// 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 (
"bytes"
"errors"
"fmt"
"net"
"net/url"
"os"
"reflect"
"runtime"
"strings"
"time"
"unicode/utf8"
)
// ignoreCN disables interpreting Common Name as a hostname. See issue 24151.
var ignoreCN = strings.Contains(os.Getenv("GODEBUG"), "x509ignoreCN=1")
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 permit a DNS or
// other name (including IP address) in the leaf certificate.
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
// NameMismatch results when the subject name of a parent certificate
// does not match the issuer name in the child.
NameMismatch
// NameConstraintsWithoutSANs results when a leaf certificate doesn't
// contain a Subject Alternative Name extension, but a CA certificate
// contains name constraints, and the Common Name can be interpreted as
// a hostname.
//
// You can avoid this error by setting the experimental GODEBUG environment
// variable to "x509ignoreCN=1", disabling Common Name matching entirely.
// This behavior might become the default in the future.
NameConstraintsWithoutSANs
// UnconstrainedName results when a CA certificate contains permitted
// name constraints, but leaf certificate contains a name of an
// unsupported or unconstrained type.
UnconstrainedName
// TooManyConstraints results when the number of comparison operations
// needed to check a certificate exceeds the limit set by
// VerifyOptions.MaxConstraintComparisions. This limit exists to
// prevent pathological certificates can consuming excessive amounts of
// CPU time to verify.
TooManyConstraints
// CANotAuthorizedForExtKeyUsage results when an intermediate or root
// certificate does not permit a requested extended key usage.
CANotAuthorizedForExtKeyUsage
)
// 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
Detail string
}
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 for this name: " + e.Detail
case CANotAuthorizedForExtKeyUsage:
return "x509: a root or intermediate certificate is not authorized for an extended key usage: " + e.Detail
case TooManyIntermediates:
return "x509: too many intermediates for path length constraint"
case IncompatibleUsage:
return "x509: certificate specifies an incompatible key usage"
case NameMismatch:
return "x509: issuer name does not match subject from issuing certificate"
case NameConstraintsWithoutSANs:
return "x509: issuer has name constraints but leaf doesn't have a SAN extension"
case UnconstrainedName:
return "x509: issuer has name constraints but leaf contains unknown or unconstrained name: " + e.Detail
}
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
if !c.hasSANExtension() && !validHostname(c.Subject.CommonName) &&
matchHostnames(toLowerCaseASCII(c.Subject.CommonName), toLowerCaseASCII(h.Host)) {
// This would have validated, if it weren't for the validHostname check on Common Name.
return "x509: Common Name is not a valid hostname: " + c.Subject.CommonName
}
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 c.commonNameAsHostname() {
valid = c.Subject.CommonName
} else {
valid = strings.Join(c.DNSNames, ", ")
}
}
if len(valid) == 0 {
return "x509: certificate is not valid for any names, but wanted to match " + h.Host
}
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]
} else {
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 {
Err error
}
func (se SystemRootsError) Error() string {
msg := "x509: failed to load system roots and no roots provided"
if se.Err != nil {
return msg + "; " + se.Err.Error()
}
return msg
}
// errNotParsed is returned when a certificate without ASN.1 contents is
// verified. Platform-specific verification needs the ASN.1 contents.
var errNotParsed = errors.New("x509: missing ASN.1 contents; use ParseCertificate")
// 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. A leaf
// certificate is accepted if it contains any of the listed values. An empty
// list means ExtKeyUsageServerAuth. To accept any key usage, include
// ExtKeyUsageAny.
//
// Certificate chains are required to nest these extended key usage values.
// (This matches the Windows CryptoAPI behavior, but not the spec.)
KeyUsages []ExtKeyUsage
// MaxConstraintComparisions is the maximum number of comparisons to
// perform when checking a given certificate's name constraints. If
// zero, a sensible default is used. This limit prevents pathological
// certificates from consuming excessive amounts of CPU time when
// validating.
