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, secp256k1.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, secp256k1.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 decodeAuthMsg(prv *ecdsa.PrivateKey, token []byte, auth []byte) (*encHandshake, error) {
var err error
h := new(encHandshake)
// generate random keypair for session
h.randomPrivKey, err = ecies.GenerateKey(rand.Reader, crypto.S256(), nil)
if err != nil {
return nil, err
}
// generate random nonce
h.respNonce = make([]byte, shaLen)
if _, err = rand.Read(h.respNonce); err != nil {
return nil, err
}
msg, err := crypto.Decrypt(prv, auth)
if err != nil {
return nil, fmt.Errorf("could not decrypt auth message (%v)", err)
}
// decode message parameters
// signature || sha3(ecdhe-random-pubk) || pubk || nonce || token-flag
h.initNonce = msg[authMsgLen-shaLen-1 : authMsgLen-1]
copy(h.remoteID[:], msg[sigLen+shaLen:sigLen+shaLen+pubLen])
rpub, err := h.remoteID.Pubkey()
if err != nil {
return nil, fmt.Errorf("bad remoteID: %#v", err)
}
h.remotePub = ecies.ImportECDSAPublic(rpub)
// recover remote random pubkey from signed message.
if token == nil {
// TODO: it is an error if the initiator has a token and we don't. check that.
// no session token means we need to generate shared secret.
// ecies shared secret is used as initial session token for new peers.
// generate shared key from prv and remote pubkey.
if token, err = h.ecdhShared(prv); err != nil {
return nil, err
}
}
signedMsg := xor(token, h.initNonce)
remoteRandomPub, err := secp256k1.RecoverPubkey(signedMsg, msg[:sigLen])
if err != nil {
return nil, err
}
// validate the sha3 of recovered pubkey
remoteRandomPubMAC := msg[sigLen : sigLen+shaLen]
shaRemoteRandomPub := crypto.Sha3(remoteRandomPub[1:])
if !bytes.Equal(remoteRandomPubMAC, shaRemoteRandomPub) {
return nil, fmt.Errorf("sha3 of recovered ephemeral pubkey does not match checksum in auth message")
}
h.remoteRandomPub, _ = importPublicKey(remoteRandomPub)
return h, 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
return ecies.ImportECDSAPublic(crypto.ToECDSAPub(pubKey65)), nil
}
func newInitiatorHandshake(remoteID discover.NodeID) (*encHandshake, error) {
// generate random initiator nonce
n := make([]byte, shaLen)
if _, err := rand.Read(n); err != nil {
return nil, err
}
// generate random keypair to use for signing
randpriv, err := ecies.GenerateKey(rand.Reader, crypto.S256(), nil)
if err != nil {
return nil, err
}
rpub, err := remoteID.Pubkey()
if err != nil {
return nil, fmt.Errorf("bad remoteID: %v", err)
}
h := &encHandshake{
initiator: true,
remoteID: remoteID,
remotePub: ecies.ImportECDSAPublic(rpub),
initNonce: n,
randomPrivKey: randpriv,
}
return h, nil
}
func Encrypt(pub *ecdsa.PublicKey, message []byte) ([]byte, error) {
return ecies.Encrypt(rand.Reader, ecies.ImportECDSAPublic(pub), message, nil, nil)
}