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path: root/src/crypto/x509/verify.go
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-rw-r--r--src/crypto/x509/verify.go476
1 files changed, 476 insertions, 0 deletions
diff --git a/src/crypto/x509/verify.go b/src/crypto/x509/verify.go
new file mode 100644
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+++ b/src/crypto/x509/verify.go
@@ -0,0 +1,476 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package x509
+
+import (
+ "fmt"
+ "net"
+ "runtime"
+ "strings"
+ "time"
+ "unicode/utf8"
+)
+
+type InvalidReason int
+
+const (
+ // NotAuthorizedToSign results when a certificate is signed by another
+ // which isn't marked as a CA certificate.
+ NotAuthorizedToSign InvalidReason = iota
+ // Expired results when a certificate has expired, based on the time
+ // given in the VerifyOptions.
+ Expired
+ // CANotAuthorizedForThisName results when an intermediate or root
+ // certificate has a name constraint which doesn't include the name
+ // being checked.
+ CANotAuthorizedForThisName
+ // TooManyIntermediates results when a path length constraint is
+ // violated.
+ TooManyIntermediates
+ // IncompatibleUsage results when the certificate's key usage indicates
+ // that it may only be used for a different purpose.
+ IncompatibleUsage
+)
+
+// CertificateInvalidError results when an odd error occurs. Users of this
+// library probably want to handle all these errors uniformly.
+type CertificateInvalidError struct {
+ Cert *Certificate
+ Reason InvalidReason
+}
+
+func (e CertificateInvalidError) Error() string {
+ switch e.Reason {
+ case NotAuthorizedToSign:
+ return "x509: certificate is not authorized to sign other certificates"
+ case Expired:
+ return "x509: certificate has expired or is not yet valid"
+ case CANotAuthorizedForThisName:
+ return "x509: a root or intermediate certificate is not authorized to sign in this domain"
+ case TooManyIntermediates:
+ return "x509: too many intermediates for path length constraint"
+ case IncompatibleUsage:
+ return "x509: certificate specifies an incompatible key usage"
+ }
+ return "x509: unknown error"
+}
+
+// HostnameError results when the set of authorized names doesn't match the
+// requested name.
+type HostnameError struct {
+ Certificate *Certificate
+ Host string
+}
+
+func (h HostnameError) Error() string {
+ c := h.Certificate
+
+ var valid string
+ if ip := net.ParseIP(h.Host); ip != nil {
+ // Trying to validate an IP
+ if len(c.IPAddresses) == 0 {
+ return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
+ }
+ for _, san := range c.IPAddresses {
+ if len(valid) > 0 {
+ valid += ", "
+ }
+ valid += san.String()
+ }
+ } else {
+ if len(c.DNSNames) > 0 {
+ valid = strings.Join(c.DNSNames, ", ")
+ } else {
+ valid = c.Subject.CommonName
+ }
+ }
+ return "x509: certificate is valid for " + valid + ", not " + h.Host
+}
+
+// UnknownAuthorityError results when the certificate issuer is unknown
+type UnknownAuthorityError struct {
+ cert *Certificate
+ // hintErr contains an error that may be helpful in determining why an
+ // authority wasn't found.
+ hintErr error
+ // hintCert contains a possible authority certificate that was rejected
+ // because of the error in hintErr.
+ hintCert *Certificate
+}
+
+func (e UnknownAuthorityError) Error() string {
+ s := "x509: certificate signed by unknown authority"
+ if e.hintErr != nil {
+ certName := e.hintCert.Subject.CommonName
+ if len(certName) == 0 {
+ if len(e.hintCert.Subject.Organization) > 0 {
+ certName = e.hintCert.Subject.Organization[0]
+ }
+ certName = "serial:" + e.hintCert.SerialNumber.String()
+ }
+ s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
+ }
+ return s
+}
+
+// SystemRootsError results when we fail to load the system root certificates.
+type SystemRootsError struct{}
+
+func (SystemRootsError) Error() string {
+ return "x509: failed to load system roots and no roots provided"
+}
+
+// VerifyOptions contains parameters for Certificate.Verify. It's a structure
+// because other PKIX verification APIs have ended up needing many options.
+type VerifyOptions struct {
+ DNSName string
+ Intermediates *CertPool
+ Roots *CertPool // if nil, the system roots are used
+ CurrentTime time.Time // if zero, the current time is used
+ // KeyUsage specifies which Extended Key Usage values are acceptable.
+ // An empty list means ExtKeyUsageServerAuth. Key usage is considered a
+ // constraint down the chain which mirrors Windows CryptoAPI behaviour,
+ // but not the spec. To accept any key usage, include ExtKeyUsageAny.
+ KeyUsages []ExtKeyUsage
+}
+
+const (
+ leafCertificate = iota
+ intermediateCertificate
+ rootCertificate
+)
+
+// isValid performs validity checks on the c.