MaxConstraintComparisions int
}
const (
leafCertificate = iota
intermediateCertificate
rootCertificate
)
// rfc2821Mailbox represents a “mailbox” (which is an email address to most
// people) by breaking it into the “local” (i.e. before the '@') and “domain”
// parts.
type rfc2821Mailbox struct {
local, domain string
}
// parseRFC2821Mailbox parses an email address into local and domain parts,
// based on the ABNF for a “Mailbox” from RFC 2821. According to RFC 5280,
// Section 4.2.1.6 that's correct for an rfc822Name from a certificate: “The
// format of an rfc822Name is a "Mailbox" as defined in RFC 2821, Section 4.1.2”.
func parseRFC2821Mailbox(in string) (mailbox rfc2821Mailbox, ok bool) {
if len(in) == 0 {
return mailbox, false
}
localPartBytes := make([]byte, 0, len(in)/2)
if in[0] == '"' {
// Quoted-string = DQUOTE *qcontent DQUOTE
// non-whitespace-control = %d1-8 / %d11 / %d12 / %d14-31 / %d127
// qcontent = qtext / quoted-pair
// qtext = non-whitespace-control /
// %d33 / %d35-91 / %d93-126
// quoted-pair = ("\" text) / obs-qp
// text = %d1-9 / %d11 / %d12 / %d14-127 / obs-text
//
// (Names beginning with “obs-” are the obsolete syntax from RFC 2822,
// Section 4. Since it has been 16 years, we no longer accept that.)
in = in[1:]
QuotedString:
for {
if len(in) == 0 {
return mailbox, false
}
c := in[0]
in = in[1:]
switch {
case c == '"':
break QuotedString
case c == '\\':
// quoted-pair
if len(in) == 0 {
return mailbox, false
}
if in[0] == 11 ||
in[0] == 12 ||
(1 <= in[0] && in[0] <= 9) ||
(14 <= in[0] && in[0] <= 127) {
localPartBytes = append(localPartBytes, in[0])
in = in[1:]
} else {
return mailbox, false
}
case c == 11 ||
c == 12 ||
// Space (char 32) is not allowed based on the
// BNF, but RFC 3696 gives an example that
// assumes that it is. Several “verified”
// errata continue to argue about this point.
// We choose to accept it.
c == 32 ||
c == 33 ||
c == 127 ||
(1 <= c && c <= 8) ||
(14 <= c && c <= 31) ||
(35 <= c && c <= 91) ||
(93 <= c && c <= 126):
// qtext
localPartBytes = append(localPartBytes, c)
default:
return mailbox, false
}
}
} else {
// Atom ("." Atom)*
NextChar:
for len(in) > 0 {
// atext from RFC 2822, Section 3.2.4
c := in[0]
switch {
case c == '\\':
// Examples given in RFC 3696 suggest that
// escaped characters can appear outside of a
// quoted string. Several “verified” errata
// continue to argue the point. We choose to
// accept it.
in = in[1:]
if len(in) == 0 {
return mailbox, false
}
fallthrough
case ('0' <= c && c <= '9') ||
('a' <= c && c <= 'z') ||
('A' <= c && c <= 'Z') ||
c == '!' || c == '#' || c == '$' || c == '%' ||
c == '&' || c == '\'' || c == '*' || c == '+' ||
c == '-' || c == '/' || c == '=' || c == '?' ||
c == '^' || c == '_' || c == '`' || c == '{' ||
c == '|' || c == '}' || c == '~' || c == '.':
localPartBytes = append(localPartBytes, in[0])
in = in[1:]
default:
break NextChar
}
}
if len(localPartBytes) == 0 {
return mailbox, false
}
// From RFC 3696, Section 3:
// “period (".") may also appear, but may not be used to start
// or end the local part, nor may two or more consecutive
// periods appear.”
