  				return nil
  1090  			}
  1091  		}
  1092  		return HostnameError{c, candidateIP}
  1093  	}
  1094  
  1095  	candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
  1096  	validCandidateName := validHostnameInput(candidateName)
  1097  
  1098  	for _, match := range c.DNSNames {
  1099  		// Ideally, we'd only match valid hostnames according to RFC 6125 like
  1100  		// browsers (more or less) do, but in practice Go is used in a wider
  1101  		// array of contexts and can't even assume DNS resolution. Instead,
  1102  		// always allow perfect matches, and only apply wildcard and trailing
  1103  		// dot processing to valid hostnames.
  1104  		if validCandidateName && validHostnamePattern(match) {
  1105  			if matchHostnames(match, candidateName) {
  1106  				return nil
  1107  			}
  1108  		} else {
  1109  			if matchExactly(match, candidateName) {
  1110  				return nil
  1111  			}
  1112  		}
  1113  	}
  1114  
  1115  	return HostnameError{c, h}
  1116  }
  1117  
  1118  func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
  1119  	usages := make([]ExtKeyUsage, len(keyUsages))
  1120  	copy(usages, keyUsages)
  1121  
  1122  	if len(chain) == 0 {
  1123  		return false
  1124  	}
  1125  
  1126  	usagesRemaining := len(usages)
  1127  
  1128  	// We walk down the list and cross out any usages that aren't supported
  1129  	// by each certificate. If we cross out all the usages, then the chain
  1130  	// is unacceptable.
  1131  
  1132  NextCert:
  1133  	for i := len(chain) - 1; i >= 0; i-- {
  1134  		cert := chain[i]
  1135  		if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
  1136  			// The certificate doesn't have any extended key usage specified.
  1137  			continue
  1138  		}
  1139  
  1140  		for _, usage := range cert.ExtKeyUsage {
  1141  			if usage == ExtKeyUsageAny {
  1142  				// The certificate is explicitly good for any usage.
  1143  				continue NextCert
  1144  			}
  1145  		}
  1146  
  1147  		const invalidUsage ExtKeyUsage = -1
  1148  
  1149  	NextRequestedUsage:
  1150  		for i, requestedUsage := range usages {
  1151  			if requestedUsage == invalidUsage {
  1152  				continue
  1153  			}
  1154  
  1155  			for _, usage := range cert.ExtKeyUsage {
  1156  				if requestedUsage == usage {
  1157  					continue NextRequestedUsage
  1158  				}
  1159  			}
  1160  
  1161  			usages[i] = invalidUsage
  1162  			usagesRemaining--
  1163  			if usagesRemaining == 0 {
  1164  				return false
  1165  			}
  1166  		}
  1167  	}
  1168  
  1169  	return true
  1170  }
  1171  

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