gmsm/smx509/x509.go

package smx509

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/asn1"
	"errors"
	"fmt"
	"io"
	"math/big"
	"net"
	"net/url"
	"strconv"
	"strings"

	"github.com/emmansun/gmsm/sm2"
)

// pkixPublicKey reflects a PKIX public key structure. See SubjectPublicKeyInfo
// in RFC 3280.
type pkixPublicKey struct {
	Algo      pkix.AlgorithmIdentifier
	BitString asn1.BitString
}

type publicKeyInfo struct {
	Raw       asn1.RawContent
	Algorithm pkix.AlgorithmIdentifier
	PublicKey asn1.BitString
}

// pkcs1PublicKey reflects the ASN.1 structure of a PKCS#1 public key.
type pkcs1PublicKey struct {
	N *big.Int
	E int
}

type ecdsaSignature struct {
	R, S *big.Int
}

// http://gmssl.org/docs/oid.html
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}

	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}
)

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 sm2.P256():
		return oidNamedCurveP256SM2, true
	}

	return nil, false
}

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 sm2.P256()
	}
	return nil
}

// ParsePKIXPublicKey parses a public key in PKIX, ASN.1 DER form.
//
// It returns a *rsa.PublicKey, *dsa.PublicKey, *ecdsa.PublicKey, or
// ed25519.PublicKey. More types might be supported in the future.
//
// This kind of key is commonly encoded in PEM blocks of type "PUBLIC KEY".
func ParsePKIXPublicKey(derBytes []byte) (interface{}, error) {
	var pki publicKeyInfo
	if rest, err := asn1.Unmarshal(derBytes, &pki); err != nil {
		if _, err := asn1.Unmarshal(derBytes, &pkcs1PublicKey{}); err == nil {
			return nil, errors.New("x509: failed to parse public key (use ParsePKCS1PublicKey instead for this key format)")
		}
		return nil, err
	} else if len(rest) != 0 {
		return nil, errors.New("x509: trailing data after ASN.1 of public-key")
	}

	if !pki.Algorithm.Algorithm.Equal(oidPublicKeyECDSA) {
		return x509.ParsePKIXPublicKey(derBytes)
	}
	keyData := &pki
	asn1Data := keyData.PublicKey.RightAlign()
	paramsData := keyData.Algorithm.Parameters.FullBytes
	namedCurveOID := new(asn1.ObjectIdentifier)
	rest, err := asn1.Unmarshal(paramsData, namedCurveOID)
	if err != nil {
		return nil, errors.New("x509: failed to parse ECDSA parameters as named curve")
	}
	if len(rest) != 0 {
		return nil, errors.New("x509: trailing data after ECDSA parameters")
	}
	if !namedCurveOID.Equal(oidNamedCurveP256SM2) {
		return x509.ParsePKIXPublicKey(derBytes)
	}
	namedCurve := sm2.P256()
	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
}

// MarshalPKIXPublicKey converts a public key to PKIX, ASN.1 DER form.
//
// The following key types are currently supported: *rsa.PublicKey, *ecdsa.PublicKey
// and ed25519.PublicKey. Unsupported key types result in an error.
//
// This kind of key is commonly encoded in PEM blocks of type "PUBLIC KEY".
func MarshalPKIXPublicKey(pub interface{}) ([]byte, error) {
	ecdPub, ok := pub.(*ecdsa.PublicKey)
	if !ok || ecdPub.Curve != sm2.P256() {
		return x509.MarshalPKIXPublicKey(pub)
	}

	publicKeyBytes, publicKeyAlgorithm, err := marshalPublicKey(ecdPub)
	if err != nil {
		return nil, err
	}

	pkix := pkixPublicKey{
		Algo: publicKeyAlgorithm,
		BitString: asn1.BitString{
			Bytes:     publicKeyBytes,
			BitLength: 8 * len(publicKeyBytes),
		},
	}

	return asn1.Marshal(pkix)
}

func marshalPublicKey(pub *ecdsa.PublicKey) (publicKeyBytes []byte, publicKeyAlgorithm pkix.AlgorithmIdentifier, err error) {
	publicKeyAlgorithm = pkix.AlgorithmIdentifier{Algorithm: oidPublicKeyECDSA}
	publicKeyBytes = elliptic.Marshal(pub.Curve, pub.X, pub.Y)
	paramBytes, err := asn1.Marshal(oidNamedCurveP256SM2)
	publicKeyAlgorithm.Parameters.FullBytes = paramBytes
	return
}

