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// Copyright 2009 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 parses X.509-encoded keys and certificates.

package x509

import (

        "bytes"

        "crypto"

        "crypto/dsa"

        "crypto/rsa"

        "crypto/sha1"

        "crypto/x509/pkix"

        "encoding/asn1"

        "encoding/pem"

        "errors"

        "io"

        "math/big"

        "time"

)

// pkixPublicKey reflects a PKIX public key structure. See SubjectPublicKeyInfo

// in RFC 3280.

type pkixPublicKey struct {

        Algo      pkix.AlgorithmIdentifier

        BitString asn1.BitString

}

// ParsePKIXPublicKey parses a DER encoded public key. These values are

// typically found in PEM blocks with "BEGIN PUBLIC KEY".

func ParsePKIXPublicKey(derBytes []byte) (pub interface{}, err error) {

        var pki publicKeyInfo

        if _, err = asn1.Unmarshal(derBytes, &pki); err != nil {

                return

        }

        algo := getPublicKeyAlgorithmFromOID(pki.Algorithm.Algorithm)

        if algo == UnknownPublicKeyAlgorithm {

                return nil, errors.New("ParsePKIXPublicKey: unknown public key algorithm")

        }

        return parsePublicKey(algo, &pki)

}

// MarshalPKIXPublicKey serialises a public key to DER-encoded PKIX format.

func MarshalPKIXPublicKey(pub interface{}) ([]byte, error) {

        var pubBytes []byte

        switch pub := pub.(type) {

        case *rsa.PublicKey:

                pubBytes, _ = asn1.Marshal(rsaPublicKey{

                        N: pub.N,

                        E: pub.E,

                })

        default:

                return nil, errors.New("MarshalPKIXPublicKey: unknown public key type")

        }

        pkix := pkixPublicKey{

                Algo: pkix.AlgorithmIdentifier{

                        Algorithm: []int{1, 2, 840, 113549, 1, 1, 1},

                        // This is a NULL parameters value which is technically

                        // superfluous, but most other code includes it and, by

                        // doing this, we match their public key hashes.

                        Parameters: asn1.RawValue{

                                Tag: 5,

                        },

                },

                BitString: asn1.BitString{

                        Bytes:     pubBytes,

                        BitLength: 8 * len(pubBytes),

                },

        }

        ret, _ := asn1.Marshal(pkix)

        return ret, nil

}

// These structures reflect the ASN.1 structure of X.509 certificates.:

type certificate struct {

        Raw                asn1.RawContent

        TBSCertificate     tbsCertificate

        SignatureAlgorithm pkix.AlgorithmIdentifier

        SignatureValue     asn1.BitString

}

type tbsCertificate struct {

        Raw                asn1.RawContent

        Version            int `asn1:"optional,explicit,default:1,tag:0"`

        SerialNumber       *big.Int

        SignatureAlgorithm pkix.AlgorithmIdentifier

        Issuer             asn1.RawValue

        Validity           validity

        Subject            asn1.RawValue

        PublicKey          publicKeyInfo

        UniqueId           asn1.BitString   `asn1:"optional,tag:1"`

        SubjectUniqueId    asn1.BitString   `asn1:"optional,tag:2"`

        Extensions         []pkix.Extension `asn1:"optional,explicit,tag:3"`

}

type dsaAlgorithmParameters struct {

        P, Q, G *big.Int

}

type dsaSignature struct {

        R, S *big.Int

}

type validity struct {

        NotBefore, NotAfter time.Time

}

type publicKeyInfo struct {

        Raw       asn1.RawContent

        Algorithm pkix.AlgorithmIdentifier

        PublicKey asn1.BitString

}

// RFC 5280,  4.2.1.1

type authKeyId struct {

        Id []byte `asn1:"optional,tag:0"`

}

type SignatureAlgorithm int

const (

        UnknownSignatureAlgorithm SignatureAlgorithm = iota

        MD2WithRSA

        MD5WithRSA

        SHA1WithRSA

        SHA256WithRSA

        SHA384WithRSA

        SHA512WithRSA

        DSAWithSHA1

        DSAWithSHA256

)

type PublicKeyAlgorithm int

const (

        UnknownPublicKeyAlgorithm PublicKeyAlgorithm = iota

        RSA

        DSA

)

