Source file src/crypto/x509/verify.go

Documentation: crypto/x509

		 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  	"errors"
		10  	"fmt"
		11  	"net"
		12  	"net/url"
		13  	"reflect"
		14  	"runtime"
		15  	"strings"
		16  	"time"
		17  	"unicode/utf8"
		18  )
		19  
		20  type InvalidReason int
		21  
		22  const (
		23  	// NotAuthorizedToSign results when a certificate is signed by another
		24  	// which isn't marked as a CA certificate.
		25  	NotAuthorizedToSign InvalidReason = iota
		26  	// Expired results when a certificate has expired, based on the time
		27  	// given in the VerifyOptions.
		28  	Expired
		29  	// CANotAuthorizedForThisName results when an intermediate or root
		30  	// certificate has a name constraint which doesn't permit a DNS or
		31  	// other name (including IP address) in the leaf certificate.
		32  	CANotAuthorizedForThisName
		33  	// TooManyIntermediates results when a path length constraint is
		34  	// violated.
		35  	TooManyIntermediates
		36  	// IncompatibleUsage results when the certificate's key usage indicates
		37  	// that it may only be used for a different purpose.
		38  	IncompatibleUsage
		39  	// NameMismatch results when the subject name of a parent certificate
		40  	// does not match the issuer name in the child.
		41  	NameMismatch
		42  	// NameConstraintsWithoutSANs is a legacy error and is no longer returned.
		43  	NameConstraintsWithoutSANs
		44  	// UnconstrainedName results when a CA certificate contains permitted
		45  	// name constraints, but leaf certificate contains a name of an
		46  	// unsupported or unconstrained type.
		47  	UnconstrainedName
		48  	// TooManyConstraints results when the number of comparison operations
		49  	// needed to check a certificate exceeds the limit set by
		50  	// VerifyOptions.MaxConstraintComparisions. This limit exists to
		51  	// prevent pathological certificates can consuming excessive amounts of
		52  	// CPU time to verify.
		53  	TooManyConstraints
		54  	// CANotAuthorizedForExtKeyUsage results when an intermediate or root
		55  	// certificate does not permit a requested extended key usage.
		56  	CANotAuthorizedForExtKeyUsage
		57  )
		58  
		59  // CertificateInvalidError results when an odd error occurs. Users of this
		60  // library probably want to handle all these errors uniformly.
		61  type CertificateInvalidError struct {
		62  	Cert	 *Certificate
		63  	Reason InvalidReason
		64  	Detail string
		65  }
		66  
		67  func (e CertificateInvalidError) Error() string {
		68  	switch e.Reason {
		69  	case NotAuthorizedToSign:
		70  		return "x509: certificate is not authorized to sign other certificates"
		71  	case Expired:
		72  		return "x509: certificate has expired or is not yet valid: " + e.Detail
		73  	case CANotAuthorizedForThisName:
		74  		return "x509: a root or intermediate certificate is not authorized to sign for this name: " + e.Detail
		75  	case CANotAuthorizedForExtKeyUsage:
		76  		return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
		77  	case TooManyIntermediates:
		78  		return "x509: too many intermediates for path length constraint"
		79  	case IncompatibleUsage:
		80  		return "x509: certificate specifies an incompatible key usage"
		81  	case NameMismatch:
		82  		return "x509: issuer name does not match subject from issuing certificate"
		83  	case NameConstraintsWithoutSANs:
		84  		return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
		85  	case UnconstrainedName:
		86  		return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
		87  	}
		88  	return "x509: unknown error"
		89  }
		90  
		91  // HostnameError results when the set of authorized names doesn't match the
		92  // requested name.
		93  type HostnameError struct {
		94  	Certificate *Certificate
		95  	Host				string
		96  }
		97  
		98  func (h HostnameError) Error() string {
		99  	c := h.Certificate
	 100  
	 101  	if !c.hasSANExtension() && matchHostnames(c.Subject.CommonName, h.Host) {
	 102  		return "x509: certificate relies on legacy Common Name field, use SANs instead"
	 103  	}
	 104  
	 105  	var valid string
	 106  	if ip := net.ParseIP(h.Host); ip != nil {
	 107  		// Trying to validate an IP
	 108  		if len(c.IPAddresses) == 0 {
	 109  			return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
	 110  		}
	 111  		for _, san := range c.IPAddresses {
	 112  			if len(valid) > 0 {
	 113  				valid += ", "
	 114  			}
	 115  			valid += san.String()
	 116  		}
	 117  	} else {
	 118  		valid = strings.Join(c.DNSNames, ", ")
	 119  	}
	 120  
	 121  	if len(valid) == 0 {
	 122  		return "x509: certificate is not valid for any names, but wanted to match " + h.Host
	 123  	}
	 124  	return "x509: certificate is valid for " + valid + ", not " + h.Host
	 125  }
	 126  
	 127  // UnknownAuthorityError results when the certificate issuer is unknown
	 128  type UnknownAuthorityError struct {
	 129  	Cert *Certificate
	 130  	// hintErr contains an error that may be helpful in determining why an
	 131  	// authority wasn't found.
