package p2p
import (
// "binary"
"crypto/ecdsa"
"crypto/rand"
"fmt"
"io"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/crypto/secp256k1"
ethlogger "github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/p2p/discover"
"github.com/obscuren/ecies"
)
var clogger = ethlogger.NewLogger("CRYPTOID")
const (
sskLen = 16 // ecies.MaxSharedKeyLength(pubKey) / 2
sigLen = 65 // elliptic S256
pubLen = 64 // 512 bit pubkey in uncompressed representation without format byte
shaLen = 32 // hash length (for nonce etc)
authMsgLen = sigLen + shaLen + pubLen + shaLen + 1
authRespLen = pubLen + shaLen + 1
eciesBytes = 65 + 16 + 32
iHSLen = authMsgLen + eciesBytes // size of the final ECIES payload sent as initiator's handshake
rHSLen = authRespLen + eciesBytes // size of the final ECIES payload sent as receiver's handshake
)
type hexkey []byte
func (self hexkey) String() string {
return fmt.Sprintf("(%d) %x", len(self), []byte(self))
}
func encHandshake(conn io.ReadWriter, prv *ecdsa.PrivateKey, dial *discover.Node) (
remoteID discover.NodeID,
sessionToken []byte,
err error,
) {
if dial == nil {
var remotePubkey []byte
sessionToken, remotePubkey, err = inboundEncHandshake(conn, prv, nil)
copy(remoteID[:], remotePubkey)
} else {
remoteID = dial.ID
sessionToken, err = outboundEncHandshake(conn, prv, remoteID[:], nil)
}
return remoteID, sessionToken, err
}
// outboundEncHandshake negotiates a session token on conn.
// it should be called on the dialing side of the connection.
//
// privateKey is the local client's private key
// remotePublicKey is the remote peer's node ID
// sessionToken is the token from a previous session with this node.
func outboundEncHandshake(conn io.ReadWriter, prvKey *ecdsa.PrivateKey, remotePublicKey []byte, sessionToken []byte) (
newSessionToken []byte,
err error,
) {
auth, initNonce, randomPrivKey, err := authMsg(prvKey, remotePublicKey, sessionToken)
if err != nil {
return nil, err
}
if sessionToken != nil {
clogger.Debugf("session-token: %v", hexkey(sessionToken))
}
clogger.Debugf("initiator-nonce: %v", hexkey(initNonce))
clogger.Debugf("initiator-random-private-key: %v", hexkey(crypto.FromECDSA(randomPrivKey)))
randomPublicKeyS, _ := exportPublicKey(&randomPrivKey.PublicKey)
clogger.Debugf("initiator-random-public-key: %v", hexkey(randomPublicKeyS))
if _, err = conn.Write(auth); err != nil {
return nil, err
}
clogger.Debugf("initiator handshake: %v", hexkey(auth))
response := make([]byte, rHSLen)
if _, err = io.ReadFull(conn, response); err != nil {
return nil, err
}
recNonce, remoteRandomPubKey, _, err := completeHandshake(response, prvKey)
if err != nil {
return nil, err
}
clogger.Debugf("receiver-nonce: %v", hexkey(recNonce))
remoteRandomPubKeyS, _ := exportPublicKey(remoteRandomPubKey)
clogger.Debugf("receiver-random-public-key: %v", hexkey(remoteRandomPubKeyS))
return newSession(initNonce, recNonce, randomPrivKey, remoteRandomPubKey)
}
// authMsg creates the initiator handshake.