// OIDs for signature algorithms

//

// pkcs-1 OBJECT IDENTIFIER ::= {

//    iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) 1 }

//

//

// RFC 3279 2.2.1 RSA Signature Algorithms

//

// md2WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 2 }

//

// md5WithRSAEncryption OBJECT IDENTIFER ::= { pkcs-1 4 }

//

// sha-1WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 5 }

//

// dsaWithSha1 OBJECT IDENTIFIER ::= {

//    iso(1) member-body(2) us(840) x9-57(10040) x9cm(4) 3 }

//

//

// RFC 4055 5 PKCS #1 Version 1.5

//

// sha256WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 11 }

//

// sha384WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 12 }

//

// sha512WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 13 }

//

//

// RFC 5758 3.1 DSA Signature Algorithms

//

// dsaWithSha356 OBJECT IDENTIFER ::= {

//    joint-iso-ccitt(2) country(16) us(840) organization(1) gov(101)

//    algorithms(4) id-dsa-with-sha2(3) 2}

//

var (

        oidSignatureMD2WithRSA    = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 2}

        oidSignatureMD5WithRSA    = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 4}

        oidSignatureSHA1WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 5}

        oidSignatureSHA256WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 11}

        oidSignatureSHA384WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 12}

        oidSignatureSHA512WithRSA = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 13}

        oidSignatureDSAWithSHA1   = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 3}

        oidSignatureDSAWithSHA256 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 4, 3, 2}

)

func getSignatureAlgorithmFromOID(oid asn1.ObjectIdentifier) SignatureAlgorithm {

        switch {

        case oid.Equal(oidSignatureMD2WithRSA):

                return MD2WithRSA

        case oid.Equal(oidSignatureMD5WithRSA):

                return MD5WithRSA

        case oid.Equal(oidSignatureSHA1WithRSA):

                return SHA1WithRSA

        case oid.Equal(oidSignatureSHA256WithRSA):

                return SHA256WithRSA

        case oid.Equal(oidSignatureSHA384WithRSA):

                return SHA384WithRSA

        case oid.Equal(oidSignatureSHA512WithRSA):

                return SHA512WithRSA

        case oid.Equal(oidSignatureDSAWithSHA1):

                return DSAWithSHA1

        case oid.Equal(oidSignatureDSAWithSHA256):

                return DSAWithSHA256

        }

        return UnknownSignatureAlgorithm

}

// RFC 3279, 2.3 Public Key Algorithms

//

// pkcs-1 OBJECT IDENTIFIER ::== { iso(1) member-body(2) us(840)

//    rsadsi(113549) pkcs(1) 1 }

//

// rsaEncryption OBJECT IDENTIFIER ::== { pkcs1-1 1 }

//

// id-dsa OBJECT IDENTIFIER ::== { iso(1) member-body(2) us(840)

//    x9-57(10040) x9cm(4) 1 }

var (

        oidPublicKeyRsa = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1}

        oidPublicKeyDsa = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 1}

)

func getPublicKeyAlgorithmFromOID(oid asn1.ObjectIdentifier) PublicKeyAlgorithm {

        switch {

        case oid.Equal(oidPublicKeyRsa):

                return RSA

        case oid.Equal(oidPublicKeyDsa):

                return DSA

        }

        return UnknownPublicKeyAlgorithm

}

// KeyUsage represents the set of actions that are valid for a given key. It's

// a bitmap of the KeyUsage* constants.

type KeyUsage int

const (

        KeyUsageDigitalSignature KeyUsage = 1 << iota

        KeyUsageContentCommitment

        KeyUsageKeyEncipherment

        KeyUsageDataEncipherment

        KeyUsageKeyAgreement

        KeyUsageCertSign

        KeyUsageCRLSign

        KeyUsageEncipherOnly

        KeyUsageDecipherOnly

)