	 132  	hintErr error
	 133  	// hintCert contains a possible authority certificate that was rejected
	 134  	// because of the error in hintErr.
	 135  	hintCert *Certificate
	 136  }
	 137  
	 138  func (e UnknownAuthorityError) Error() string {
	 139  	s := "x509: certificate signed by unknown authority"
	 140  	if e.hintErr != nil {
	 141  		certName := e.hintCert.Subject.CommonName
	 142  		if len(certName) == 0 {
	 143  			if len(e.hintCert.Subject.Organization) > 0 {
	 144  				certName = e.hintCert.Subject.Organization[0]
	 145  			} else {
	 146  				certName = "serial:" + e.hintCert.SerialNumber.String()
	 147  			}
	 148  		}
	 149  		s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
	 150  	}
	 151  	return s
	 152  }
	 153  
	 154  // SystemRootsError results when we fail to load the system root certificates.
	 155  type SystemRootsError struct {
	 156  	Err error
	 157  }
	 158  
	 159  func (se SystemRootsError) Error() string {
	 160  	msg := "x509: failed to load system roots and no roots provided"
	 161  	if se.Err != nil {
	 162  		return msg + "; " + se.Err.Error()
	 163  	}
	 164  	return msg
	 165  }
	 166  
	 167  func (se SystemRootsError) Unwrap() error { return se.Err }
	 168  
	 169  // errNotParsed is returned when a certificate without ASN.1 contents is
	 170  // verified. Platform-specific verification needs the ASN.1 contents.
	 171  var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
	 172  
	 173  // VerifyOptions contains parameters for Certificate.Verify.
	 174  type VerifyOptions struct {
	 175  	// DNSName, if set, is checked against the leaf certificate with
	 176  	// Certificate.VerifyHostname or the platform verifier.
	 177  	DNSName string
	 178  
	 179  	// Intermediates is an optional pool of certificates that are not trust
	 180  	// anchors, but can be used to form a chain from the leaf certificate to a
	 181  	// root certificate.
	 182  	Intermediates *CertPool
	 183  	// Roots is the set of trusted root certificates the leaf certificate needs
	 184  	// to chain up to. If nil, the system roots or the platform verifier are used.
	 185  	Roots *CertPool
	 186  
	 187  	// CurrentTime is used to check the validity of all certificates in the
	 188  	// chain. If zero, the current time is used.
	 189  	CurrentTime time.Time
	 190  
	 191  	// KeyUsages specifies which Extended Key Usage values are acceptable. A
	 192  	// chain is accepted if it allows any of the listed values. An empty list
	 193  	// means ExtKeyUsageServerAuth. To accept any key usage, include ExtKeyUsageAny.
	 194  	KeyUsages []ExtKeyUsage
	 195  
	 196  	// MaxConstraintComparisions is the maximum number of comparisons to
	 197  	// perform when checking a given certificate's name constraints. If
	 198  	// zero, a sensible default is used. This limit prevents pathological
	 199  	// certificates from consuming excessive amounts of CPU time when
	 200  	// validating. It does not apply to the platform verifier.
	 201  	MaxConstraintComparisions int
	 202  }
	 203  
	 204  const (
	 205  	leafCertificate = iota
	 206  	intermediateCertificate
	 207  	rootCertificate
	 208  )
	 209  
	 210  // rfc2821Mailbox represents a “mailbox” (which is an email address to most
	 211  // people) by breaking it into the “local” (i.e. before the '@') and “domain”
	 212  // parts.
	 213  type rfc2821Mailbox struct {
	 214  	local, domain string
	 215  }
	 216  
	 217  // parseRFC2821Mailbox parses an email address into local and domain parts,
	 218  // based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
	 219  // Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
	 220  // format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
	 221  func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
	 222  	if len(in) == 0 {
	 223  		return mailbox, false
	 224  	}
	 225  
	 226  	localPartBytes := make([]byte, 0, len(in)/2)
	 227  
	 228  	if in[0] == '"' {
	 229  		// Quoted-string = DQUOTE *qcontent DQUOTE
	 230  		// non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
	 231  		// qcontent = qtext / quoted-pair
	 232  		// qtext = non-whitespace-control /
	 233  		//				 %d33 / %d35-91 / %d93-126
	 234  		// quoted-pair = ("\" text) / obs-qp
	 235  		// text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
	 236  		//
	 237  		// (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
	 238  		// Section 4. Since it has been 16 years, we no longer accept that.)
	 239  		in = in[1:]
	 240  	QuotedString:
	 241  		for {
	 242  			if len(in) == 0 {
	 243  				return mailbox, false
	 244  			}
	 245  			c := in[0]
	 246  			in = in[1:]
	 247  
	 248  			switch {
	 249  			case c == '"':
	 250  				break QuotedString
	 251  
	 252  			case c == '\\':
	 253  				// quoted-pair
	 254  				if len(in) == 0 {
	 255  					return mailbox, false
	 256  				}
	 257  				if in[0] == 11 ||
	 258  					in[0] == 12 ||
	 259  					(1 <= in[0] && in[0] <= 9) ||
	 260  					(14 <= in[0] && in[0] <= 127) {
	 261  					localPartBytes = append(localPartBytes, in[0])
	 262  					in = in[1:]
	 263  				} else {
	 264  					return mailbox, false
	 265  				}
	 266  
	 267  			case c == 11 ||
	 268  				c == 12 ||
	 269  				// Space (char 32) is not allowed based on the
	 270  				// BNF, but RFC 3696 gives an example that
	 271  				// assumes that it is. Several “verified”
	 272  				// errata continue to argue about this point.
