func (h *encHandshake) handleAuthMsg(msg *authMsgV4, prv *ecdsa.PrivateKey) error {
// Import the remote identity.
h.initNonce = msg.Nonce[:]
h.remoteID = msg.InitiatorPubkey
rpub, err := h.remoteID.Pubkey()
if err != nil {
return fmt.Errorf("bad remoteID: %#v", err)
}
h.remotePub = ecies.ImportECDSAPublic(rpub)
// Generate random keypair for ECDH.
// If a private key is already set, use it instead of generating one (for testing).
if h.randomPrivKey == nil {
h.randomPrivKey, err = ecies.GenerateKey(rand.Reader, crypto.S256(), nil)
if err != nil {
return err
}
}
// Check the signature.
token, err := h.staticSharedSecret(prv)
if err != nil {
return err
}
signedMsg := xor(token, h.initNonce)
remoteRandomPub, err := secp256k1.RecoverPubkey(signedMsg, msg.Signature[:])
if err != nil {
return err
}
h.remoteRandomPub, _ = importPublicKey(remoteRandomPub)
return nil
}
// makeAuthMsg creates the initiator handshake message.
func (h *encHandshake) makeAuthMsg(prv *ecdsa.PrivateKey, token []byte) (*authMsgV4, error) {
rpub, err := h.remoteID.Pubkey()
if err != nil {
return nil, fmt.Errorf("bad remoteID: %v", err)
}
h.remotePub = ecies.ImportECDSAPublic(rpub)
// Generate random initiator nonce.
h.initNonce = make([]byte, shaLen)
if _, err := rand.Read(h.initNonce); err != nil {
return nil, err
}
// Generate random keypair to for ECDH.
h.randomPrivKey, err = ecies.GenerateKey(rand.Reader, crypto.S256(), nil)
if err != nil {
return nil, err
}
// Sign known message: static-shared-secret ^ nonce
token, err = h.staticSharedSecret(prv)
if err != nil {
return nil, err
}
signed := xor(token, h.initNonce)
signature, err := crypto.Sign(signed, h.randomPrivKey.ExportECDSA())
if err != nil {
return nil, err
}
msg := new(authMsgV4)
copy(msg.Signature[:], signature)
copy(msg.InitiatorPubkey[:], crypto.FromECDSAPub(&prv.PublicKey)[1:])
copy(msg.Nonce[:], h.initNonce)
msg.Version = 4
return msg, nil
}
func TestSharedSecret(t *testing.T) {
prv0, _ := crypto.GenerateKey() // = ecdsa.GenerateKey(crypto.S256(), rand.Reader)
pub0 := &prv0.PublicKey
prv1, _ := crypto.GenerateKey()
pub1 := &prv1.PublicKey
ss0, err := ecies.ImportECDSA(prv0).GenerateShared(ecies.ImportECDSAPublic(pub1), sskLen, sskLen)
if err != nil {
return
}
ss1, err := ecies.ImportECDSA(prv1).GenerateShared(ecies.ImportECDSAPublic(pub0), sskLen, sskLen)
if err != nil {
return
}
t.Logf("Secret:\n%v %x\n%v %x", len(ss0), ss0, len(ss0), ss1)
if !bytes.Equal(ss0, ss1) {
t.Errorf("dont match :(")
}
}
// importPublicKey unmarshals 512 bit public keys.
func importPublicKey(pubKey []byte) (*ecies.PublicKey, error) {
var pubKey65 []byte
switch len(pubKey) {
case 64:
// add 'uncompressed key' flag
pubKey65 = append([]byte{0x04}, pubKey...)
case 65:
pubKey65 = pubKey
default:
return nil, fmt.Errorf("invalid public key length %v (expect 64/65)", len(pubKey))
}
// TODO: fewer pointless conversions
pub := crypto.ToECDSAPub(pubKey65)
if pub.X == nil {
return nil, fmt.Errorf("invalid public key")
}
return ecies.ImportECDSAPublic(pub), nil
}
func Encrypt(pub *ecdsa.PublicKey, message []byte) ([]byte, error) {
return ecies.Encrypt(rand.Reader, ecies.ImportECDSAPublic(pub), message, nil, nil)
}