// CreateCertificateRequest creates a new certificate request based on a
// template. The following members of template are used:
//
//  - SignatureAlgorithm
//  - Subject
//  - DNSNames
//  - EmailAddresses
//  - IPAddresses
//  - URIs
//  - ExtraExtensions
//  - Attributes (deprecated)
//
// priv is the private key to sign the CSR with, and the corresponding public
// key will be included in the CSR. It must implement crypto.Signer and its
// Public() method must return a *rsa.PublicKey or a *ecdsa.PublicKey or a
// ed25519.PublicKey. (A *rsa.PrivateKey, *ecdsa.PrivateKey or
// ed25519.PrivateKey satisfies this.)
//
// The returned slice is the certificate request in DER encoding.
func CreateCertificateRequest(rand io.Reader, template *x509.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")
	}
	privKey, ok := key.(*sm2.PrivateKey)
	if !ok {
		return x509.CreateCertificateRequest(rand, template, priv)
	}
	var sigAlgo = pkix.AlgorithmIdentifier{}
	sigAlgo.Algorithm = oidSignatureSM2WithSM3

	var publicKeyBytes []byte
	var publicKeyAlgorithm pkix.AlgorithmIdentifier
	publicKeyBytes, publicKeyAlgorithm, err = marshalPublicKey(key.Public().(*ecdsa.PublicKey))
	if err != nil {
		return nil, err
	}

	var extensions []pkix.Extension

	if (len(template.DNSNames) > 0 || len(template.EmailAddresses) > 0 || len(template.IPAddresses) > 0 || len(template.URIs) > 0) &&
		!oidInExtensions(oidExtensionSubjectAltName, template.ExtraExtensions) {
		sanBytes, err := marshalSANs(template.DNSNames, template.EmailAddresses, template.IPAddresses, template.URIs)
		if err != nil {
			return nil, err
		}

		extensions = append(extensions, pkix.Extension{
			Id:    oidExtensionSubjectAltName,
			Value: sanBytes,
		})
	}

	extensions = append(extensions, template.ExtraExtensions...)

	// Make a copy of template.Attributes because we may alter it below.
	attributes := make([]pkix.AttributeTypeAndValueSET, 0, len(template.Attributes))
	for _, attr := range template.Attributes {
		values := make([][]pkix.AttributeTypeAndValue, len(attr.Value))
		copy(values, attr.Value)
		attributes = append(attributes, pkix.AttributeTypeAndValueSET{
			Type:  attr.Type,
			Value: values,
		})
	}

	extensionsAppended := false
	if len(extensions) > 0 {
		// Append the extensions to an existing attribute if possible.
		for _, atvSet := range attributes {
			if !atvSet.Type.Equal(oidExtensionRequest) || len(atvSet.Value) == 0 {
				continue
			}

			// specifiedExtensions contains all the extensions that we
			// found specified via template.Attributes.
			specifiedExtensions := make(map[string]bool)

			for _, atvs := range atvSet.Value {
				for _, atv := range atvs {
					specifiedExtensions[atv.Type.String()] = true
				}
			}

			newValue := make([]pkix.AttributeTypeAndValue, 0, len(atvSet.Value[0])+len(extensions))
			newValue = append(newValue, atvSet.Value[0]...)

			for _, e := range extensions {
				if specifiedExtensions[e.Id.String()] {
					// Attributes already contained a value for
					// this extension and it takes priority.
					continue
				}

				newValue = append(newValue, pkix.AttributeTypeAndValue{
					// There is no place for the critical
					// flag in an AttributeTypeAndValue.
					Type:  e.Id,
					Value: e.Value,
				})
			}

			atvSet.Value[0] = newValue
			extensionsAppended = true
			break
		}
	}

	rawAttributes, err := newRawAttributes(attributes)
	if err != nil {
		return
	}

	// If not included in attributes, add a new attribute for the
	// extensions.
	if len(extensions) > 0 && !extensionsAppended {
		attr := struct {
			Type  asn1.ObjectIdentifier
			Value [][]pkix.Extension `asn1:"set"`
		}{
			Type:  oidExtensionRequest,
			Value: [][]pkix.Extension{extensions},
		}

