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ec_key.go
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ec_key.go
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package libtrust
import (
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/x509"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
"io"
"math/big"
)
/*
* EC DSA PUBLIC KEY
*/
// ecPublicKey implements a libtrust.PublicKey using elliptic curve digital
// signature algorithms.
type ecPublicKey struct {
*ecdsa.PublicKey
curveName string
signatureAlgorithm *signatureAlgorithm
extended map[string]interface{}
}
func fromECPublicKey(cryptoPublicKey *ecdsa.PublicKey) (*ecPublicKey, error) {
curve := cryptoPublicKey.Curve
switch {
case curve == elliptic.P256():
return &ecPublicKey{cryptoPublicKey, "P-256", es256, map[string]interface{}{}}, nil
case curve == elliptic.P384():
return &ecPublicKey{cryptoPublicKey, "P-384", es384, map[string]interface{}{}}, nil
case curve == elliptic.P521():
return &ecPublicKey{cryptoPublicKey, "P-521", es512, map[string]interface{}{}}, nil
default:
return nil, errors.New("unsupported elliptic curve")
}
}
// KeyType returns the key type for elliptic curve keys, i.e., "EC".
func (k *ecPublicKey) KeyType() string {
return "EC"
}
// CurveName returns the elliptic curve identifier.
// Possible values are "P-256", "P-384", and "P-521".
func (k *ecPublicKey) CurveName() string {
return k.curveName
}
// KeyID returns a distinct identifier which is unique to this Public Key.
func (k *ecPublicKey) KeyID() string {
return keyIDFromCryptoKey(k)
}
func (k *ecPublicKey) String() string {
return fmt.Sprintf("EC Public Key <%s>", k.KeyID())
}
// Verify verifyies the signature of the data in the io.Reader using this
// PublicKey. The alg parameter should identify the digital signature
// algorithm which was used to produce the signature and should be supported
// by this public key. Returns a nil error if the signature is valid.
func (k *ecPublicKey) Verify(data io.Reader, alg string, signature []byte) error {
// For EC keys there is only one supported signature algorithm depending
// on the curve parameters.
if k.signatureAlgorithm.HeaderParam() != alg {
return fmt.Errorf("unable to verify signature: EC Public Key with curve %q does not support signature algorithm %q", k.curveName, alg)
}
// signature is the concatenation of (r, s), base64Url encoded.
sigLength := len(signature)
expectedOctetLength := 2 * ((k.Params().BitSize + 7) >> 3)
if sigLength != expectedOctetLength {
return fmt.Errorf("signature length is %d octets long, should be %d", sigLength, expectedOctetLength)
}
rBytes, sBytes := signature[:sigLength/2], signature[sigLength/2:]
r := new(big.Int).SetBytes(rBytes)
s := new(big.Int).SetBytes(sBytes)
hasher := k.signatureAlgorithm.HashID().New()
_, err := io.Copy(hasher, data)
if err != nil {
return fmt.Errorf("error reading data to sign: %s", err)
}
hash := hasher.Sum(nil)
if !ecdsa.Verify(k.PublicKey, hash, r, s) {
return errors.New("invalid signature")
}
return nil
}
// CryptoPublicKey returns the internal object which can be used as a
// crypto.PublicKey for use with other standard library operations. The type
// is either *rsa.PublicKey or *ecdsa.PublicKey
func (k *ecPublicKey) CryptoPublicKey() crypto.PublicKey {
return k.PublicKey
}
func (k *ecPublicKey) toMap() map[string]interface{} {
jwk := make(map[string]interface{})
for k, v := range k.extended {
jwk[k] = v
}
jwk["kty"] = k.KeyType()
jwk["kid"] = k.KeyID()
jwk["crv"] = k.CurveName()
xBytes := k.X.Bytes()
yBytes := k.Y.Bytes()
octetLength := (k.Params().BitSize + 7) >> 3
// MUST include leading zeros in the output so that x, y are each
// *octetLength* bytes long.
xBuf := make([]byte, octetLength-len(xBytes), octetLength)
yBuf := make([]byte, octetLength-len(yBytes), octetLength)
xBuf = append(xBuf, xBytes...)
yBuf = append(yBuf, yBytes...)
jwk["x"] = joseBase64UrlEncode(xBuf)
jwk["y"] = joseBase64UrlEncode(yBuf)
return jwk
}
// MarshalJSON serializes this Public Key using the JWK JSON serialization format for
// elliptic curve keys.
func (k *ecPublicKey) MarshalJSON() (data []byte, err error) {
return json.Marshal(k.toMap())
}
// PEMBlock serializes this Public Key to DER-encoded PKIX format.
func (k *ecPublicKey) PEMBlock() (*pem.Block, error) {
derBytes, err := x509.MarshalPKIXPublicKey(k.PublicKey)
if err != nil {
return nil, fmt.Errorf("unable to serialize EC PublicKey to DER-encoded PKIX format: %s", err)
}
k.extended["kid"] = k.KeyID() // For display purposes.
return createPemBlock("PUBLIC KEY", derBytes, k.extended)
}
func (k *ecPublicKey) AddExtendedField(field string, value interface{}) {
k.extended[field] = value
}
func (k *ecPublicKey) GetExtendedField(field string) interface{} {
v, ok := k.extended[field]
if !ok {
return nil
}
return v
}
func ecPublicKeyFromMap(jwk map[string]interface{}) (*ecPublicKey, error) {
// JWK key type (kty) has already been determined to be "EC".
