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/sha256"
    11  	"crypto/x509/pkix"
    12  	"encoding/hex"
    13  	"errors"
    14  	"fmt"
    15  	"iter"
    16  	"maps"
    17  	"net"
    18  	"net/netip"
    19  	"runtime"
    20  	"slices"
    21  	"strings"
    22  	"time"
    23  	"unicode/utf8"
    24  )
    25  
    26  type InvalidReason int
    27  
    28  const (
    29  	// NotAuthorizedToSign results when a certificate is signed by another
    30  	// which isn't marked as a CA certificate.
    31  	NotAuthorizedToSign InvalidReason = iota
    32  	// Expired results when a certificate has expired, based on the time
    33  	// given in the VerifyOptions.
    34  	Expired
    35  	// CANotAuthorizedForThisName results when an intermediate or root
    36  	// certificate has a name constraint which doesn't permit a DNS or
    37  	// other name (including IP address) in the leaf certificate.
    38  	CANotAuthorizedForThisName
    39  	// TooManyIntermediates results when a path length constraint is
    40  	// violated.
    41  	TooManyIntermediates
    42  	// IncompatibleUsage results when the certificate's key usage indicates
    43  	// that it may only be used for a different purpose.
    44  	IncompatibleUsage
    45  	// NameMismatch results when the subject name of a parent certificate
    46  	// does not match the issuer name in the child.
    47  	NameMismatch
    48  	// NameConstraintsWithoutSANs is a legacy error and is no longer returned.
    49  	NameConstraintsWithoutSANs
    50  	// UnconstrainedName results when a CA certificate contains permitted
    51  	// name constraints, but leaf certificate contains a name of an
    52  	// unsupported or unconstrained type.
    53  	UnconstrainedName
    54  	// TooManyConstraints results when the number of comparison operations
    55  	// needed to check a certificate exceeds the limit set by
    56  	// VerifyOptions.MaxConstraintComparisions. This limit exists to
    57  	// prevent pathological certificates can consuming excessive amounts of
    58  	// CPU time to verify.
    59  	TooManyConstraints
    60  	// CANotAuthorizedForExtKeyUsage results when an intermediate or root
    61  	// certificate does not permit a requested extended key usage.
    62  	CANotAuthorizedForExtKeyUsage
    63  	// NoValidChains results when there are no valid chains to return.
    64  	NoValidChains
    65  )
    66  
    67  // CertificateInvalidError results when an odd error occurs. Users of this
    68  // library probably want to handle all these errors uniformly.
    69  type CertificateInvalidError struct {
    70  	Cert   *Certificate
    71  	Reason InvalidReason
    72  	Detail string
    73  }
    74  
    75  func (e CertificateInvalidError) Error() string {
    76  	switch e.Reason {
    77  	case NotAuthorizedToSign:
    78  		return "x509: certificate is not authorized to sign other certificates"
    79  	case Expired:
    80  		return "x509: certificate has expired or is not yet valid: " + e.Detail
    81  	case CANotAuthorizedForThisName:
    82  		return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail
    83  	case CANotAuthorizedForExtKeyUsage:
    84  		return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
    85  	case TooManyIntermediates:
    86  		return "x509: too many intermediates for path length constraint"
    87  	case IncompatibleUsage:
    88  		return "x509: certificate specifies an incompatible key usage"
    89  	case NameMismatch:
    90  		return "x509: issuer name does not match subject from issuing certificate"
    91  	case NameConstraintsWithoutSANs:
    92  		return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
    93  	case UnconstrainedName:
    94  		return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
    95  	case NoValidChains:
    96  		s := "x509: no valid chains built"
    97  		if e.Detail != "" {
    98  			s = fmt.Sprintf("%s: %s", s, e.Detail)
    99  		}
   100  		return s
   101  	}
   102  	return "x509: unknown error"
   103  }
   104  
   105  // HostnameError results when the set of authorized names doesn't match the
   106  // requested name.
   107  type HostnameError struct {
   108  	Certificate *Certificate
   109  	Host        string
   110  }
   111  
   112  func (h HostnameError) Error() string {
   113  	c := h.Certificate
   114  	maxNamesIncluded := 100
   115  
   116  	if !c.hasSANExtension() && matchHostnames(c.Subject.CommonName, splitHostname(h.Host)) {
   117  		return "x509: certificate relies on legacy Common Name field, use SANs instead"
   118  	}
   119  
   120  	var valid strings.Builder
   121  	if ip := net.ParseIP(h.Host); ip != nil {
   122  		// Trying to validate an IP
   123  		if len(c.IPAddresses) == 0 {
   124  			return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
   125  		}
   126  		if len(c.IPAddresses) >= maxNamesIncluded {
   127  			return fmt.Sprintf("x509: certificate is valid for %d IP SANs, but none matched %s", len(c.IPAddresses), h.Host)
   128  		}
   129  		for _, san := range c.IPAddresses {
   130  			if valid.Len() > 0 {
   131  				valid.WriteString(", ")
   132  			}
   133  			valid.WriteString(san.String())
   134  		}
   135  	} else {
   136  		if len(c.DNSNames) >= maxNamesIncluded {
   137  			return fmt.Sprintf("x509: certificate is valid for %d names, but none matched %s", len(c.DNSNames), h.Host)
   138  		}
   139  		valid.WriteString(strings.Join(c.DNSNames, ", "))
   140  	}
   141  
   142  	if valid.Len() == 0 {
   143  		return "x509: certificate is not valid for any names, but wanted to match " + h.Host
   144  	}
   145  	return "x509: certificate is valid for " + valid.String() + ", not " + h.Host
   146  }
   147  
   148  // UnknownAuthorityError results when the certificate issuer is unknown
   149  type UnknownAuthorityError struct {
   150  	Cert *Certificate
   151  	// hintErr contains an error that may be helpful in determining why an
   152  	// authority wasn't found.
   153  	hintErr error
   154  	// hintCert contains a possible authority certificate that was rejected
   155  	// because of the error in hintErr.
   156  	hintCert *Certificate
   157  }
   158  
   159  func (e UnknownAuthorityError) Error() string {
   160  	s := "x509: certificate signed by unknown authority"
   161  	if e.hintErr != nil {
   162  		certName := e.hintCert.Subject.CommonName
   163  		if len(certName) == 0 {
   164  			if len(e.hintCert.Subject.Organization) > 0 {
   165  				certName = e.hintCert.Subject.Organization[0]
   166  			} else {
   167  				certName = "serial:" + e.hintCert.SerialNumber.String()
   168  			}
   169  		}
   170  		s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
   171  	}
   172  	return s
   173  }
   174  
   175  // SystemRootsError results when we fail to load the system root certificates.
   176  type SystemRootsError struct {
   177  	Err error
   178  }
   179  
   180  func (se SystemRootsError) Error() string {
   181  	msg := "x509: failed to load system roots and no roots provided"
   182  	if se.Err != nil {
   183  		return msg + "; " + se.Err.Error()
   184  	}
   185  	return msg
   186  }
   187  
   188  func (se SystemRootsError) Unwrap() error { return se.Err }
   189  
   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")
   193  
   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 or the platform verifier.