// RFC 5280, 4.2.1.12  Extended Key Usage

//

// anyExtendedKeyUsage OBJECT IDENTIFIER ::= { id-ce-extKeyUsage 0 }

//

// id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }

//

// id-kp-serverAuth             OBJECT IDENTIFIER ::= { id-kp 1 }

// id-kp-clientAuth             OBJECT IDENTIFIER ::= { id-kp 2 }

// id-kp-codeSigning            OBJECT IDENTIFIER ::= { id-kp 3 }

// id-kp-emailProtection        OBJECT IDENTIFIER ::= { id-kp 4 }

// id-kp-timeStamping           OBJECT IDENTIFIER ::= { id-kp 8 }

// id-kp-OCSPSigning            OBJECT IDENTIFIER ::= { id-kp 9 }

var (

        oidExtKeyUsageAny             = asn1.ObjectIdentifier{2, 5, 29, 37, 0}

        oidExtKeyUsageServerAuth      = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 1}

        oidExtKeyUsageClientAuth      = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 2}

        oidExtKeyUsageCodeSigning     = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 3}

        oidExtKeyUsageEmailProtection = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 4}

        oidExtKeyUsageTimeStamping    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 8}

        oidExtKeyUsageOCSPSigning     = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 9}

)

// ExtKeyUsage represents an extended set of actions that are valid for a given key.

// Each of the ExtKeyUsage* constants define a unique action.

type ExtKeyUsage int

const (

        ExtKeyUsageAny ExtKeyUsage = iota

        ExtKeyUsageServerAuth

        ExtKeyUsageClientAuth

        ExtKeyUsageCodeSigning

        ExtKeyUsageEmailProtection

        ExtKeyUsageTimeStamping

        ExtKeyUsageOCSPSigning

)

// A Certificate represents an X.509 certificate.

type Certificate struct {

        Raw                     []byte // Complete ASN.1 DER content (certificate, signature algorithm and signature).

        RawTBSCertificate       []byte // Certificate part of raw ASN.1 DER content.

        RawSubjectPublicKeyInfo []byte // DER encoded SubjectPublicKeyInfo.

        RawSubject              []byte // DER encoded Subject

        RawIssuer               []byte // DER encoded Issuer

        Signature          []byte

        SignatureAlgorithm SignatureAlgorithm

        PublicKeyAlgorithm PublicKeyAlgorithm

        PublicKey          interface{}

        Version             int

        SerialNumber        *big.Int

        Issuer              pkix.Name

        Subject             pkix.Name

        NotBefore, NotAfter time.Time // Validity bounds.

        KeyUsage            KeyUsage

        ExtKeyUsage        []ExtKeyUsage           // Sequence of extended key usages.

        UnknownExtKeyUsage []asn1.ObjectIdentifier // Encountered extended key usages unknown to this package.

        BasicConstraintsValid bool // if true then the next two fields are valid.

        IsCA                  bool

        MaxPathLen            int

        SubjectKeyId   []byte

        AuthorityKeyId []byte

        // Subject Alternate Name values

        DNSNames       []string

        EmailAddresses []string

        // Name constraints

        PermittedDNSDomainsCritical bool // if true then the name constraints are marked critical.

        PermittedDNSDomains         []string

        PolicyIdentifiers []asn1.ObjectIdentifier

}

// UnsupportedAlgorithmError results from attempting to perform an operation

// that involves algorithms that are not currently implemented.

type UnsupportedAlgorithmError struct{}

func (UnsupportedAlgorithmError) Error() string {

        return "cannot verify signature: algorithm unimplemented"

}

// ConstraintViolationError results when a requested usage is not permitted by

// a certificate. For example: checking a signature when the public key isn't a

// certificate signing key.

type ConstraintViolationError struct{}

func (ConstraintViolationError) Error() string {

        return "invalid signature: parent certificate cannot sign this kind of certificate"

}

func (c *Certificate) Equal(other *Certificate) bool {

        return bytes.Equal(c.Raw, other.Raw)

}

// CheckSignatureFrom verifies that the signature on c is a valid signature

// from parent.

