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feat: add processIssuing (#152)
[bytom/vapor.git] / vendor / github.com / bytom / crypto / sm2 / x509.go
diff --git a/vendor/github.com/bytom/crypto/sm2/x509.go b/vendor/github.com/bytom/crypto/sm2/x509.go
new file mode 100644 (file)
index 0000000..d786ca2
--- /dev/null
@@ -0,0 +1,2514 @@
+// crypto/x509 add sm2 support
+package sm2
+
+import (
+       "bytes"
+       "crypto"
+       "crypto/dsa"
+       "crypto/ecdsa"
+       "crypto/elliptic"
+       "crypto/md5"
+       "crypto/rand"
+       "crypto/rsa"
+       "crypto/sha1"
+       "crypto/sha256"
+       "crypto/sha512"
+       "crypto/x509/pkix"
+       "encoding/asn1"
+       "encoding/pem"
+       "errors"
+       "fmt"
+       "hash"
+       "io"
+       "io/ioutil"
+       "math/big"
+       "net"
+       "os"
+       "strconv"
+       "time"
+
+       "golang.org/x/crypto/ripemd160"
+       "golang.org/x/crypto/sha3"
+
+       "github.com/bytom/crypto/sm3"
+)
+
+// 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".
+//
+// Supported key types include RSA, DSA, and ECDSA. Unknown key
+// types result in an error.
+//
+// On success, pub will be of type *rsa.PublicKey, *dsa.PublicKey,
+// or *ecdsa.PublicKey.
+func ParsePKIXPublicKey(derBytes []byte) (pub interface{}, err error) {
+       var pki publicKeyInfo
+
+       if rest, err := asn1.Unmarshal(derBytes, &pki); err != nil {
+               return nil, err
+       } else if len(rest) != 0 {
+               return nil, errors.New("x509: trailing data after ASN.1 of public-key")
+       }
+       algo := getPublicKeyAlgorithmFromOID(pki.Algorithm.Algorithm)
+       if algo == UnknownPublicKeyAlgorithm {
+               return nil, errors.New("x509: unknown public key algorithm")
+       }
+       return parsePublicKey(algo, &pki)
+}
+
+func marshalPublicKey(pub interface{}) (publicKeyBytes []byte, publicKeyAlgorithm pkix.AlgorithmIdentifier, err error) {
+       switch pub := pub.(type) {
+       case *rsa.PublicKey:
+               publicKeyBytes, err = asn1.Marshal(rsaPublicKey{
+                       N: pub.N,
+                       E: pub.E,
+               })
+               if err != nil {
+                       return nil, pkix.AlgorithmIdentifier{}, err
+               }
+               publicKeyAlgorithm.Algorithm = oidPublicKeyRSA
+               // This is a NULL parameters value which is required by
+               // https://tools.ietf.org/html/rfc3279#section-2.3.1.
+               publicKeyAlgorithm.Parameters = asn1.RawValue{
+                       Tag: 5,
+               }
+       case *ecdsa.PublicKey:
+               publicKeyBytes = elliptic.Marshal(pub.Curve, pub.X, pub.Y)
+               oid, ok := oidFromNamedCurve(pub.Curve)
+               if !ok {
+                       return nil, pkix.AlgorithmIdentifier{}, errors.New("x509: unsupported elliptic curve")
+               }
+               publicKeyAlgorithm.Algorithm = oidPublicKeyECDSA
+               var paramBytes []byte
+               paramBytes, err = asn1.Marshal(oid)
+               if err != nil {
+                       return
+               }
+               publicKeyAlgorithm.Parameters.FullBytes = paramBytes
+       case *PublicKey:
+               publicKeyBytes = elliptic.Marshal(pub.Curve, pub.X, pub.Y)
+               oid, ok := oidFromNamedCurve(pub.Curve)
+               if !ok {
+                       return nil, pkix.AlgorithmIdentifier{}, errors.New("x509: unsupported SM2 curve")
+               }
+               publicKeyAlgorithm.Algorithm = oidPublicKeyECDSA
+               var paramBytes []byte
+               paramBytes, err = asn1.Marshal(oid)
+               if err != nil {
+                       return
+               }
+               publicKeyAlgorithm.Parameters.FullBytes = paramBytes
+       default:
+               return nil, pkix.AlgorithmIdentifier{}, errors.New("x509: only RSA and ECDSA(SM2) public keys supported")
+       }
+
+       return publicKeyBytes, publicKeyAlgorithm, nil
+}
+
+// MarshalPKIXPublicKey serialises a public key to DER-encoded PKIX format.
+func MarshalPKIXPublicKey(pub interface{}) ([]byte, error) {
+       var publicKeyBytes []byte
+       var publicKeyAlgorithm pkix.AlgorithmIdentifier
+       var err error
+
+       if publicKeyBytes, publicKeyAlgorithm, err = marshalPublicKey(pub); err != nil {
+               return nil, err
+       }
+
+       pkix := pkixPublicKey{
+               Algo: publicKeyAlgorithm,
+               BitString: asn1.BitString{
+                       Bytes:     publicKeyBytes,
+                       BitLength: 8 * len(publicKeyBytes),
+               },
+       }
+
+       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:0,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 ecdsaSignature dsaSignature
+
+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
+
+type Hash uint
+
+func init() {
+       RegisterHash(MD4, nil)
+       RegisterHash(MD5, md5.New)
+       RegisterHash(SHA1, sha1.New)
+       RegisterHash(SHA224, sha256.New224)
+       RegisterHash(SHA256, sha256.New)
+       RegisterHash(SHA384, sha512.New384)
+       RegisterHash(SHA512, sha512.New)
+       RegisterHash(MD5SHA1, nil)
+       RegisterHash(RIPEMD160, ripemd160.New)
+       RegisterHash(SHA3_224, sha3.New224)
+       RegisterHash(SHA3_256, sha3.New256)
+       RegisterHash(SHA3_384, sha3.New384)
+       RegisterHash(SHA3_512, sha3.New512)
+       RegisterHash(SHA512_224, sha512.New512_224)
+       RegisterHash(SHA512_256, sha512.New512_256)
+       RegisterHash(SM3, sm3.New)
+}
+
+// HashFunc simply returns the value of h so that Hash implements SignerOpts.
+func (h Hash) HashFunc() crypto.Hash {
+       return crypto.Hash(h)
+}
+
+const (
+       MD4        Hash = 1 + iota // import golang.org/x/crypto/md4
+       MD5                        // import crypto/md5
+       SHA1                       // import crypto/sha1
+       SHA224                     // import crypto/sha256
+       SHA256                     // import crypto/sha256
+       SHA384                     // import crypto/sha512
+       SHA512                     // import crypto/sha512
+       MD5SHA1                    // no implementation; MD5+SHA1 used for TLS RSA
+       RIPEMD160                  // import golang.org/x/crypto/ripemd160
+       SHA3_224                   // import golang.org/x/crypto/sha3
+       SHA3_256                   // import golang.org/x/crypto/sha3
+       SHA3_384                   // import golang.org/x/crypto/sha3
+       SHA3_512                   // import golang.org/x/crypto/sha3
+       SHA512_224                 // import crypto/sha512
+       SHA512_256                 // import crypto/sha512
+       SM3
+       maxHash
+)
+
+var digestSizes = []uint8{
+       MD4:        16,
+       MD5:        16,
+       SHA1:       20,
+       SHA224:     28,
+       SHA256:     32,
+       SHA384:     48,
+       SHA512:     64,
+       SHA512_224: 28,
+       SHA512_256: 32,
+       SHA3_224:   28,
+       SHA3_256:   32,
+       SHA3_384:   48,
+       SHA3_512:   64,
+       MD5SHA1:    36,
+       RIPEMD160:  20,
+       SM3:        32,
+}
+
+// Size returns the length, in bytes, of a digest resulting from the given hash
+// function. It doesn't require that the hash function in question be linked
+// into the program.
+func (h Hash) Size() int {
+       if h > 0 && h < maxHash {
+               return int(digestSizes[h])
+       }
+       panic("crypto: Size of unknown hash function")
+}
+
+var hashes = make([]func() hash.Hash, maxHash)
+
+// New returns a new hash.Hash calculating the given hash function. New panics
+// if the hash function is not linked into the binary.
+func (h Hash) New() hash.Hash {
+       if h > 0 && h < maxHash {
+               f := hashes[h]
+               if f != nil {
+                       return f()
+               }
+       }
+       panic("crypto: requested hash function #" + strconv.Itoa(int(h)) + " is unavailable")
+}
+
+// Available reports whether the given hash function is linked into the binary.
+func (h Hash) Available() bool {
+       return h < maxHash && hashes[h] != nil
+}
+
+// RegisterHash registers a function that returns a new instance of the given
+// hash function. This is intended to be called from the init function in
+// packages that implement hash functions.