   198  	DNSName string
   199  
   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
   202  	// root certificate.
   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.
   206  	Roots *CertPool
   207  
   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
   211  
   212  	// KeyUsages specifies which Extended Key Usage values are acceptable. A
   213  	// chain is accepted if it allows any of the listed values. An empty list
   214  	// means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
   215  	KeyUsages []ExtKeyUsage
   216  
   217  	// MaxConstraintComparisions is the maximum number of comparisons to
   218  	// perform when checking a given certificate's name constraints. If
   219  	// zero, a sensible default is used. This limit prevents pathological
   220  	// certificates from consuming excessive amounts of CPU time when
   221  	// validating. It does not apply to the platform verifier.
   222  	MaxConstraintComparisions int
   223  
   224  	// CertificatePolicies specifies which certificate policy OIDs are
   225  	// acceptable during policy validation. An empty CertificatePolices
   226  	// field implies any valid policy is acceptable.
   227  	CertificatePolicies []OID
   228  
   229  	// The following policy fields are unexported, because we do not expect
   230  	// users to actually need to use them, but are useful for testing the
   231  	// policy validation code.
   232  
   233  	// inhibitPolicyMapping indicates if policy mapping should be allowed
   234  	// during path validation.
   235  	inhibitPolicyMapping bool
   236  
   237  	// requireExplicitPolicy indidicates if explicit policies must be present
   238  	// for each certificate being validated.
   239  	requireExplicitPolicy bool
   240  
   241  	// inhibitAnyPolicy indicates if the anyPolicy policy should be
   242  	// processed if present in a certificate being validated.
   243  	inhibitAnyPolicy bool
   244  }
   245  
   246  const (
   247  	leafCertificate = iota
   248  	intermediateCertificate
   249  	rootCertificate
   250  )
   251  
   252  // rfc2821Mailbox represents a “mailbox” (which is an email address to most
   253  // people) by breaking it into the “local” (i.e. before the '@') and “domain”
   254  // parts.
   255  type rfc2821Mailbox struct {
   256  	local, domain string
   257  }
   258  
   259  func (s rfc2821Mailbox) String() string {
   260  	return fmt.Sprintf("%s@%s", s.local, s.domain)
   261  }
   262  
   263  // parseRFC2821Mailbox parses an email address into local and domain parts,
   264  // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
   265  // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
   266  // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
   267  func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
   268  	if len(in) == 0 {
   269  		return mailbox, false
   270  	}
   271  
   272  	localPartBytes := make([]byte, 0, len(in)/2)
   273  
   274  	if in[0] == '"' {
   275  		// Quoted-string = DQUOTE *qcontent DQUOTE
   276  		// non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
   277  		// qcontent = qtext / quoted-pair
   278  		// qtext = non-whitespace-control /
   279  		//         %d33 / %d35-91 / %d93-126
   280  		// quoted-pair = ("\" text) / obs-qp
   281  		// text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
   282  		//
   283  		// (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
   284  		// Section 4. Since it has been 16 years, we no longer accept that.)
   285  		in = in[1:]
   286  	QuotedString:
   287  		for {
   288  			if len(in) == 0 {
   289  				return mailbox, false
   290  			}
   291  			c := in[0]
   292  			in = in[1:]
   293  
   294  			switch {
   295  			case c == '"':
   296  				break QuotedString
   297  
   298  			case c == '\\':
   299  				// quoted-pair
   300  				if len(in) == 0 {
   301  					return mailbox, false
   302  				}
   303  				if in[0] == 11 ||
   304  					in[0] == 12 ||
   305  					(1 <= in[0] && in[0] <= 9) ||
   306  					(14 <= in[0] && in[0] <= 127) {
   307  					localPartBytes = append(localPartBytes, in[0])
   308  					in = in[1:]
   309  				} else {
   310  					return mailbox, false
   311  				}
   312  
   313  			case c == 11 ||
   314  				c == 12 ||
   315  				// Space (char 32) is not allowed based on the
   316  				// BNF, but RFC 3696 gives an example that
   317  				// assumes that it is. Several “verified”
   318  				// errata continue to argue about this point.
   319  				// We choose to accept it.
   320  				c == 32 ||
   321  				c == 33 ||
   322  				c == 127 ||
   323  				(1 <= c && c <= 8) ||
   324  				(14 <= c && c <= 31) ||
   325  				(35 <= c && c <= 91) ||
   326  				(93 <= c && c <= 126):
   327  				// qtext
   328  				localPartBytes = append(localPartBytes, c)
   329  
   330  			default:
   331  				return mailbox, false
   332  			}
   333  		}
   334  	} else {
   335  		// Atom ("." Atom)*
   336  	NextChar:
   337  		for len(in) > 0 {
   338  			// atext from RFC 2822, Section 3.2.4
   339  			c := in[0]
   340  
   341  			switch {
   342  			case c == '\\':
   343  				// Examples given in RFC 3696 suggest that
   344  				// escaped characters can appear outside of a
   345  				// quoted string. Several “verified” errata
   346  				// continue to argue the point. We choose to
   347  				// accept it.
   348  				in = in[1:]
   349  				if len(in) == 0 {
   350  					return mailbox, false
   351  				}
   352  				fallthrough
   353  
   354  			case ('0' <= c && c <= '9') ||
   355  				('a' <= c && c <= 'z') ||
   356  				('A' <= c && c <= 'Z') ||
   357  				c == '!' || c == '#' || c == '$' || c == '%' ||
   358  				c == '&' || c == '\'' || c == '*' || c == '+' ||
   359  				c == '-' || c == '/' || c == '=' || c == '?' ||
   360  				c == '^' || c == '_' || c == '`' || c == '{' ||
   361  				c == '|' || c == '}' || c == '~' || c == '.':
   362  				localPartBytes = append(localPartBytes, in[0])
   363  				in = in[1:]
   364  
   365  			default:
   366  				break NextChar
   367  			}
   368  		}
   369  
   370  		if len(localPartBytes) == 0 {
   371  			return mailbox, false
   372  		}
   373  
   374  		// From RFC 3696, Section 3:
   375  		// “period (".") may also appear, but may not be used to start
   376  		// or end the local part, nor may two or more consecutive
   377  		// periods appear.”
   378  		twoDots := []byte{'.', '.'}
   379  		if localPartBytes[0] == '.' ||
   380  			localPartBytes[len(localPartBytes)-1] == '.' ||
   381  			bytes.Contains(localPartBytes, twoDots) {
   382  			return mailbox, false
   383  		}
   384  	}
   385  
   386  	if len(in) == 0 || in[0] != '@' {
   387  		return mailbox, false
   388  	}
   389  	in = in[1:]
   390  
   391  	// The RFC species a format for domains, but that's known to be
   392  	// violated in practice so we accept that anything after an '@' is the
   393  	// domain part.