func (c *Certificate) CheckSignatureFrom(parent *Certificate) (err error) {

        // RFC 5280, 4.2.1.9:

        // "If the basic constraints extension is not present in a version 3

        // certificate, or the extension is present but the cA boolean is not

        // asserted, then the certified public key MUST NOT be used to verify

        // certificate signatures."

        if parent.Version == 3 && !parent.BasicConstraintsValid ||

                parent.BasicConstraintsValid && !parent.IsCA {

                return ConstraintViolationError{}

        }

        if parent.KeyUsage != 0 && parent.KeyUsage&KeyUsageCertSign == 0 {

                return ConstraintViolationError{}

        }

        if parent.PublicKeyAlgorithm == UnknownPublicKeyAlgorithm {

                return UnsupportedAlgorithmError{}

        }

        // TODO(agl): don't ignore the path length constraint.

        return parent.CheckSignature(c.SignatureAlgorithm, c.RawTBSCertificate, c.Signature)

}

// CheckSignature verifies that signature is a valid signature over signed from

// c's public key.

func (c *Certificate) CheckSignature(algo SignatureAlgorithm, signed, signature []byte) (err error) {

        var hashType crypto.Hash

        switch algo {

        case SHA1WithRSA, DSAWithSHA1:

                hashType = crypto.SHA1

        case SHA256WithRSA, DSAWithSHA256:

                hashType = crypto.SHA256

        case SHA384WithRSA:

                hashType = crypto.SHA384

        case SHA512WithRSA:

                hashType = crypto.SHA512

        default:

                return UnsupportedAlgorithmError{}

        }

        h := hashType.New()

        if h == nil {

                return UnsupportedAlgorithmError{}

        }

        h.Write(signed)

        digest := h.Sum(nil)

        switch pub := c.PublicKey.(type) {

        case *rsa.PublicKey:

                return rsa.VerifyPKCS1v15(pub, hashType, digest, signature)

        case *dsa.PublicKey:

                dsaSig := new(dsaSignature)

                if _, err := asn1.Unmarshal(signature, dsaSig); err != nil {

                        return err

                }

                if dsaSig.R.Sign() <= 0 || dsaSig.S.Sign() <= 0 {

                        return errors.New("DSA signature contained zero or negative values")

                }

                if !dsa.Verify(pub, digest, dsaSig.R, dsaSig.S) {

                        return errors.New("DSA verification failure")

                }

                return

        }

        return UnsupportedAlgorithmError{}

}

// CheckCRLSignature checks that the signature in crl is from c.

func (c *Certificate) CheckCRLSignature(crl *pkix.CertificateList) (err error) {

        algo := getSignatureAlgorithmFromOID(crl.SignatureAlgorithm.Algorithm)

        return c.CheckSignature(algo, crl.TBSCertList.Raw, crl.SignatureValue.RightAlign())

}

type UnhandledCriticalExtension struct{}

func (h UnhandledCriticalExtension) Error() string {

        return "unhandled critical extension"

}

type basicConstraints struct {

        IsCA       bool `asn1:"optional"`

        MaxPathLen int  `asn1:"optional"`

}

// RFC 5280 4.2.1.4

type policyInformation struct {

        Policy asn1.ObjectIdentifier

        // policyQualifiers omitted

}

// RFC 5280, 4.2.1.10

type nameConstraints struct {

        Permitted []generalSubtree `asn1:"optional,tag:0"`

        Excluded  []generalSubtree `asn1:"optional,tag:1"`

}

type generalSubtree struct {

        Name string `asn1:"tag:2,optional,ia5"`

        Min  int    `asn1:"optional,tag:0"`

        Max  int    `asn1:"optional,tag:1"`

}

func parsePublicKey(algo PublicKeyAlgorithm, keyData *publicKeyInfo) (interface{}, error) {

        asn1Data := keyData.PublicKey.RightAlign()

        switch algo {

        case RSA:

                p := new(rsaPublicKey)