+func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
+ now := opts.CurrentTime
+ if now.IsZero() {
+ now = time.Now()
+ }
+ if now.Before(c.NotBefore) || now.After(c.NotAfter) {
+ return CertificateInvalidError{c, Expired}
+ }
+
+ if len(c.PermittedDNSDomains) > 0 {
+ ok := false
+ for _, domain := range c.PermittedDNSDomains {
+ if opts.DNSName == domain ||
+ (strings.HasSuffix(opts.DNSName, domain) &&
+ len(opts.DNSName) >= 1+len(domain) &&
+ opts.DNSName[len(opts.DNSName)-len(domain)-1] == '.') {
+ ok = true
+ break
+ }
+ }
+
+ if !ok {
+ return CertificateInvalidError{c, CANotAuthorizedForThisName}
+ }
+ }
+
+ // KeyUsage status flags are ignored. From Engineering Security, Peter
+ // Gutmann: A European government CA marked its signing certificates as
+ // being valid for encryption only, but no-one noticed. Another
+ // European CA marked its signature keys as not being valid for
+ // signatures. A different CA marked its own trusted root certificate
+ // as being invalid for certificate signing. Another national CA
+ // distributed a certificate to be used to encrypt data for the
+ // country’s tax authority that was marked as only being usable for
+ // digital signatures but not for encryption. Yet another CA reversed
+ // the order of the bit flags in the keyUsage due to confusion over
+ // encoding endianness, essentially setting a random keyUsage in
+ // certificates that it issued. Another CA created a self-invalidating
+ // certificate by adding a certificate policy statement stipulating
+ // that the certificate had to be used strictly as specified in the
+ // keyUsage, and a keyUsage containing a flag indicating that the RSA
+ // encryption key could only be used for Diffie-Hellman key agreement.
+
+ if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
+ return CertificateInvalidError{c, NotAuthorizedToSign}
+ }
+
+ if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
+ numIntermediates := len(currentChain) - 1
+ if numIntermediates > c.MaxPathLen {
+ return CertificateInvalidError{c, TooManyIntermediates}
+ }
+ }
+
+ return nil
+}
+
+// Verify attempts to verify c by building one or more chains from c to a
+// certificate in opts.Roots, using certificates in opts.Intermediates if
+// needed. If successful, it returns one or more chains where the first
+// element of the chain is c and the last element is from opts.Roots.
+//
+// If opts.Roots is nil and system roots are unavailable the returned error
+// will be of type SystemRootsError.
+//
+// WARNING: this doesn't do any revocation checking.
+func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
+ // Use Windows's own verification and chain building.
+ if opts.Roots == nil && runtime.GOOS == "windows" {
+ return c.systemVerify(&opts)
+ }
+
+ if opts.Roots == nil {
+ opts.Roots = systemRootsPool()
+ if opts.Roots == nil {
+ return nil, SystemRootsError{}
+ }
+ }
+
+ err = c.isValid(leafCertificate, nil, &opts)
+ if err != nil {
+ return
+ }
+
+ if len(opts.DNSName) > 0 {
+ err = c.VerifyHostname(opts.DNSName)
+ if err != nil {
+ return
+ }
+ }
+
+ candidateChains, err := c.buildChains(make(map[int][][]*Certificate), []*Certificate{c}, &opts)
+ if err != nil {
+ return
+ }
+
+ keyUsages := opts.KeyUsages
+ if len(keyUsages) == 0 {
+ keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
+ }
+
+ // If any key usage is acceptable then we're done.
+ for _, usage := range keyUsages {
+ if usage == ExtKeyUsageAny {
+ chains = candidateChains
+ return
+ }
+ }
+
+ for _, candidate := range candidateChains {
+ if checkChainForKeyUsage(candidate, keyUsages) {
+ chains = append(chains, candidate)
+ }
+ }
+
+ if len(chains) == 0 {
+ err = CertificateInvalidError{c, IncompatibleUsage}
+ }
+
+ return
+}
+
+func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
+ n := make([]*Certificate, len(chain)+1)
+ copy(n, chain)
+ n[len(chain)] = cert
+ return n
+}
+
+func (c *Certificate) buildChains(cache map[int][][]*Certificate, currentChain []*Certificate, opts *VerifyOptions) (chains [][]*Certificate, err error) {
+ possibleRoots, failedRoot, rootErr := opts.Roots.findVerifiedParents(c)
+ for _, rootNum := range possibleRoots {
+ root := opts.Roots.certs[rootNum]
+ err = root.isValid(rootCertificate, currentChain, opts)
+ if err != nil {
+ continue
+ }
+ chains = append(chains, appendToFreshChain(currentChain, root))
+ }
+
+ possibleIntermediates, failedIntermediate, intermediateErr := opts.Intermediates.findVerifiedParents(c)
+nextIntermediate:
+ for _, intermediateNum := range possibleIntermediates {
+ intermediate := opts.Intermediates.certs[intermediateNum]
+ for _, cert := range currentChain {
+ if cert == intermediate {
+ continue nextIntermediate
+ }
+ }
+ err = intermediate.isValid(intermediateCertificate, currentChain, opts)
+ if err != nil {
+ continue
+ }
+ var childChains [][]*Certificate
+ childChains, ok := cache[intermediateNum]
+ if !ok {
+ childChains, err = intermediate.buildChains(cache, appendToFreshChain(currentChain, intermediate), opts)
+ cache[intermediateNum] = childChains
+ }
+ chains = append(chains, childChains...)