   394  	if !domainNameValid(in, false) {
   395  		return mailbox, false
   396  	}
   397  
   398  	// Reject domain names containing @.
   399  	if strings.ContainsRune(in, '@') {
   400  		return mailbox, false
   401  	}
   402  
   403  	mailbox.local = string(localPartBytes)
   404  	mailbox.domain = in
   405  	return mailbox, true
   406  }
   407  
   408  // domainToReverseLabels converts a textual domain name like foo.example.com to
   409  // the list of labels in reverse order, e.g. ["com", "example", "foo"].
   410  func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
   411  	reverseLabels = make([]string, 0, strings.Count(domain, ".")+1)
   412  	for len(domain) > 0 {
   413  		if i := strings.LastIndexByte(domain, '.'); i == -1 {
   414  			reverseLabels = append(reverseLabels, domain)
   415  			domain = ""
   416  		} else {
   417  			reverseLabels = append(reverseLabels, domain[i+1:])
   418  			domain = domain[:i]
   419  			if i == 0 { // domain == ""
   420  				// domain is prefixed with an empty label, append an empty
   421  				// string to reverseLabels to indicate this.
   422  				reverseLabels = append(reverseLabels, "")
   423  			}
   424  		}
   425  	}
   426  
   427  	if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
   428  		// An empty label at the end indicates an absolute value.
   429  		return nil, false
   430  	}
   431  
   432  	for _, label := range reverseLabels {
   433  		if len(label) == 0 {
   434  			// Empty labels are otherwise invalid.
   435  			return nil, false
   436  		}
   437  
   438  		for _, c := range label {
   439  			if c < 33 || c > 126 {
   440  				// Invalid character.
   441  				return nil, false
   442  			}
   443  		}
   444  	}
   445  
   446  	return reverseLabels, true
   447  }
   448  
   449  // isValid performs validity checks on c given that it is a candidate to append
   450  // to the chain in currentChain.
   451  func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
   452  	if len(c.UnhandledCriticalExtensions) > 0 {
   453  		return UnhandledCriticalExtension{}
   454  	}
   455  
   456  	if len(currentChain) > 0 {
   457  		child := currentChain[len(currentChain)-1]
   458  		if !bytes.Equal(child.RawIssuer, c.RawSubject) {
   459  			return CertificateInvalidError{c, NameMismatch, ""}
   460  		}
   461  	}
   462  
   463  	now := opts.CurrentTime
   464  	if now.IsZero() {
   465  		now = time.Now()
   466  	}
   467  	if now.Before(c.NotBefore) {
   468  		return CertificateInvalidError{
   469  			Cert:   c,
   470  			Reason: Expired,
   471  			Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
   472  		}
   473  	} else if now.After(c.NotAfter) {
   474  		return CertificateInvalidError{
   475  			Cert:   c,
   476  			Reason: Expired,
   477  			Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
   478  		}
   479  	}
   480  
   481  	if certType == intermediateCertificate || certType == rootCertificate {
   482  		if len(currentChain) == 0 {
   483  			return errors.New("x509: internal error: empty chain when appending CA cert")
   484  		}
   485  	}
   486  
   487  	// KeyUsage status flags are ignored. From Engineering Security, Peter
   488  	// Gutmann: A European government CA marked its signing certificates as
   489  	// being valid for encryption only, but no-one noticed. Another
   490  	// European CA marked its signature keys as not being valid for
   491  	// signatures. A different CA marked its own trusted root certificate
   492  	// as being invalid for certificate signing. Another national CA
   493  	// distributed a certificate to be used to encrypt data for the
   494  	// country’s tax authority that was marked as only being usable for
   495  	// digital signatures but not for encryption. Yet another CA reversed
   496  	// the order of the bit flags in the keyUsage due to confusion over
   497  	// encoding endianness, essentially setting a random keyUsage in
   498  	// certificates that it issued. Another CA created a self-invalidating
   499  	// certificate by adding a certificate policy statement stipulating
   500  	// that the certificate had to be used strictly as specified in the
   501  	// keyUsage, and a keyUsage containing a flag indicating that the RSA
   502  	// encryption key could only be used for Diffie-Hellman key agreement.
   503  
   504  	if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
   505  		return CertificateInvalidError{c, NotAuthorizedToSign, ""}
   506  	}
   507  
   508  	if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
   509  		numIntermediates := len(currentChain) - 1
   510  		if numIntermediates > c.MaxPathLen {
   511  			return CertificateInvalidError{c, TooManyIntermediates, ""}
   512  		}
   513  	}
   514  
   515  	return nil
   516  }
   517  
   518  // Verify attempts to verify c by building one or more chains from c to a
   519  // certificate in opts.Roots, using certificates in opts.Intermediates if
   520  // needed. If successful, it returns one or more chains where the first
   521  // element of the chain is c and the last element is from opts.Roots.
   522  //
   523  // If opts.Roots is nil, the platform verifier might be used, and
   524  // verification details might differ from what is described below. If system
   525  // roots are unavailable the returned error will be of type SystemRootsError.
   526  //
   527  // Name constraints in the intermediates will be applied to all names claimed
   528  // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
   529  // example.com if an intermediate doesn't permit it, even if example.com is not
   530  // the name being validated. Note that DirectoryName constraints are not
   531  // supported.
   532  //
   533  // Name constraint validation follows the rules from RFC 5280, with the
   534  // addition that DNS name constraints may use the leading period format
   535  // defined for emails and URIs. When a constraint has a leading period
   536  // it indicates that at least one additional label must be prepended to
   537  // the constrained name to be considered valid.
   538  //
   539  // Extended Key Usage values are enforced nested down a chain, so an intermediate
   540  // or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
   541  // list. (While this is not specified, it is common practice in order to limit
   542  // the types of certificates a CA can issue.)
   543  //
   544  // Certificates that use SHA1WithRSA and ECDSAWithSHA1 signatures are not supported,
   545  // and will not be used to build chains.
   546  //
   547  // Certificates other than c in the returned chains should not be modified.
   548  //
   549  // WARNING: this function doesn't do any revocation checking.
   550  func (c *Certificate) Verify(opts VerifyOptions) ([][]*Certificate, error) {
   551  	// Platform-specific verification needs the ASN.1 contents so
   552  	// this makes the behavior consistent across platforms.
   553  	if len(c.Raw) == 0 {
   554  		return nil, errNotParsed
   555  	}
   556  	for i := 0; i < opts.Intermediates.len(); i++ {
   557  		c, _, err := opts.Intermediates.cert(i)
   558  		if err != nil {
   559  			return nil, fmt.Errorf("crypto/x509: error fetching intermediate: %w", err)
   560  		}
   561  		if len(c.Raw) == 0 {
   562  			return nil, errNotParsed
   563  		}
   564  	}
   565  
   566  	// Use platform verifiers, where available, if Roots is from SystemCertPool.
   567  	if runtime.GOOS == "windows" || runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
   568  		// Don't use the system verifier if the system pool was replaced with a non-system pool,
   569  		// i.e. if SetFallbackRoots was called with x509usefallbackroots=1.
