pkcs8.go

     1  // Copyright 2011 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/ed25519"
    11  	"crypto/rsa"
    12  	"crypto/x509/pkix"
    13  	"encoding/asn1"
    14  	"errors"
    15  	"fmt"
    16  )
    17  
    18  // pkcs8 reflects an ASN.1, PKCS #8 PrivateKey. See
    19  // ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-8/pkcs-8v1_2.asn
    20  // and RFC 5208.
    21  type pkcs8 struct {
    22  	Version    int
    23  	Algo       pkix.AlgorithmIdentifier
    24  	PrivateKey []byte
    25  	// optional attributes omitted.
    26  }
    27  
    28  // ParsePKCS8PrivateKey parses an unencrypted private key in PKCS #8, ASN.1 DER form.
    29  //
    30  // It returns a *[rsa.PrivateKey], an *[ecdsa.PrivateKey], an [ed25519.PrivateKey] (not
    31  // a pointer), or an *[ecdh.PrivateKey] (for X25519). More types might be supported
    32  // in the future.
    33  //
    34  // This kind of key is commonly encoded in PEM blocks of type "PRIVATE KEY".
    35  func ParsePKCS8PrivateKey(der []byte) (key any, err error) {
    36  	var privKey pkcs8
    37  	if _, err := asn1.Unmarshal(der, &privKey); err != nil {
    38  		if _, err := asn1.Unmarshal(der, &ecPrivateKey{}); err == nil {
    39  			return nil, errors.New("x509: failed to parse private key (use ParseECPrivateKey instead for this key format)")
    40  		}
    41  		if _, err := asn1.Unmarshal(der, &pkcs1PrivateKey{}); err == nil {
    42  			return nil, errors.New("x509: failed to parse private key (use ParsePKCS1PrivateKey instead for this key format)")
    43  		}
    44  		return nil, err
    45  	}
    46  	switch {
    47  	case privKey.Algo.Algorithm.Equal(oidPublicKeyRSA):
    48  		key, err = ParsePKCS1PrivateKey(privKey.PrivateKey)
    49  		if err != nil {
    50  			return nil, errors.New("x509: failed to parse RSA private key embedded in PKCS#8: " + err.Error())
    51  		}
    52  		return key, nil
    53  
    54  	case privKey.Algo.Algorithm.Equal(oidPublicKeyECDSA):
    55  		bytes := privKey.Algo.Parameters.FullBytes
    56  		namedCurveOID := new(asn1.ObjectIdentifier)
    57  		if _, err := asn1.Unmarshal(bytes, namedCurveOID); err != nil {
    58  			namedCurveOID = nil
    59  		}
    60  		key, err = parseECPrivateKey(namedCurveOID, privKey.PrivateKey)
    61  		if err != nil {
    62  			return nil, errors.New("x509: failed to parse EC private key embedded in PKCS#8: " + err.Error())
    63  		}
    64  		return key, nil
    65  
    66  	case privKey.Algo.Algorithm.Equal(oidPublicKeyEd25519):
    67  		if l := len(privKey.Algo.Parameters.FullBytes); l != 0 {
    68  			return nil, errors.New("x509: invalid Ed25519 private key parameters")
    69  		}
    70  		var curvePrivateKey []byte
    71  		if _, err := asn1.Unmarshal(privKey.PrivateKey, &curvePrivateKey); err != nil {
    72  			return nil, fmt.Errorf("x509: invalid Ed25519 private key: %v", err)
    73  		}
    74  		if l := len(curvePrivateKey); l != ed25519.SeedSize {
    75  			return nil, fmt.Errorf("x509: invalid Ed25519 private key length: %d", l)
    76  		}
    77  		return ed25519.NewKeyFromSeed(curvePrivateKey), nil
    78  
    79  	case privKey.Algo.Algorithm.Equal(oidPublicKeyX25519):
    80  		if l := len(privKey.Algo.Parameters.FullBytes); l != 0 {
    81  			return nil, errors.New("x509: invalid X25519 private key parameters")
    82  		}
    83  		var curvePrivateKey []byte
    84  		if _, err := asn1.Unmarshal(privKey.PrivateKey, &curvePrivateKey); err != nil {
    85  			return nil, fmt.Errorf("x509: invalid X25519 private key: %v", err)
    86  		}
    87  		return ecdh.X25519().NewPrivateKey(curvePrivateKey)
    88  
    89  	default:
    90  		return nil, fmt.Errorf("x509: PKCS#8 wrapping contained private key with unknown algorithm: %v", privKey.Algo.Algorithm)
    91  	}
    92  }
    93  
    94  // MarshalPKCS8PrivateKey converts a private key to PKCS #8, ASN.1 DER form.
