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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package x509
import (
"crypto/ecdsa"
"crypto/elliptic"
"encoding/asn1"
"errors"
"fmt"
"math/big"
)
const ecPrivKeyVersion = 1
// ecPrivateKey reflects an ASN.1 Elliptic Curve Private Key Structure.
// References:
// RFC5915
// SEC1 - http://www.secg.org/download/aid-780/sec1-v2.pdf
// Per RFC5915 the NamedCurveOID is marked as ASN.1 OPTIONAL, however in
// most cases it is not.
type ecPrivateKey struct {
Version int
PrivateKey []byte
NamedCurveOID asn1.ObjectIdentifier `asn1:"optional,explicit,tag:0"`
PublicKey asn1.BitString `asn1:"optional,explicit,tag:1"`
}
// ParseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure.
func ParseECPrivateKey(der []byte) (key *ecdsa.PrivateKey, err error) {
return parseECPrivateKey(nil, der)
}
// MarshalECPrivateKey marshals an EC private key into ASN.1, DER format.
func MarshalECPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) {
oid, ok := oidFromNamedCurve(key.Curve)
if !ok {
return nil, errors.New("x509: unknown elliptic curve")
}
return asn1.Marshal(ecPrivateKey{
Version: 1,
PrivateKey: key.D.Bytes(),
NamedCurveOID: oid,
PublicKey: asn1.BitString{Bytes: elliptic.Marshal(key.Curve, key.X, key.Y)},
})
}
// parseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure.
// The OID for the named curve may be provided from another source (such as
// the PKCS8 container) - if it is provided then use this instead of the OID
// that may exist in the EC private key structure.
func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *ecdsa.PrivateKey, err error) {
var privKey ecPrivateKey
if _, err := asn1.Unmarshal(der, &privKey); err != nil {
return nil, errors.New("x509: failed to parse EC private key: " + err.Error())
}
if privKey.Version != ecPrivKeyVersion {
return nil, fmt.Errorf("x509: unknown EC private key version %d", privKey.Version)
}
var curve elliptic.Curve
if namedCurveOID != nil {
curve = namedCurveFromOID(*namedCurveOID)
} else {
curve = namedCurveFromOID(privKey.NamedCurveOID)
}
if curve == nil {
return nil, errors.New("x509: unknown elliptic curve")
}
k := new(big.Int).SetBytes(privKey.PrivateKey)
if k.Cmp(curve.Params().N) >= 0 {
return nil, errors.New("x509: invalid elliptic curve private key value")
}
priv := new(ecdsa.PrivateKey)
priv.Curve = curve
priv.D = k
priv.X, priv.Y = curve.ScalarBaseMult(privKey.PrivateKey)
return priv, nil
}
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