   570  		systemPool := systemRootsPool()
   571  		if opts.Roots == nil && (systemPool == nil || systemPool.systemPool) {
   572  			return c.systemVerify(&opts)
   573  		}
   574  		if opts.Roots != nil && opts.Roots.systemPool {
   575  			platformChains, err := c.systemVerify(&opts)
   576  			// If the platform verifier succeeded, or there are no additional
   577  			// roots, return the platform verifier result. Otherwise, continue
   578  			// with the Go verifier.
   579  			if err == nil || opts.Roots.len() == 0 {
   580  				return platformChains, err
   581  			}
   582  		}
   583  	}
   584  
   585  	if opts.Roots == nil {
   586  		opts.Roots = systemRootsPool()
   587  		if opts.Roots == nil {
   588  			return nil, SystemRootsError{systemRootsErr}
   589  		}
   590  	}
   591  
   592  	err := c.isValid(leafCertificate, nil, &opts)
   593  	if err != nil {
   594  		return nil, err
   595  	}
   596  
   597  	if len(opts.DNSName) > 0 {
   598  		err = c.VerifyHostname(opts.DNSName)
   599  		if err != nil {
   600  			return nil, err
   601  		}
   602  	}
   603  
   604  	var candidateChains [][]*Certificate
   605  	if opts.Roots.contains(c) {
   606  		candidateChains = [][]*Certificate{{c}}
   607  	} else {
   608  		candidateChains, err = c.buildChains([]*Certificate{c}, nil, &opts)
   609  		if err != nil {
   610  			return nil, err
   611  		}
   612  	}
   613  
   614  	anyKeyUsage := false
   615  	for _, eku := range opts.KeyUsages {
   616  		if eku == ExtKeyUsageAny {
   617  			// The presence of anyExtendedKeyUsage overrides any other key usage.
   618  			anyKeyUsage = true
   619  			break
   620  		}
   621  	}
   622  
   623  	if len(opts.KeyUsages) == 0 {
   624  		opts.KeyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
   625  	}
   626  
   627  	var invalidPoliciesChains int
   628  	var incompatibleKeyUsageChains int
   629  	var constraintsHintErr error
   630  	candidateChains = slices.DeleteFunc(candidateChains, func(chain []*Certificate) bool {
   631  		if !policiesValid(chain, opts) {
   632  			invalidPoliciesChains++
   633  			return true
   634  		}
   635  		// If any key usage is acceptable, no need to check the chain for
   636  		// key usages.
   637  		if !anyKeyUsage && !checkChainForKeyUsage(chain, opts.KeyUsages) {
   638  			incompatibleKeyUsageChains++
   639  			return true
   640  		}
   641  		if err := checkChainConstraints(chain); err != nil {
   642  			if constraintsHintErr == nil {
   643  				constraintsHintErr = CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
   644  			}
   645  			return true
   646  		}
   647  		if containsDistrustedSPKIHash(chain) {
   648  			return true
   649  		}
   650  		return false
   651  	})
   652  
   653  	if len(candidateChains) == 0 {
   654  		if constraintsHintErr != nil {
   655  			return nil, constraintsHintErr // Preserve previous constraint behavior
   656  		}
   657  		var details []string
   658  		if incompatibleKeyUsageChains > 0 {
   659  			if invalidPoliciesChains == 0 {
   660  				return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
   661  			}
   662  			details = append(details, fmt.Sprintf("%d candidate chains with incompatible key usage", incompatibleKeyUsageChains))
   663  		}
   664  		if invalidPoliciesChains > 0 {
   665  			details = append(details, fmt.Sprintf("%d candidate chains with invalid policies", invalidPoliciesChains))
   666  		}
   667  		err = CertificateInvalidError{c, NoValidChains, strings.Join(details, ", ")}
   668  		return nil, err
   669  	}
   670  
   671  	return candidateChains, nil
   672  }
   673  
   674  func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
   675  	n := make([]*Certificate, len(chain)+1)
   676  	copy(n, chain)
   677  	n[len(chain)] = cert
   678  	return n
   679  }
   680  
   681  // alreadyInChain checks whether a candidate certificate is present in a chain.
   682  // Rather than doing a direct byte for byte equivalency check, we check if the
   683  // subject, public key, and SAN, if present, are equal. This prevents loops that
   684  // are created by mutual cross-signatures, or other cross-signature bridge
   685  // oddities.
   686  func alreadyInChain(candidate *Certificate, chain []*Certificate) bool {
   687  	type pubKeyEqual interface {
   688  		Equal(crypto.PublicKey) bool
   689  	}
   690  
   691  	var candidateSAN *pkix.Extension
   692  	for _, ext := range candidate.Extensions {
   693  		if ext.Id.Equal(oidExtensionSubjectAltName) {
   694  			candidateSAN = &ext
   695  			break
   696  		}
   697  	}
   698  
   699  	for _, cert := range chain {
   700  		if !bytes.Equal(candidate.RawSubject, cert.RawSubject) {
   701  			continue
   702  		}
   703  		// We enforce the canonical encoding of SPKI (by only allowing the
   704  		// correct AI parameter encodings in parseCertificate), so it's safe to
   705  		// directly compare the raw bytes.
   706  		if !bytes.Equal(candidate.RawSubjectPublicKeyInfo, cert.RawSubjectPublicKeyInfo) {
   707  			continue
   708  		}
   709  		var certSAN *pkix.Extension
   710  		for _, ext := range cert.Extensions {
   711  			if ext.Id.Equal(oidExtensionSubjectAltName) {
   712  				certSAN = &ext
   713  				break
   714  			}
   715  		}
   716  		if candidateSAN == nil && certSAN == nil {
   717  			return true
   718  		} else if candidateSAN == nil || certSAN == nil {
   719  			return false
   720  		}
   721  		if bytes.Equal(candidateSAN.Value, certSAN.Value) {
   722  			return true
   723  		}
   724  	}
   725  	return false
   726  }
   727  
   728  // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
   729  // that an invocation of buildChains will (transitively) make. Most chains are
   730  // less than 15 certificates long, so this leaves space for multiple chains and
   731  // for failed checks due to different intermediates having the same Subject.