                _, err := asn1.Unmarshal(asn1Data, p)

                if err != nil {

                        return nil, err

                }

                pub := &rsa.PublicKey{

                        E: p.E,

                        N: p.N,

                }

                return pub, nil

        case DSA:

                var p *big.Int

                _, err := asn1.Unmarshal(asn1Data, &p)

                if err != nil {

                        return nil, err

                }

                paramsData := keyData.Algorithm.Parameters.FullBytes

                params := new(dsaAlgorithmParameters)

                _, err = asn1.Unmarshal(paramsData, params)

                if err != nil {

                        return nil, err

                }

                if p.Sign() <= 0 || params.P.Sign() <= 0 || params.Q.Sign() <= 0 || params.G.Sign() <= 0 {

                        return nil, errors.New("zero or negative DSA parameter")

                }

                pub := &dsa.PublicKey{

                        Parameters: dsa.Parameters{

                                P: params.P,

                                Q: params.Q,

                                G: params.G,

                        },

                        Y: p,

                }

                return pub, nil

        default:

                return nil, nil

        }

        panic("unreachable")

}

func parseCertificate(in *certificate) (*Certificate, error) {

        out := new(Certificate)

        out.Raw = in.Raw

        out.RawTBSCertificate = in.TBSCertificate.Raw

        out.RawSubjectPublicKeyInfo = in.TBSCertificate.PublicKey.Raw

        out.RawSubject = in.TBSCertificate.Subject.FullBytes

        out.RawIssuer = in.TBSCertificate.Issuer.FullBytes

        out.Signature = in.SignatureValue.RightAlign()

        out.SignatureAlgorithm =

                getSignatureAlgorithmFromOID(in.TBSCertificate.SignatureAlgorithm.Algorithm)

        out.PublicKeyAlgorithm =

                getPublicKeyAlgorithmFromOID(in.TBSCertificate.PublicKey.Algorithm.Algorithm)

        var err error

        out.PublicKey, err = parsePublicKey(out.PublicKeyAlgorithm, &in.TBSCertificate.PublicKey)

        if err != nil {

                return nil, err

        }

        if in.TBSCertificate.SerialNumber.Sign() < 0 {

                return nil, errors.New("negative serial number")

        }

        out.Version = in.TBSCertificate.Version + 1

        out.SerialNumber = in.TBSCertificate.SerialNumber

        var issuer, subject pkix.RDNSequence

        if _, err := asn1.Unmarshal(in.TBSCertificate.Subject.FullBytes, &subject); err != nil {

                return nil, err

        }

        if _, err := asn1.Unmarshal(in.TBSCertificate.Issuer.FullBytes, &issuer); err != nil {

                return nil, err

        }

        out.Issuer.FillFromRDNSequence(&issuer)

        out.Subject.FillFromRDNSequence(&subject)

        out.NotBefore = in.TBSCertificate.Validity.NotBefore

        out.NotAfter = in.TBSCertificate.Validity.NotAfter

        for _, e := range in.TBSCertificate.Extensions {

                if len(e.Id) == 4 && e.Id[0] == 2 && e.Id[1] == 5 && e.Id[2] == 29 {

                        switch e.Id[3] {

                        case 15:

                                // RFC 5280, 4.2.1.3

                                var usageBits asn1.BitString

                                _, err := asn1.Unmarshal(e.Value, &usageBits)

                                if err == nil {

                                        var usage int

                                        for i := 0; i < 9; i++ {

                                                if usageBits.At(i) != 0 {

                                                        usage |= 1 << uint(i)

                                                }

                                        }

                                        out.KeyUsage = KeyUsage(usage)

                                        continue

                                }

                        case 19:

                                // RFC 5280, 4.2.1.9

                                var constraints basicConstraints

                                _, err := asn1.Unmarshal(e.Value, &constraints)

                                if err == nil {

                                        out.BasicConstraintsValid = true

                                        out.IsCA = constraints.IsCA

                                        out.MaxPathLen = constraints.MaxPathLen

                                        continue

                                }

                        case 17:

