sec1.go

Documentation: crypto/x509

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