twoDots := []byte{'.', '.'}
if localPartBytes[0] == '.' ||
localPartBytes[len(localPartBytes)-1] == '.' ||
bytes.Contains(localPartBytes, twoDots) {
return mailbox, false
}
}
if len(in) == 0 || in[0] != '@' {
return mailbox, false
}
in = in[1:]
// The RFC species a format for domains, but that's known to be
// violated in practice so we accept that anything after an '@' is the
// domain part.
if _, ok := domainToReverseLabels(in); !ok {
return mailbox, false
}
mailbox.local = string(localPartBytes)
mailbox.domain = in
return mailbox, true
}
// domainToReverseLabels converts a textual domain name like foo.example.com to
// the list of labels in reverse order, e.g. ["com", "example", "foo"].
func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
for len(domain) > 0 {
if i := strings.LastIndexByte(domain, '.'); i == -1 {
reverseLabels = append(reverseLabels, domain)
domain = ""
} else {
reverseLabels = append(reverseLabels, domain[i+1:])
domain = domain[:i]
}
}
if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
// An empty label at the end indicates an absolute value.
return nil, false
}
for _, label := range reverseLabels {
if len(label) == 0 {
// Empty labels are otherwise invalid.
return nil, false
}
for _, c := range label {
if c < 33 || c > 126 {
// Invalid character.
return nil, false
}
}
}
return reverseLabels, true
}
func matchEmailConstraint(mailbox rfc2821Mailbox, constraint string) (bool, error) {
// If the constraint contains an @, then it specifies an exact mailbox
// name.
if strings.Contains(constraint, "@") {
constraintMailbox, ok := parseRFC2821Mailbox(constraint)
if !ok {
return false, fmt.Errorf("x509: internal error: cannot parse constraint %q", constraint)
}
return mailbox.local == constraintMailbox.local && strings.EqualFold(mailbox.domain, constraintMailbox.domain), nil
}
// Otherwise the constraint is like a DNS constraint of the domain part
// of the mailbox.
return matchDomainConstraint(mailbox.domain, constraint)
}
func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
// From RFC 5280, Section 4.2.1.10:
// “a uniformResourceIdentifier that does not include an authority
// component with a host name specified as a fully qualified domain
// name (e.g., if the URI either does not include an authority
// component or includes an authority component in which the host name
// is specified as an IP address), then the application MUST reject the
// certificate.”
host := uri.Host
if len(host) == 0 {
return false, fmt.Errorf("URI with empty host (%q) cannot be matched against constraints", uri.String())
}
if strings.Contains(host, ":") && !strings.HasSuffix(host, "]") {
var err error
host, _, err = net.SplitHostPort(uri.Host)
if err != nil {
return false, err
}
}
if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
net.ParseIP(host) != nil {
return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
}
return matchDomainConstraint(host, constraint)
}
func matchIPConstraint(ip net.IP, constraint *net.IPNet) (bool, error) {
if len(ip) != len(constraint.IP) {
return false, nil
}
for i := range ip {
if mask := constraint.Mask[i]; ip[i]&mask != constraint.IP[i]&mask {
return false, nil
}
}
return true, nil
}
func matchDomainConstraint(domain, constraint string) (bool, error) {
// The meaning of zero length constraints is not specified, but this
// code follows NSS and accepts them as matching everything.
if len(constraint) == 0 {
return true, nil
}
domainLabels, ok := domainToReverseLabels(domain)
if !ok {
return false, fmt.Errorf("x509: internal error: cannot parse domain %q", domain)
}
// RFC 5280 says that a leading period in a domain name means that at
// least one label must be prepended, but only for URI and email
// constraints, not DNS constraints. The code also supports that
// behaviour for DNS constraints.