                                // RFC 5280, 4.2.1.6

                                // SubjectAltName ::= GeneralNames

                                //

                                // GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

                                //

                                // GeneralName ::= CHOICE {

                                //      otherName                       [0]     OtherName,

                                //      rfc822Name                      [1]     IA5String,

                                //      dNSName                         [2]     IA5String,

                                //      x400Address                     [3]     ORAddress,

                                //      directoryName                   [4]     Name,

                                //      ediPartyName                    [5]     EDIPartyName,

                                //      uniformResourceIdentifier       [6]     IA5String,

                                //      iPAddress                       [7]     OCTET STRING,

                                //      registeredID                    [8]     OBJECT IDENTIFIER }

                                var seq asn1.RawValue

                                _, err := asn1.Unmarshal(e.Value, &seq)

                                if err != nil {

                                        return nil, err

                                }

                                if !seq.IsCompound || seq.Tag != 16 || seq.Class != 0 {

                                        return nil, asn1.StructuralError{Msg: "bad SAN sequence"}

                                }

                                parsedName := false

                                rest := seq.Bytes

                                for len(rest) > 0 {

                                        var v asn1.RawValue

                                        rest, err = asn1.Unmarshal(rest, &v)

                                        if err != nil {

                                                return nil, err

                                        }

                                        switch v.Tag {

                                        case 1:

                                                out.EmailAddresses = append(out.EmailAddresses, string(v.Bytes))

                                                parsedName = true

                                        case 2:

                                                out.DNSNames = append(out.DNSNames, string(v.Bytes))

                                                parsedName = true

                                        }

                                }

                                if parsedName {

                                        continue

                                }

                                // If we didn't parse any of the names then we

                                // fall through to the critical check below.

                        case 30:

                                // RFC 5280, 4.2.1.10

                                // NameConstraints ::= SEQUENCE {

                                //      permittedSubtrees       [0]     GeneralSubtrees OPTIONAL,

                                //      excludedSubtrees        [1]     GeneralSubtrees OPTIONAL }

                                //

                                // GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

                                //

                                // GeneralSubtree ::= SEQUENCE {

                                //      base                    GeneralName,

                                //      minimum         [0]     BaseDistance DEFAULT 0,

                                //      maximum         [1]     BaseDistance OPTIONAL }

                                //

                                // BaseDistance ::= INTEGER (0..MAX)

                                var constraints nameConstraints

                                _, err := asn1.Unmarshal(e.Value, &constraints)

                                if err != nil {

                                        return nil, err

                                }

                                if len(constraints.Excluded) > 0 && e.Critical {

                                        return out, UnhandledCriticalExtension{}

                                }

                                for _, subtree := range constraints.Permitted {

                                        if subtree.Min > 0 || subtree.Max > 0 || len(subtree.Name) == 0 {

                                                if e.Critical {

                                                        return out, UnhandledCriticalExtension{}

                                                }

                                                continue

                                        }

                                        out.PermittedDNSDomains = append(out.PermittedDNSDomains, subtree.Name)

                                }

                                continue

                        case 35:

                                // RFC 5280, 4.2.1.1

                                var a authKeyId

                                _, err = asn1.Unmarshal(e.Value, &a)

                                if err != nil {

                                        return nil, err

                                }

                                out.AuthorityKeyId = a.Id

                                continue

                        case 37:

                                // RFC 5280, 4.2.1.12.  Extended Key Usage

                                // id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }

                                //

                                // ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

                                //

                                // KeyPurposeId ::= OBJECT IDENTIFIER

                                var keyUsage []asn1.ObjectIdentifier

                                _, err = asn1.Unmarshal(e.Value, &keyUsage)

                                if err != nil {

                                        return nil, err

                                }

                                for _, u := range keyUsage {

                                        switch {

                                        case u.Equal(oidExtKeyUsageAny):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageAny)

                                        case u.Equal(oidExtKeyUsageServerAuth):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageServerAuth)

                                        case u.Equal(oidExtKeyUsageClientAuth):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageClientAuth)

                                        case u.Equal(oidExtKeyUsageCodeSigning):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageCodeSigning)

