sec1.go

     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/ecdh"
     9  	"crypto/ecdsa"
    10  	"crypto/elliptic"
    11  	"encoding/asn1"
    12  	"errors"
    13  	"fmt"
    14  	"math/big"
    15  )
    16  
    17  const ecPrivKeyVersion = 1
    18  
    19  // ecPrivateKey reflects an ASN.1 Elliptic Curve Private Key Structure.
    20  // References:
    21  //
    22  //	RFC 5915
    23  //	SEC1 - http://www.secg.org/sec1-v2.pdf
    24  //
    25  // Per RFC 5915 the NamedCurveOID is marked as ASN.1 OPTIONAL, however in
    26  // most cases it is not.
    27  type ecPrivateKey struct {
    28  	Version       int
    29  	PrivateKey    []byte
    30  	NamedCurveOID asn1.ObjectIdentifier `asn1:"optional,explicit,tag:0"`
    31  	PublicKey     asn1.BitString        `asn1:"optional,explicit,tag:1"`
    32  }
    33  
    34  // ParseECPrivateKey parses an EC private key in SEC 1, ASN.1 DER form.
    35  //
    36  // This kind of key is commonly encoded in PEM blocks of type "EC PRIVATE KEY".
    37  func ParseECPrivateKey(der []byte) (*ecdsa.PrivateKey, error) {
    38  	return parseECPrivateKey(nil, der)
    39  }
    40  
    41  // MarshalECPrivateKey converts an EC private key to SEC 1, ASN.1 DER form.
    42  //
    43  // This kind of key is commonly encoded in PEM blocks of type "EC PRIVATE KEY".
    44  // For a more flexible key format which is not EC specific, use
    45  // [MarshalPKCS8PrivateKey].
    46  func MarshalECPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) {
    47  	oid, ok := oidFromNamedCurve(key.Curve)
    48  	if !ok {
    49  		return nil, errors.New("x509: unknown elliptic curve")
    50  	}
    51  
    52  	return marshalECPrivateKeyWithOID(key, oid)
    53  }
    54  
    55  // marshalECPrivateKeyWithOID marshals an EC private key into ASN.1, DER format and
    56  // sets the curve ID to the given OID, or omits it if OID is nil.
    57  func marshalECPrivateKeyWithOID(key *ecdsa.PrivateKey, oid asn1.ObjectIdentifier) ([]byte, error) {
    58  	if !key.Curve.IsOnCurve(key.X, key.Y) {
    59  		return nil, errors.New("invalid elliptic key public key")
    60  	}
    61  	privateKey := make([]byte, (key.Curve.Params().N.BitLen()+7)/8)
    62  	return asn1.Marshal(ecPrivateKey{
    63  		Version:       1,
    64  		PrivateKey:    key.D.FillBytes(privateKey),
    65  		NamedCurveOID: oid,
    66  		PublicKey:     asn1.BitString{Bytes: elliptic.Marshal(key.Curve, key.X, key.Y)},
    67  	})
    68  }
    69  
    70  // marshalECDHPrivateKey marshals an EC private key into ASN.1, DER format
    71  // suitable for NIST curves.
    72  func marshalECDHPrivateKey(key *ecdh.PrivateKey) ([]byte, error) {
    73  	return asn1.Marshal(ecPrivateKey{
    74  		Version:    1,
    75  		PrivateKey: key.Bytes(),
    76  		PublicKey:  asn1.BitString{Bytes: key.PublicKey().Bytes()},
    77  	})
    78  }
    79  
    80  // parseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure.
    81  // The OID for the named curve may be provided from another source (such as
    82  // the PKCS8 container) - if it is provided then use this instead of the OID
    83  // that may exist in the EC private key structure.
    84  func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *ecdsa.PrivateKey, err error) {
    85  	var privKey ecPrivateKey
    86  	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
    87  		if _, err := asn1.Unmarshal(der, &pkcs8{}); err == nil {
    88  			return nil, errors.New("x509: failed to parse private key (use ParsePKCS8PrivateKey instead for this key format)")
    89  		}
    90  		if _, err := asn1.Unmarshal(der, &pkcs1PrivateKey{}); err == nil {
    91  			return nil, errors.New("x509: failed to parse private key (use ParsePKCS1PrivateKey instead for this key format)")
    92  		}
    93  		return nil, errors.New("x509: failed to parse EC private key: " + err.Error())
    94  	}
    95  	if privKey.Version != ecPrivKeyVersion {
    96  		return nil, fmt.Errorf("x509: unknown EC private key version %d", privKey.Version)
    97  	}
    98  
    99  	var curve elliptic.Curve
   100  	if namedCurveOID != nil {
   101  		curve = namedCurveFromOID(*namedCurveOID)
   102  	} else {
   103  		curve = namedCurveFromOID(privKey.NamedCurveOID)
   104  	}
   105  	if curve == nil {
   106  		return nil, errors.New("x509: unknown elliptic curve")
   107  	}
   108  
   109  	k := new(big.Int).SetBytes(privKey.PrivateKey)
   110  	curveOrder := curve.Params().N
   111  	if k.Cmp(curveOrder) >= 0 {
   112  		return nil, errors.New("x509: invalid elliptic curve private key value")
   113  	}
   114  	priv := new(ecdsa.PrivateKey)
   115  	priv.Curve = curve
   116  	priv.D = k
   117  
   118  	privateKey := make([]byte, (curveOrder.BitLen()+7)/8)
   119  
   120  	// Some private keys have leading zero padding. This is invalid
   121  	// according to [SEC1], but this code will ignore it.
   122  	for len(privKey.PrivateKey) > len(privateKey) {
   123  		if privKey.PrivateKey[0] != 0 {
   124  			return nil, errors.New("x509: invalid private key length")
   125  		}
   126  		privKey.PrivateKey = privKey.PrivateKey[1:]
   127  	}
   128  
   129  	// Some private keys remove all leading zeros, this is also invalid
   130  	// according to [SEC1] but since OpenSSL used to do this, we ignore
   131  	// this too.
   132  	copy(privateKey[len(privateKey)-len(privKey.PrivateKey):], privKey.PrivateKey)
   133  	priv.X, priv.Y = curve.ScalarBaseMult(privateKey)
   134  
   135  	return priv, nil
   136  }
   137
View as plain text