mustHaveSubdomains := false
if constraint[0] == '.' {
mustHaveSubdomains = true
constraint = constraint[1:]
}
constraintLabels, ok := domainToReverseLabels(constraint)
if !ok {
return false, fmt.Errorf("x509: internal error: cannot parse domain %q", constraint)
}
if len(domainLabels) < len(constraintLabels) ||
(mustHaveSubdomains && len(domainLabels) == len(constraintLabels)) {
return false, nil
}
for i, constraintLabel := range constraintLabels {
if !strings.EqualFold(constraintLabel, domainLabels[i]) {
return false, nil
}
}
return true, nil
}
// checkNameConstraints checks that c permits a child certificate to claim the
// given name, of type nameType. The argument parsedName contains the parsed
// form of name, suitable for passing to the match function. The total number
// of comparisons is tracked in the given count and should not exceed the given
// limit.
func (c *Certificate) checkNameConstraints(count *int,
maxConstraintComparisons int,
nameType string,
name string,
parsedName interface{},
match func(parsedName, constraint interface{}) (match bool, err error),
permitted, excluded interface{}) error {
excludedValue := reflect.ValueOf(excluded)
*count += excludedValue.Len()
if *count > maxConstraintComparisons {
return CertificateInvalidError{c, TooManyConstraints, ""}
}
for i := 0; i < excludedValue.Len(); i++ {
constraint := excludedValue.Index(i).Interface()
match, err := match(parsedName, constraint)
if err != nil {
return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
}
if match {
return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is excluded by constraint %q", nameType, name, constraint)}
}
}
permittedValue := reflect.ValueOf(permitted)
*count += permittedValue.Len()
if *count > maxConstraintComparisons {
return CertificateInvalidError{c, TooManyConstraints, ""}
}
ok := true
for i := 0; i < permittedValue.Len(); i++ {
constraint := permittedValue.Index(i).Interface()
var err error
if ok, err = match(parsedName, constraint); err != nil {
return CertificateInvalidError{c, CANotAuthorizedForThisName, err.Error()}
}
if ok {
break
}
}
if !ok {
return CertificateInvalidError{c, CANotAuthorizedForThisName, fmt.Sprintf("%s %q is not permitted by any constraint", nameType, name)}
}
return nil
}
// isValid performs validity checks on c given that it is a candidate to append
// to the chain in currentChain.
func (c *Certificate) isValid(certType int, currentChain []*Certificate, opts *VerifyOptions) error {
if len(c.UnhandledCriticalExtensions) > 0 {
return UnhandledCriticalExtension{}
}
if len(currentChain) > 0 {
child := currentChain[len(currentChain)-1]
if !bytes.Equal(child.RawIssuer, c.RawSubject) {
return CertificateInvalidError{c, NameMismatch, ""}
}
}
now := opts.CurrentTime
if now.IsZero() {
now = time.Now()
}
if now.Before(c.NotBefore) || now.After(c.NotAfter) {
return CertificateInvalidError{c, Expired, ""}
}
maxConstraintComparisons := opts.MaxConstraintComparisions
if maxConstraintComparisons == 0 {
maxConstraintComparisons = 250000
}
comparisonCount := 0
var leaf *Certificate
if certType == intermediateCertificate || certType == rootCertificate {
if len(currentChain) == 0 {
return errors.New("x509: internal error: empty chain when appending CA cert")
}
leaf = currentChain[0]
}
checkNameConstraints := (certType == intermediateCertificate || certType == rootCertificate) && c.hasNameConstraints()
if checkNameConstraints && leaf.commonNameAsHostname() {
// This is the deprecated, legacy case of depending on the commonName as
// a hostname. We don't enforce name constraints against the CN, but
// VerifyHostname will look for hostnames in there if there are no SANs.