+func RegisterHash(h Hash, f func() hash.Hash) {
+       if h >= maxHash {
+               panic("crypto: RegisterHash of unknown hash function")
+       }
+       hashes[h] = f
+}
+
+const (
+       UnknownSignatureAlgorithm SignatureAlgorithm = iota
+       MD2WithRSA
+       MD5WithRSA
+       //      SM3WithRSA reserve
+       SHA1WithRSA
+       SHA256WithRSA
+       SHA384WithRSA
+       SHA512WithRSA
+       DSAWithSHA1
+       DSAWithSHA256
+       ECDSAWithSHA1
+       ECDSAWithSHA256
+       ECDSAWithSHA384
+       ECDSAWithSHA512
+       SHA256WithRSAPSS
+       SHA384WithRSAPSS
+       SHA512WithRSAPSS
+       SM2WithSM3
+       SM2WithSHA1
+       SM2WithSHA256
+)
+
+func (algo SignatureAlgorithm) isRSAPSS() bool {
+       switch algo {
+       case SHA256WithRSAPSS, SHA384WithRSAPSS, SHA512WithRSAPSS:
+               return true
+       default:
+               return false
+       }
+}
+
+var algoName = [...]string{
+       MD2WithRSA:  "MD2-RSA",
+       MD5WithRSA:  "MD5-RSA",
+       SHA1WithRSA: "SHA1-RSA",
+       //      SM3WithRSA:       "SM3-RSA", reserve
+       SHA256WithRSA:    "SHA256-RSA",
+       SHA384WithRSA:    "SHA384-RSA",
+       SHA512WithRSA:    "SHA512-RSA",
+       SHA256WithRSAPSS: "SHA256-RSAPSS",
+       SHA384WithRSAPSS: "SHA384-RSAPSS",
+       SHA512WithRSAPSS: "SHA512-RSAPSS",
+       DSAWithSHA1:      "DSA-SHA1",
+       DSAWithSHA256:    "DSA-SHA256",
+       ECDSAWithSHA1:    "ECDSA-SHA1",
+       ECDSAWithSHA256:  "ECDSA-SHA256",
+       ECDSAWithSHA384:  "ECDSA-SHA384",
+       ECDSAWithSHA512:  "ECDSA-SHA512",
+       SM2WithSM3:       "SM2-SM3",
+       SM2WithSHA1:      "SM2-SHA1",
+       SM2WithSHA256:    "SM2-SHA256",
+}
+
+func (algo SignatureAlgorithm) String() string {
+       if 0 < algo && int(algo) < len(algoName) {
+               return algoName[algo]
+       }
+       return strconv.Itoa(int(algo))
+}
+
+type PublicKeyAlgorithm int
+
+const (
+       UnknownPublicKeyAlgorithm PublicKeyAlgorithm = iota
+       RSA
+       DSA
+       ECDSA
+)
+
+// 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 IDENTIFIER ::= { 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 3279 2.2.3 ECDSA Signature Algorithm
+//
+// ecdsa-with-SHA1 OBJECT IDENTIFIER ::= {
+//       iso(1) member-body(2) us(840) ansi-x962(10045)
+//    signatures(4) ecdsa-with-SHA1(1)}
+//
+//
+// 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
+//
+// dsaWithSha256 OBJECT IDENTIFIER ::= {
+//    joint-iso-ccitt(2) country(16) us(840) organization(1) gov(101)
+//    csor(3) algorithms(4) id-dsa-with-sha2(3) 2}
+//
+// RFC 5758 3.2 ECDSA Signature Algorithm
+//
+// ecdsa-with-SHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
+//    us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 2 }
+//
+// ecdsa-with-SHA384 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
+//    us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 3 }
+//
+// ecdsa-with-SHA512 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
+//    us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 4 }
+
+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}
+       oidSignatureRSAPSS          = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 10}
+       oidSignatureDSAWithSHA1     = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 3}
+       oidSignatureDSAWithSHA256   = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 3, 2}
+       oidSignatureECDSAWithSHA1   = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 1}
+       oidSignatureECDSAWithSHA256 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 2}
+       oidSignatureECDSAWithSHA384 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 3}
+       oidSignatureECDSAWithSHA512 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 4}
+       oidSignatureSM2WithSM3      = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 501}
+       oidSignatureSM2WithSHA1     = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 502}
+       oidSignatureSM2WithSHA256   = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 503}
+       //      oidSignatureSM3WithRSA      = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 504}
+
+       oidSM3    = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 401, 1}
+       oidSHA256 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 1}
+       oidSHA384 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 2}
+       oidSHA512 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 3}
+
+       oidMGF1 = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 8}
+
+       // oidISOSignatureSHA1WithRSA means the same as oidSignatureSHA1WithRSA
+       // but it's specified by ISO. Microsoft's makecert.exe has been known
+       // to produce certificates with this OID.
+       oidISOSignatureSHA1WithRSA = asn1.ObjectIdentifier{1, 3, 14, 3, 2, 29}
+)
+
+var signatureAlgorithmDetails = []struct {
+       algo       SignatureAlgorithm
+       oid        asn1.ObjectIdentifier
+       pubKeyAlgo PublicKeyAlgorithm
+       hash       Hash
+}{
+       {MD2WithRSA, oidSignatureMD2WithRSA, RSA, Hash(0) /* no value for MD2 */},
+       {MD5WithRSA, oidSignatureMD5WithRSA, RSA, MD5},
+       {SHA1WithRSA, oidSignatureSHA1WithRSA, RSA, SHA1},
+       {SHA1WithRSA, oidISOSignatureSHA1WithRSA, RSA, SHA1},
+       {SHA256WithRSA, oidSignatureSHA256WithRSA, RSA, SHA256},
+       {SHA384WithRSA, oidSignatureSHA384WithRSA, RSA, SHA384},
+       {SHA512WithRSA, oidSignatureSHA512WithRSA, RSA, SHA512},
+       {SHA256WithRSAPSS, oidSignatureRSAPSS, RSA, SHA256},
+       {SHA384WithRSAPSS, oidSignatureRSAPSS, RSA, SHA384},
+       {SHA512WithRSAPSS, oidSignatureRSAPSS, RSA, SHA512},
+       {DSAWithSHA1, oidSignatureDSAWithSHA1, DSA, SHA1},
+       {DSAWithSHA256, oidSignatureDSAWithSHA256, DSA, SHA256},
+       {ECDSAWithSHA1, oidSignatureECDSAWithSHA1, ECDSA, SHA1},
+       {ECDSAWithSHA256, oidSignatureECDSAWithSHA256, ECDSA, SHA256},
+       {ECDSAWithSHA384, oidSignatureECDSAWithSHA384, ECDSA, SHA384},
+       {ECDSAWithSHA512, oidSignatureECDSAWithSHA512, ECDSA, SHA512},
+       {SM2WithSM3, oidSignatureSM2WithSM3, ECDSA, SM3},
+       {SM2WithSHA1, oidSignatureSM2WithSHA1, ECDSA, SHA1},
+       {SM2WithSHA256, oidSignatureSM2WithSHA256, ECDSA, SHA256},
+       //      {SM3WithRSA, oidSignatureSM3WithRSA, RSA, SM3},
+}
+
+// pssParameters reflects the parameters in an AlgorithmIdentifier that
+// specifies RSA PSS. See https://tools.ietf.org/html/rfc3447#appendix-A.2.3
+type pssParameters struct {
+       // The following three fields are not marked as
+       // optional because the default values specify SHA-1,
+       // which is no longer suitable for use in signatures.
+       Hash         pkix.AlgorithmIdentifier `asn1:"explicit,tag:0"`
+       MGF          pkix.AlgorithmIdentifier `asn1:"explicit,tag:1"`
+       SaltLength   int                      `asn1:"explicit,tag:2"`
+       TrailerField int                      `asn1:"optional,explicit,tag:3,default:1"`
+}
+
+// rsaPSSParameters returns an asn1.RawValue suitable for use as the Parameters
+// in an AlgorithmIdentifier that specifies RSA PSS.
+func rsaPSSParameters(hashFunc Hash) asn1.RawValue {
+       var hashOID asn1.ObjectIdentifier
+
+       switch hashFunc {
+       case SHA256:
+               hashOID = oidSHA256
+       case SHA384:
+               hashOID = oidSHA384
+       case SHA512:
+               hashOID = oidSHA512
+       }
+
+       params := pssParameters{
+               Hash: pkix.AlgorithmIdentifier{
+                       Algorithm: hashOID,
+                       Parameters: asn1.RawValue{
+                               Tag: 5, /* ASN.1 NULL */
+                       },
+               },
+               MGF: pkix.AlgorithmIdentifier{
+                       Algorithm: oidMGF1,
+               },
+               SaltLength:   hashFunc.Size(),
+               TrailerField: 1,
+       }
+
+       mgf1Params := pkix.AlgorithmIdentifier{
+               Algorithm: hashOID,
+               Parameters: asn1.RawValue{
+                       Tag: 5, /* ASN.1 NULL */
+               },
+       }
+
+       var err error
+       params.MGF.Parameters.FullBytes, err = asn1.Marshal(mgf1Params)
+       if err != nil {
+               panic(err)
+       }
+
+       serialized, err := asn1.Marshal(params)
+       if err != nil {
+               panic(err)
+       }
+
+       return asn1.RawValue{FullBytes: serialized}
+}
+
+func getSignatureAlgorithmFromAI(ai pkix.AlgorithmIdentifier) SignatureAlgorithm {
+       if !ai.Algorithm.Equal(oidSignatureRSAPSS) {
+               for _, details := range signatureAlgorithmDetails {
+                       if ai.Algorithm.Equal(details.oid) {
+                               return details.algo
+                       }
+               }
+               return UnknownSignatureAlgorithm
+       }
+
+       // RSA PSS is special because it encodes important parameters
+       // in the Parameters.
+
+       var params pssParameters
+       if _, err := asn1.Unmarshal(ai.Parameters.FullBytes, &params); err != nil {
+               return UnknownSignatureAlgorithm
+       }
+
+       var mgf1HashFunc pkix.AlgorithmIdentifier
+       if _, err := asn1.Unmarshal(params.MGF.Parameters.FullBytes, &mgf1HashFunc); err != nil {
+               return UnknownSignatureAlgorithm
+       }
+
+       // PSS is greatly overburdened with options. This code forces
+       // them into three buckets by requiring that the MGF1 hash
+       // function always match the message hash function (as
+       // recommended in
+       // https://tools.ietf.org/html/rfc3447#section-8.1), that the
+       // salt length matches the hash length, and that the trailer
+       // field has the default value.