	 273  				// We choose to accept it.
	 274  				c == 32 ||
	 275  				c == 33 ||
	 276  				c == 127 ||
	 277  				(1 <= c && c <= 8) ||
	 278  				(14 <= c && c <= 31) ||
	 279  				(35 <= c && c <= 91) ||
	 280  				(93 <= c && c <= 126):
	 281  				// qtext
	 282  				localPartBytes = append(localPartBytes, c)
	 283  
	 284  			default:
	 285  				return mailbox, false
	 286  			}
	 287  		}
	 288  	} else {
	 289  		// Atom ("." Atom)*
	 290  	NextChar:
	 291  		for len(in) > 0 {
	 292  			// atext from RFC 2822, Section 3.2.4
	 293  			c := in[0]
	 294  
	 295  			switch {
	 296  			case c == '\\':
	 297  				// Examples given in RFC 3696 suggest that
	 298  				// escaped characters can appear outside of a
	 299  				// quoted string. Several “verified” errata
	 300  				// continue to argue the point. We choose to
	 301  				// accept it.
	 302  				in = in[1:]
	 303  				if len(in) == 0 {
	 304  					return mailbox, false
	 305  				}
	 306  				fallthrough
	 307  
	 308  			case ('0' <= c && c <= '9') ||
	 309  				('a' <= c && c <= 'z') ||
	 310  				('A' <= c && c <= 'Z') ||
	 311  				c == '!' || c == '#' || c == '$' || c == '%' ||
	 312  				c == '&' || c == '\'' || c == '*' || c == '+' ||
	 313  				c == '-' || c == '/' || c == '=' || c == '?' ||
	 314  				c == '^' || c == '_' || c == '`' || c == '{' ||
	 315  				c == '|' || c == '}' || c == '~' || c == '.':
	 316  				localPartBytes = append(localPartBytes, in[0])
	 317  				in = in[1:]
	 318  
	 319  			default:
	 320  				break NextChar
	 321  			}
	 322  		}
	 323  
	 324  		if len(localPartBytes) == 0 {
	 325  			return mailbox, false
	 326  		}
	 327  
	 328  		// From RFC 3696, Section 3:
	 329  		// “period (".") may also appear, but may not be used to start
	 330  		// or end the local part, nor may two or more consecutive
	 331  		// periods appear.”
	 332  		twoDots := []byte{'.', '.'}
	 333  		if localPartBytes[0] == '.' ||
	 334  			localPartBytes[len(localPartBytes)-1] == '.' ||
	 335  			bytes.Contains(localPartBytes, twoDots) {
	 336  			return mailbox, false
	 337  		}
	 338  	}
	 339  
	 340  	if len(in) == 0 || in[0] != '@' {
	 341  		return mailbox, false
	 342  	}
	 343  	in = in[1:]
	 344  
	 345  	// The RFC species a format for domains, but that's known to be
	 346  	// violated in practice so we accept that anything after an '@' is the
	 347  	// domain part.
	 348  	if _, ok := domainToReverseLabels(in); !ok {
	 349  		return mailbox, false
	 350  	}
	 351  
	 352  	mailbox.local = string(localPartBytes)
	 353  	mailbox.domain = in
	 354  	return mailbox, true
	 355  }
	 356  
	 357  // domainToReverseLabels converts a textual domain name like foo.example.com to
	 358  // the list of labels in reverse order, e.g. ["com", "example", "foo"].
	 359  func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
	 360  	for len(domain) > 0 {
	 361  		if i := strings.LastIndexByte(domain, '.'); i == -1 {
	 362  			reverseLabels = append(reverseLabels, domain)
	 363  			domain = ""
	 364  		} else {
	 365  			reverseLabels = append(reverseLabels, domain[i+1:])
	 366  			domain = domain[:i]
	 367  		}
	 368  	}
	 369  
	 370  	if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
	 371  		// An empty label at the end indicates an absolute value.
	 372  		return nil, false
	 373  	}
	 374  
	 375  	for _, label := range reverseLabels {
	 376  		if len(label) == 0 {
	 377  			// Empty labels are otherwise invalid.
	 378  			return nil, false
	 379  		}
	 380  
	 381  		for _, c := range label {
	 382  			if c < 33 || c > 126 {
	 383  				// Invalid character.
	 384  				return nil, false
	 385  			}
	 386  		}
	 387  	}
	 388  
	 389  	return reverseLabels, true
	 390  }
	 391  
	 392  func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
	 393  	// If the constraint contains an @, then it specifies an exact mailbox
	 394  	// name.
	 395  	if strings.Contains(constraint, "@") {
	 396  		constraintMailbox, ok := parseRFC2821Mailbox(constraint)
	 397  		if !ok {
	 398  			return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
	 399  		}
	 400  		return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
	 401  	}
	 402  
	 403  	// Otherwise the constraint is like a DNS constraint of the domain part
	 404  	// of the mailbox.