                                        case u.Equal(oidExtKeyUsageEmailProtection):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageEmailProtection)

                                        case u.Equal(oidExtKeyUsageTimeStamping):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageTimeStamping)

                                        case u.Equal(oidExtKeyUsageOCSPSigning):

                                                out.ExtKeyUsage = append(out.ExtKeyUsage, ExtKeyUsageOCSPSigning)

                                        default:

                                                out.UnknownExtKeyUsage = append(out.UnknownExtKeyUsage, u)

                                        }

                                }

                                continue

                        case 14:

                                // RFC 5280, 4.2.1.2

                                var keyid []byte

                                _, err = asn1.Unmarshal(e.Value, &keyid)

                                if err != nil {

                                        return nil, err

                                }

                                out.SubjectKeyId = keyid

                                continue

                        case 32:

                                // RFC 5280 4.2.1.4: Certificate Policies

                                var policies []policyInformation

                                if _, err = asn1.Unmarshal(e.Value, &policies); err != nil {

                                        return nil, err

                                }

                                out.PolicyIdentifiers = make([]asn1.ObjectIdentifier, len(policies))

                                for i, policy := range policies {

                                        out.PolicyIdentifiers[i] = policy.Policy

                                }

                        }

                }

                if e.Critical {

                        return out, UnhandledCriticalExtension{}

                }

        }

        return out, nil

}

// ParseCertificate parses a single certificate from the given ASN.1 DER data.

func ParseCertificate(asn1Data []byte) (*Certificate, error) {

        var cert certificate

        rest, err := asn1.Unmarshal(asn1Data, &cert)

        if err != nil {

                return nil, err

        }

        if len(rest) > 0 {

                return nil, asn1.SyntaxError{Msg: "trailing data"}

        }

        return parseCertificate(&cert)

}

// ParseCertificates parses one or more certificates from the given ASN.1 DER

// data. The certificates must be concatenated with no intermediate padding.

func ParseCertificates(asn1Data []byte) ([]*Certificate, error) {

        var v []*certificate

        for len(asn1Data) > 0 {

                cert := new(certificate)

                var err error

                asn1Data, err = asn1.Unmarshal(asn1Data, cert)

                if err != nil {

                        return nil, err

                }

                v = append(v, cert)

        }

        ret := make([]*Certificate, len(v))

        for i, ci := range v {

                cert, err := parseCertificate(ci)

                if err != nil {

                        return nil, err

                }

                ret[i] = cert

        }

        return ret, nil

}

func reverseBitsInAByte(in byte) byte {

        b1 := in>>4 | in<<4

        b2 := b1>>2&0x33 | b1<<2&0xcc

        b3 := b2>>1&0x55 | b2<<1&0xaa

        return b3

}

var (

        oidExtensionSubjectKeyId        = []int{2, 5, 29, 14}

        oidExtensionKeyUsage            = []int{2, 5, 29, 15}

        oidExtensionAuthorityKeyId      = []int{2, 5, 29, 35}

        oidExtensionBasicConstraints    = []int{2, 5, 29, 19}

        oidExtensionSubjectAltName      = []int{2, 5, 29, 17}

        oidExtensionCertificatePolicies = []int{2, 5, 29, 32}

        oidExtensionNameConstraints     = []int{2, 5, 29, 30}

)

func buildExtensions(template *Certificate) (ret []pkix.Extension, err error) {

        ret = make([]pkix.Extension, 7 /* maximum number of elements. */ )

        n := 0

        if template.KeyUsage != 0 {

                ret[n].Id = oidExtensionKeyUsage

                ret[n].Critical = true

                var a [2]byte

                a[0] = reverseBitsInAByte(byte(template.KeyUsage))

                a[1] = reverseBitsInAByte(byte(template.KeyUsage >> 8))

                l := 1

                if a[1] != 0 {

                        l = 2

                }

                ret[n].Value, err = asn1.Marshal(asn1.BitString{Bytes: a[0:l], BitLength: l * 8})