+       asn1NULL := []byte{0x05, 0x00}
+       if !bytes.Equal(params.Hash.Parameters.FullBytes, asn1NULL) ||
+               !params.MGF.Algorithm.Equal(oidMGF1) ||
+               !mgf1HashFunc.Algorithm.Equal(params.Hash.Algorithm) ||
+               !bytes.Equal(mgf1HashFunc.Parameters.FullBytes, asn1NULL) ||
+               params.TrailerField != 1 {
+               return UnknownSignatureAlgorithm
+       }
+
+       switch {
+       case params.Hash.Algorithm.Equal(oidSHA256) && params.SaltLength == 32:
+               return SHA256WithRSAPSS
+       case params.Hash.Algorithm.Equal(oidSHA384) && params.SaltLength == 48:
+               return SHA384WithRSAPSS
+       case params.Hash.Algorithm.Equal(oidSHA512) && params.SaltLength == 64:
+               return SHA512WithRSAPSS
+       }
+
+       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 }
+//
+// RFC 5480, 2.1.1 Unrestricted Algorithm Identifier and Parameters
+//
+// id-ecPublicKey OBJECT IDENTIFIER ::= {
+//       iso(1) member-body(2) us(840) ansi-X9-62(10045) keyType(2) 1 }
+var (
+       oidPublicKeyRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 1}
+       oidPublicKeyDSA   = asn1.ObjectIdentifier{1, 2, 840, 10040, 4, 1}
+       oidPublicKeyECDSA = asn1.ObjectIdentifier{1, 2, 840, 10045, 2, 1}
+)
+
+func getPublicKeyAlgorithmFromOID(oid asn1.ObjectIdentifier) PublicKeyAlgorithm {
+       switch {
+       case oid.Equal(oidPublicKeyRSA):
+               return RSA
+       case oid.Equal(oidPublicKeyDSA):
+               return DSA
+       case oid.Equal(oidPublicKeyECDSA):
+               return ECDSA
+       }
+       return UnknownPublicKeyAlgorithm
+}
+
+// RFC 5480, 2.1.1.1. Named Curve
+//
+// secp224r1 OBJECT IDENTIFIER ::= {
+//   iso(1) identified-organization(3) certicom(132) curve(0) 33 }
+//
+// secp256r1 OBJECT IDENTIFIER ::= {
+//   iso(1) member-body(2) us(840) ansi-X9-62(10045) curves(3)
+//   prime(1) 7 }
+//
+// secp384r1 OBJECT IDENTIFIER ::= {
+//   iso(1) identified-organization(3) certicom(132) curve(0) 34 }
+//
+// secp521r1 OBJECT IDENTIFIER ::= {
+//   iso(1) identified-organization(3) certicom(132) curve(0) 35 }
+//
+// NB: secp256r1 is equivalent to prime256v1
+var (
+       oidNamedCurveP224    = asn1.ObjectIdentifier{1, 3, 132, 0, 33}
+       oidNamedCurveP256    = asn1.ObjectIdentifier{1, 2, 840, 10045, 3, 1, 7}
+       oidNamedCurveP384    = asn1.ObjectIdentifier{1, 3, 132, 0, 34}
+       oidNamedCurveP521    = asn1.ObjectIdentifier{1, 3, 132, 0, 35}
+       oidNamedCurveP256SM2 = asn1.ObjectIdentifier{1, 2, 156, 10197, 1, 301} // I get the SM2 ID through parsing the pem file generated by gmssl
+)
+
+func namedCurveFromOID(oid asn1.ObjectIdentifier) elliptic.Curve {
+       switch {
+       case oid.Equal(oidNamedCurveP224):
+               return elliptic.P224()
+       case oid.Equal(oidNamedCurveP256):
+               return elliptic.P256()
+       case oid.Equal(oidNamedCurveP384):
+               return elliptic.P384()
+       case oid.Equal(oidNamedCurveP521):
+               return elliptic.P521()
+       case oid.Equal(oidNamedCurveP256SM2):
+               return P256Sm2()
+       }
+       return nil
+}
+
+func oidFromNamedCurve(curve elliptic.Curve) (asn1.ObjectIdentifier, bool) {
+       switch curve {
+       case elliptic.P224():
+               return oidNamedCurveP224, true
+       case elliptic.P256():
+               return oidNamedCurveP256, true
+       case elliptic.P384():
+               return oidNamedCurveP384, true
+       case elliptic.P521():
+               return oidNamedCurveP521, true
+       case P256Sm2():
+               return oidNamedCurveP256SM2, true
+       }
+       return nil, false
+}
+
+// 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}
+       oidExtKeyUsageIPSECEndSystem             = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 5}
+       oidExtKeyUsageIPSECTunnel                = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 6}
+       oidExtKeyUsageIPSECUser                  = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 7}
+       oidExtKeyUsageTimeStamping               = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 8}
+       oidExtKeyUsageOCSPSigning                = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 3, 9}
+       oidExtKeyUsageMicrosoftServerGatedCrypto = asn1.ObjectIdentifier{1, 3, 6, 1, 4, 1, 311, 10, 3, 3}
+       oidExtKeyUsageNetscapeServerGatedCrypto  = asn1.ObjectIdentifier{2, 16, 840, 1, 113730, 4, 1}
+)
+
+// 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
+       ExtKeyUsageIPSECEndSystem
+       ExtKeyUsageIPSECTunnel
+       ExtKeyUsageIPSECUser
+       ExtKeyUsageTimeStamping
+       ExtKeyUsageOCSPSigning
+       ExtKeyUsageMicrosoftServerGatedCrypto
+       ExtKeyUsageNetscapeServerGatedCrypto
+)
+
+// extKeyUsageOIDs contains the mapping between an ExtKeyUsage and its OID.
+var extKeyUsageOIDs = []struct {
+       extKeyUsage ExtKeyUsage
+       oid         asn1.ObjectIdentifier
+}{
+       {ExtKeyUsageAny, oidExtKeyUsageAny},
+       {ExtKeyUsageServerAuth, oidExtKeyUsageServerAuth},
+       {ExtKeyUsageClientAuth, oidExtKeyUsageClientAuth},
+       {ExtKeyUsageCodeSigning, oidExtKeyUsageCodeSigning},
+       {ExtKeyUsageEmailProtection, oidExtKeyUsageEmailProtection},
+       {ExtKeyUsageIPSECEndSystem, oidExtKeyUsageIPSECEndSystem},
+       {ExtKeyUsageIPSECTunnel, oidExtKeyUsageIPSECTunnel},
+       {ExtKeyUsageIPSECUser, oidExtKeyUsageIPSECUser},
+       {ExtKeyUsageTimeStamping, oidExtKeyUsageTimeStamping},
+       {ExtKeyUsageOCSPSigning, oidExtKeyUsageOCSPSigning},
+       {ExtKeyUsageMicrosoftServerGatedCrypto, oidExtKeyUsageMicrosoftServerGatedCrypto},
+       {ExtKeyUsageNetscapeServerGatedCrypto, oidExtKeyUsageNetscapeServerGatedCrypto},
+}
+
+func extKeyUsageFromOID(oid asn1.ObjectIdentifier) (eku ExtKeyUsage, ok bool) {
+       for _, pair := range extKeyUsageOIDs {
+               if oid.Equal(pair.oid) {
+                       return pair.extKeyUsage, true
+               }
+       }
+       return
+}
+
+func oidFromExtKeyUsage(eku ExtKeyUsage) (oid asn1.ObjectIdentifier, ok bool) {
+       for _, pair := range extKeyUsageOIDs {
+               if eku == pair.extKeyUsage {
+                       return pair.oid, true
+               }
+       }
+       return
+}
+
+// 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
+
+       // Extensions contains raw X.509 extensions. When parsing certificates,
+       // this can be used to extract non-critical extensions that are not
+       // parsed by this package. When marshaling certificates, the Extensions
+       // field is ignored, see ExtraExtensions.
+       Extensions []pkix.Extension
+
+       // ExtraExtensions contains extensions to be copied, raw, into any
+       // marshaled certificates. Values override any extensions that would
+       // otherwise be produced based on the other fields. The ExtraExtensions
+       // field is not populated when parsing certificates, see Extensions.
+       ExtraExtensions []pkix.Extension
+
+       // UnhandledCriticalExtensions contains a list of extension IDs that
+       // were not (fully) processed when parsing. Verify will fail if this
+       // slice is non-empty, unless verification is delegated to an OS
+       // library which understands all the critical extensions.
+       //
+       // Users can access these extensions using Extensions and can remove
+       // elements from this slice if they believe that they have been
+       // handled.
+       UnhandledCriticalExtensions []asn1.ObjectIdentifier
+
+       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
+       // MaxPathLenZero indicates that BasicConstraintsValid==true and
+       // MaxPathLen==0 should be interpreted as an actual maximum path length
+       // of zero. Otherwise, that combination is interpreted as MaxPathLen
+       // not being set.
+       MaxPathLenZero bool
+
+       SubjectKeyId   []byte
+       AuthorityKeyId []byte
+
+       // RFC 5280, 4.2.2.1 (Authority Information Access)
+       OCSPServer            []string
+       IssuingCertificateURL []string
+
+       // Subject Alternate Name values
+       DNSNames       []string
+       EmailAddresses []string
+       IPAddresses    []net.IP
+
+       // Name constraints
+       PermittedDNSDomainsCritical bool // if true then the name constraints are marked critical.
+       PermittedDNSDomains         []string
+
+       // CRL Distribution Points
+       CRLDistributionPoints []string
+
+       PolicyIdentifiers []asn1.ObjectIdentifier
+}
+
+// ErrUnsupportedAlgorithm results from attempting to perform an operation that
+// involves algorithms that are not currently implemented.
+var ErrUnsupportedAlgorithm = errors.New("x509: cannot verify signature: algorithm unimplemented")
+
+// An InsecureAlgorithmError
+type InsecureAlgorithmError SignatureAlgorithm
+
+func (e InsecureAlgorithmError) Error() string {
+       return fmt.Sprintf("x509: cannot verify signature: insecure algorithm %v", SignatureAlgorithm(e))
+}
+
+// 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 "x509: invalid signature: parent certificate cannot sign this kind of certificate"
+}
+
+func (c *Certificate) Equal(other *Certificate) bool {
+       return bytes.Equal(c.Raw, other.Raw)
+}
+
+// Entrust have a broken root certificate (CN=Entrust.net Certification
+// Authority (2048)) which isn't marked as a CA certificate and is thus invalid
+// according to PKIX.
+// We recognise this certificate by its SubjectPublicKeyInfo and exempt it
+// from the Basic Constraints requirement.
+// See http://www.entrust.net/knowledge-base/technote.cfm?tn=7869
+//
+// TODO(agl): remove this hack once their reissued root is sufficiently
+// widespread.