+ }
+
+ if len(chains) > 0 {
+ err = nil
+ }
+
+ if len(chains) == 0 && err == nil {
+ hintErr := rootErr
+ hintCert := failedRoot
+ if hintErr == nil {
+ hintErr = intermediateErr
+ hintCert = failedIntermediate
+ }
+ err = UnknownAuthorityError{c, hintErr, hintCert}
+ }
+
+ return
+}
+
+func matchHostnames(pattern, host string) bool {
+ if len(pattern) == 0 || len(host) == 0 {
+ return false
+ }
+
+ patternParts := strings.Split(pattern, ".")
+ hostParts := strings.Split(host, ".")
+
+ if len(patternParts) != len(hostParts) {
+ return false
+ }
+
+ for i, patternPart := range patternParts {
+ if patternPart == "*" {
+ continue
+ }
+ if patternPart != hostParts[i] {
+ return false
+ }
+ }
+
+ return true
+}
+
+// toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
+// an explicitly ASCII function to avoid any sharp corners resulting from
+// performing Unicode operations on DNS labels.
+func toLowerCaseASCII(in string) string {
+ // If the string is already lower-case then there's nothing to do.
+ isAlreadyLowerCase := true
+ for _, c := range in {
+ if c == utf8.RuneError {
+ // If we get a UTF-8 error then there might be
+ // upper-case ASCII bytes in the invalid sequence.
+ isAlreadyLowerCase = false
+ break
+ }
+ if 'A' <= c && c <= 'Z' {
+ isAlreadyLowerCase = false
+ break
+ }
+ }
+
+ if isAlreadyLowerCase {
+ return in
+ }
+
+ out := []byte(in)
+ for i, c := range out {
+ if 'A' <= c && c <= 'Z' {
+ out[i] += 'a' - 'A'
+ }
+ }
+ return string(out)
+}
+
+// VerifyHostname returns nil if c is a valid certificate for the named host.
+// Otherwise it returns an error describing the mismatch.
+func (c *Certificate) VerifyHostname(h string) error {
+ // IP addresses may be written in [ ].
+ candidateIP := h
+ if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
+ candidateIP = h[1 : len(h)-1]
+ }
+ if ip := net.ParseIP(candidateIP); ip != nil {
+ // We only match IP addresses against IP SANs.
+ // https://tools.ietf.org/html/rfc6125#appendix-B.2
+ for _, candidate := range c.IPAddresses {
+ if ip.Equal(candidate) {
+ return nil
+ }
+ }
+ return HostnameError{c, candidateIP}
+ }
+
+ lowered := toLowerCaseASCII(h)
+
+ if len(c.DNSNames) > 0 {
+ for _, match := range c.DNSNames {
+ if matchHostnames(toLowerCaseASCII(match), lowered) {
+ return nil
+ }
+ }
+ // If Subject Alt Name is given, we ignore the common name.
+ } else if matchHostnames(toLowerCaseASCII(c.Subject.CommonName), lowered) {
+ return nil
+ }
+
+ return HostnameError{c, h}
+}
+
+func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
+ usages := make([]ExtKeyUsage, len(keyUsages))
+ copy(usages, keyUsages)
+
+ if len(chain) == 0 {
+ return false
+ }
+
+ usagesRemaining := len(usages)
+
+ // We walk down the list and cross out any usages that aren't supported
+ // by each certificate. If we cross out all the usages, then the chain
+ // is unacceptable.
+
+NextCert:
+ for i := len(chain) - 1; i >= 0; i-- {
+ cert := chain[i]
+ if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
+ // The certificate doesn't have any extended key usage specified.
+ continue
+ }
+
+ for _, usage := range cert.ExtKeyUsage {
+ if usage == ExtKeyUsageAny {
+ // The certificate is explicitly good for any usage.
+ continue NextCert
+ }
+ }
+
+ const invalidUsage ExtKeyUsage = -1
+
+ NextRequestedUsage:
+ for i, requestedUsage := range usages {
+ if requestedUsage == invalidUsage {
+ continue
+ }
+
+ for _, usage := range cert.ExtKeyUsage {
+ if requestedUsage == usage {
+ continue NextRequestedUsage
+ } else if requestedUsage == ExtKeyUsageServerAuth &&
+ (usage == ExtKeyUsageNetscapeServerGatedCrypto ||
+ usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
+ // In order to support COMODO
+ // certificate chains, we have to
+ // accept Netscape or Microsoft SGC
+ // usages as equal to ServerAuth.
+ continue NextRequestedUsage
+ }
+ }
+
+ usages[i] = invalidUsage
+ usagesRemaining--
+ if usagesRemaining == 0 {
+ return false
+ }
+ }
+ }
+
+ return true
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-13 15:03:42 +0000