   732  const maxChainSignatureChecks = 100
   733  
   734  var errSignatureLimit = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
   735  
   736  func (c *Certificate) buildChains(currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
   737  	var (
   738  		hintErr  error
   739  		hintCert *Certificate
   740  	)
   741  
   742  	considerCandidate := func(certType int, candidate potentialParent) {
   743  		if sigChecks == nil {
   744  			sigChecks = new(int)
   745  		}
   746  		*sigChecks++
   747  		if *sigChecks > maxChainSignatureChecks {
   748  			err = errSignatureLimit
   749  			return
   750  		}
   751  
   752  		if candidate.cert.PublicKey == nil || alreadyInChain(candidate.cert, currentChain) {
   753  			return
   754  		}
   755  
   756  		if err := c.CheckSignatureFrom(candidate.cert); err != nil {
   757  			if hintErr == nil {
   758  				hintErr = err
   759  				hintCert = candidate.cert
   760  			}
   761  			return
   762  		}
   763  
   764  		err = candidate.cert.isValid(certType, currentChain, opts)
   765  		if err != nil {
   766  			if hintErr == nil {
   767  				hintErr = err
   768  				hintCert = candidate.cert
   769  			}
   770  			return
   771  		}
   772  
   773  		if candidate.constraint != nil {
   774  			if err := candidate.constraint(currentChain); err != nil {
   775  				if hintErr == nil {
   776  					hintErr = err
   777  					hintCert = candidate.cert
   778  				}
   779  				return
   780  			}
   781  		}
   782  
   783  		switch certType {
   784  		case rootCertificate:
   785  			chains = append(chains, appendToFreshChain(currentChain, candidate.cert))
   786  		case intermediateCertificate:
   787  			var childChains [][]*Certificate
   788  			childChains, err = candidate.cert.buildChains(appendToFreshChain(currentChain, candidate.cert), sigChecks, opts)
   789  			chains = append(chains, childChains...)
   790  		}
   791  	}
   792  
   793  candidateLoop:
   794  	for _, parents := range []struct {
   795  		certType   int
   796  		potentials []potentialParent
   797  	}{
   798  		{rootCertificate, opts.Roots.findPotentialParents(c)},
   799  		{intermediateCertificate, opts.Intermediates.findPotentialParents(c)},
   800  	} {
   801  		for _, parent := range parents.potentials {
   802  			considerCandidate(parents.certType, parent)
   803  			if err == errSignatureLimit {
   804  				break candidateLoop
   805  			}
   806  		}
   807  	}
   808  
   809  	if len(chains) > 0 {
   810  		err = nil
   811  	}
   812  	if len(chains) == 0 && err == nil {
   813  		err = UnknownAuthorityError{c, hintErr, hintCert}
   814  	}
   815  
   816  	return
   817  }
   818  
   819  func validHostnamePattern(host string) bool { return validHostname(host, true) }
   820  func validHostnameInput(host string) bool   { return validHostname(host, false) }
   821  
   822  // validHostname reports whether host is a valid hostname that can be matched or
   823  // matched against according to RFC 6125 2.2, with some leniency to accommodate
   824  // legacy values.
   825  func validHostname(host string, isPattern bool) bool {
   826  	if !isPattern {
   827  		host = strings.TrimSuffix(host, ".")
   828  	}
   829  	if len(host) == 0 {
   830  		return false
   831  	}
   832  	if host == "*" {
   833  		// Bare wildcards are not allowed, they are not valid DNS names,
   834  		// nor are they allowed per RFC 6125.
   835  		return false
   836  	}
   837  
   838  	for i, part := range strings.Split(host, ".") {
   839  		if part == "" {
   840  			// Empty label.
   841  			return false
   842  		}
   843  		if isPattern && i == 0 && part == "*" {
   844  			// Only allow full left-most wildcards, as those are the only ones
   845  			// we match, and matching literal '*' characters is probably never
   846  			// the expected behavior.
   847  			continue
   848  		}
   849  		for j, c := range part {
   850  			if 'a' <= c && c <= 'z' {
   851  				continue
   852  			}
   853  			if '0' <= c && c <= '9' {
   854  				continue
   855  			}
   856  			if 'A' <= c && c <= 'Z' {
   857  				continue
   858  			}
   859  			if c == '-' && j != 0 {
   860  				continue
   861  			}
   862  			if c == '_' {
   863  				// Not a valid character in hostnames, but commonly
   864  				// found in deployments outside the WebPKI.
   865  				continue
   866  			}
   867  			return false
   868  		}
   869  	}
   870  
   871  	return true
   872  }
   873  
   874  func matchExactly(hostA, hostB string) bool {
   875  	if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
   876  		return false
   877  	}
   878  	return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
   879  }
   880  
   881  func matchHostnames(pattern string, hostParts []string) bool {
   882  	pattern = toLowerCaseASCII(pattern)
   883  
   884  	if len(pattern) == 0 || len(hostParts) == 0 {
   885  		return false
   886  	}
   887  
   888  	patternParts := strings.Split(pattern, ".")
   889  
   890  	if len(patternParts) != len(hostParts) {
   891  		return false
   892  	}
   893  
   894  	for i, patternPart := range patternParts {
   895  		if i == 0 && patternPart == "*" {
   896  			continue
   897  		}
   898  		if patternPart != hostParts[i] {
   899  			return false
   900  		}
   901  	}
   902  
   903  	return true
   904  }
   905  
   906  // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
   907  // an explicitly ASCII function to avoid any sharp corners resulting from
   908  // performing Unicode operations on DNS labels.
   909  func toLowerCaseASCII(in string) string {
   910  	// If the string is already lower-case then there's nothing to do.
   911  	isAlreadyLowerCase := true
   912  	for _, c := range in {
   913  		if c == utf8.RuneError {
   914  			// If we get a UTF-8 error then there might be
   915  			// upper-case ASCII bytes in the invalid sequence.
   916  			isAlreadyLowerCase = false
   917  			break
   918  		}
   919  		if 'A' <= c && c <= 'Z' {
   920  			isAlreadyLowerCase = false
   921  			break
   922  		}
   923  	}
   924  
   925  	if isAlreadyLowerCase {
   926  		return in
   927  	}
   928  
   929  	out := []byte(in)
   930  	for i, c := range out {
   931  		if 'A' <= c && c <= 'Z' {
   932  			out[i] += 'a' - 'A'
   933  		}
   934  	}
   935  	return string(out)
   936  }
   937  
   938  // VerifyHostname returns nil if c is a valid certificate for the named host.
   939  // Otherwise it returns an error describing the mismatch.
   940  //
   941  // IP addresses can be optionally enclosed in square brackets and are checked
   942  // against the IPAddresses field. Other names are checked case insensitively
   943  // against the DNSNames field. If the names are valid hostnames, the certificate
   944  // fields can have a wildcard as the complete left-most label (e.g. *.example.com).
   945  //
   946  // Note that the legacy Common Name field is ignored.
   947  func (c *Certificate) VerifyHostname(h string) error {
   948  	// IP addresses may be written in [ ].
   949  	candidateIP := h
   950  	if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
   951  		candidateIP = h[1 : len(h)-1]
   952  	}
   953  	// We use netip.ParseAddr() to allow IPv6 scoped addresses.
   954  	if addr, err := netip.ParseAddr(candidateIP); err == nil {
   955  		// We only match IP addresses against IP SANs.
   956  		// See RFC 6125, Appendix B.2.
