1 // Copyright 2012 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package x509 6 7 import ( 8 "crypto/ecdsa" 9 "crypto/elliptic" 10 "encoding/asn1" 11 "errors" 12 "fmt" 13 "math/big" 14 ) 15 16 const ecPrivKeyVersion = 1 17 18 // ecPrivateKey reflects an ASN.1 Elliptic Curve Private Key Structure. 19 // References: 20 // RFC5915 21 // SEC1 - http://www.secg.org/sec1-v2.pdf 22 // Per RFC5915 the NamedCurveOID is marked as ASN.1 OPTIONAL, however in 23 // most cases it is not. 24 type ecPrivateKey struct { 25 Version int 26 PrivateKey []byte 27 NamedCurveOID asn1.ObjectIdentifier `asn1:"optional,explicit,tag:0"` 28 PublicKey asn1.BitString `asn1:"optional,explicit,tag:1"` 29 } 30 31 // ParseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure. 32 func ParseECPrivateKey(der []byte) (key *ecdsa.PrivateKey, err error) { 33 return parseECPrivateKey(nil, der) 34 } 35 36 // MarshalECPrivateKey marshals an EC private key into ASN.1, DER format. 37 func MarshalECPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) { 38 oid, ok := oidFromNamedCurve(key.Curve) 39 if !ok { 40 return nil, errors.New("x509: unknown elliptic curve") 41 } 42 return asn1.Marshal(ecPrivateKey{ 43 Version: 1, 44 PrivateKey: key.D.Bytes(), 45 NamedCurveOID: oid, 46 PublicKey: asn1.BitString{Bytes: elliptic.Marshal(key.Curve, key.X, key.Y)}, 47 }) 48 } 49 50 // parseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure. 51 // The OID for the named curve may be provided from another source (such as 52 // the PKCS8 container) - if it is provided then use this instead of the OID 53 // that may exist in the EC private key structure. 54 func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *ecdsa.PrivateKey, err error) { 55 var privKey ecPrivateKey 56 if _, err := asn1.Unmarshal(der, &privKey); err != nil { 57 return nil, errors.New("x509: failed to parse EC private key: " + err.Error()) 58 } 59 if privKey.Version != ecPrivKeyVersion { 60 return nil, fmt.Errorf("x509: unknown EC private key version %d", privKey.Version) 61 } 62 63 var curve elliptic.Curve 64 if namedCurveOID != nil { 65 curve = namedCurveFromOID(*namedCurveOID) 66 } else { 67 curve = namedCurveFromOID(privKey.NamedCurveOID) 68 } 69 if curve == nil { 70 return nil, errors.New("x509: unknown elliptic curve") 71 } 72 73 k := new(big.Int).SetBytes(privKey.PrivateKey) 74 if k.Cmp(curve.Params().N) >= 0 { 75 return nil, errors.New("x509: invalid elliptic curve private key value") 76 } 77 priv := new(ecdsa.PrivateKey) 78 priv.Curve = curve 79 priv.D = k 80 priv.X, priv.Y = curve.ScalarBaseMult(privKey.PrivateKey) 81 82 return priv, nil 83 } 84