		b, err := asn1.Marshal(attr)
		if err != nil {
			return nil, errors.New("x509: failed to serialise extensions attribute: " + err.Error())
		}

		var rawValue asn1.RawValue
		if _, err := asn1.Unmarshal(b, &rawValue); err != nil {
			return nil, err
		}

		rawAttributes = append(rawAttributes, rawValue)
	}

	asn1Subject := template.RawSubject
	if len(asn1Subject) == 0 {
		asn1Subject, err = asn1.Marshal(template.Subject.ToRDNSequence())
		if err != nil {
			return nil, err
		}
	}

	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

	signed := tbsCSRContents

	signature, err := privKey.SignWithSM2(rand, nil, signed)
	if err != nil {
		return
	}

	return asn1.Marshal(certificateRequest{
		TBSCSR:             tbsCSR,
		SignatureAlgorithm: sigAlgo,
		SignatureValue: asn1.BitString{
			Bytes:     signature,
			BitLength: len(signature) * 8,
		},
	})
}

// 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}
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}
)

// 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
}

// oidNotInExtensions reports 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
}

const (
	nameTypeEmail = 1
	nameTypeDNS   = 2
	nameTypeURI   = 6
	nameTypeIP    = 7
)

// marshalSANs marshals a list of addresses into a the contents of an X.509
// SubjectAlternativeName extension.
func marshalSANs(dnsNames, emailAddresses []string, ipAddresses []net.IP, uris []*url.URL) (derBytes []byte, err error) {
	var rawValues []asn1.RawValue
	for _, name := range dnsNames {
		rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeDNS, Class: 2, Bytes: []byte(name)})
	}
	for _, email := range emailAddresses {
		rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeEmail, 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: nameTypeIP, Class: 2, Bytes: ip})
	}
	for _, uri := range uris {
		rawValues = append(rawValues, asn1.RawValue{Tag: nameTypeURI, Class: 2, Bytes: []byte(uri.String())})
	}
	return asn1.Marshal(rawValues)
}

// ParseCertificateRequest parses a single certificate request from the
// given ASN.1 DER data.
func ParseCertificateRequest(asn1Data []byte) (*x509.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"}
	}
	if !csr.SignatureAlgorithm.Algorithm.Equal(oidSignatureSM2WithSM3) {
		return x509.ParseCertificateRequest(asn1Data)
	}
	return parseCertificateRequest(&csr)
}

func parseCertificateRequest(in *certificateRequest) (*x509.CertificateRequest, error) {
	if !oidSignatureSM2WithSM3.Equal(in.SignatureAlgorithm.Algorithm) {
		return nil, errors.New("unsupport signature algorithm")
	}
	out := &x509.CertificateRequest{
		Raw:                      in.Raw,
		RawTBSCertificateRequest: in.TBSCSR.Raw,
		RawSubjectPublicKeyInfo:  in.TBSCSR.PublicKey.Raw,
		RawSubject:               in.TBSCSR.Subject.FullBytes,

		Signature: in.SignatureValue.RightAlign(),

		PublicKeyAlgorithm: getPublicKeyAlgorithmFromOID(in.TBSCSR.PublicKey.Algorithm.Algorithm),

		Version:    in.TBSCSR.Version,
		Attributes: parseRawAttributes(in.TBSCSR.RawAttributes),
	}

	var err error
	out.PublicKey, err = parsePublicKey(&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, out.URIs, err = parseSANExtension(extension.Value)
			if err != nil {
				return nil, err
			}
		}
	}

	return out, nil
}

func parsePublicKey(keyData *publicKeyInfo) (interface{}, error) {
	asn1Data := keyData.PublicKey.RightAlign()
	paramsData := keyData.Algorithm.Parameters.FullBytes
	namedCurveOID := new(asn1.ObjectIdentifier)
	rest, err := asn1.Unmarshal(paramsData, namedCurveOID)
	if err != nil {
		return nil, errors.New("x509: failed to parse ECDSA parameters as named curve")
	}
	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
}

