mirror of
https://github.com/autc04/Retro68.git
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502 lines
14 KiB
Go
502 lines
14 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package x509
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import (
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"errors"
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"fmt"
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"net"
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"runtime"
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"strings"
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"time"
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"unicode/utf8"
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)
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type InvalidReason int
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const (
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// NotAuthorizedToSign results when a certificate is signed by another
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// which isn't marked as a CA certificate.
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NotAuthorizedToSign InvalidReason = iota
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// Expired results when a certificate has expired, based on the time
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// given in the VerifyOptions.
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Expired
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// CANotAuthorizedForThisName results when an intermediate or root
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// certificate has a name constraint which doesn't include the name
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// being checked.
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CANotAuthorizedForThisName
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// TooManyIntermediates results when a path length constraint is
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// violated.
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TooManyIntermediates
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// IncompatibleUsage results when the certificate's key usage indicates
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// that it may only be used for a different purpose.
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IncompatibleUsage
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)
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// CertificateInvalidError results when an odd error occurs. Users of this
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// library probably want to handle all these errors uniformly.
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type CertificateInvalidError struct {
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Cert *Certificate
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Reason InvalidReason
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}
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func (e CertificateInvalidError) Error() string {
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switch e.Reason {
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case NotAuthorizedToSign:
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return "x509: certificate is not authorized to sign other certificates"
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case Expired:
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return "x509: certificate has expired or is not yet valid"
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case CANotAuthorizedForThisName:
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return "x509: a root or intermediate certificate is not authorized to sign in this domain"
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case TooManyIntermediates:
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return "x509: too many intermediates for path length constraint"
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case IncompatibleUsage:
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return "x509: certificate specifies an incompatible key usage"
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}
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return "x509: unknown error"
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}
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// HostnameError results when the set of authorized names doesn't match the
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// requested name.
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type HostnameError struct {
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Certificate *Certificate
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Host string
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}
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func (h HostnameError) Error() string {
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c := h.Certificate
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var valid string
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if ip := net.ParseIP(h.Host); ip != nil {
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// Trying to validate an IP
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if len(c.IPAddresses) == 0 {
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return "x509: cannot validate certificate for " + h.Host + " because it doesn't contain any IP SANs"
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}
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for _, san := range c.IPAddresses {
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if len(valid) > 0 {
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valid += ", "
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}
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valid += san.String()
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}
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} else {
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if len(c.DNSNames) > 0 {
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valid = strings.Join(c.DNSNames, ", ")
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} else {
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valid = c.Subject.CommonName
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}
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}
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return "x509: certificate is valid for " + valid + ", not " + h.Host
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}
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// UnknownAuthorityError results when the certificate issuer is unknown
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type UnknownAuthorityError struct {
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cert *Certificate
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// hintErr contains an error that may be helpful in determining why an
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// authority wasn't found.
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hintErr error
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// hintCert contains a possible authority certificate that was rejected
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// because of the error in hintErr.
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hintCert *Certificate
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}
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func (e UnknownAuthorityError) Error() string {
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s := "x509: certificate signed by unknown authority"
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if e.hintErr != nil {
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certName := e.hintCert.Subject.CommonName
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if len(certName) == 0 {
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if len(e.hintCert.Subject.Organization) > 0 {
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certName = e.hintCert.Subject.Organization[0]
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}
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certName = "serial:" + e.hintCert.SerialNumber.String()
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}
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s += fmt.Sprintf(" (possibly because of %q while trying to verify candidate authority certificate %q)", e.hintErr, certName)
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}
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return s
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}
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// SystemRootsError results when we fail to load the system root certificates.
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type SystemRootsError struct{}
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func (SystemRootsError) Error() string {
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return "x509: failed to load system roots and no roots provided"
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}
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// errNotParsed is returned when a certificate without ASN.1 contents is
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// verified. Platform-specific verification needs the ASN.1 contents.
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var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
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// VerifyOptions contains parameters for Certificate.Verify. It's a structure
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// because other PKIX verification APIs have ended up needing many options.
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type VerifyOptions struct {
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DNSName string
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Intermediates *CertPool
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Roots *CertPool // if nil, the system roots are used
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CurrentTime time.Time // if zero, the current time is used
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// KeyUsage specifies which Extended Key Usage values are acceptable.
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// An empty list means ExtKeyUsageServerAuth. Key usage is considered a
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// constraint down the chain which mirrors Windows CryptoAPI behaviour,
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// but not the spec. To accept any key usage, include ExtKeyUsageAny.
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KeyUsages []ExtKeyUsage
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}
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const (
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leafCertificate = iota
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intermediateCertificate
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rootCertificate
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)
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// isValid performs validity checks on the c.