	 405  	return matchDomainConstraint(mailbox.domain, constraint)
	 406  }
	 407  
	 408  func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
	 409  	// From RFC 5280, Section 4.2.1.10:
	 410  	// “a uniformResourceIdentifier that does not include an authority
	 411  	// component with a host name specified as a fully qualified domain
	 412  	// name (e.g., if the URI either does not include an authority
	 413  	// component or includes an authority component in which the host name
	 414  	// is specified as an IP address), then the application MUST reject the
	 415  	// certificate.”
	 416  
	 417  	host := uri.Host
	 418  	if len(host) == 0 {
	 419  		return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
	 420  	}
	 421  
	 422  	if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
	 423  		var err error
	 424  		host, _, err = net.SplitHostPort(uri.Host)
	 425  		if err != nil {
	 426  			return false, err
	 427  		}
	 428  	}
	 429  
	 430  	if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
	 431  		net.ParseIP(host) != nil {
	 432  		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
	 433  	}
	 434  
	 435  	return matchDomainConstraint(host, constraint)
	 436  }
	 437  
	 438  func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
	 439  	if len(ip) != len(constraint.IP) {
	 440  		return false, nil
	 441  	}
	 442  
	 443  	for i := range ip {
	 444  		if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
	 445  			return false, nil
	 446  		}
	 447  	}
	 448  
	 449  	return true, nil
	 450  }
	 451  
	 452  func matchDomainConstraint(domain, constraint string) (bool, error) {
	 453  	// The meaning of zero length constraints is not specified, but this
	 454  	// code follows NSS and accepts them as matching everything.
	 455  	if len(constraint) == 0 {
	 456  		return true, nil
	 457  	}
	 458  
	 459  	domainLabels, ok := domainToReverseLabels(domain)
	 460  	if !ok {
	 461  		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
	 462  	}
	 463  
	 464  	// RFC 5280 says that a leading period in a domain name means that at
	 465  	// least one label must be prepended, but only for URI and email
	 466  	// constraints, not DNS constraints. The code also supports that
	 467  	// behaviour for DNS constraints.
	 468  
	 469  	mustHaveSubdomains := false
	 470  	if constraint[0] == '.' {
	 471  		mustHaveSubdomains = true
	 472  		constraint = constraint[1:]
	 473  	}
	 474  
	 475  	constraintLabels, ok := domainToReverseLabels(constraint)
	 476  	if !ok {
	 477  		return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
	 478  	}
	 479  
	 480  	if len(domainLabels) < len(constraintLabels) ||
	 481  		(mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
	 482  		return false, nil
	 483  	}
	 484  
	 485  	for i, constraintLabel := range constraintLabels {
	 486  		if !strings.EqualFold(constraintLabel, domainLabels[i]) {
	 487  			return false, nil
	 488  		}
	 489  	}
	 490  
	 491  	return true, nil
	 492  }
	 493  
	 494  // checkNameConstraints checks that c permits a child certificate to claim the
	 495  // given name, of type nameType. The argument parsedName contains the parsed
	 496  // form of name, suitable for passing to the match function. The total number
	 497  // of comparisons is tracked in the given count and should not exceed the given
	 498  // limit.
	 499  func (c *Certificate) checkNameConstraints(count *int,
	 500  	maxConstraintComparisons int,
	 501  	nameType string,
	 502  	name string,
	 503  	parsedName interface{},
	 504  	match func(parsedName, constraint interface{}) (match bool, err error),
	 505  	permitted, excluded interface{}) error {
	 506  
	 507  	excludedValue := reflect.ValueOf(excluded)
	 508  
	 509  	*count += excludedValue.Len()
	 510  	if *count > maxConstraintComparisons {
	 511  		return CertificateInvalidError{c, TooManyConstraints, ""}
	 512  	}
	 513  
	 514  	for i := 0; i < excludedValue.Len(); i++ {
	 515  		constraint := excludedValue.Index(i).Interface()
	 516  		match, err := match(parsedName, constraint)
	 517  		if err != nil {
	 518  			return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
	 519  		}
	 520  
	 521  		if match {
	 522  			return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
	 523  		}
	 524  	}
	 525  
	 526  	permittedValue := reflect.ValueOf(permitted)
	 527  
	 528  	*count += permittedValue.Len()
	 529  	if *count > maxConstraintComparisons {
	 530  		return CertificateInvalidError{c, TooManyConstraints, ""}
	 531  	}
	 532  
	 533  	ok := true
	 534  	for i := 0; i < permittedValue.Len(); i++ {
	 535  		constraint := permittedValue.Index(i).Interface()
	 536  
	 537  		var err error
	 538  		if ok, err = match(parsedName, constraint); err != nil {
	 539  			return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
	 540  		}
	 541  
	 542  		if ok {
	 543  			break
	 544  		}
	 545  	}
	 546  
	 547  	if !ok {
	 548  		return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
	 549  	}
	 550  
	 551  	return nil
	 552  }
	 553  
	 554  // isValid performs validity checks on c given that it is a candidate to append
	 555  // to the chain in currentChain.
