github.com/xushiwei/go@v0.0.0-20130601165731-2b9d83f45bc9/src/pkg/crypto/x509/sec1.go (about)

     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/download/aid-780/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  // parseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure.
    37  // The OID for the named curve may be provided from another source (such as
    38  // the PKCS8 container) - if it is provided then use this instead of the OID
    39  // that may exist in the EC private key structure.
    40  func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *ecdsa.PrivateKey, err error) {
    41  	var privKey ecPrivateKey
    42  	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
    43  		return nil, errors.New("crypto/x509: failed to parse EC private key: " + err.Error())
    44  	}
    45  	if privKey.Version != ecPrivKeyVersion {
    46  		return nil, fmt.Errorf("crypto/x509: unknown EC private key version %d", privKey.Version)
    47  	}
    48  
    49  	var curve elliptic.Curve
    50  	if namedCurveOID != nil {
    51  		curve = namedCurveFromOID(*namedCurveOID)
    52  	} else {
    53  		curve = namedCurveFromOID(privKey.NamedCurveOID)
    54  	}
    55  	if curve == nil {
    56  		return nil, errors.New("crypto/x509: unknown elliptic curve")
    57  	}
    58  
    59  	k := new(big.Int).SetBytes(privKey.PrivateKey)
    60  	if k.Cmp(curve.Params().N) >= 0 {
    61  		return nil, errors.New("crypto/x509: invalid elliptic curve private key value")
    62  	}
    63  	priv := new(ecdsa.PrivateKey)
    64  	priv.Curve = curve
    65  	priv.D = k
    66  	priv.X, priv.Y = curve.ScalarBaseMult(privKey.PrivateKey)
    67  
    68  	return priv, nil
    69  }