// Need to extract 'crv', 'x', 'y', and 'kid' and check for
// consistency.
// Get the curve identifier value.
crv, err := stringFromMap(jwk, "crv")
if err != nil {
return nil, fmt.Errorf("JWK EC Public Key curve identifier: %s", err)
}
var (
curve elliptic.Curve
sigAlg *signatureAlgorithm
)
switch {
case crv == "P-256":
curve = elliptic.P256()
sigAlg = es256
case crv == "P-384":
curve = elliptic.P384()
sigAlg = es384
case crv == "P-521":
curve = elliptic.P521()
sigAlg = es512
default:
return nil, fmt.Errorf("JWK EC Public Key curve identifier not supported: %q\n", crv)
}
// Get the X and Y coordinates for the public key point.
xB64Url, err := stringFromMap(jwk, "x")
if err != nil {
return nil, fmt.Errorf("JWK EC Public Key x-coordinate: %s", err)
}
x, err := parseECCoordinate(xB64Url, curve)
if err != nil {
return nil, fmt.Errorf("JWK EC Public Key x-coordinate: %s", err)
}
yB64Url, err := stringFromMap(jwk, "y")
if err != nil {
return nil, fmt.Errorf("JWK EC Public Key y-coordinate: %s", err)
}
y, err := parseECCoordinate(yB64Url, curve)
if err != nil {
return nil, fmt.Errorf("JWK EC Public Key y-coordinate: %s", err)
}
key := &ecPublicKey{
PublicKey: &ecdsa.PublicKey{Curve: curve, X: x, Y: y},
curveName: crv, signatureAlgorithm: sigAlg,
}
// Key ID is optional too, but if it exists, it should match the key.
_, ok := jwk["kid"]
if ok {
kid, err := stringFromMap(jwk, "kid")
if err != nil {
return nil, fmt.Errorf("JWK EC Public Key ID: %s", err)
}
if kid != key.KeyID() {
return nil, fmt.Errorf("JWK EC Public Key ID does not match: %s", kid)
}
}
key.extended = jwk
return key, nil
}
/*
* EC DSA PRIVATE KEY
*/
// ecPrivateKey implements a JWK Private Key using elliptic curve digital signature
// algorithms.
type ecPrivateKey struct {
ecPublicKey
*ecdsa.PrivateKey
}
func fromECPrivateKey(cryptoPrivateKey *ecdsa.PrivateKey) (*ecPrivateKey, error) {
publicKey, err := fromECPublicKey(&cryptoPrivateKey.PublicKey)
if err != nil {
return nil, err
}
return &ecPrivateKey{*publicKey, cryptoPrivateKey}, nil
}
// PublicKey returns the Public Key data associated with this Private Key.
func (k *ecPrivateKey) PublicKey() PublicKey {
return &k.ecPublicKey
}
func (k *ecPrivateKey) String() string {
return fmt.Sprintf("EC Private Key <%s>", k.KeyID())
}
// Sign signs the data read from the io.Reader using a signature algorithm supported
// by the elliptic curve private key. If the specified hashing algorithm is
// supported by this key, that hash function is used to generate the signature
// otherwise the the default hashing algorithm for this key is used. Returns
// the signature and the name of the JWK signature algorithm used, e.g.,
// "ES256", "ES384", "ES512".
func (k *ecPrivateKey) Sign(data io.Reader, hashID crypto.Hash) (signature []byte, alg string, err error) {
// Generate a signature of the data using the internal alg.
// The given hashId is only a suggestion, and since EC keys only support
// on signature/hash algorithm given the curve name, we disregard it for
// the elliptic curve JWK signature implementation.
hasher := k.signatureAlgorithm.HashID().New()
_, err = io.Copy(hasher, data)
if err != nil {
return nil, "", fmt.Errorf("error reading data to sign: %s", err)
}
hash := hasher.Sum(nil)
r, s, err := ecdsa.Sign(rand.Reader, k.PrivateKey, hash)
if err != nil {
return nil, "", fmt.Errorf("error producing signature: %s", err)
}
rBytes, sBytes := r.Bytes(), s.Bytes()
octetLength := (k.ecPublicKey.Params().BitSize + 7) >> 3
// MUST include leading zeros in the output
rBuf := make([]byte, octetLength-len(rBytes), octetLength)
sBuf := make([]byte, octetLength-len(sBytes), octetLength)
rBuf = append(rBuf, rBytes...)