   957  		ip := net.IP(addr.AsSlice())
   958  		for _, candidate := range c.IPAddresses {
   959  			if ip.Equal(candidate) {
   960  				return nil
   961  			}
   962  		}
   963  		return HostnameError{c, ip.String()}
   964  	}
   965  
   966  	candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
   967  	validCandidateName := validHostnameInput(candidateName)
   968  	hostParts := splitHostname(candidateName)
   969  
   970  	for _, match := range c.DNSNames {
   971  		// Ideally, we'd only match valid hostnames according to RFC 6125 like
   972  		// browsers (more or less) do, but in practice Go is used in a wider
   973  		// array of contexts and can't even assume DNS resolution. Instead,
   974  		// always allow perfect matches, and only apply wildcard and trailing
   975  		// dot processing to valid hostnames.
   976  		if validCandidateName && validHostnamePattern(match) {
   977  			if matchHostnames(match, hostParts) {
   978  				return nil
   979  			}
   980  		} else {
   981  			if matchExactly(match, candidateName) {
   982  				return nil
   983  			}
   984  		}
   985  	}
   986  
   987  	return HostnameError{c, h}
   988  }
   989  
   990  func splitHostname(host string) []string {
   991  	return strings.Split(toLowerCaseASCII(strings.TrimSuffix(host, ".")), ".")
   992  }
   993  
   994  func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
   995  	usages := make([]ExtKeyUsage, len(keyUsages))
   996  	copy(usages, keyUsages)
   997  
   998  	if len(chain) == 0 {
   999  		return false
  1000  	}
  1001  
  1002  	usagesRemaining := len(usages)
  1003  
  1004  	// We walk down the list and cross out any usages that aren't supported
  1005  	// by each certificate. If we cross out all the usages, then the chain
  1006  	// is unacceptable.
  1007  
  1008  NextCert:
  1009  	for i := len(chain) - 1; i >= 0; i-- {
  1010  		cert := chain[i]
  1011  		if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
  1012  			// The certificate doesn't have any extended key usage specified.
  1013  			continue
  1014  		}
  1015  
  1016  		for _, usage := range cert.ExtKeyUsage {
  1017  			if usage == ExtKeyUsageAny {
  1018  				// The certificate is explicitly good for any usage.
  1019  				continue NextCert
  1020  			}
  1021  		}
  1022  
  1023  		const invalidUsage = -1
  1024  
  1025  	NextRequestedUsage:
  1026  		for i, requestedUsage := range usages {
  1027  			if requestedUsage == invalidUsage {
  1028  				continue
  1029  			}
  1030  
  1031  			for _, usage := range cert.ExtKeyUsage {
  1032  				if requestedUsage == usage {
  1033  					continue NextRequestedUsage
  1034  				}
  1035  			}
  1036  
  1037  			usages[i] = invalidUsage
  1038  			usagesRemaining--
  1039  			if usagesRemaining == 0 {
  1040  				return false
  1041  			}
  1042  		}
  1043  	}
  1044  
  1045  	return true
  1046  }
  1047  
  1048  func mustNewOIDFromInts(ints []uint64) OID {
  1049  	oid, err := OIDFromInts(ints)
  1050  	if err != nil {
  1051  		panic(fmt.Sprintf("OIDFromInts(%v) unexpected error: %v", ints, err))
  1052  	}
  1053  	return oid
  1054  }
  1055  
  1056  type policyGraphNode struct {
  1057  	validPolicy       OID
  1058  	expectedPolicySet []OID
  1059  	// we do not implement qualifiers, so we don't track qualifier_set
  1060  
  1061  	parents  map[*policyGraphNode]bool
  1062  	children map[*policyGraphNode]bool
  1063  }
  1064  
  1065  func newPolicyGraphNode(valid OID, parents []*policyGraphNode) *policyGraphNode {
  1066  	n := &policyGraphNode{
  1067  		validPolicy:       valid,
  1068  		expectedPolicySet: []OID{valid},
  1069  		children:          map[*policyGraphNode]bool{},
  1070  		parents:           map[*policyGraphNode]bool{},
  1071  	}
  1072  	for _, p := range parents {
  1073  		p.children[n] = true
  1074  		n.parents[p] = true
  1075  	}
  1076  	return n
  1077  }
  1078  
  1079  type policyGraph struct {
  1080  	strata []map[string]*policyGraphNode
  1081  	// map of OID -> nodes at strata[depth-1] with OID in their expectedPolicySet
  1082  	parentIndex map[string][]*policyGraphNode
  1083  	depth       int
  1084  }
  1085  
  1086  var anyPolicyOID = mustNewOIDFromInts([]uint64{2, 5, 29, 32, 0})
  1087  
  1088  func newPolicyGraph() *policyGraph {
  1089  	root := policyGraphNode{
  1090  		validPolicy:       anyPolicyOID,
  1091  		expectedPolicySet: []OID{anyPolicyOID},
  1092  		children:          map[*policyGraphNode]bool{},
  1093  		parents:           map[*policyGraphNode]bool{},
  1094  	}
  1095  	return &policyGraph{
  1096  		depth:  0,
  1097  		strata: []map[string]*policyGraphNode{{string(anyPolicyOID.der): &root}},
  1098  	}
  1099  }
  1100  
  1101  func (pg *policyGraph) insert(n *policyGraphNode) {
  1102  	pg.strata[pg.depth][string(n.validPolicy.der)] = n
  1103  }
  1104  
  1105  func (pg *policyGraph) parentsWithExpected(expected OID) []*policyGraphNode {
  1106  	if pg.depth == 0 {
  1107  		return nil
  1108  	}
  1109  	return pg.parentIndex[string(expected.der)]
  1110  }
  1111  
  1112  func (pg *policyGraph) parentWithAnyPolicy() *policyGraphNode {
  1113  	if pg.depth == 0 {
  1114  		return nil
  1115  	}
  1116  	return pg.strata[pg.depth-1][string(anyPolicyOID.der)]
  1117  }
  1118  