// parseRawAttributes Unmarshals RawAttributes into 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 RFC 2986, Section 4.1.
	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
}

func forEachSAN(extension []byte, callback func(tag int, data []byte) error) 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
	rest, err := asn1.Unmarshal(extension, &seq)
	if err != nil {
		return err
	} else if len(rest) != 0 {
		return errors.New("x509: trailing data after X.509 extension")
	}
	if !seq.IsCompound || seq.Tag != 16 || seq.Class != 0 {
		return asn1.StructuralError{Msg: "bad SAN sequence"}
	}

	rest = seq.Bytes
	for len(rest) > 0 {
		var v asn1.RawValue
		rest, err = asn1.Unmarshal(rest, &v)
		if err != nil {
			return err
		}

		if err := callback(v.Tag, v.Bytes); err != nil {
			return err
		}
	}

	return nil
}

// domainToReverseLabels converts a textual domain name like foo.example.com to
// the list of labels in reverse order, e.g. ["com", "example", "foo"].
func domainToReverseLabels(domain string) (reverseLabels []string, ok bool) {
	for len(domain) > 0 {
		if i := strings.LastIndexByte(domain, '.'); i == -1 {
			reverseLabels = append(reverseLabels, domain)
			domain = ""
		} else {
			reverseLabels = append(reverseLabels, domain[i+1:])
			domain = domain[:i]
		}
	}

	if len(reverseLabels) > 0 && len(reverseLabels[0]) == 0 {
		// An empty label at the end indicates an absolute value.
		return nil, false
	}

	for _, label := range reverseLabels {
		if len(label) == 0 {
			// Empty labels are otherwise invalid.
			return nil, false
		}

		for _, c := range label {
			if c < 33 || c > 126 {
				// Invalid character.
				return nil, false
			}
		}
	}

	return reverseLabels, true
}

func parseSANExtension(value []byte) (dnsNames, emailAddresses []string, ipAddresses []net.IP, uris []*url.URL, err error) {
	err = forEachSAN(value, func(tag int, data []byte) error {
		switch tag {
		case nameTypeEmail:
			emailAddresses = append(emailAddresses, string(data))
		case nameTypeDNS:
			dnsNames = append(dnsNames, string(data))
		case nameTypeURI:
			uri, err := url.Parse(string(data))
			if err != nil {
				return fmt.Errorf("x509: cannot parse URI %q: %s", string(data), err)
			}
			if len(uri.Host) > 0 {
				if _, ok := domainToReverseLabels(uri.Host); !ok {
					return fmt.Errorf("x509: cannot parse URI %q: invalid domain", string(data))
				}
			}
			uris = append(uris, uri)
		case nameTypeIP:
			switch len(data) {
			case net.IPv4len, net.IPv6len:
				ipAddresses = append(ipAddresses, data)
			default:
				return errors.New("x509: cannot parse IP address of length " + strconv.Itoa(len(data)))
			}
		}

		return nil
	})

	return
}

// 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) x509.PublicKeyAlgorithm {
	if oid.Equal(oidPublicKeyECDSA) {
		return x509.ECDSA
	}
	return x509.UnknownPublicKeyAlgorithm
}

// CheckSignature reports whether the signature on c is valid.
func CheckSignature(c *x509.CertificateRequest) error {
	if c.PublicKeyAlgorithm == x509.ECDSA {
		pub, ok := c.PublicKey.(*ecdsa.PublicKey)
		if ok && strings.EqualFold(sm2.P256().Params().Name, pub.Curve.Params().Name) {
			return checkSignature(c, pub)
		}
	}
	return c.CheckSignature()
}

// CheckSignature verifies that signature is a valid signature over signed from
// a crypto.PublicKey.
func checkSignature(c *x509.CertificateRequest, publicKey *ecdsa.PublicKey) (err error) {
	signed := c.RawTBSCertificateRequest
	ecdsaSig := new(ecdsaSignature)
	if rest, err := asn1.Unmarshal(c.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")
	}
	if !sm2.VerifyWithSM2(publicKey, nil, signed, ecdsaSig.R, ecdsaSig.S) {
		return errors.New("x509: ECDSA verification failure")
	}
	return
}