	 556  func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
	 557  	if len(c.UnhandledCriticalExtensions) > 0 {
	 558  		return UnhandledCriticalExtension{}
	 559  	}
	 560  
	 561  	if len(currentChain) > 0 {
	 562  		child := currentChain[len(currentChain)-1]
	 563  		if !bytes.Equal(child.RawIssuer, c.RawSubject) {
	 564  			return CertificateInvalidError{c, NameMismatch, ""}
	 565  		}
	 566  	}
	 567  
	 568  	now := opts.CurrentTime
	 569  	if now.IsZero() {
	 570  		now = time.Now()
	 571  	}
	 572  	if now.Before(c.NotBefore) {
	 573  		return CertificateInvalidError{
	 574  			Cert:	 c,
	 575  			Reason: Expired,
	 576  			Detail: fmt.Sprintf("current time %s is before %s", now.Format(time.RFC3339), c.NotBefore.Format(time.RFC3339)),
	 577  		}
	 578  	} else if now.After(c.NotAfter) {
	 579  		return CertificateInvalidError{
	 580  			Cert:	 c,
	 581  			Reason: Expired,
	 582  			Detail: fmt.Sprintf("current time %s is after %s", now.Format(time.RFC3339), c.NotAfter.Format(time.RFC3339)),
	 583  		}
	 584  	}
	 585  
	 586  	maxConstraintComparisons := opts.MaxConstraintComparisions
	 587  	if maxConstraintComparisons == 0 {
	 588  		maxConstraintComparisons = 250000
	 589  	}
	 590  	comparisonCount := 0
	 591  
	 592  	var leaf *Certificate
	 593  	if certType == intermediateCertificate || certType == rootCertificate {
	 594  		if len(currentChain) == 0 {
	 595  			return errors.New("x509: internal error: empty chain when appending CA cert")
	 596  		}
	 597  		leaf = currentChain[0]
	 598  	}
	 599  
	 600  	if (certType == intermediateCertificate || certType == rootCertificate) &&
	 601  		c.hasNameConstraints() && leaf.hasSANExtension() {
	 602  		err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
	 603  			switch tag {
	 604  			case nameTypeEmail:
	 605  				name := string(data)
	 606  				mailbox, ok := parseRFC2821Mailbox(name)
	 607  				if !ok {
	 608  					return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
	 609  				}
	 610  
	 611  				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
	 612  					func(parsedName, constraint interface{}) (bool, error) {
	 613  						return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
	 614  					}, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
	 615  					return err
	 616  				}
	 617  
	 618  			case nameTypeDNS:
	 619  				name := string(data)
	 620  				if _, ok := domainToReverseLabels(name); !ok {
	 621  					return fmt.Errorf("x509: cannot parse dnsName %q", name)
	 622  				}
	 623  
	 624  				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
	 625  					func(parsedName, constraint interface{}) (bool, error) {
	 626  						return matchDomainConstraint(parsedName.(string), constraint.(string))
	 627  					}, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
	 628  					return err
	 629  				}
	 630  
	 631  			case nameTypeURI:
	 632  				name := string(data)
	 633  				uri, err := url.Parse(name)
	 634  				if err != nil {
	 635  					return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
	 636  				}
	 637  
	 638  				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
	 639  					func(parsedName, constraint interface{}) (bool, error) {
	 640  						return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
	 641  					}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
	 642  					return err
	 643  				}
	 644  
	 645  			case nameTypeIP:
	 646  				ip := net.IP(data)
	 647  				if l := len(ip); l != net.IPv4len && l != net.IPv6len {
	 648  					return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
	 649  				}
	 650  
	 651  				if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
	 652  					func(parsedName, constraint interface{}) (bool, error) {
	 653  						return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
	 654  					}, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
	 655  					return err
	 656  				}
	 657  
	 658  			default:
	 659  				// Unknown SAN types are ignored.
	 660  			}
	 661  
	 662  			return nil
	 663  		})
	 664  
	 665  		if err != nil {
	 666  			return err
	 667  		}
	 668  	}
	 669  
	 670  	// KeyUsage status flags are ignored. From Engineering Security, Peter
	 671  	// Gutmann: A European government CA marked its signing certificates as
	 672  	// being valid for encryption only, but no-one noticed. Another
	 673  	// European CA marked its signature keys as not being valid for
	 674  	// signatures. A different CA marked its own trusted root certificate
	 675  	// as being invalid for certificate signing. Another national CA
	 676  	// distributed a certificate to be used to encrypt data for the
	 677  	// country’s tax authority that was marked as only being usable for
	 678  	// digital signatures but not for encryption. Yet another CA reversed
	 679  	// the order of the bit flags in the keyUsage due to confusion over
	 680  	// encoding endianness, essentially setting a random keyUsage in
	 681  	// certificates that it issued. Another CA created a self-invalidating
	 682  	// certificate by adding a certificate policy statement stipulating
	 683  	// that the certificate had to be used strictly as specified in the
	 684  	// keyUsage, and a keyUsage containing a flag indicating that the RSA
	 685  	// encryption key could only be used for Diffie-Hellman key agreement.