  1119  func (pg *policyGraph) parents() iter.Seq[*policyGraphNode] {
  1120  	if pg.depth == 0 {
  1121  		return nil
  1122  	}
  1123  	return maps.Values(pg.strata[pg.depth-1])
  1124  }
  1125  
  1126  func (pg *policyGraph) leaves() map[string]*policyGraphNode {
  1127  	return pg.strata[pg.depth]
  1128  }
  1129  
  1130  func (pg *policyGraph) leafWithPolicy(policy OID) *policyGraphNode {
  1131  	return pg.strata[pg.depth][string(policy.der)]
  1132  }
  1133  
  1134  func (pg *policyGraph) deleteLeaf(policy OID) {
  1135  	n := pg.strata[pg.depth][string(policy.der)]
  1136  	if n == nil {
  1137  		return
  1138  	}
  1139  	for p := range n.parents {
  1140  		delete(p.children, n)
  1141  	}
  1142  	for c := range n.children {
  1143  		delete(c.parents, n)
  1144  	}
  1145  	delete(pg.strata[pg.depth], string(policy.der))
  1146  }
  1147  
  1148  func (pg *policyGraph) validPolicyNodes() []*policyGraphNode {
  1149  	var validNodes []*policyGraphNode
  1150  	for i := pg.depth; i >= 0; i-- {
  1151  		for _, n := range pg.strata[i] {
  1152  			if n.validPolicy.Equal(anyPolicyOID) {
  1153  				continue
  1154  			}
  1155  
  1156  			if len(n.parents) == 1 {
  1157  				for p := range n.parents {
  1158  					if p.validPolicy.Equal(anyPolicyOID) {
  1159  						validNodes = append(validNodes, n)
  1160  					}
  1161  				}
  1162  			}
  1163  		}
  1164  	}
  1165  	return validNodes
  1166  }
  1167  
  1168  func (pg *policyGraph) prune() {
  1169  	for i := pg.depth - 1; i > 0; i-- {
  1170  		for _, n := range pg.strata[i] {
  1171  			if len(n.children) == 0 {
  1172  				for p := range n.parents {
  1173  					delete(p.children, n)
  1174  				}
  1175  				delete(pg.strata[i], string(n.validPolicy.der))
  1176  			}
  1177  		}
  1178  	}
  1179  }
  1180  
  1181  func (pg *policyGraph) incrDepth() {
  1182  	pg.parentIndex = map[string][]*policyGraphNode{}
  1183  	for _, n := range pg.strata[pg.depth] {
  1184  		for _, e := range n.expectedPolicySet {
  1185  			pg.parentIndex[string(e.der)] = append(pg.parentIndex[string(e.der)], n)
  1186  		}
  1187  	}
  1188  
  1189  	pg.depth++
  1190  	pg.strata = append(pg.strata, map[string]*policyGraphNode{})
  1191  }
  1192  
  1193  func policiesValid(chain []*Certificate, opts VerifyOptions) bool {
  1194  	// The following code implements the policy verification algorithm as
  1195  	// specified in RFC 5280 and updated by RFC 9618. In particular the
  1196  	// following sections are replaced by RFC 9618:
  1197  	//	* 6.1.2 (a)
  1198  	//	* 6.1.3 (d)
  1199  	//	* 6.1.3 (e)
  1200  	//	* 6.1.3 (f)
  1201  	//	* 6.1.4 (b)
  1202  	//	* 6.1.5 (g)
  1203  
  1204  	if len(chain) == 1 {
  1205  		return true
  1206  	}
  1207  
  1208  	// n is the length of the chain minus the trust anchor
  1209  	n := len(chain) - 1
  1210  
  1211  	pg := newPolicyGraph()
  1212  	var inhibitAnyPolicy, explicitPolicy, policyMapping int
  1213  	if !opts.inhibitAnyPolicy {
  1214  		inhibitAnyPolicy = n + 1
  1215  	}
  1216  	if !opts.requireExplicitPolicy {
  1217  		explicitPolicy = n + 1
  1218  	}
  1219  	if !opts.inhibitPolicyMapping {
  1220  		policyMapping = n + 1
  1221  	}
  1222  
  1223  	initialUserPolicySet := map[string]bool{}
  1224  	for _, p := range opts.CertificatePolicies {
  1225  		initialUserPolicySet[string(p.der)] = true
  1226  	}
  1227  	// If the user does not pass any policies, we consider
  1228  	// that equivalent to passing anyPolicyOID.
  1229  	if len(initialUserPolicySet) == 0 {
  1230  		initialUserPolicySet[string(anyPolicyOID.der)] = true
  1231  	}
  1232  
  1233  	for i := n - 1; i >= 0; i-- {
  1234  		cert := chain[i]
  1235  
  1236  		isSelfSigned := bytes.Equal(cert.RawIssuer, cert.RawSubject)
  1237  
  1238  		// 6.1.3 (e) -- as updated by RFC 9618
  1239  		if len(cert.Policies) == 0 {
  1240  			pg = nil
  1241  		}
  1242  
  1243  		// 6.1.3 (f) -- as updated by RFC 9618
  1244  		if explicitPolicy == 0 && pg == nil {
  1245  			return false
  1246  		}
  1247  
  1248  		if pg != nil {
  1249  			pg.incrDepth()
  1250  
  1251  			policies := map[string]bool{}
  1252  
  1253  			// 6.1.3 (d) (1) -- as updated by RFC 9618
  1254  			for _, policy := range cert.Policies {
  1255  				policies[string(policy.der)] = true
  1256  
  1257  				if policy.Equal(anyPolicyOID) {
  1258  					continue
  1259  				}
  1260  
  1261  				// 6.1.3 (d) (1) (i) -- as updated by RFC 9618
  1262  				parents := pg.parentsWithExpected(policy)
  1263  				if len(parents) == 0 {
  1264  					// 6.1.3 (d) (1) (ii) -- as updated by RFC 9618
  1265  					if anyParent := pg.parentWithAnyPolicy(); anyParent != nil {
  1266  						parents = []*policyGraphNode{anyParent}
  1267  					}
  1268  				}
  1269  				if len(parents) > 0 {
  1270  					pg.insert(newPolicyGraphNode(policy, parents))
  1271  				}
  1272  			}
  1273  
  1274  			// 6.1.3 (d) (2) -- as updated by RFC 9618
  1275  			// NOTE: in the check "n-i < n" our i is different from the i in the specification.
  1276  			// In the specification chains go from the trust anchor to the leaf, whereas our
  1277  			// chains go from the leaf to the trust anchor, so our i's our inverted. Our
  1278  			// check here matches the check "i < n" in the specification.