    95  //
    96  // The following key types are currently supported: *[rsa.PrivateKey],
    97  // *[ecdsa.PrivateKey], [ed25519.PrivateKey] (not a pointer), and *[ecdh.PrivateKey].
    98  // Unsupported key types result in an error.
    99  //
   100  // This kind of key is commonly encoded in PEM blocks of type "PRIVATE KEY".
   101  func MarshalPKCS8PrivateKey(key any) ([]byte, error) {
   102  	var privKey pkcs8
   103  
   104  	switch k := key.(type) {
   105  	case *rsa.PrivateKey:
   106  		privKey.Algo = pkix.AlgorithmIdentifier{
   107  			Algorithm:  oidPublicKeyRSA,
   108  			Parameters: asn1.NullRawValue,
   109  		}
   110  		privKey.PrivateKey = MarshalPKCS1PrivateKey(k)
   111  
   112  	case *ecdsa.PrivateKey:
   113  		oid, ok := oidFromNamedCurve(k.Curve)
   114  		if !ok {
   115  			return nil, errors.New("x509: unknown curve while marshaling to PKCS#8")
   116  		}
   117  		oidBytes, err := asn1.Marshal(oid)
   118  		if err != nil {
   119  			return nil, errors.New("x509: failed to marshal curve OID: " + err.Error())
   120  		}
   121  		privKey.Algo = pkix.AlgorithmIdentifier{
   122  			Algorithm: oidPublicKeyECDSA,
   123  			Parameters: asn1.RawValue{
   124  				FullBytes: oidBytes,
   125  			},
   126  		}
   127  		if privKey.PrivateKey, err = marshalECPrivateKeyWithOID(k, nil); err != nil {
   128  			return nil, errors.New("x509: failed to marshal EC private key while building PKCS#8: " + err.Error())
   129  		}
   130  
   131  	case ed25519.PrivateKey:
   132  		privKey.Algo = pkix.AlgorithmIdentifier{
   133  			Algorithm: oidPublicKeyEd25519,
   134  		}
   135  		curvePrivateKey, err := asn1.Marshal(k.Seed())
   136  		if err != nil {
   137  			return nil, fmt.Errorf("x509: failed to marshal private key: %v", err)
   138  		}
   139  		privKey.PrivateKey = curvePrivateKey
   140  
   141  	case *ecdh.PrivateKey:
   142  		if k.Curve() == ecdh.X25519() {
   143  			privKey.Algo = pkix.AlgorithmIdentifier{
   144  				Algorithm: oidPublicKeyX25519,
   145  			}
   146  			var err error
   147  			if privKey.PrivateKey, err = asn1.Marshal(k.Bytes()); err != nil {
   148  				return nil, fmt.Errorf("x509: failed to marshal private key: %v", err)
   149  			}
   150  		} else {
   151  			oid, ok := oidFromECDHCurve(k.Curve())
   152  			if !ok {
   153  				return nil, errors.New("x509: unknown curve while marshaling to PKCS#8")
   154  			}
   155  			oidBytes, err := asn1.Marshal(oid)
   156  			if err != nil {
   157  				return nil, errors.New("x509: failed to marshal curve OID: " + err.Error())
   158  			}
   159  			privKey.Algo = pkix.AlgorithmIdentifier{
   160  				Algorithm: oidPublicKeyECDSA,
   161  				Parameters: asn1.RawValue{
   162  					FullBytes: oidBytes,
   163  				},
   164  			}
   165  			if privKey.PrivateKey, err = marshalECDHPrivateKey(k); err != nil {
   166  				return nil, errors.New("x509: failed to marshal EC private key while building PKCS#8: " + err.Error())
   167  			}
   168  		}
   169  
   170  	default:
   171  		return nil, fmt.Errorf("x509: unknown key type while marshaling PKCS#8: %T", key)
   172  	}
   173  
   174  	return asn1.Marshal(privKey)
   175  }
   176
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