	 686  
	 687  	if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
	 688  		return CertificateInvalidError{c, NotAuthorizedToSign, ""}
	 689  	}
	 690  
	 691  	if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
	 692  		numIntermediates := len(currentChain) - 1
	 693  		if numIntermediates > c.MaxPathLen {
	 694  			return CertificateInvalidError{c, TooManyIntermediates, ""}
	 695  		}
	 696  	}
	 697  
	 698  	return nil
	 699  }
	 700  
	 701  // Verify attempts to verify c by building one or more chains from c to a
	 702  // certificate in opts.Roots, using certificates in opts.Intermediates if
	 703  // needed. If successful, it returns one or more chains where the first
	 704  // element of the chain is c and the last element is from opts.Roots.
	 705  //
	 706  // If opts.Roots is nil, the platform verifier might be used, and
	 707  // verification details might differ from what is described below. If system
	 708  // roots are unavailable the returned error will be of type SystemRootsError.
	 709  //
	 710  // Name constraints in the intermediates will be applied to all names claimed
	 711  // in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
	 712  // example.com if an intermediate doesn't permit it, even if example.com is not
	 713  // the name being validated. Note that DirectoryName constraints are not
	 714  // supported.
	 715  //
	 716  // Name constraint validation follows the rules from RFC 5280, with the
	 717  // addition that DNS name constraints may use the leading period format
	 718  // defined for emails and URIs. When a constraint has a leading period
	 719  // it indicates that at least one additional label must be prepended to
	 720  // the constrained name to be considered valid.
	 721  //
	 722  // Extended Key Usage values are enforced nested down a chain, so an intermediate
	 723  // or root that enumerates EKUs prevents a leaf from asserting an EKU not in that
	 724  // list. (While this is not specified, it is common practice in order to limit
	 725  // the types of certificates a CA can issue.)
	 726  //
	 727  // WARNING: this function doesn't do any revocation checking.
	 728  func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
	 729  	// Platform-specific verification needs the ASN.1 contents so
	 730  	// this makes the behavior consistent across platforms.
	 731  	if len(c.Raw) == 0 {
	 732  		return nil, errNotParsed
	 733  	}
	 734  	for i := 0; i < opts.Intermediates.len(); i++ {
	 735  		c, err := opts.Intermediates.cert(i)
	 736  		if err != nil {
	 737  			return nil, fmt.Errorf("crypto/x509: error fetching intermediate: %w", err)
	 738  		}
	 739  		if len(c.Raw) == 0 {
	 740  			return nil, errNotParsed
	 741  		}
	 742  	}
	 743  
	 744  	// Use Windows's own verification and chain building.
	 745  	if opts.Roots == nil && runtime.GOOS == "windows" {
	 746  		return c.systemVerify(&opts)
	 747  	}
	 748  
	 749  	if opts.Roots == nil {
	 750  		opts.Roots = systemRootsPool()
	 751  		if opts.Roots == nil {
	 752  			return nil, SystemRootsError{systemRootsErr}
	 753  		}
	 754  	}
	 755  
	 756  	err = c.isValid(leafCertificate, nil, &opts)
	 757  	if err != nil {
	 758  		return
	 759  	}
	 760  
	 761  	if len(opts.DNSName) > 0 {
	 762  		err = c.VerifyHostname(opts.DNSName)
	 763  		if err != nil {
	 764  			return
	 765  		}
	 766  	}
	 767  
	 768  	var candidateChains [][]*Certificate
	 769  	if opts.Roots.contains(c) {
	 770  		candidateChains = append(candidateChains, []*Certificate{c})
	 771  	} else {
	 772  		if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
	 773  			return nil, err
	 774  		}
	 775  	}
	 776  
	 777  	keyUsages := opts.KeyUsages
	 778  	if len(keyUsages) == 0 {
	 779  		keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
	 780  	}
	 781  
	 782  	// If any key usage is acceptable then we're done.
	 783  	for _, usage := range keyUsages {
	 784  		if usage == ExtKeyUsageAny {
	 785  			return candidateChains, nil
	 786  		}
	 787  	}
	 788  
	 789  	for _, candidate := range candidateChains {
	 790  		if checkChainForKeyUsage(candidate, keyUsages) {
	 791  			chains = append(chains, candidate)
	 792  		}
	 793  	}
	 794  
	 795  	if len(chains) == 0 {
	 796  		return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
	 797  	}
	 798  
	 799  	return chains, nil
	 800  }
	 801  
	 802  func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
	 803  	n := make([]*Certificate, len(chain)+1)
	 804  	copy(n, chain)
	 805  	n[len(chain)] = cert
	 806  	return n
	 807  }
	 808  
	 809  // maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
	 810  // that an invocation of buildChains will (transitively) make. Most chains are
	 811  // less than 15 certificates long, so this leaves space for multiple chains and
	 812  // for failed checks due to different intermediates having the same Subject.