+var entrustBrokenSPKI = []byte{
+       0x30, 0x82, 0x01, 0x22, 0x30, 0x0d, 0x06, 0x09,
+       0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01,
+       0x01, 0x05, 0x00, 0x03, 0x82, 0x01, 0x0f, 0x00,
+       0x30, 0x82, 0x01, 0x0a, 0x02, 0x82, 0x01, 0x01,
+       0x00, 0x97, 0xa3, 0x2d, 0x3c, 0x9e, 0xde, 0x05,
+       0xda, 0x13, 0xc2, 0x11, 0x8d, 0x9d, 0x8e, 0xe3,
+       0x7f, 0xc7, 0x4b, 0x7e, 0x5a, 0x9f, 0xb3, 0xff,
+       0x62, 0xab, 0x73, 0xc8, 0x28, 0x6b, 0xba, 0x10,
+       0x64, 0x82, 0x87, 0x13, 0xcd, 0x57, 0x18, 0xff,
+       0x28, 0xce, 0xc0, 0xe6, 0x0e, 0x06, 0x91, 0x50,
+       0x29, 0x83, 0xd1, 0xf2, 0xc3, 0x2a, 0xdb, 0xd8,
+       0xdb, 0x4e, 0x04, 0xcc, 0x00, 0xeb, 0x8b, 0xb6,
+       0x96, 0xdc, 0xbc, 0xaa, 0xfa, 0x52, 0x77, 0x04,
+       0xc1, 0xdb, 0x19, 0xe4, 0xae, 0x9c, 0xfd, 0x3c,
+       0x8b, 0x03, 0xef, 0x4d, 0xbc, 0x1a, 0x03, 0x65,
+       0xf9, 0xc1, 0xb1, 0x3f, 0x72, 0x86, 0xf2, 0x38,
+       0xaa, 0x19, 0xae, 0x10, 0x88, 0x78, 0x28, 0xda,
+       0x75, 0xc3, 0x3d, 0x02, 0x82, 0x02, 0x9c, 0xb9,
+       0xc1, 0x65, 0x77, 0x76, 0x24, 0x4c, 0x98, 0xf7,
+       0x6d, 0x31, 0x38, 0xfb, 0xdb, 0xfe, 0xdb, 0x37,
+       0x02, 0x76, 0xa1, 0x18, 0x97, 0xa6, 0xcc, 0xde,
+       0x20, 0x09, 0x49, 0x36, 0x24, 0x69, 0x42, 0xf6,
+       0xe4, 0x37, 0x62, 0xf1, 0x59, 0x6d, 0xa9, 0x3c,
+       0xed, 0x34, 0x9c, 0xa3, 0x8e, 0xdb, 0xdc, 0x3a,
+       0xd7, 0xf7, 0x0a, 0x6f, 0xef, 0x2e, 0xd8, 0xd5,
+       0x93, 0x5a, 0x7a, 0xed, 0x08, 0x49, 0x68, 0xe2,
+       0x41, 0xe3, 0x5a, 0x90, 0xc1, 0x86, 0x55, 0xfc,
+       0x51, 0x43, 0x9d, 0xe0, 0xb2, 0xc4, 0x67, 0xb4,
+       0xcb, 0x32, 0x31, 0x25, 0xf0, 0x54, 0x9f, 0x4b,
+       0xd1, 0x6f, 0xdb, 0xd4, 0xdd, 0xfc, 0xaf, 0x5e,
+       0x6c, 0x78, 0x90, 0x95, 0xde, 0xca, 0x3a, 0x48,
+       0xb9, 0x79, 0x3c, 0x9b, 0x19, 0xd6, 0x75, 0x05,
+       0xa0, 0xf9, 0x88, 0xd7, 0xc1, 0xe8, 0xa5, 0x09,
+       0xe4, 0x1a, 0x15, 0xdc, 0x87, 0x23, 0xaa, 0xb2,
+       0x75, 0x8c, 0x63, 0x25, 0x87, 0xd8, 0xf8, 0x3d,
+       0xa6, 0xc2, 0xcc, 0x66, 0xff, 0xa5, 0x66, 0x68,
+       0x55, 0x02, 0x03, 0x01, 0x00, 0x01,
+}
+
+// CheckSignatureFrom verifies that the signature on c is a valid signature
+// from parent.
+func (c *Certificate) CheckSignatureFrom(parent *Certificate) 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."
+       // (except for Entrust, see comment above entrustBrokenSPKI)
+       if (parent.Version == 3 && !parent.BasicConstraintsValid ||
+               parent.BasicConstraintsValid && !parent.IsCA) &&
+               !bytes.Equal(c.RawSubjectPublicKeyInfo, entrustBrokenSPKI) {
+               return ConstraintViolationError{}
+       }
+
+       if parent.KeyUsage != 0 && parent.KeyUsage&KeyUsageCertSign == 0 {
+               return ConstraintViolationError{}
+       }
+
+       if parent.PublicKeyAlgorithm == UnknownPublicKeyAlgorithm {
+               return ErrUnsupportedAlgorithm
+       }
+
+       // 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) error {
+       return checkSignature(algo, signed, signature, c.PublicKey)
+}
+
+// CheckSignature verifies that signature is a valid signature over signed from
+// a crypto.PublicKey.
+func checkSignature(algo SignatureAlgorithm, signed, signature []byte, publicKey crypto.PublicKey) (err error) {
+       var hashType Hash
+
+       switch algo {
+       case SHA1WithRSA, DSAWithSHA1, ECDSAWithSHA1, SM2WithSHA1:
+               hashType = SHA1
+       case SHA256WithRSA, SHA256WithRSAPSS, DSAWithSHA256, ECDSAWithSHA256, SM2WithSHA256:
+               hashType = SHA256
+       case SHA384WithRSA, SHA384WithRSAPSS, ECDSAWithSHA384:
+               hashType = SHA384
+       case SHA512WithRSA, SHA512WithRSAPSS, ECDSAWithSHA512:
+               hashType = SHA512
+       case MD2WithRSA, MD5WithRSA:
+               return InsecureAlgorithmError(algo)
+       case SM2WithSM3: // SM3WithRSA reserve
+               hashType = SM3
+       default:
+               return ErrUnsupportedAlgorithm
+       }
+
+       if !hashType.Available() {
+               return ErrUnsupportedAlgorithm
+       }
+       h := hashType.New()
+
+       h.Write(signed)
+       digest := h.Sum(nil)
+
+       switch pub := publicKey.(type) {
+       case *rsa.PublicKey:
+               if algo.isRSAPSS() {
+                       return rsa.VerifyPSS(pub, crypto.Hash(hashType), digest, signature, &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash})
+               } else {
+                       return rsa.VerifyPKCS1v15(pub, crypto.Hash(hashType), digest, signature)
+               }
+       case *dsa.PublicKey:
+               dsaSig := new(dsaSignature)
+               if rest, err := asn1.Unmarshal(signature, dsaSig); err != nil {
+                       return err
+               } else if len(rest) != 0 {
+                       return errors.New("x509: trailing data after DSA signature")
+               }
+               if dsaSig.R.Sign() <= 0 || dsaSig.S.Sign() <= 0 {
+                       return errors.New("x509: DSA signature contained zero or negative values")
+               }
+               if !dsa.Verify(pub, digest, dsaSig.R, dsaSig.S) {
+                       return errors.New("x509: DSA verification failure")
+               }
+               return
+       case *ecdsa.PublicKey:
+               ecdsaSig := new(ecdsaSignature)
+               if rest, err := asn1.Unmarshal(signature, ecdsaSig); err != nil {
+                       return err
+               } else if len(rest) != 0 {
+                       return errors.New("x509: trailing data after ECDSA signature")
+               }
+               if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
+                       return errors.New("x509: ECDSA signature contained zero or negative values")
+               }
+               switch pub.Curve {
+               case P256Sm2():
+                       if !Verify(&PublicKey{
+                               Curve: pub.Curve,
+                               X:     pub.X,
+                               Y:     pub.Y,
+                       }, digest, ecdsaSig.R, ecdsaSig.S) {
+                               return errors.New("x509: SM2 verification failure")
+                       }
+               default:
+                       if !ecdsa.Verify(pub, digest, ecdsaSig.R, ecdsaSig.S) {
+                               return errors.New("x509: ECDSA verification failure")
+                       }
+               }
+               return
+       }
+       return ErrUnsupportedAlgorithm
+}
+
+// CheckCRLSignature checks that the signature in crl is from c.
+func (c *Certificate) CheckCRLSignature(crl *pkix.CertificateList) error {
+       algo := getSignatureAlgorithmFromAI(crl.SignatureAlgorithm)
+       return c.CheckSignature(algo, crl.TBSCertList.Raw, crl.SignatureValue.RightAlign())
+}
+
+type UnhandledCriticalExtension struct{}
+
+func (h UnhandledCriticalExtension) Error() string {
+       return "x509: unhandled critical extension"
+}
+
+type basicConstraints struct {
+       IsCA       bool `asn1:"optional"`
+       MaxPathLen int  `asn1:"optional,default:-1"`
+}
+
+// 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"`
+}
+
+// RFC 5280, 4.2.2.1
+type authorityInfoAccess struct {
+       Method   asn1.ObjectIdentifier
+       Location asn1.RawValue
+}
+
+// RFC 5280, 4.2.1.14
+type distributionPoint struct {
+       DistributionPoint distributionPointName `asn1:"optional,tag:0"`
+       Reason            asn1.BitString        `asn1:"optional,tag:1"`
+       CRLIssuer         asn1.RawValue         `asn1:"optional,tag:2"`
+}
+
+type distributionPointName struct {
+       FullName     asn1.RawValue    `asn1:"optional,tag:0"`
+       RelativeName pkix.RDNSequence `asn1:"optional,tag:1"`
+}
+
+// asn1Null is the ASN.1 encoding of a NULL value.
+var asn1Null = []byte{5, 0}
+
+func parsePublicKey(algo PublicKeyAlgorithm, keyData *publicKeyInfo) (interface{}, error) {
+       asn1Data := keyData.PublicKey.RightAlign()
+       switch algo {
+       case RSA:
+               // RSA public keys must have a NULL in the parameters
+               // (https://tools.ietf.org/html/rfc3279#section-2.3.1).