func authMsg(prvKey *ecdsa.PrivateKey, remotePubKeyS, sessionToken []byte) (
auth, initNonce []byte,
randomPrvKey *ecdsa.PrivateKey,
err error,
) {
// session init, common to both parties
remotePubKey, err := importPublicKey(remotePubKeyS)
if err != nil {
return
}
var tokenFlag byte // = 0x00
if sessionToken == nil {
// no session token found 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 sessionToken, err = ecies.ImportECDSA(prvKey).GenerateShared(ecies.ImportECDSAPublic(remotePubKey), sskLen, sskLen); err != nil {
return
}
// tokenFlag = 0x00 // redundant
} else {
// for known peers, we use stored token from the previous session
tokenFlag = 0x01
}
//E(remote-pubk, S(ecdhe-random, ecdh-shared-secret^nonce) || H(ecdhe-random-pubk) || pubk || nonce || 0x0)
// E(remote-pubk, S(ecdhe-random, token^nonce) || H(ecdhe-random-pubk) || pubk || nonce || 0x1)
// allocate msgLen long message,
var msg []byte = make([]byte, authMsgLen)
initNonce = msg[authMsgLen-shaLen-1 : authMsgLen-1]
if _, err = rand.Read(initNonce); err != nil {
return
}
// create known message
// ecdh-shared-secret^nonce for new peers
// token^nonce for old peers
var sharedSecret = xor(sessionToken, initNonce)
// generate random keypair to use for signing
if randomPrvKey, err = crypto.GenerateKey(); err != nil {
return
}
// sign shared secret (message known to both parties): shared-secret
var signature []byte
// signature = sign(ecdhe-random, shared-secret)
// uses secp256k1.Sign
if signature, err = crypto.Sign(sharedSecret, randomPrvKey); err != nil {
return
}
// message
// signed-shared-secret || H(ecdhe-random-pubk) || pubk || nonce || 0x0
copy(msg, signature) // copy signed-shared-secret
// H(ecdhe-random-pubk)
var randomPubKey64 []byte
if randomPubKey64, err = exportPublicKey(&randomPrvKey.PublicKey); err != nil {
return
}
var pubKey64 []byte
if pubKey64, err = exportPublicKey(&prvKey.PublicKey); err != nil {
return
}
copy(msg[sigLen:sigLen+shaLen], crypto.Sha3(randomPubKey64))
// pubkey copied to the correct segment.
copy(msg[sigLen+shaLen:sigLen+shaLen+pubLen], pubKey64)
// nonce is already in the slice
// stick tokenFlag byte to the end
msg[authMsgLen-1] = tokenFlag
// encrypt using remote-pubk
// auth = eciesEncrypt(remote-pubk, msg)
if auth, err = crypto.Encrypt(remotePubKey, msg); err != nil {
return
}
return
}
// completeHandshake is called when the initiator receives an
// authentication response (aka receiver handshake). It completes the
// handshake by reading off parameters the remote peer provides needed
// to set up the secure session.
func completeHandshake(auth []byte, prvKey *ecdsa.PrivateKey) (
respNonce []byte,
remoteRandomPubKey *ecdsa.PublicKey,
tokenFlag bool,
err error,
) {
var msg []byte
// they prove that msg is meant for me,
// I prove I possess private key if i can read it
if msg, err = crypto.Decrypt(prvKey, auth); err != nil {
return
}
respNonce = msg[pubLen : pubLen+shaLen]
var remoteRandomPubKeyS = msg[:pubLen]
if remoteRandomPubKey, err = importPublicKey(remoteRandomPubKeyS); err != nil {
return
}
if msg[authRespLen-1] == 0x01 {
tokenFlag = true
}
return
}
// inboundEncHandshake negotiates a session token on conn.
// it should be called on the listening side of the connection.
//
// privateKey is the local client's private key
// sessionToken is the token from a previous session with this node.
func inboundEncHandshake(conn io.ReadWriter, prvKey *ecdsa.PrivateKey, sessionToken []byte) (
token, remotePubKey []byte,
err error,
) {
// we are listening connection. we are responders in the
// handshake. Extract info from the authentication. The initiator
// starts by sending us a handshake that we need to respond to. so
// we read auth message first, then respond.
auth := make([]byte, iHSLen)
if _, err := io.ReadFull(conn, auth); err != nil {
return nil, nil, err
}
response, recNonce, initNonce, remotePubKey, randomPrivKey, remoteRandomPubKey, err := authResp(auth, sessionToken, prvKey)
if err != nil {
return nil, nil, err
}
clogger.Debugf("receiver-nonce: %v", hexkey(recNonce))
clogger.Debugf("receiver-random-priv-key: %v", hexkey(crypto.FromECDSA(randomPrivKey)))
if _, err = conn.Write(response); err != nil {
return nil, nil, err
}
clogger.Debugf("receiver handshake:\n%v", hexkey(response))
token, err = newSession(initNonce, recNonce, randomPrivKey, remoteRandomPubKey)
return token, remotePubKey, err
}
// authResp is called by peer if it accepted (but not
// initiated) the connection from the remote. It is passed the initiator
// handshake received and the session token belonging to the
// remote initiator.