	 813  const maxChainSignatureChecks = 100
	 814  
	 815  func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
	 816  	var (
	 817  		hintErr	error
	 818  		hintCert *Certificate
	 819  	)
	 820  
	 821  	considerCandidate := func(certType int, candidate *Certificate) {
	 822  		for _, cert := range currentChain {
	 823  			if cert.Equal(candidate) {
	 824  				return
	 825  			}
	 826  		}
	 827  
	 828  		if sigChecks == nil {
	 829  			sigChecks = new(int)
	 830  		}
	 831  		*sigChecks++
	 832  		if *sigChecks > maxChainSignatureChecks {
	 833  			err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
	 834  			return
	 835  		}
	 836  
	 837  		if err := c.CheckSignatureFrom(candidate); err != nil {
	 838  			if hintErr == nil {
	 839  				hintErr = err
	 840  				hintCert = candidate
	 841  			}
	 842  			return
	 843  		}
	 844  
	 845  		err = candidate.isValid(certType, currentChain, opts)
	 846  		if err != nil {
	 847  			return
	 848  		}
	 849  
	 850  		switch certType {
	 851  		case rootCertificate:
	 852  			chains = append(chains, appendToFreshChain(currentChain, candidate))
	 853  		case intermediateCertificate:
	 854  			if cache == nil {
	 855  				cache = make(map[*Certificate][][]*Certificate)
	 856  			}
	 857  			childChains, ok := cache[candidate]
	 858  			if !ok {
	 859  				childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
	 860  				cache[candidate] = childChains
	 861  			}
	 862  			chains = append(chains, childChains...)
	 863  		}
	 864  	}
	 865  
	 866  	for _, root := range opts.Roots.findPotentialParents(c) {
	 867  		considerCandidate(rootCertificate, root)
	 868  	}
	 869  	for _, intermediate := range opts.Intermediates.findPotentialParents(c) {
	 870  		considerCandidate(intermediateCertificate, intermediate)
	 871  	}
	 872  
	 873  	if len(chains) > 0 {
	 874  		err = nil
	 875  	}
	 876  	if len(chains) == 0 && err == nil {
	 877  		err = UnknownAuthorityError{c, hintErr, hintCert}
	 878  	}
	 879  
	 880  	return
	 881  }
	 882  
	 883  func validHostnamePattern(host string) bool { return validHostname(host, true) }
	 884  func validHostnameInput(host string) bool	 { return validHostname(host, false) }
	 885  
	 886  // validHostname reports whether host is a valid hostname that can be matched or
	 887  // matched against according to RFC 6125 2.2, with some leniency to accommodate
	 888  // legacy values.
	 889  func validHostname(host string, isPattern bool) bool {
	 890  	if !isPattern {
	 891  		host = strings.TrimSuffix(host, ".")
	 892  	}
	 893  	if len(host) == 0 {
	 894  		return false
	 895  	}
	 896  
	 897  	for i, part := range strings.Split(host, ".") {
	 898  		if part == "" {
	 899  			// Empty label.
	 900  			return false
	 901  		}
	 902  		if isPattern && i == 0 && part == "*" {
	 903  			// Only allow full left-most wildcards, as those are the only ones
	 904  			// we match, and matching literal '*' characters is probably never
	 905  			// the expected behavior.
	 906  			continue
	 907  		}
	 908  		for j, c := range part {
	 909  			if 'a' <= c && c <= 'z' {
	 910  				continue
	 911  			}
	 912  			if '0' <= c && c <= '9' {
	 913  				continue
	 914  			}
	 915  			if 'A' <= c && c <= 'Z' {
	 916  				continue
	 917  			}
	 918  			if c == '-' && j != 0 {
	 919  				continue
	 920  			}
	 921  			if c == '_' {
	 922  				// Not a valid character in hostnames, but commonly
	 923  				// found in deployments outside the WebPKI.
	 924  				continue
	 925  			}
	 926  			return false
	 927  		}
	 928  	}
	 929  
	 930  	return true
	 931  }
	 932  
	 933  func matchExactly(hostA, hostB string) bool {
	 934  	if hostA == "" || hostA == "." || hostB == "" || hostB == "." {
	 935  		return false
	 936  	}
	 937  	return toLowerCaseASCII(hostA) == toLowerCaseASCII(hostB)
	 938  }
	 939  
	 940  func matchHostnames(pattern, host string) bool {
	 941  	pattern = toLowerCaseASCII(pattern)
	 942  	host = toLowerCaseASCII(strings.TrimSuffix(host, "."))
	 943  
	 944  	if len(pattern) == 0 || len(host) == 0 {
	 945  		return false
	 946  	}
	 947  
	 948  	patternParts := strings.Split(pattern, ".")
	 949  	hostParts := strings.Split(host, ".")
	 950  
	 951  	if len(patternParts) != len(hostParts) {
	 952  		return false
	 953  	}
	 954  
	 955  	for i, patternPart := range patternParts {
	 956  		if i == 0 && patternPart == "*" {
	 957  			continue
	 958  		}
	 959  		if patternPart != hostParts[i] {
	 960  			return false
	 961  		}
	 962  	}
	 963  
	 964  	return true
	 965  }
	 966  
	 967  // toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
	 968  // an explicitly ASCII function to avoid any sharp corners resulting from
	 969  // performing Unicode operations on DNS labels.
	 970  func toLowerCaseASCII(in string) string {
	 971  	// If the string is already lower-case then there's nothing to do.