+               if !bytes.Equal(keyData.Algorithm.Parameters.FullBytes, asn1Null) {
+                       return nil, errors.New("x509: RSA key missing NULL parameters")
+               }
+
+               p := new(rsaPublicKey)
+               rest, err := asn1.Unmarshal(asn1Data, p)
+               if err != nil {
+                       return nil, err
+               }
+               if len(rest) != 0 {
+                       return nil, errors.New("x509: trailing data after RSA public key")
+               }
+
+               if p.N.Sign() <= 0 {
+                       return nil, errors.New("x509: RSA modulus is not a positive number")
+               }
+               if p.E <= 0 {
+                       return nil, errors.New("x509: RSA public exponent is not a positive number")
+               }
+
+               pub := &rsa.PublicKey{
+                       E: p.E,
+                       N: p.N,
+               }
+               return pub, nil
+       case DSA:
+               var p *big.Int
+               rest, err := asn1.Unmarshal(asn1Data, &p)
+               if err != nil {
+                       return nil, err
+               }
+               if len(rest) != 0 {
+                       return nil, errors.New("x509: trailing data after DSA public key")
+               }
+               paramsData := keyData.Algorithm.Parameters.FullBytes
+               params := new(dsaAlgorithmParameters)
+               rest, err = asn1.Unmarshal(paramsData, params)
+               if err != nil {
+                       return nil, err
+               }
+               if len(rest) != 0 {
+                       return nil, errors.New("x509: trailing data after DSA parameters")
+               }
+               if p.Sign() <= 0 || params.P.Sign() <= 0 || params.Q.Sign() <= 0 || params.G.Sign() <= 0 {
+                       return nil, errors.New("x509: 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
+       case ECDSA:
+               paramsData := keyData.Algorithm.Parameters.FullBytes
+               namedCurveOID := new(asn1.ObjectIdentifier)
+               rest, err := asn1.Unmarshal(paramsData, namedCurveOID)
+               if err != nil {
+                       return nil, err
+               }
+               if len(rest) != 0 {
+                       return nil, errors.New("x509: trailing data after ECDSA parameters")
+               }
+               namedCurve := namedCurveFromOID(*namedCurveOID)
+               if namedCurve == nil {
+                       return nil, errors.New("x509: unsupported elliptic curve")
+               }
+               x, y := elliptic.Unmarshal(namedCurve, asn1Data)
+               if x == nil {
+                       return nil, errors.New("x509: failed to unmarshal elliptic curve point")
+               }
+               pub := &ecdsa.PublicKey{
+                       Curve: namedCurve,
+                       X:     x,
+                       Y:     y,
+               }
+               return pub, nil
+       default:
+               return nil, nil
+       }
+}
+
+func parseSANExtension(value []byte) (dnsNames, emailAddresses []string, ipAddresses []net.IP, err error) {
+       // 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
+       var rest []byte
+       if rest, err = asn1.Unmarshal(value, &seq); err != nil {
+               return
+       } else if len(rest) != 0 {
+               err = errors.New("x509: trailing data after X.509 extension")
+               return
+       }
+       if !seq.IsCompound || seq.Tag != 16 || seq.Class != 0 {
+               err = asn1.StructuralError{Msg: "bad SAN sequence"}
+               return
+       }
+
+       rest = seq.Bytes
+       for len(rest) > 0 {
+               var v asn1.RawValue
+               rest, err = asn1.Unmarshal(rest, &v)
+               if err != nil {
+                       return
+               }
+               switch v.Tag {
+               case 1:
+                       emailAddresses = append(emailAddresses, string(v.Bytes))
+               case 2:
+                       dnsNames = append(dnsNames, string(v.Bytes))
+               case 7:
+                       switch len(v.Bytes) {
+                       case net.IPv4len, net.IPv6len:
+                               ipAddresses = append(ipAddresses, v.Bytes)
+                       default:
+                               err = errors.New("x509: certificate contained IP address of length " + strconv.Itoa(len(v.Bytes)))
+                               return
+                       }
+               }
+       }
+
+       return
+}
+
+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 =
+               getSignatureAlgorithmFromAI(in.TBSCertificate.SignatureAlgorithm)
+
+       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
+       }
+
+       out.Version = in.TBSCertificate.Version + 1
+       out.SerialNumber = in.TBSCertificate.SerialNumber
+
+       var issuer, subject pkix.RDNSequence
+       if rest, err := asn1.Unmarshal(in.TBSCertificate.Subject.FullBytes, &subject); err != nil {
+               return nil, err
+       } else if len(rest) != 0 {
+               return nil, errors.New("x509: trailing data after X.509 subject")
+       }
+       if rest, err := asn1.Unmarshal(in.TBSCertificate.Issuer.FullBytes, &issuer); err != nil {
+               return nil, err
+       } else if len(rest) != 0 {
+               return nil, errors.New("x509: trailing data after X.509 subject")
+       }
+
+       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 {
+               out.Extensions = append(out.Extensions, e)
+               unhandled := false
+
+               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
+                               if rest, err := asn1.Unmarshal(e.Value, &usageBits); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 KeyUsage")
+                               }
+
+                               var usage int
+                               for i := 0; i < 9; i++ {
+                                       if usageBits.At(i) != 0 {
+                                               usage |= 1 << uint(i)
+                                       }
+                               }
+                               out.KeyUsage = KeyUsage(usage)
+
+                       case 19:
+                               // RFC 5280, 4.2.1.9
+                               var constraints basicConstraints
+                               if rest, err := asn1.Unmarshal(e.Value, &constraints); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 BasicConstraints")
+                               }
+
+                               out.BasicConstraintsValid = true
+                               out.IsCA = constraints.IsCA
+                               out.MaxPathLen = constraints.MaxPathLen
+                               out.MaxPathLenZero = out.MaxPathLen == 0
+
+                       case 17:
+                               out.DNSNames, out.EmailAddresses, out.IPAddresses, err = parseSANExtension(e.Value)
+                               if err != nil {
+                                       return nil, err
+                               }
+
+                               if len(out.DNSNames) == 0 && len(out.EmailAddresses) == 0 && len(out.IPAddresses) == 0 {
+                                       // If we didn't parse anything then we do the critical check, below.
+                                       unhandled = true
+                               }
+
+                       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
+                               if rest, err := asn1.Unmarshal(e.Value, &constraints); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 NameConstraints")
+                               }
+
+                               if len(constraints.Excluded) > 0 && e.Critical {
+                                       return out, UnhandledCriticalExtension{}
+                               }
+
+                               for _, subtree := range constraints.Permitted {
+                                       if len(subtree.Name) == 0 {
+                                               if e.Critical {
+                                                       return out, UnhandledCriticalExtension{}
+                                               }
+                                               continue
+                                       }
+                                       out.PermittedDNSDomains = append(out.PermittedDNSDomains, subtree.Name)
+                               }
+
+                       case 31:
+                               // RFC 5280, 4.2.1.13
+
+                               // CRLDistributionPoints ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint
+                               //
+                               // DistributionPoint ::= SEQUENCE {
+                               //     distributionPoint       [0]     DistributionPointName OPTIONAL,
+                               //     reasons                 [1]     ReasonFlags OPTIONAL,
+                               //     cRLIssuer               [2]     GeneralNames OPTIONAL }
+                               //
+                               // DistributionPointName ::= CHOICE {
+                               //     fullName                [0]     GeneralNames,
+                               //     nameRelativeToCRLIssuer [1]     RelativeDistinguishedName }
+
+                               var cdp []distributionPoint
+                               if rest, err := asn1.Unmarshal(e.Value, &cdp); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 CRL distribution point")
+                               }
+
+                               for i := range cdp {
+                                       // use index & pointer here to avoid value copy (each iteration copies 200 bytes)
+                                       dp := &cdp[i]
+                                       // Per RFC 5280, 4.2.1.13, one of distributionPoint or cRLIssuer may be empty.
+                                       if len(dp.DistributionPoint.FullName.Bytes) == 0 {
+                                               continue
+                                       }
+
+                                       var n asn1.RawValue
+                                       if _, err := asn1.Unmarshal(dp.DistributionPoint.FullName.Bytes, &n); err != nil {
+                                               return nil, err
+                                       }
+                                       // Trailing data after the fullName is
+                                       // allowed because other elements of
+                                       // the SEQUENCE can appear.
+
+                                       if n.Tag == 6 {
+                                               out.CRLDistributionPoints = append(out.CRLDistributionPoints, string(n.Bytes))
+                                       }
+                               }
+
+                       case 35:
+                               // RFC 5280, 4.2.1.1
+                               var a authKeyId
+                               if rest, err := asn1.Unmarshal(e.Value, &a); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 authority key-id")
+                               }
+                               out.AuthorityKeyId = a.Id
+
+                       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
+                               if rest, err := asn1.Unmarshal(e.Value, &keyUsage); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 ExtendedKeyUsage")
+                               }
+
+                               for _, u := range keyUsage {
+                                       if extKeyUsage, ok := extKeyUsageFromOID(u); ok {
+                                               out.ExtKeyUsage = append(out.ExtKeyUsage, extKeyUsage)
+                                       } else {
+                                               out.UnknownExtKeyUsage = append(out.UnknownExtKeyUsage, u)
+                                       }
+                               }
+
+                       case 14:
+                               // RFC 5280, 4.2.1.2
+                               var keyid []byte
+                               if rest, err := asn1.Unmarshal(e.Value, &keyid); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 key-id")
+                               }
+                               out.SubjectKeyId = keyid
+
+                       case 32:
+                               // RFC 5280 4.2.1.4: Certificate Policies
+                               var policies []policyInformation
+                               if rest, err := asn1.Unmarshal(e.Value, &policies); err != nil {
+                                       return nil, err
+                               } else if len(rest) != 0 {
+                                       return nil, errors.New("x509: trailing data after X.509 certificate policies")
+                               }
+                               out.PolicyIdentifiers = make([]asn1.ObjectIdentifier, len(policies))
+                               for i, policy := range policies {
+                                       out.PolicyIdentifiers[i] = policy.Policy
+                               }
+
+                       default:
+                               // Unknown extensions are recorded if critical.
+                               unhandled = true
+                       }
+               } else if e.Id.Equal(oidExtensionAuthorityInfoAccess) {
+                       // RFC 5280 4.2.2.1: Authority Information Access
+                       var aia []authorityInfoAccess
+                       if rest, err := asn1.Unmarshal(e.Value, &aia); err != nil {
+                               return nil, err
+                       } else if len(rest) != 0 {
+                               return nil, errors.New("x509: trailing data after X.509 authority information")
+                       }
+
+                       for _, v := range aia {
+                               // GeneralName: uniformResourceIdentifier [6] IA5String
+                               if v.Location.Tag != 6 {
+                                       continue
+                               }
+                               if v.Method.Equal(oidAuthorityInfoAccessOcsp) {
+                                       out.OCSPServer = append(out.OCSPServer, string(v.Location.Bytes))
+                               } else if v.Method.Equal(oidAuthorityInfoAccessIssuers) {
+                                       out.IssuingCertificateURL = append(out.IssuingCertificateURL, string(v.Location.Bytes))
+                               }
+                       }
+               } else {
+                       // Unknown extensions are recorded if critical.
+                       unhandled = true
+               }
+
+               if e.Critical && unhandled {
+                       out.UnhandledCriticalExtensions = append(out.UnhandledCriticalExtensions, e.Id)
+               }
+       }
+
+       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
+}
+
+// asn1BitLength returns the bit-length of bitString by considering the
+// most-significant bit in a byte to be the "first" bit. This convention
+// matches ASN.1, but differs from almost everything else.
+func asn1BitLength(bitString []byte) int {
+       bitLen := len(bitString) * 8
+
+       for i := range bitString {
+               b := bitString[len(bitString)-i-1]
+
+               for bit := uint(0); bit < 8; bit++ {
+                       if (b>>bit)&1 == 1 {
+                               return bitLen
+                       }
+                       bitLen--
+               }
+       }
+
+       return 0
+}
+
+var (
+       oidExtensionSubjectKeyId          = []int{2, 5, 29, 14}
+       oidExtensionKeyUsage              = []int{2, 5, 29, 15}
+       oidExtensionExtendedKeyUsage      = []int{2, 5, 29, 37}
+       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}
+       oidExtensionCRLDistributionPoints = []int{2, 5, 29, 31}
+       oidExtensionAuthorityInfoAccess   = []int{1, 3, 6, 1, 5, 5, 7, 1, 1}
+)
+
+var (
+       oidAuthorityInfoAccessOcsp    = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 48, 1}
+       oidAuthorityInfoAccessIssuers = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 48, 2}
+)
+
+// oidNotInExtensions returns whether an extension with the given oid exists in
+// extensions.
+func oidInExtensions(oid asn1.ObjectIdentifier, extensions []pkix.Extension) bool {
+       for _, e := range extensions {
+               if e.Id.Equal(oid) {
+                       return true
+               }
+       }
+       return false
+}
+
+// marshalSANs marshals a list of addresses into a the contents of an X.509
+// SubjectAlternativeName extension.