                if err != nil {

                        return

                }

                n++

        }

        if template.BasicConstraintsValid {

                ret[n].Id = oidExtensionBasicConstraints

                ret[n].Value, err = asn1.Marshal(basicConstraints{template.IsCA, template.MaxPathLen})

                ret[n].Critical = true

                if err != nil {

                        return

                }

                n++

        }

        if len(template.SubjectKeyId) > 0 {

                ret[n].Id = oidExtensionSubjectKeyId

                ret[n].Value, err = asn1.Marshal(template.SubjectKeyId)

                if err != nil {

                        return

                }

                n++

        }

        if len(template.AuthorityKeyId) > 0 {

                ret[n].Id = oidExtensionAuthorityKeyId

                ret[n].Value, err = asn1.Marshal(authKeyId{template.AuthorityKeyId})

                if err != nil {

                        return

                }

                n++

        }

        if len(template.DNSNames) > 0 {

                ret[n].Id = oidExtensionSubjectAltName

                rawValues := make([]asn1.RawValue, len(template.DNSNames))

                for i, name := range template.DNSNames {

                        rawValues[i] = asn1.RawValue{Tag: 2, Class: 2, Bytes: []byte(name)}

                }

                ret[n].Value, err = asn1.Marshal(rawValues)

                if err != nil {

                        return

                }

                n++

        }

        if len(template.PolicyIdentifiers) > 0 {

                ret[n].Id = oidExtensionCertificatePolicies

                policies := make([]policyInformation, len(template.PolicyIdentifiers))

                for i, policy := range template.PolicyIdentifiers {

                        policies[i].Policy = policy

                }

                ret[n].Value, err = asn1.Marshal(policies)

                if err != nil {

                        return

                }

                n++

        }

        if len(template.PermittedDNSDomains) > 0 {

                ret[n].Id = oidExtensionNameConstraints

                ret[n].Critical = template.PermittedDNSDomainsCritical

                var out nameConstraints

                out.Permitted = make([]generalSubtree, len(template.PermittedDNSDomains))

                for i, permitted := range template.PermittedDNSDomains {

                        out.Permitted[i] = generalSubtree{Name: permitted}

                }

                ret[n].Value, err = asn1.Marshal(out)

                if err != nil {

                        return

                }

                n++

        }

        // Adding another extension here? Remember to update the maximum number

        // of elements in the make() at the top of the function.

        return ret[0:n], nil

}

var (

        oidSHA1WithRSA = []int{1, 2, 840, 113549, 1, 1, 5}

        oidRSA         = []int{1, 2, 840, 113549, 1, 1, 1}

)

func subjectBytes(cert *Certificate) ([]byte, error) {

        if len(cert.RawSubject) > 0 {

                return cert.RawSubject, nil

        }

        return asn1.Marshal(cert.Subject.ToRDNSequence())

}

// CreateCertificate creates a new certificate based on a template. The

// following members of template are used: SerialNumber, Subject, NotBefore,

// NotAfter, KeyUsage, BasicConstraintsValid, IsCA, MaxPathLen, SubjectKeyId,

// DNSNames, PermittedDNSDomainsCritical, PermittedDNSDomains.

//

// The certificate is signed by parent. If parent is equal to template then the

// certificate is self-signed. The parameter pub is the public key of the

// signee and priv is the private key of the signer.

//

// The returned slice is the certificate in DER encoding.

//

// The only supported key type is RSA (*rsa.PublicKey for pub, *rsa.PrivateKey

// for priv).

func CreateCertificate(rand io.Reader, template, parent *Certificate, pub interface{}, priv interface{}) (cert []byte, err error) {

        rsaPub, ok := pub.(*rsa.PublicKey)

        if !ok {

                return nil, errors.New("x509: non-RSA public keys not supported")

        }

        rsaPriv, ok := priv.(*rsa.PrivateKey)

        if !ok {

                return nil, errors.New("x509: non-RSA private keys not supported")

        }

        asn1PublicKey, err := asn1.Marshal(rsaPublicKey{

                N: rsaPub.N,

                E: rsaPub.E,

        })

        if err != nil {

                return