  1279  			if policies[string(anyPolicyOID.der)] && (inhibitAnyPolicy > 0 || (n-i < n && isSelfSigned)) {
  1280  				missing := map[string][]*policyGraphNode{}
  1281  				leaves := pg.leaves()
  1282  				for p := range pg.parents() {
  1283  					for _, expected := range p.expectedPolicySet {
  1284  						if leaves[string(expected.der)] == nil {
  1285  							missing[string(expected.der)] = append(missing[string(expected.der)], p)
  1286  						}
  1287  					}
  1288  				}
  1289  
  1290  				for oidStr, parents := range missing {
  1291  					pg.insert(newPolicyGraphNode(OID{der: []byte(oidStr)}, parents))
  1292  				}
  1293  			}
  1294  
  1295  			// 6.1.3 (d) (3) -- as updated by RFC 9618
  1296  			pg.prune()
  1297  
  1298  			if i != 0 {
  1299  				// 6.1.4 (b) -- as updated by RFC 9618
  1300  				if len(cert.PolicyMappings) > 0 {
  1301  					// collect map of issuer -> []subject
  1302  					mappings := map[string][]OID{}
  1303  
  1304  					for _, mapping := range cert.PolicyMappings {
  1305  						if policyMapping > 0 {
  1306  							if mapping.IssuerDomainPolicy.Equal(anyPolicyOID) || mapping.SubjectDomainPolicy.Equal(anyPolicyOID) {
  1307  								// Invalid mapping
  1308  								return false
  1309  							}
  1310  							mappings[string(mapping.IssuerDomainPolicy.der)] = append(mappings[string(mapping.IssuerDomainPolicy.der)], mapping.SubjectDomainPolicy)
  1311  						} else {
  1312  							// 6.1.4 (b) (3) (i) -- as updated by RFC 9618
  1313  							pg.deleteLeaf(mapping.IssuerDomainPolicy)
  1314  						}
  1315  					}
  1316  
  1317  					// 6.1.4 (b) (3) (ii) -- as updated by RFC 9618
  1318  					pg.prune()
  1319  
  1320  					for issuerStr, subjectPolicies := range mappings {
  1321  						// 6.1.4 (b) (1) -- as updated by RFC 9618
  1322  						if matching := pg.leafWithPolicy(OID{der: []byte(issuerStr)}); matching != nil {
  1323  							matching.expectedPolicySet = subjectPolicies
  1324  						} else if matching := pg.leafWithPolicy(anyPolicyOID); matching != nil {
  1325  							// 6.1.4 (b) (2) -- as updated by RFC 9618
  1326  							n := newPolicyGraphNode(OID{der: []byte(issuerStr)}, []*policyGraphNode{matching})
  1327  							n.expectedPolicySet = subjectPolicies
  1328  							pg.insert(n)
  1329  						}
  1330  					}
  1331  				}
  1332  			}
  1333  		}
  1334  
  1335  		if i != 0 {
  1336  			// 6.1.4 (h)
  1337  			if !isSelfSigned {
  1338  				if explicitPolicy > 0 {
  1339  					explicitPolicy--
  1340  				}
  1341  				if policyMapping > 0 {
  1342  					policyMapping--
  1343  				}
  1344  				if inhibitAnyPolicy > 0 {
  1345  					inhibitAnyPolicy--
  1346  				}
  1347  			}
  1348  
  1349  			// 6.1.4 (i)
  1350  			if (cert.RequireExplicitPolicy > 0 || cert.RequireExplicitPolicyZero) && cert.RequireExplicitPolicy < explicitPolicy {
  1351  				explicitPolicy = cert.RequireExplicitPolicy
  1352  			}
  1353  			if (cert.InhibitPolicyMapping > 0 || cert.InhibitPolicyMappingZero) && cert.InhibitPolicyMapping < policyMapping {
  1354  				policyMapping = cert.InhibitPolicyMapping
  1355  			}
  1356  			// 6.1.4 (j)
  1357  			if (cert.InhibitAnyPolicy > 0 || cert.InhibitAnyPolicyZero) && cert.InhibitAnyPolicy < inhibitAnyPolicy {
  1358  				inhibitAnyPolicy = cert.InhibitAnyPolicy
  1359  			}
  1360  		}
  1361  	}
  1362  
  1363  	// 6.1.5 (a)
  1364  	if explicitPolicy > 0 {
  1365  		explicitPolicy--
  1366  	}
  1367  
  1368  	// 6.1.5 (b)
  1369  	if chain[0].RequireExplicitPolicyZero {
  1370  		explicitPolicy = 0
  1371  	}
  1372  
  1373  	// 6.1.5 (g) (1) -- as updated by RFC 9618
  1374  	var validPolicyNodeSet []*policyGraphNode
  1375  	// 6.1.5 (g) (2) -- as updated by RFC 9618
  1376  	if pg != nil {
  1377  		validPolicyNodeSet = pg.validPolicyNodes()
  1378  		// 6.1.5 (g) (3) -- as updated by RFC 9618
  1379  		if currentAny := pg.leafWithPolicy(anyPolicyOID); currentAny != nil {
  1380  			validPolicyNodeSet = append(validPolicyNodeSet, currentAny)
  1381  		}
  1382  	}
  1383  
  1384  	// 6.1.5 (g) (4) -- as updated by RFC 9618
  1385  	authorityConstrainedPolicySet := map[string]bool{}
  1386  	for _, n := range validPolicyNodeSet {
  1387  		authorityConstrainedPolicySet[string(n.validPolicy.der)] = true
  1388  	}
  1389  	// 6.1.5 (g) (5) -- as updated by RFC 9618
  1390  	userConstrainedPolicySet := maps.Clone(authorityConstrainedPolicySet)
  1391  	// 6.1.5 (g) (6) -- as updated by RFC 9618
  1392  	if len(initialUserPolicySet) != 1 || !initialUserPolicySet[string(anyPolicyOID.der)] {
  1393  		// 6.1.5 (g) (6) (i) -- as updated by RFC 9618
  1394  		for p := range userConstrainedPolicySet {
  1395  			if !initialUserPolicySet[p] {
  1396  				delete(userConstrainedPolicySet, p)
  1397  			}
  1398  		}
  1399  		// 6.1.5 (g) (6) (ii) -- as updated by RFC 9618
  1400  		if authorityConstrainedPolicySet[string(anyPolicyOID.der)] {
  1401  			for policy := range initialUserPolicySet {
  1402  				userConstrainedPolicySet[policy] = true
  1403  			}
  1404  		}
  1405  	}
  1406  
  1407  	if explicitPolicy == 0 && len(userConstrainedPolicySet) == 0 {
  1408  		return false
  1409  	}
  1410  
  1411  	return true
  1412  }
  1413  
  1414  // distrustedSPKIHashes contains hashes of SPKIs from certificates which
  1415  // we don't consider to be trustworthy. We use these hashes to filter out
  1416  // chains returned by Verify
  1417  var distrustedSPKIHashes = map[string]struct{}{
  1418  	"ebed6475c2c2d80fcb199f3fe8dd6e6b3ce60b77eb15d4e42c3dec0c6f5b5105": {},
  1419  	"49dd353dc2b919a3770645117d0e60c16115e7d1bc259eefe734b00ea434fe5f": {},
  1420  	"e0254c7fcdc265e2f0f8a428dabb75ab4ae039b4872d62f5ee57f0877d5a8a41": {},
  1421  	"5c0660a2b164910d8ff589c18e14552e9e0ec237dcefe2cb736d41a4811f81a0": {},
  1422  	"43bffa19d6ef651451f6841e019931e96f6f2eaeff28ab4b6f1ce4576de2717b": {},
  1423  	"63ecefee431d49523bc1136c4e72d0206a477086caf606cd5cf025686c109cf8": {},
  1424  	"ec4ffa1ad0ac88081314b7aaffef6a91f97cd57291bb5ba686c5415f5eb4f6b6": {},
  1425  	"92c063d67e8f14db71d288e11266ffdaf69cbf115f7bab14f3bc2f68d25e0e30": {},
  1426  }
  1427  
  1428  // containsDistrustedSPKIHash checks if any of the certificates in the chain
  1429  // have an SPKI whose hash is present in the distrustedSPKIHashes map.
  1430  func containsDistrustedSPKIHash(chain []*Certificate) bool {
  1431  	for _, c := range chain {
  1432  		h := sha256.Sum256(c.RawSubjectPublicKeyInfo)
  1433  		if _, ok := distrustedSPKIHashes[hex.EncodeToString(h[:])]; ok {
  1434  			return true
  1435  		}
  1436  	}
  1437  	return false
  1438  }
  1439  

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