+func marshalSANs(dnsNames, emailAddresses []string, ipAddresses []net.IP) (derBytes []byte, err error) {
+       var rawValues []asn1.RawValue
+       for _, name := range dnsNames {
+               rawValues = append(rawValues, asn1.RawValue{Tag: 2, Class: 2, Bytes: []byte(name)})
+       }
+       for _, email := range emailAddresses {
+               rawValues = append(rawValues, asn1.RawValue{Tag: 1, Class: 2, Bytes: []byte(email)})
+       }
+       for _, rawIP := range ipAddresses {
+               // If possible, we always want to encode IPv4 addresses in 4 bytes.
+               ip := rawIP.To4()
+               if ip == nil {
+                       ip = rawIP
+               }
+               rawValues = append(rawValues, asn1.RawValue{Tag: 7, Class: 2, Bytes: ip})
+       }
+       return asn1.Marshal(rawValues)
+}
+
+func buildExtensions(template *Certificate) (ret []pkix.Extension, err error) {
+       ret = make([]pkix.Extension, 10 /* maximum number of elements. */)
+       n := 0
+
+       if template.KeyUsage != 0 &&
+               !oidInExtensions(oidExtensionKeyUsage, template.ExtraExtensions) {
+               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
+               }
+
+               bitString := a[:l]
+               ret[n].Value, err = asn1.Marshal(asn1.BitString{Bytes: bitString, BitLength: asn1BitLength(bitString)})
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if (len(template.ExtKeyUsage) > 0 || len(template.UnknownExtKeyUsage) > 0) &&
+               !oidInExtensions(oidExtensionExtendedKeyUsage, template.ExtraExtensions) {
+               ret[n].Id = oidExtensionExtendedKeyUsage
+
+               var oids []asn1.ObjectIdentifier
+               for _, u := range template.ExtKeyUsage {
+                       if oid, ok := oidFromExtKeyUsage(u); ok {
+                               oids = append(oids, oid)
+                       } else {
+                               panic("internal error")
+                       }
+               }
+
+               oids = append(oids, template.UnknownExtKeyUsage...)
+
+               ret[n].Value, err = asn1.Marshal(oids)
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if template.BasicConstraintsValid && !oidInExtensions(oidExtensionBasicConstraints, template.ExtraExtensions) {
+               // Leaving MaxPathLen as zero indicates that no maximum path
+               // length is desired, unless MaxPathLenZero is set. A value of
+               // -1 causes encoding/asn1 to omit the value as desired.
+               maxPathLen := template.MaxPathLen
+               if maxPathLen == 0 && !template.MaxPathLenZero {
+                       maxPathLen = -1
+               }
+               ret[n].Id = oidExtensionBasicConstraints
+               ret[n].Value, err = asn1.Marshal(basicConstraints{template.IsCA, maxPathLen})
+               ret[n].Critical = true
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if len(template.SubjectKeyId) > 0 && !oidInExtensions(oidExtensionSubjectKeyId, template.ExtraExtensions) {
+               ret[n].Id = oidExtensionSubjectKeyId
+               ret[n].Value, err = asn1.Marshal(template.SubjectKeyId)
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if len(template.AuthorityKeyId) > 0 && !oidInExtensions(oidExtensionAuthorityKeyId, template.ExtraExtensions) {
+               ret[n].Id = oidExtensionAuthorityKeyId
+               ret[n].Value, err = asn1.Marshal(authKeyId{template.AuthorityKeyId})
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if (len(template.OCSPServer) > 0 || len(template.IssuingCertificateURL) > 0) &&
+               !oidInExtensions(oidExtensionAuthorityInfoAccess, template.ExtraExtensions) {
+               ret[n].Id = oidExtensionAuthorityInfoAccess
+               var aiaValues []authorityInfoAccess
+               for _, name := range template.OCSPServer {
+                       aiaValues = append(aiaValues, authorityInfoAccess{
+                               Method:   oidAuthorityInfoAccessOcsp,
+                               Location: asn1.RawValue{Tag: 6, Class: 2, Bytes: []byte(name)},
+                       })
+               }
+               for _, name := range template.IssuingCertificateURL {
+                       aiaValues = append(aiaValues, authorityInfoAccess{
+                               Method:   oidAuthorityInfoAccessIssuers,
+                               Location: asn1.RawValue{Tag: 6, Class: 2, Bytes: []byte(name)},
+                       })
+               }
+               ret[n].Value, err = asn1.Marshal(aiaValues)
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if (len(template.DNSNames) > 0 || len(template.EmailAddresses) > 0 || len(template.IPAddresses) > 0) &&
+               !oidInExtensions(oidExtensionSubjectAltName, template.ExtraExtensions) {
+               ret[n].Id = oidExtensionSubjectAltName
+               ret[n].Value, err = marshalSANs(template.DNSNames, template.EmailAddresses, template.IPAddresses)
+               if err != nil {
+                       return
+               }
+               n++
+       }
+
+       if len(template.PolicyIdentifiers) > 0 &&
+               !oidInExtensions(oidExtensionCertificatePolicies, template.ExtraExtensions) {
+               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 &&
+               !oidInExtensions(oidExtensionNameConstraints, template.ExtraExtensions) {
+               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++
+       }
+
+       if len(template.CRLDistributionPoints) > 0 &&
+               !oidInExtensions(oidExtensionCRLDistributionPoints, template.ExtraExtensions) {
+               ret[n].Id = oidExtensionCRLDistributionPoints
+
+               var crlDp []distributionPoint
+               for _, name := range template.CRLDistributionPoints {
+                       rawFullName, _ := asn1.Marshal(asn1.RawValue{Tag: 6, Class: 2, Bytes: []byte(name)})
+
+                       dp := distributionPoint{
+                               DistributionPoint: distributionPointName{
+                                       FullName: asn1.RawValue{Tag: 0, Class: 2, IsCompound: true, Bytes: rawFullName},
+                               },
+                       }
+                       crlDp = append(crlDp, dp)
+               }
+
+               ret[n].Value, err = asn1.Marshal(crlDp)
+               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 append(ret[:n], template.ExtraExtensions...), nil
+}
+
+func subjectBytes(cert *Certificate) ([]byte, error) {
+       if len(cert.RawSubject) > 0 {
+               return cert.RawSubject, nil
+       }
+
+       return asn1.Marshal(cert.Subject.ToRDNSequence())
+}
+
+// signingParamsForPublicKey returns the parameters to use for signing with
+// priv. If requestedSigAlgo is not zero then it overrides the default
+// signature algorithm.
+func signingParamsForPublicKey(pub interface{}, requestedSigAlgo SignatureAlgorithm) (hashFunc Hash, sigAlgo pkix.AlgorithmIdentifier, err error) {
+       var pubType PublicKeyAlgorithm
+
+       switch pub := pub.(type) {
+       case *rsa.PublicKey:
+               pubType = RSA
+               hashFunc = SHA256
+               sigAlgo.Algorithm = oidSignatureSHA256WithRSA
+               sigAlgo.Parameters = asn1.RawValue{
+                       Tag: 5,
+               }
+
+       case *ecdsa.PublicKey:
+               pubType = ECDSA
+               switch pub.Curve {
+               case elliptic.P224(), elliptic.P256():
+                       hashFunc = SHA256
+                       sigAlgo.Algorithm = oidSignatureECDSAWithSHA256
+               case elliptic.P384():
+                       hashFunc = SHA384
+                       sigAlgo.Algorithm = oidSignatureECDSAWithSHA384
+               case elliptic.P521():
+                       hashFunc = SHA512
+                       sigAlgo.Algorithm = oidSignatureECDSAWithSHA512
+               default:
+                       err = errors.New("x509: unknown elliptic curve")
+               }
+       case *PublicKey:
+               pubType = ECDSA
+               switch pub.Curve {
+               case P256Sm2():
+                       hashFunc = SM3
+                       sigAlgo.Algorithm = oidSignatureSM2WithSM3
+               default:
+                       err = errors.New("x509: unknown SM2 curve")
+               }
+       default:
+               err = errors.New("x509: only RSA and ECDSA keys supported")
+       }
+
+       if err != nil {
+               return
+       }
+
+       if requestedSigAlgo == 0 {
+               return
+       }
+
+       found := false
+       for _, details := range signatureAlgorithmDetails {
+               if details.algo == requestedSigAlgo {
+                       if details.pubKeyAlgo != pubType {
+                               err = errors.New("x509: requested SignatureAlgorithm does not match private key type")
+                               return
+                       }
+                       sigAlgo.Algorithm, hashFunc = details.oid, details.hash
+                       if hashFunc == 0 {
+                               err = errors.New("x509: cannot sign with hash function requested")
+                               return
+                       }
+                       if requestedSigAlgo.isRSAPSS() {
+                               sigAlgo.Parameters = rsaPSSParameters(hashFunc)
+                       }
+                       found = true
+                       break
+               }
+       }
+
+       if !found {
+               err = errors.New("x509: unknown SignatureAlgorithm")
+       }
+
+       return
+}
+
+// CreateCertificate creates a new certificate based on a template. The
+// following members of template are used: SerialNumber, Subject, NotBefore,
+// NotAfter, KeyUsage, ExtKeyUsage, UnknownExtKeyUsage, BasicConstraintsValid,
+// IsCA, MaxPathLen, SubjectKeyId, DNSNames, PermittedDNSDomainsCritical,
+// PermittedDNSDomains, SignatureAlgorithm.
+//
+// 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.
+//
+// All keys types that are implemented via crypto.Signer are supported (This
+// includes *rsa.PublicKey and *ecdsa.PublicKey.)