sBuf = append(sBuf, sBytes...)
signature = append(rBuf, sBuf...)
alg = k.signatureAlgorithm.HeaderParam()
return
}
// CryptoPrivateKey returns the internal object which can be used as a
// crypto.PublicKey for use with other standard library operations. The type
// is either *rsa.PublicKey or *ecdsa.PublicKey
func (k *ecPrivateKey) CryptoPrivateKey() crypto.PrivateKey {
return k.PrivateKey
}
func (k *ecPrivateKey) toMap() map[string]interface{} {
jwk := k.ecPublicKey.toMap()
dBytes := k.D.Bytes()
// The length of this octet string MUST be ceiling(log-base-2(n)/8)
// octets (where n is the order of the curve). This is because the private
// key d must be in the interval [1, n-1] so the bitlength of d should be
// no larger than the bitlength of n-1. The easiest way to find the octet
// length is to take bitlength(n-1), add 7 to force a carry, and shift this
// bit sequence right by 3, which is essentially dividing by 8 and adding
// 1 if there is any remainder. Thus, the private key value d should be
// output to (bitlength(n-1)+7)>>3 octets.
n := k.ecPublicKey.Params().N
octetLength := (new(big.Int).Sub(n, big.NewInt(1)).BitLen() + 7) >> 3
// Create a buffer with the necessary zero-padding.
dBuf := make([]byte, octetLength-len(dBytes), octetLength)
dBuf = append(dBuf, dBytes...)
jwk["d"] = joseBase64UrlEncode(dBuf)
return jwk
}
// MarshalJSON serializes this Private Key using the JWK JSON serialization format for
// elliptic curve keys.
func (k *ecPrivateKey) MarshalJSON() (data []byte, err error) {
return json.Marshal(k.toMap())
}
// PEMBlock serializes this Private Key to DER-encoded PKIX format.
func (k *ecPrivateKey) PEMBlock() (*pem.Block, error) {
derBytes, err := x509.MarshalECPrivateKey(k.PrivateKey)
if err != nil {
return nil, fmt.Errorf("unable to serialize EC PrivateKey to DER-encoded PKIX format: %s", err)
}
k.extended["keyID"] = k.KeyID() // For display purposes.
return createPemBlock("EC PRIVATE KEY", derBytes, k.extended)
}
func ecPrivateKeyFromMap(jwk map[string]interface{}) (*ecPrivateKey, error) {
dB64Url, err := stringFromMap(jwk, "d")
if err != nil {
return nil, fmt.Errorf("JWK EC Private Key: %s", err)
}
// JWK key type (kty) has already been determined to be "EC".
// Need to extract the public key information, then extract the private
// key value 'd'.
publicKey, err := ecPublicKeyFromMap(jwk)
if err != nil {
return nil, err
}
d, err := parseECPrivateParam(dB64Url, publicKey.Curve)
if err != nil {
return nil, fmt.Errorf("JWK EC Private Key d-param: %s", err)
}
key := &ecPrivateKey{
ecPublicKey: *publicKey,
PrivateKey: &ecdsa.PrivateKey{
PublicKey: *publicKey.PublicKey,
D: d,
},
}
return key, nil
}
/*
* Key Generation Functions.
*/
func generateECPrivateKey(curve elliptic.Curve) (k *ecPrivateKey, err error) {
k = new(ecPrivateKey)
k.PrivateKey, err = ecdsa.GenerateKey(curve, rand.Reader)
if err != nil {
return nil, err
}
k.ecPublicKey.PublicKey = &k.PrivateKey.PublicKey
k.extended = make(map[string]interface{})
return
}
// GenerateECP256PrivateKey generates a key pair using elliptic curve P-256.
func GenerateECP256PrivateKey() (PrivateKey, error) {
k, err := generateECPrivateKey(elliptic.P256())
if err != nil {
return nil, fmt.Errorf("error generating EC P-256 key: %s", err)
}
k.curveName = "P-256"
k.signatureAlgorithm = es256
return k, nil
}
// GenerateECP384PrivateKey generates a key pair using elliptic curve P-384.
func GenerateECP384PrivateKey() (PrivateKey, error) {
k, err := generateECPrivateKey(elliptic.P384())
if err != nil {
return nil, fmt.Errorf("error generating EC P-384 key: %s", err)
}
k.curveName = "P-384"
k.signatureAlgorithm = es384
return k, nil
}
// GenerateECP521PrivateKey generates aß key pair using elliptic curve P-521.
func GenerateECP521PrivateKey() (PrivateKey, error) {
k, err := generateECPrivateKey(elliptic.P521())
if err != nil {
return nil, fmt.Errorf("error generating EC P-521 key: %s", err)
}
k.curveName = "P-521"
k.signatureAlgorithm = es512
return k, nil
}