	 972  	isAlreadyLowerCase := true
	 973  	for _, c := range in {
	 974  		if c == utf8.RuneError {
	 975  			// If we get a UTF-8 error then there might be
	 976  			// upper-case ASCII bytes in the invalid sequence.
	 977  			isAlreadyLowerCase = false
	 978  			break
	 979  		}
	 980  		if 'A' <= c && c <= 'Z' {
	 981  			isAlreadyLowerCase = false
	 982  			break
	 983  		}
	 984  	}
	 985  
	 986  	if isAlreadyLowerCase {
	 987  		return in
	 988  	}
	 989  
	 990  	out := []byte(in)
	 991  	for i, c := range out {
	 992  		if 'A' <= c && c <= 'Z' {
	 993  			out[i] += 'a' - 'A'
	 994  		}
	 995  	}
	 996  	return string(out)
	 997  }
	 998  
	 999  // VerifyHostname returns nil if c is a valid certificate for the named host.
	1000  // Otherwise it returns an error describing the mismatch.
	1001  //
	1002  // IP addresses can be optionally enclosed in square brackets and are checked
	1003  // against the IPAddresses field. Other names are checked case insensitively
	1004  // against the DNSNames field. If the names are valid hostnames, the certificate
	1005  // fields can have a wildcard as the left-most label.
	1006  //
	1007  // Note that the legacy Common Name field is ignored.
	1008  func (c *Certificate) VerifyHostname(h string) error {
	1009  	// IP addresses may be written in [ ].
	1010  	candidateIP := h
	1011  	if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
	1012  		candidateIP = h[1 : len(h)-1]
	1013  	}
	1014  	if ip := net.ParseIP(candidateIP); ip != nil {
	1015  		// We only match IP addresses against IP SANs.
	1016  		// See RFC 6125, Appendix B.2.
	1017  		for _, candidate := range c.IPAddresses {
	1018  			if ip.Equal(candidate) {
	1019  				return nil
	1020  			}
	1021  		}
	1022  		return HostnameError{c, candidateIP}
	1023  	}
	1024  
	1025  	candidateName := toLowerCaseASCII(h) // Save allocations inside the loop.
	1026  	validCandidateName := validHostnameInput(candidateName)
	1027  
	1028  	for _, match := range c.DNSNames {
	1029  		// Ideally, we'd only match valid hostnames according to RFC 6125 like
	1030  		// browsers (more or less) do, but in practice Go is used in a wider
	1031  		// array of contexts and can't even assume DNS resolution. Instead,
	1032  		// always allow perfect matches, and only apply wildcard and trailing
	1033  		// dot processing to valid hostnames.
	1034  		if validCandidateName && validHostnamePattern(match) {
	1035  			if matchHostnames(match, candidateName) {
	1036  				return nil
	1037  			}
	1038  		} else {
	1039  			if matchExactly(match, candidateName) {
	1040  				return nil
	1041  			}
	1042  		}
	1043  	}
	1044  
	1045  	return HostnameError{c, h}
	1046  }
	1047  
	1048  func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
	1049  	usages := make([]ExtKeyUsage, len(keyUsages))
	1050  	copy(usages, keyUsages)
	1051  
	1052  	if len(chain) == 0 {
	1053  		return false
	1054  	}
	1055  
	1056  	usagesRemaining := len(usages)
	1057  
	1058  	// We walk down the list and cross out any usages that aren't supported
	1059  	// by each certificate. If we cross out all the usages, then the chain
	1060  	// is unacceptable.
	1061  
	1062  NextCert:
	1063  	for i := len(chain) - 1; i >= 0; i-- {
	1064  		cert := chain[i]
	1065  		if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
	1066  			// The certificate doesn't have any extended key usage specified.
	1067  			continue
	1068  		}
	1069  
	1070  		for _, usage := range cert.ExtKeyUsage {
	1071  			if usage == ExtKeyUsageAny {
	1072  				// The certificate is explicitly good for any usage.
	1073  				continue NextCert
	1074  			}
	1075  		}
	1076  
	1077  		const invalidUsage ExtKeyUsage = -1
	1078  
	1079  	NextRequestedUsage:
	1080  		for i, requestedUsage := range usages {
	1081  			if requestedUsage == invalidUsage {
	1082  				continue
	1083  			}
	1084  
	1085  			for _, usage := range cert.ExtKeyUsage {
	1086  				if requestedUsage == usage {
	1087  					continue NextRequestedUsage
	1088  				} else if requestedUsage == ExtKeyUsageServerAuth &&
	1089  					(usage == ExtKeyUsageNetscapeServerGatedCrypto ||
	1090  						usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
	1091  					// In order to support COMODO
	1092  					// certificate chains, we have to
	1093  					// accept Netscape or Microsoft SGC
	1094  					// usages as equal to ServerAuth.
	1095  					continue NextRequestedUsage
	1096  				}
	1097  			}
	1098  
	1099  			usages[i] = invalidUsage
	1100  			usagesRemaining--
	1101  			if usagesRemaining == 0 {
	1102  				return false
	1103  			}
	1104  		}
	1105  	}
	1106  
	1107  	return true
	1108  }
	1109  

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