//
// The first return value is the authentication response (aka receiver
// handshake) that is to be sent to the remote initiator.
func authResp(auth, sessionToken []byte, prvKey *ecdsa.PrivateKey) (
authResp, respNonce, initNonce, remotePubKeyS []byte,
randomPrivKey *ecdsa.PrivateKey,
remoteRandomPubKey *ecdsa.PublicKey,
err error,
) {
// they prove that msg is meant for me,
// I prove I possess private key if i can read it
msg, err := crypto.Decrypt(prvKey, auth)
if err != nil {
return
}
remotePubKeyS = msg[sigLen+shaLen : sigLen+shaLen+pubLen]
remotePubKey, _ := importPublicKey(remotePubKeyS)
var tokenFlag byte
if sessionToken == nil {
// no session token found 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 sessionToken, err = ecies.ImportECDSA(prvKey).GenerateShared(ecies.ImportECDSAPublic(remotePubKey), sskLen, sskLen); err != nil {
return
}
// tokenFlag = 0x00 // redundant
} else {
// for known peers, we use stored token from the previous session
tokenFlag = 0x01
}
// the initiator nonce is read off the end of the message
initNonce = msg[authMsgLen-shaLen-1 : authMsgLen-1]
// I prove that i own prv key (to derive shared secret, and read
// nonce off encrypted msg) and that I own shared secret they
// prove they own the private key belonging to ecdhe-random-pubk
// we can now reconstruct the signed message and recover the peers
// pubkey
var signedMsg = xor(sessionToken, initNonce)
var remoteRandomPubKeyS []byte
if remoteRandomPubKeyS, err = secp256k1.RecoverPubkey(signedMsg, msg[:sigLen]); err != nil {
return
}
// convert to ECDSA standard
if remoteRandomPubKey, err = importPublicKey(remoteRandomPubKeyS); err != nil {
return
}
// now we find ourselves a long task too, fill it random
var resp = make([]byte, authRespLen)
// generate shaLen long nonce
respNonce = resp[pubLen : pubLen+shaLen]
if _, err = rand.Read(respNonce); err != nil {
return
}
// generate random keypair for session
if randomPrivKey, err = crypto.GenerateKey(); err != nil {
return
}
// responder auth message
// E(remote-pubk, ecdhe-random-pubk || nonce || 0x0)
var randomPubKeyS []byte
if randomPubKeyS, err = exportPublicKey(&randomPrivKey.PublicKey); err != nil {
return
}
copy(resp[:pubLen], randomPubKeyS)
// nonce is already in the slice
resp[authRespLen-1] = tokenFlag
// encrypt using remote-pubk
// auth = eciesEncrypt(remote-pubk, msg)
// why not encrypt with ecdhe-random-remote
if authResp, err = crypto.Encrypt(remotePubKey, resp); err != nil {
return
}
return
}
// newSession is called after the handshake is completed. The
// arguments are values negotiated in the handshake. The return value
// is a new session Token to be remembered for the next time we
// connect with this peer.
func newSession(initNonce, respNonce []byte, privKey *ecdsa.PrivateKey, remoteRandomPubKey *ecdsa.PublicKey) ([]byte, error) {
// 3) Now we can trust ecdhe-random-pubk to derive new keys
//ecdhe-shared-secret = ecdh.agree(ecdhe-random, remote-ecdhe-random-pubk)
pubKey := ecies.ImportECDSAPublic(remoteRandomPubKey)
dhSharedSecret, err := ecies.ImportECDSA(privKey).GenerateShared(pubKey, sskLen, sskLen)
if err != nil {
return nil, err
}
sharedSecret := crypto.Sha3(dhSharedSecret, crypto.Sha3(respNonce, initNonce))
sessionToken := crypto.Sha3(sharedSecret)
return sessionToken, nil
}
// importPublicKey unmarshals 512 bit public keys.
func importPublicKey(pubKey []byte) (pubKeyEC *ecdsa.PublicKey, err 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))
}
return crypto.ToECDSAPub(pubKey65), nil
}
func exportPublicKey(pubKeyEC *ecdsa.PublicKey) (pubKey []byte, err error) {
if pubKeyEC == nil {
return nil, fmt.Errorf("no ECDSA public key given")
}
return crypto.FromECDSAPub(pubKeyEC)[1:], nil
}
func xor(one, other []byte) (xor []byte) {
xor = make([]byte, len(one))
for i := 0; i < len(one); i++ {
xor[i] = one[i] ^ other[i]
}
return xor
}