+func CreateCertificate(rand io.Reader, template, parent *Certificate, pub, priv interface{}) (cert []byte, err error) {
+       key, ok := priv.(crypto.Signer)
+       if !ok {
+               return nil, errors.New("x509: certificate private key does not implement crypto.Signer")
+       }
+
+       if template.SerialNumber == nil {
+               return nil, errors.New("x509: no SerialNumber given")
+       }
+
+       hashFunc, signatureAlgorithm, err := signingParamsForPublicKey(key.Public(), template.SignatureAlgorithm)
+       if err != nil {
+               return nil, err
+       }
+
+       publicKeyBytes, publicKeyAlgorithm, err := marshalPublicKey(pub)
+       if err != nil {
+               return nil, err
+       }
+
+       asn1Issuer, err := subjectBytes(parent)
+       if err != nil {
+               return
+       }
+
+       asn1Subject, err := subjectBytes(template)
+       if err != nil {
+               return
+       }
+
+       if !bytes.Equal(asn1Issuer, asn1Subject) && len(parent.SubjectKeyId) > 0 {
+               template.AuthorityKeyId = parent.SubjectKeyId
+       }
+
+       extensions, err := buildExtensions(template)
+       if err != nil {
+               return
+       }
+       encodedPublicKey := asn1.BitString{BitLength: len(publicKeyBytes) * 8, Bytes: publicKeyBytes}
+       c := tbsCertificate{
+               Version:            2,
+               SerialNumber:       template.SerialNumber,
+               SignatureAlgorithm: signatureAlgorithm,
+               Issuer:             asn1.RawValue{FullBytes: asn1Issuer},
+               Validity:           validity{template.NotBefore.UTC(), template.NotAfter.UTC()},
+               Subject:            asn1.RawValue{FullBytes: asn1Subject},
+               PublicKey:          publicKeyInfo{nil, publicKeyAlgorithm, encodedPublicKey},
+               Extensions:         extensions,
+       }
+
+       tbsCertContents, err := asn1.Marshal(c)
+       if err != nil {
+               return
+       }
+
+       c.Raw = tbsCertContents
+
+       h := hashFunc.New()
+       h.Write(tbsCertContents)
+       digest := h.Sum(nil)
+
+       var signerOpts crypto.SignerOpts
+       signerOpts = hashFunc
+       if template.SignatureAlgorithm != 0 && template.SignatureAlgorithm.isRSAPSS() {
+               signerOpts = &rsa.PSSOptions{
+                       SaltLength: rsa.PSSSaltLengthEqualsHash,
+                       Hash:       crypto.Hash(hashFunc),
+               }
+       }
+
+       var signature []byte
+       signature, err = key.Sign(rand, digest, signerOpts)
+       if err != nil {
+               return
+       }
+
+       return asn1.Marshal(certificate{
+               nil,
+               c,
+               signatureAlgorithm,
+               asn1.BitString{Bytes: signature, BitLength: len(signature) * 8},
+       })
+}
+
+// pemCRLPrefix is the magic string that indicates that we have a PEM encoded
+// CRL.
+var pemCRLPrefix = []byte("-----BEGIN X509 CRL")
+
+// pemType is the type of a PEM encoded CRL.
+var pemType = "X509 CRL"
+
+// ParseCRL parses a CRL from the given bytes. It's often the case that PEM
+// encoded CRLs will appear where they should be DER encoded, so this function
+// will transparently handle PEM encoding as long as there isn't any leading
+// garbage.
+func ParseCRL(crlBytes []byte) (*pkix.CertificateList, error) {
+       if bytes.HasPrefix(crlBytes, pemCRLPrefix) {
+               block, _ := pem.Decode(crlBytes)
+               if block != nil && block.Type == pemType {
+                       crlBytes = block.Bytes
+               }
+       }
+       return ParseDERCRL(crlBytes)
+}
+
+// ParseDERCRL parses a DER encoded CRL from the given bytes.
+func ParseDERCRL(derBytes []byte) (*pkix.CertificateList, error) {
+       certList := new(pkix.CertificateList)
+       if rest, err := asn1.Unmarshal(derBytes, certList); err != nil {
+               return nil, err
+       } else if len(rest) != 0 {
+               return nil, errors.New("x509: trailing data after CRL")
+       }
+       return certList, nil
+}
+
+// CreateCRL returns a DER encoded CRL, signed by this Certificate, that
+// contains the given list of revoked certificates.
+func (c *Certificate) CreateCRL(rand io.Reader, priv interface{}, revokedCerts []pkix.RevokedCertificate, now, expiry time.Time) (crlBytes []byte, err error) {
+       key, ok := priv.(crypto.Signer)
+       if !ok {
+               return nil, errors.New("x509: certificate private key does not implement crypto.Signer")
+       }
+
+       hashFunc, signatureAlgorithm, err := signingParamsForPublicKey(key.Public(), 0)
+       if err != nil {
+               return nil, err
+       }
+
+       // Force revocation times to UTC per RFC 5280.
+       revokedCertsUTC := make([]pkix.RevokedCertificate, len(revokedCerts))
+       for i, rc := range revokedCerts {
+               rc.RevocationTime = rc.RevocationTime.UTC()
+               revokedCertsUTC[i] = rc
+       }
+
+       tbsCertList := pkix.TBSCertificateList{
+               Version:             1,
+               Signature:           signatureAlgorithm,
+               Issuer:              c.Subject.ToRDNSequence(),
+               ThisUpdate:          now.UTC(),
+               NextUpdate:          expiry.UTC(),
+               RevokedCertificates: revokedCertsUTC,
+       }
+
+       // Authority Key Id
+       if len(c.SubjectKeyId) > 0 {
+               var aki pkix.Extension
+               aki.Id = oidExtensionAuthorityKeyId
+               aki.Value, err = asn1.Marshal(authKeyId{Id: c.SubjectKeyId})
+               if err != nil {
+                       return
+               }
+               tbsCertList.Extensions = append(tbsCertList.Extensions, aki)
+       }
+
+       tbsCertListContents, err := asn1.Marshal(tbsCertList)
+       if err != nil {
+               return
+       }
+
+       h := hashFunc.New()
+       h.Write(tbsCertListContents)
+       digest := h.Sum(nil)
+
+       var signature []byte
+       signature, err = key.Sign(rand, digest, hashFunc)
+       if err != nil {
+               return
+       }
+
+       return asn1.Marshal(pkix.CertificateList{
+               TBSCertList:        tbsCertList,
+               SignatureAlgorithm: signatureAlgorithm,
+               SignatureValue:     asn1.BitString{Bytes: signature, BitLength: len(signature) * 8},
+       })
+}
+
+// CertificateRequest represents a PKCS #10, certificate signature request.
+type CertificateRequest struct {
+       Raw                      []byte // Complete ASN.1 DER content (CSR, signature algorithm and signature).
+       RawTBSCertificateRequest []byte // Certificate request info part of raw ASN.1 DER content.
+       RawSubjectPublicKeyInfo  []byte // DER encoded SubjectPublicKeyInfo.
+       RawSubject               []byte // DER encoded Subject.
+
+       Version            int
+       Signature          []byte
+       SignatureAlgorithm SignatureAlgorithm
+
+       PublicKeyAlgorithm PublicKeyAlgorithm
+       PublicKey          interface{}
+
+       Subject pkix.Name
+
+       // Attributes is the dried husk of a bug and shouldn't be used.
+       Attributes []pkix.AttributeTypeAndValueSET
+
+       // Extensions contains raw X.509 extensions. When parsing CSRs, this
+       // can be used to extract extensions that are not parsed by this
+       // package.
+       Extensions []pkix.Extension
+
+       // ExtraExtensions contains extensions to be copied, raw, into any
+       // marshaled CSR. Values override any extensions that would otherwise
+       // be produced based on the other fields but are overridden by any
+       // extensions specified in Attributes.
+       //
+       // The ExtraExtensions field is not populated when parsing CSRs, see
+       // Extensions.
+       ExtraExtensions []pkix.Extension
+
+       // Subject Alternate Name values.
+       DNSNames       []string
+       EmailAddresses []string
+       IPAddresses    []net.IP
+}
+
+// These structures reflect the ASN.1 structure of X.509 certificate
+// signature requests (see RFC 2986):
+
+type tbsCertificateRequest struct {
+       Raw           asn1.RawContent
+       Version       int
+       Subject       asn1.RawValue
+       PublicKey     publicKeyInfo
+       RawAttributes []asn1.RawValue `asn1:"tag:0"`
+}
+
+type certificateRequest struct {
+       Raw                asn1.RawContent
+       TBSCSR             tbsCertificateRequest
+       SignatureAlgorithm pkix.AlgorithmIdentifier
+       SignatureValue     asn1.BitString
+}
+
+// oidExtensionRequest is a PKCS#9 OBJECT IDENTIFIER that indicates requested
+// extensions in a CSR.
+var oidExtensionRequest = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 14}
+
+// newRawAttributes converts AttributeTypeAndValueSETs from a template
+// CertificateRequest's Attributes into tbsCertificateRequest RawAttributes.
+func newRawAttributes(attributes []pkix.AttributeTypeAndValueSET) ([]asn1.RawValue, error) {
+       var rawAttributes []asn1.RawValue
+       b, err := asn1.Marshal(attributes)
+       if err != nil {
+               return nil, err
+       }
+       rest, err := asn1.Unmarshal(b, &rawAttributes)
+       if err != nil {
+               return nil, err
+       }
+       if len(rest) != 0 {
+               return nil, errors.New("x509: failed to unmarshal raw CSR Attributes")
+       }
+       return rawAttributes, nil
+}
+
+// parseRawAttributes Unmarshals RawAttributes intos AttributeTypeAndValueSETs.
+func parseRawAttributes(rawAttributes []asn1.RawValue) []pkix.AttributeTypeAndValueSET {
+       var attributes []pkix.AttributeTypeAndValueSET
+       for _, rawAttr := range rawAttributes {
+               var attr pkix.AttributeTypeAndValueSET
+               rest, err := asn1.Unmarshal(rawAttr.FullBytes, &attr)
+               // Ignore attributes that don't parse into pkix.AttributeTypeAndValueSET
+               // (i.e.: challengePassword or unstructuredName).
+               if err == nil && len(rest) == 0 {
+                       attributes = append(attributes, attr)
+               }
+       }
+       return attributes
+}
+
+// parseCSRExtensions parses the attributes from a CSR and extracts any
+// requested extensions.
+func parseCSRExtensions(rawAttributes []asn1.RawValue) ([]pkix.Extension, error) {
+       // pkcs10Attribute reflects the Attribute structure from section 4.1 of
+       // https://tools.ietf.org/html/rfc2986.
+       type pkcs10Attribute struct {
+               Id     asn1.ObjectIdentifier
+               Values []asn1.RawValue `asn1:"set"`
+       }
+
+       var ret []pkix.Extension
+       for _, rawAttr := range rawAttributes {
+               var attr pkcs10Attribute
+               if rest, err := asn1.Unmarshal(rawAttr.FullBytes, &attr); err != nil || len(rest) != 0 || len(attr.Values) == 0 {
+                       // Ignore attributes that don't parse.
+                       continue
+               }
+
+               if !attr.Id.Equal(oidExtensionRequest) {
+                       continue
+               }
+
+               var extensions []pkix.Extension
+               if _, err := asn1.Unmarshal(attr.Values[0].FullBytes, &extensions); err != nil {
+                       return nil, err
+               }
+               ret = append(ret, extensions...)
+       }
+
+       return ret, nil
+}
+
+// CreateCertificateRequest creates a new certificate request based on a template.
+// The following members of template are used: Subject, Attributes,
+// SignatureAlgorithm, Extensions, DNSNames, EmailAddresses, and IPAddresses.
+// The private key is the private key of the signer.
+//
+// The returned slice is the certificate request in DER encoding.
+//
+// All keys types that are implemented via crypto.Signer are supported (This
+// includes *rsa.PublicKey and *ecdsa.PublicKey.)