// In order to ensure VerifyHostname will not accept an unchecked name,
// return an error here.
return CertificateInvalidError{c, NameConstraintsWithoutSANs, ""}
} else if checkNameConstraints && leaf.hasSANExtension() {
err := forEachSAN(leaf.getSANExtension(), func(tag int, data []byte) error {
switch tag {
case nameTypeEmail:
name := string(data)
mailbox, ok := parseRFC2821Mailbox(name)
if !ok {
return fmt.Errorf("x509: cannot parse rfc822Name %q", mailbox)
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "email address", name, mailbox,
func(parsedName, constraint interface{}) (bool, error) {
return matchEmailConstraint(parsedName.(rfc2821Mailbox), constraint.(string))
}, c.PermittedEmailAddresses, c.ExcludedEmailAddresses); err != nil {
return err
}
case nameTypeDNS:
name := string(data)
if _, ok := domainToReverseLabels(name); !ok {
return fmt.Errorf("x509: cannot parse dnsName %q", name)
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "DNS name", name, name,
func(parsedName, constraint interface{}) (bool, error) {
return matchDomainConstraint(parsedName.(string), constraint.(string))
}, c.PermittedDNSDomains, c.ExcludedDNSDomains); err != nil {
return err
}
case nameTypeURI:
name := string(data)
uri, err := url.Parse(name)
if err != nil {
return fmt.Errorf("x509: internal error: URI SAN %q failed to parse", name)
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "URI", name, uri,
func(parsedName, constraint interface{}) (bool, error) {
return matchURIConstraint(parsedName.(*url.URL), constraint.(string))
}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
return err
}
case nameTypeIP:
ip := net.IP(data)
if l := len(ip); l != net.IPv4len && l != net.IPv6len {
return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
}
if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,
func(parsedName, constraint interface{}) (bool, error) {
return matchIPConstraint(parsedName.(net.IP), constraint.(*net.IPNet))
}, c.PermittedIPRanges, c.ExcludedIPRanges); err != nil {
return err
}
default:
// Unknown SAN types are ignored.
}
return nil
})
if err != nil {
return err
}
}
// 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.
//
// Name constraints in the intermediates will be applied to all names claimed
// in the chain, not just opts.DNSName. Thus it is invalid for a leaf to claim
// example.com if an intermediate doesn't permit it, even if example.com is not
// the name being validated. Note that DirectoryName constraints are not
// supported.
//
// Extended Key Usage values are enforced down a chain, so an intermediate or
// root that enumerates EKUs prevents a leaf from asserting an EKU not in that
// list.
//
// WARNING: this function doesn't do any revocation checking.
func (c *Certificate) Verify(opts VerifyOptions) (chains [][]*Certificate, err error) {
// Platform-specific verification needs the ASN.1 contents so
// this makes the behavior consistent across platforms.
if len(c.Raw) == 0 {
return nil, errNotParsed
}
if opts.Intermediates != nil {
for _, intermediate := range opts.Intermediates.certs {
if len(intermediate.Raw) == 0 {
return nil, errNotParsed
}
}
}
// 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{systemRootsErr}
}
}
err = c.isValid(leafCertificate, nil, &opts)
if err != nil {
return
}
if len(opts.DNSName) > 0 {
err = c.VerifyHostname(opts.DNSName)
if err != nil {
return
}
}
var candidateChains [][]*Certificate
if opts.Roots.contains(c) {
candidateChains = append(candidateChains, []*Certificate{c})
} else {
if candidateChains, err = c.buildChains(nil, []*Certificate{c}, nil, &opts); err != nil {
return nil, err
}
}
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 {
return candidateChains, nil
}
}
for _, candidate := range candidateChains {
if checkChainForKeyUsage(candidate, keyUsages) {
chains = append(chains, candidate)
}
}
if len(chains) == 0 {
return nil, CertificateInvalidError{c, IncompatibleUsage, ""}
}
return chains, nil
}
func appendToFreshChain(chain []*Certificate, cert *Certificate) []*Certificate {
n := make([]*Certificate, len(chain)+1)
copy(n, chain)
n[len(chain)] = cert
return n
}
// maxChainSignatureChecks is the maximum number of CheckSignatureFrom calls
// that an invocation of buildChains will (tranistively) make. Most chains are
// less than 15 certificates long, so this leaves space for multiple chains and
// for failed checks due to different intermediates having the same Subject.
