Subversion Repositories openrisc

// 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 (
        "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
)

// 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 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"
        }
        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 {
        var valid string
        c := h.Certificate
        if len(c.DNSNames) > 0 {
                valid = strings.Join(c.DNSNames, ", ")
        } else {
                valid = c.Subject.CommonName
        }
        return "certificate is valid for " + valid + ", not " + h.Host
}

// UnknownAuthorityError results when the certificate issuer is unknown
type UnknownAuthorityError struct {
        cert *Certificate
}

func (e UnknownAuthorityError) Error() string {
        return "x509: certificate signed by unknown authority"
}

// 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
        CurrentTime   time.Time // if zero, the current time is used
}

const (
        leafCertificate = iota
        intermediateCertificate
        rootCertificate
)

// isValid performs validity checks on the c.
func (c *Certificate) isValid(certType int, 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 {
                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] == '.') {
                                continue
                        }

                        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}
        }

        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 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) {
        err = c.isValid(leafCertificate, &opts)
        if err != nil {
                return
        }
        if len(opts.DNSName) > 0 {
                err = c.VerifyHostname(opts.DNSName)
                if err != nil {
                        return
                }
        }
        return c.buildChains(make(map[int][][]*Certificate), []*Certificate{c}, &opts)
}

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) {
        for _, rootNum := range opts.Roots.findVerifiedParents(c) {
                root := opts.Roots.certs[rootNum]
                err = root.isValid(rootCertificate, opts)
                if err != nil {
                        continue
                }
                chains = append(chains, appendToFreshChain(currentChain, root))
        }

nextIntermediate:
        for _, intermediateNum := range opts.Intermediates.findVerifiedParents(c) {
                intermediate := opts.Intermediates.certs[intermediateNum]
                for _, cert := range currentChain {
                        if cert == intermediate {
                                continue nextIntermediate
                        }
                }
                err = intermediate.isValid(intermediateCertificate, 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 {
                err = UnknownAuthorityError{c}
        }

        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 {
        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}
}