libgo: Merge from revision 18783:00cce3a34d7e of master library.

[official-gcc.git] / libgo / go / crypto / x509 / verify.go

// 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 (e 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.
//
// 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
}