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func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
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now := opts.CurrentTime
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if now.IsZero() {
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now = time.Now()
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}
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if now.Before(c.NotBefore) || now.After(c.NotAfter) {
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return CertificateInvalidError{c, Expired}
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}
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if len(c.PermittedDNSDomains) > 0 {
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ok := false
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for _, domain := range c.PermittedDNSDomains {
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if opts.DNSName == domain ||
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(strings.HasSuffix(opts.DNSName, domain) &&
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len(opts.DNSName) >= 1+len(domain) &&
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opts.DNSName[len(opts.DNSName)-len(domain)-1] == '.') {
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ok = true
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break
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}
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}
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if !ok {
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return CertificateInvalidError{c, CANotAuthorizedForThisName}
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}
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}
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// KeyUsage status flags are ignored. From Engineering Security, Peter
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// Gutmann: A European government CA marked its signing certificates as
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// being valid for encryption only, but no-one noticed. Another
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// European CA marked its signature keys as not being valid for
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// signatures. A different CA marked its own trusted root certificate
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// as being invalid for certificate signing. Another national CA
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// distributed a certificate to be used to encrypt data for the
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// country’s tax authority that was marked as only being usable for
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// digital signatures but not for encryption. Yet another CA reversed
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// the order of the bit flags in the keyUsage due to confusion over
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// encoding endianness, essentially setting a random keyUsage in
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// certificates that it issued. Another CA created a self-invalidating
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// certificate by adding a certificate policy statement stipulating
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// that the certificate had to be used strictly as specified in the
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// keyUsage, and a keyUsage containing a flag indicating that the RSA
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// encryption key could only be used for Diffie-Hellman key agreement.
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if certType == intermediateCertificate && (!c.BasicConstraintsValid || !c.IsCA) {
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return CertificateInvalidError{c, NotAuthorizedToSign}
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}
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if c.BasicConstraintsValid && c.MaxPathLen >= 0 {
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numIntermediates := len(currentChain) - 1
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if numIntermediates > c.MaxPathLen {
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return CertificateInvalidError{c, TooManyIntermediates}
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}
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}
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return nil
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}
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// Verify attempts to verify c by building one or more chains from c to a
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// certificate in opts.Roots, using certificates in opts.Intermediates if
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// needed. If successful, it returns one or more chains where the first
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// element of the chain is c and the last element is from opts.Roots.
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//
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// If opts.Roots is nil and system roots are unavailable the returned error
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// will be of type SystemRootsError.
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//
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// WARNING: this doesn't do any revocation checking.
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func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
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// Platform-specific verification needs the ASN.1 contents so
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// this makes the behaviour consistent across platforms.
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if len(c.Raw) == 0 {
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return nil, errNotParsed
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}
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if opts.Intermediates != nil {
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for _, intermediate := range opts.Intermediates.certs {
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if len(intermediate.Raw) == 0 {
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return nil, errNotParsed
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}
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}
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}
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// Use Windows's own verification and chain building.
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if opts.Roots == nil && runtime.GOOS == "windows" {
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return c.systemVerify(&opts)
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}
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if len(c.UnhandledCriticalExtensions) > 0 {
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return nil, UnhandledCriticalExtension{}
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}
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if opts.Roots == nil {
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opts.Roots = systemRootsPool()
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if opts.Roots == nil {
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return nil, SystemRootsError{}
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}
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}
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err = c.isValid(leafCertificate, nil, &opts)
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if err != nil {
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return
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}
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if len(opts.DNSName) > 0 {
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err = c.VerifyHostname(opts.DNSName)
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if err != nil {
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return
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}
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}
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candidateChains, err := c.buildChains(make(map[int][][]*Certificate), []*Certificate{c}, &opts)
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if err != nil {
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return
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}
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keyUsages := opts.KeyUsages
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if len(keyUsages) == 0 {
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keyUsages = []ExtKeyUsage{ExtKeyUsageServerAuth}
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}
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// If any key usage is acceptable then we're done.
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for _, usage := range keyUsages {
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if usage == ExtKeyUsageAny {
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chains = candidateChains
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return
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}
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}
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for _, candidate := range candidateChains {
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if checkChainForKeyUsage(candidate, keyUsages) {
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chains = append(chains, candidate)
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}
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}
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if len(chains) == 0 {
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err = CertificateInvalidError{c, IncompatibleUsage}
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}
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return
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}
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func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
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n := make([]*Certificate, len(chain)+1)
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copy(n, chain)
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n[len(chain)] = cert
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return n
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}
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func (c *Certificate) buildChains(cache map[int][][]*Certificate, currentChain []*Certificate, opts *VerifyOptions) (chains [][]*Certificate, err error) {
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possibleRoots, failedRoot, rootErr := opts.Roots.findVerifiedParents(c)
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for _, rootNum := range possibleRoots {
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root := opts.Roots.certs[rootNum]
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err = root.isValid(rootCertificate, currentChain, opts)
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if err != nil {
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continue
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}
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chains = append(chains, appendToFreshChain(currentChain, root))
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}
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possibleIntermediates, failedIntermediate, intermediateErr := opts.Intermediates.findVerifiedParents(c)
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nextIntermediate:
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for _, intermediateNum := range possibleIntermediates {
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intermediate := opts.Intermediates.certs[intermediateNum]
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for _, cert := range currentChain {
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if cert == intermediate {
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continue nextIntermediate
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}
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}
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err = intermediate.isValid(intermediateCertificate, currentChain, opts)
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if err != nil {
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continue
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}
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var childChains [][]*Certificate
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childChains, ok := cache[intermediateNum]
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if !ok {
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childChains, err = intermediate.buildChains(cache, appendToFreshChain(currentChain, intermediate), opts)
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cache[intermediateNum] = childChains
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}
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chains = append(chains, childChains...)