const maxChainSignatureChecks = 100
func (c *Certificate) buildChains(cache map[*Certificate][][]*Certificate, currentChain []*Certificate, sigChecks *int, opts *VerifyOptions) (chains [][]*Certificate, err error) {
var (
hintErr error
hintCert *Certificate
)
considerCandidate := func(certType int, candidate *Certificate) {
for _, cert := range currentChain {
if cert.Equal(candidate) {
return
}
}
if sigChecks == nil {
sigChecks = new(int)
}
*sigChecks++
if *sigChecks > maxChainSignatureChecks {
err = errors.New("x509: signature check attempts limit reached while verifying certificate chain")
return
}
if err := c.CheckSignatureFrom(candidate); err != nil {
if hintErr == nil {
hintErr = err
hintCert = candidate
}
return
}
err = candidate.isValid(certType, currentChain, opts)
if err != nil {
return
}
switch certType {
case rootCertificate:
chains = append(chains, appendToFreshChain(currentChain, candidate))
case intermediateCertificate:
if cache == nil {
cache = make(map[*Certificate][][]*Certificate)
}
childChains, ok := cache[candidate]
if !ok {
childChains, err = candidate.buildChains(cache, appendToFreshChain(currentChain, candidate), sigChecks, opts)
cache[candidate] = childChains
}
chains = append(chains, childChains...)
}
}
for _, rootNum := range opts.Roots.findPotentialParents(c) {
considerCandidate(rootCertificate, opts.Roots.certs[rootNum])
}
for _, intermediateNum := range opts.Intermediates.findPotentialParents(c) {
considerCandidate(intermediateCertificate, opts.Intermediates.certs[intermediateNum])
}
if len(chains) > 0 {
err = nil
}
if len(chains) == 0 && err == nil {
err = UnknownAuthorityError{c, hintErr, hintCert}
}
return
}
// validHostname reports whether host is a valid hostname that can be matched or
// matched against according to RFC 6125 2.2, with some leniency to accommodate
// legacy values.
func validHostname(host string) bool {
host = strings.TrimSuffix(host, ".")
if len(host) == 0 {
return false
}
for i, part := range strings.Split(host, ".") {
if part == "" {
// Empty label.
return false
}
if i == 0 && part == "*" {
// Only allow full left-most wildcards, as those are the only ones
// we match, and matching literal '*' characters is probably never
// the expected behavior.
continue
}
for j, c := range part {
if 'a' <= c && c <= 'z' {
continue
}
if '0' <= c && c <= '9' {
continue
}
if 'A' <= c && c <= 'Z' {
continue
}
if c == '-' && j != 0 {
continue
}
if c == '_' || c == ':' {
// Not valid characters in hostnames, but commonly
// found in deployments outside the WebPKI.
continue
}
return false
}
}
return true
}
// commonNameAsHostname reports whether the Common Name field should be
// considered the hostname that the certificate is valid for. This is a legacy
// behavior, disabled if the Subject Alt Name extension is present.
//
// It applies the strict validHostname check to the Common Name field, so that
// certificates without SANs can still be validated against CAs with name
// constraints if there is no risk the CN would be matched as a hostname.
// See NameConstraintsWithoutSANs and issue 24151.
func (c *Certificate) commonNameAsHostname() bool {
return !ignoreCN && !c.hasSANExtension() && validHostname(c.Subject.CommonName)
}
func matchHostnames(pattern, host string) bool {
host = strings.TrimSuffix(host, ".")
pattern = strings.TrimSuffix(pattern, ".")
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 i == 0 && 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.
// See RFC 6125, Appendix B.2.
for _, candidate := range c.IPAddresses {
if ip.Equal(candidate) {
return nil
}
}
return HostnameError{c, candidateIP}
}
lowered := toLowerCaseASCII(h)
if c.commonNameAsHostname() {
if matchHostnames(toLowerCaseASCII(c.Subject.CommonName), lowered) {
return nil
}
} else {
for _, match := range c.DNSNames {
if matchHostnames(toLowerCaseASCII(match), 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
}
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