+func CreateCertificateRequest(rand io.Reader, template *CertificateRequest, priv interface{}) (csr []byte, err error) {
+       key, ok := priv.(crypto.Signer)
+       if !ok {
+               return nil, errors.New("x509: certificate private key does not implement crypto.Signer")
+       }
+
+       var hashFunc Hash
+       var sigAlgo pkix.AlgorithmIdentifier
+       hashFunc, sigAlgo, err = signingParamsForPublicKey(key.Public(), template.SignatureAlgorithm)
+       if err != nil {
+               return nil, err
+       }
+
+       var publicKeyBytes []byte
+       var publicKeyAlgorithm pkix.AlgorithmIdentifier
+       publicKeyBytes, publicKeyAlgorithm, err = marshalPublicKey(key.Public())
+       if err != nil {
+               return nil, err
+       }
+
+       var extensions []pkix.Extension
+
+       if (len(template.DNSNames) > 0 || len(template.EmailAddresses) > 0 || len(template.IPAddresses) > 0) &&
+               !oidInExtensions(oidExtensionSubjectAltName, template.ExtraExtensions) {
+               sanBytes, err := marshalSANs(template.DNSNames, template.EmailAddresses, template.IPAddresses)
+               if err != nil {
+                       return nil, err
+               }
+
+               extensions = append(extensions, pkix.Extension{
+                       Id:    oidExtensionSubjectAltName,
+                       Value: sanBytes,
+               })
+       }
+
+       extensions = append(extensions, template.ExtraExtensions...)
+
+       var attributes []pkix.AttributeTypeAndValueSET
+       attributes = append(attributes, template.Attributes...)
+
+       if len(extensions) > 0 {
+               // specifiedExtensions contains all the extensions that we
+               // found specified via template.Attributes.
+               specifiedExtensions := make(map[string]bool)
+
+               for _, atvSet := range template.Attributes {
+                       if !atvSet.Type.Equal(oidExtensionRequest) {
+                               continue
+                       }
+
+                       for _, atvs := range atvSet.Value {
+                               for _, atv := range atvs {
+                                       specifiedExtensions[atv.Type.String()] = true
+                               }
+                       }
+               }
+
+               atvs := make([]pkix.AttributeTypeAndValue, 0, len(extensions))
+               for _, e := range extensions {
+                       if specifiedExtensions[e.Id.String()] {
+                               // Attributes already contained a value for
+                               // this extension and it takes priority.
+                               continue
+                       }
+
+                       atvs = append(atvs, pkix.AttributeTypeAndValue{
+                               // There is no place for the critical flag in a CSR.
+                               Type:  e.Id,
+                               Value: e.Value,
+                       })
+               }
+
+               // Append the extensions to an existing attribute if possible.
+               appended := false
+               for _, atvSet := range attributes {
+                       if !atvSet.Type.Equal(oidExtensionRequest) || len(atvSet.Value) == 0 {
+                               continue
+                       }
+
+                       atvSet.Value[0] = append(atvSet.Value[0], atvs...)
+                       appended = true
+                       break
+               }
+
+               // Otherwise, add a new attribute for the extensions.
+               if !appended {
+                       attributes = append(attributes, pkix.AttributeTypeAndValueSET{
+                               Type: oidExtensionRequest,
+                               Value: [][]pkix.AttributeTypeAndValue{
+                                       atvs,
+                               },
+                       })
+               }
+       }
+
+       asn1Subject := template.RawSubject
+       if len(asn1Subject) == 0 {
+               asn1Subject, err = asn1.Marshal(template.Subject.ToRDNSequence())
+               if err != nil {
+                       return
+               }
+       }
+
+       rawAttributes, err := newRawAttributes(attributes)
+       if err != nil {
+               return
+       }
+
+       tbsCSR := tbsCertificateRequest{
+               Version: 0, // PKCS #10, RFC 2986
+               Subject: asn1.RawValue{FullBytes: asn1Subject},
+               PublicKey: publicKeyInfo{
+                       Algorithm: publicKeyAlgorithm,
+                       PublicKey: asn1.BitString{
+                               Bytes:     publicKeyBytes,
+                               BitLength: len(publicKeyBytes) * 8,
+                       },
+               },
+               RawAttributes: rawAttributes,
+       }
+
+       tbsCSRContents, err := asn1.Marshal(tbsCSR)
+       if err != nil {
+               return
+       }
+       tbsCSR.Raw = tbsCSRContents
+
+       h := hashFunc.New()
+       h.Write(tbsCSRContents)
+       digest := h.Sum(nil)
+
+       var signature []byte
+       signature, err = key.Sign(rand, digest, hashFunc)
+       if err != nil {
+               return
+       }
+
+       return asn1.Marshal(certificateRequest{
+               TBSCSR:             tbsCSR,
+               SignatureAlgorithm: sigAlgo,
+               SignatureValue: asn1.BitString{
+                       Bytes:     signature,
+                       BitLength: len(signature) * 8,
+               },
+       })
+}
+
+// ParseCertificateRequest parses a single certificate request from the
+// given ASN.1 DER data.
+func ParseCertificateRequest(asn1Data []byte) (*CertificateRequest, error) {
+       var csr certificateRequest
+
+       rest, err := asn1.Unmarshal(asn1Data, &csr)
+       if err != nil {
+               return nil, err
+       } else if len(rest) != 0 {
+               return nil, asn1.SyntaxError{Msg: "trailing data"}
+       }
+
+       return parseCertificateRequest(&csr)
+}
+
+func parseCertificateRequest(in *certificateRequest) (*CertificateRequest, error) {
+       out := &CertificateRequest{
+               Raw: in.Raw,
+               RawTBSCertificateRequest: in.TBSCSR.Raw,
+               RawSubjectPublicKeyInfo:  in.TBSCSR.PublicKey.Raw,
+               RawSubject:               in.TBSCSR.Subject.FullBytes,
+
+               Signature:          in.SignatureValue.RightAlign(),
+               SignatureAlgorithm: getSignatureAlgorithmFromAI(in.SignatureAlgorithm),
+
+               PublicKeyAlgorithm: getPublicKeyAlgorithmFromOID(in.TBSCSR.PublicKey.Algorithm.Algorithm),
+
+               Version:    in.TBSCSR.Version,
+               Attributes: parseRawAttributes(in.TBSCSR.RawAttributes),
+       }
+
+       var err error
+       out.PublicKey, err = parsePublicKey(out.PublicKeyAlgorithm, &in.TBSCSR.PublicKey)
+       if err != nil {
+               return nil, err
+       }
+
+       var subject pkix.RDNSequence
+       if rest, err := asn1.Unmarshal(in.TBSCSR.Subject.FullBytes, &subject); err != nil {
+               return nil, err
+       } else if len(rest) != 0 {
+               return nil, errors.New("x509: trailing data after X.509 Subject")
+       }
+
+       out.Subject.FillFromRDNSequence(&subject)
+
+       if out.Extensions, err = parseCSRExtensions(in.TBSCSR.RawAttributes); err != nil {
+               return nil, err
+       }
+
+       for _, extension := range out.Extensions {
+               if extension.Id.Equal(oidExtensionSubjectAltName) {
+                       out.DNSNames, out.EmailAddresses, out.IPAddresses, err = parseSANExtension(extension.Value)
+                       if err != nil {
+                               return nil, err
+                       }
+               }
+       }
+
+       return out, nil
+}
+
+// CheckSignature reports whether the signature on c is valid.
+func (c *CertificateRequest) CheckSignature() error {
+       return checkSignature(c.SignatureAlgorithm, c.RawTBSCertificateRequest, c.Signature, c.PublicKey)
+}
+
+func ReadCertificateRequestFromMem(data []byte) (*CertificateRequest, error) {
+       block, _ := pem.Decode(data)
+       if block == nil {
+               return nil, errors.New("failed to decode certificate request")
+       }
+       return ParseCertificateRequest(block.Bytes)
+}
+
+func ReadCertificateRequestFromPem(FileName string) (*CertificateRequest, error) {
+       data, err := ioutil.ReadFile(FileName)
+       if err != nil {
+               return nil, err
+       }
+       return ReadCertificateRequestFromMem(data)
+}
+
+func CreateCertificateRequestToMem(template *CertificateRequest, privKey *PrivateKey) ([]byte, error) {
+       der, err := CreateCertificateRequest(rand.Reader, template, privKey)
+       if err != nil {
+               return nil, err
+       }
+       block := &pem.Block{
+               Type:  "CERTIFICATE REQUEST",
+               Bytes: der,
+       }
+       return pem.EncodeToMemory(block), nil
+}
+
+func CreateCertificateRequestToPem(FileName string, template *CertificateRequest,
+       privKey *PrivateKey) (bool, error) {
+       der, err := CreateCertificateRequest(rand.Reader, template, privKey)
+       if err != nil {
+               return false, err
+       }
+       block := &pem.Block{
+               Type:  "CERTIFICATE REQUEST",
+               Bytes: der,
+       }
+       file, err := os.Create(FileName)
+       if err != nil {
+               return false, err
+       }
+       defer file.Close()
+       err = pem.Encode(file, block)
+       if err != nil {
+               return false, err
+       }
+       return true, nil
+}
+
+func ReadCertificateFromMem(data []byte) (*Certificate, error) {
+       block, _ := pem.Decode(data)
+       if block == nil {
+               return nil, errors.New("failed to decode certificate request")
+       }
+       return ParseCertificate(block.Bytes)
+}
+
+func ReadCertificateFromPem(FileName string) (*Certificate, error) {
+       data, err := ioutil.ReadFile(FileName)
+       if err != nil {
+               return nil, err
+       }
+       return ReadCertificateFromMem(data)
+}
+
+func CreateCertificateToMem(template, parent *Certificate, pubKey *PublicKey, privKey *PrivateKey) ([]byte, error) {
+       der, err := CreateCertificate(rand.Reader, template, parent, pubKey, privKey)
+       if err != nil {
+               return nil, err
+       }
+       block := &pem.Block{
+               Type:  "CERTIFICATE",
+               Bytes: der,
+       }
+       return pem.EncodeToMemory(block), nil
+}
+
+func CreateCertificateToPem(FileName string, template, parent *Certificate, pubKey *PublicKey, privKey *PrivateKey) (bool, error) {
+       der, err := CreateCertificate(rand.Reader, template, parent, pubKey, privKey)
+       if err != nil {
+               return false, err
+       }
+       block := &pem.Block{
+               Type:  "CERTIFICATE",
+               Bytes: der,
+       }
+       file, err := os.Create(FileName)
+       if err != nil {
+               return false, err
+       }
+       defer file.Close()
+       err = pem.Encode(file, block)
+       if err != nil {
+               return false, err
+       }
+       return true, nil
+}