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}
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if len(chains) > 0 {
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err = nil
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}
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if len(chains) == 0 && err == nil {
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hintErr := rootErr
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hintCert := failedRoot
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if hintErr == nil {
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hintErr = intermediateErr
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hintCert = failedIntermediate
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}
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err = UnknownAuthorityError{c, hintErr, hintCert}
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}
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return
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}
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func matchHostnames(pattern, host string) bool {
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host = strings.TrimSuffix(host, ".")
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pattern = strings.TrimSuffix(pattern, ".")
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if len(pattern) == 0 || len(host) == 0 {
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return false
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}
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patternParts := strings.Split(pattern, ".")
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hostParts := strings.Split(host, ".")
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if len(patternParts) != len(hostParts) {
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return false
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}
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for i, patternPart := range patternParts {
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if i == 0 && patternPart == "*" {
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continue
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}
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if patternPart != hostParts[i] {
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return false
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}
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}
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return true
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}
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// toLowerCaseASCII returns a lower-case version of in. See RFC 6125 6.4.1. We use
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// an explicitly ASCII function to avoid any sharp corners resulting from
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// performing Unicode operations on DNS labels.
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func toLowerCaseASCII(in string) string {
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// If the string is already lower-case then there's nothing to do.
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isAlreadyLowerCase := true
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for _, c := range in {
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if c == utf8.RuneError {
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// If we get a UTF-8 error then there might be
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// upper-case ASCII bytes in the invalid sequence.
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isAlreadyLowerCase = false
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break
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}
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if 'A' <= c && c <= 'Z' {
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isAlreadyLowerCase = false
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break
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}
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}
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if isAlreadyLowerCase {
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return in
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}
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out := []byte(in)
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for i, c := range out {
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if 'A' <= c && c <= 'Z' {
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out[i] += 'a' - 'A'
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}
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}
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return string(out)
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}
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// VerifyHostname returns nil if c is a valid certificate for the named host.
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// Otherwise it returns an error describing the mismatch.
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func (c *Certificate) VerifyHostname(h string) error {
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// IP addresses may be written in [ ].
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candidateIP := h
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if len(h) >= 3 && h[0] == '[' && h[len(h)-1] == ']' {
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candidateIP = h[1 : len(h)-1]
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}
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if ip := net.ParseIP(candidateIP); ip != nil {
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// We only match IP addresses against IP SANs.
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// https://tools.ietf.org/html/rfc6125#appendix-B.2
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for _, candidate := range c.IPAddresses {
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if ip.Equal(candidate) {
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return nil
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}
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}
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return HostnameError{c, candidateIP}
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}
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lowered := toLowerCaseASCII(h)
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if len(c.DNSNames) > 0 {
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for _, match := range c.DNSNames {
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if matchHostnames(toLowerCaseASCII(match), lowered) {
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return nil
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}
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}
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// If Subject Alt Name is given, we ignore the common name.
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} else if matchHostnames(toLowerCaseASCII(c.Subject.CommonName), lowered) {
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return nil
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}
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return HostnameError{c, h}
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}
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func checkChainForKeyUsage(chain []*Certificate, keyUsages []ExtKeyUsage) bool {
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usages := make([]ExtKeyUsage, len(keyUsages))
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copy(usages, keyUsages)
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if len(chain) == 0 {
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return false
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}
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usagesRemaining := len(usages)
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// We walk down the list and cross out any usages that aren't supported
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// by each certificate. If we cross out all the usages, then the chain
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// is unacceptable.
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NextCert:
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for i := len(chain) - 1; i >= 0; i-- {
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cert := chain[i]
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if len(cert.ExtKeyUsage) == 0 && len(cert.UnknownExtKeyUsage) == 0 {
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// The certificate doesn't have any extended key usage specified.
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continue
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}
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for _, usage := range cert.ExtKeyUsage {
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if usage == ExtKeyUsageAny {
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// The certificate is explicitly good for any usage.
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continue NextCert
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}
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}
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const invalidUsage ExtKeyUsage = -1
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NextRequestedUsage:
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for i, requestedUsage := range usages {
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if requestedUsage == invalidUsage {
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continue
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}
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for _, usage := range cert.ExtKeyUsage {
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if requestedUsage == usage {
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continue NextRequestedUsage
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} else if requestedUsage == ExtKeyUsageServerAuth &&
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(usage == ExtKeyUsageNetscapeServerGatedCrypto ||
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usage == ExtKeyUsageMicrosoftServerGatedCrypto) {
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// In order to support COMODO
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// certificate chains, we have to
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// accept Netscape or Microsoft SGC
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// usages as equal to ServerAuth.
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continue NextRequestedUsage
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}
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}
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usages[i] = invalidUsage
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usagesRemaining--
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if usagesRemaining == 0 {
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return false
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}
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}
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}
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return true
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}
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