package p2p import ( "crypto/ecdsa" "crypto/rand" "fmt" "github.com/ethereum/go-ethereum/crypto" "github.com/obscuren/ecies" "github.com/obscuren/secp256k1-go" ) var ( sskLen int = 16 // ecies.MaxSharedKeyLength(pubKey) / 2 sigLen int = 65 // elliptic S256 keyLen int = 32 // ECDSA msgLen int = sigLen + 3*keyLen + 1 // 162 resLen int = 65 // ) // aesSecret, macSecret, egressMac, ingress type secretRW struct { aesSecret, macSecret, egressMac, ingressMac []byte } type cryptoId struct { prvKey *ecdsa.PrivateKey pubKey *ecdsa.PublicKey pubKeyDER []byte } func newCryptoId(id ClientIdentity) (self *cryptoId, err error) { // will be at server init var prvKeyDER []byte = id.PrivKey() if prvKeyDER == nil { err = fmt.Errorf("no private key for client") return } // initialise ecies private key via importing DER encoded keys (known via our own clientIdentity) var prvKey = crypto.ToECDSA(prvKeyDER) if prvKey == nil { err = fmt.Errorf("invalid private key for client") return } self = &cryptoId{ prvKey: prvKey, // initialise public key from the imported private key pubKey: &prvKey.PublicKey, // to be created at server init shared between peers and sessions // for reuse, call wth ReadAt, no reset seek needed } self.pubKeyDER = id.Pubkey() return } func (self *cryptoId) Run(remotePubKeyDER []byte) (rw *secretRW) { if self.initiator { auth, initNonce, randomPrvKey, randomPubKey, err := initiator.initAuth(remotePubKeyDER, sessionToken) respNonce, remoteRandomPubKey, _, _ := initiator.verifyAuthResp(response) } else { // we are listening connection. we are responders in the haandshake. // Extract info from the authentication. The initiator starts by sending us a handshake that we need to respond to. response, remoteRespNonce, remoteInitNonce, remoteRandomPrivKey, _ := responder.verifyAuth(auth, sessionToken, pubInit) } initSessionToken, initSecretRW, _ := initiator.newSession(initNonce, respNonce, auth, randomPrvKey, remoteRandomPubKey) respSessionToken, respSecretRW, _ := responder.newSession(remoteInitNonce, remoteRespNonce, auth, remoteRandomPrivKey, randomPubKey) } /* startHandshake is called by peer if it initiated the connection. By protocol spec, the party who initiates the connection (initiator) will send an 'auth' packet New: authInitiator -> E(remote-pubk, S(ecdhe-random, ecdh-shared-secret^nonce) || H(ecdhe-random-pubk) || pubk || nonce || 0x0) authRecipient -> E(remote-pubk, ecdhe-random-pubk || nonce || 0x0) Known: authInitiator = E(remote-pubk, S(ecdhe-random, token^nonce) || H(ecdhe-random-pubk) || pubk || nonce || 0x1) authRecipient = E(remote-pubk, ecdhe-random-pubk || nonce || 0x1) // token found authRecipient = E(remote-pubk, ecdhe-random-pubk || nonce || 0x0) // token not found The caller provides the public key of the peer as conjuctured from lookup based on IP:port, given as user input or proven by signatures. The caller must have access to persistant information about the peers, and pass the previous session token as an argument to cryptoId. The handshake is the process by which the peers establish their connection for a session. */ func (self *cryptoId) startHandshake(remotePubKeyDER, sessionToken []byte) (auth []byte, initNonce []byte, randomPrvKey *ecdsa.PrivateKey, randomPubKey *ecdsa.PublicKey, err error) { // session init, common to both parties remotePubKey := crypto.ToECDSAPub(remotePubKeyDER) if remotePubKey == nil { err = fmt.Errorf("invalid remote public key") return } 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(self.prvKey).GenerateShared(ecies.ImportECDSAPublic(remotePubKey), sskLen, sskLen); err != nil { return } // this will not stay here ;) fmt.Printf("secret generated: %v %x", len(sessionToken), sessionToken) // 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, msgLen) // generate sskLen long nonce initNonce = msg[msgLen-keyLen-1 : msgLen-1] // nonce = msg[msgLen-sskLen-1 : msgLen-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 } fmt.Printf("signature generated: %v %x", len(signature), signature) // message // signed-shared-secret || H(ecdhe-random-pubk) || pubk || nonce || 0x0 copy(msg, signature) // copy signed-shared-secret // H(ecdhe-random-pubk) copy(msg[sigLen:sigLen+keyLen], crypto.Sha3(crypto.FromECDSAPub(&randomPrvKey.PublicKey))) // pubkey copied to the correct segment. copy(msg[sigLen+keyLen:sigLen+2*keyLen], self.pubKeyDER) // nonce is already in the slice // stick tokenFlag byte to the end msg[msgLen-1] = tokenFlag fmt.Printf("plaintext message generated: %v %x", len(msg), msg) // encrypt using remote-pubk // auth = eciesEncrypt(remote-pubk, msg) if auth, err = crypto.Encrypt(remotePubKey, msg); err != nil { return } fmt.Printf("encrypted message generated: %v %x\n used pubkey: %x\n", len(auth), auth, crypto.FromECDSAPub(remotePubKey)) return } // verifyAuth is called by peer if it accepted (but not initiated) the connection func (self *cryptoId) respondToHandshake(auth, sessionToken []byte, remotePubKey *ecdsa.PublicKey) (authResp []byte, respNonce []byte, initNonce []byte, randomPrvKey *ecdsa.PrivateKey, err error) { var msg []byte fmt.Printf("encrypted message received: %v %x\n used pubkey: %x\n", len(auth), auth, crypto.FromECDSAPub(self.pubKey)) // they prove that msg is meant for me, // I prove I possess private key if i can read it if msg, err = crypto.Decrypt(self.prvKey, auth); err != nil { return } fmt.Printf("\nplaintext message retrieved: %v %x\n", len(msg), msg) 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(self.prvKey).GenerateShared(ecies.ImportECDSAPublic(remotePubKey), sskLen, sskLen); err != nil { return } fmt.Printf("secret generated: %v %x", len(sessionToken), sessionToken) // 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[msgLen-keyLen-1 : msgLen-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 remoteRandomPubKeyDER []byte if remoteRandomPubKeyDER, err = secp256k1.RecoverPubkey(signedMsg, msg[:sigLen]); err != nil { return } // convert to ECDSA standard remoteRandomPubKey := crypto.ToECDSAPub(remoteRandomPubKeyDER) if remoteRandomPubKey == nil { err = fmt.Errorf("invalid remote public key") return } // now we find ourselves a long task too, fill it random var resp = make([]byte, resLen) // generate keyLen long nonce respNonce = msg[resLen-keyLen-1 : msgLen-1] if _, err = rand.Read(respNonce); err != nil { return } // generate random keypair for session if randomPrvKey, err = crypto.GenerateKey(); err != nil { return } // responder auth message // E(remote-pubk, ecdhe-random-pubk || nonce || 0x0) copy(resp[:keyLen], crypto.FromECDSAPub(&randomPrvKey.PublicKey)) // nonce is already in the slice resp[resLen-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 } func (self *cryptoId) completeHandshake(auth []byte) (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(self.prvKey, auth); err != nil { return } respNonce = msg[resLen-keyLen-1 : resLen-1] var remoteRandomPubKeyDER = msg[:keyLen] remoteRandomPubKey = crypto.ToECDSAPub(remoteRandomPubKeyDER) if remoteRandomPubKey == nil { err = fmt.Errorf("invalid ecdh random remote public key") return } if msg[resLen-1] == 0x01 { tokenFlag = true } return } func (self *cryptoId) newSession(initNonce, respNonce, auth []byte, privKey *ecdsa.PrivateKey, remoteRandomPubKey *ecdsa.PublicKey) (sessionToken []byte, rw *secretRW, err error) { // 3) Now we can trust ecdhe-random-pubk to derive new keys //ecdhe-shared-secret = ecdh.agree(ecdhe-random, remote-ecdhe-random-pubk) var dhSharedSecret []byte pubKey := ecies.ImportECDSAPublic(remoteRandomPubKey) if dhSharedSecret, err = ecies.ImportECDSA(privKey).GenerateShared(pubKey, sskLen, sskLen); err != nil { return } // shared-secret = crypto.Sha3(ecdhe-shared-secret || crypto.Sha3(nonce || initiator-nonce)) var sharedSecret = crypto.Sha3(append(dhSharedSecret, crypto.Sha3(append(respNonce, initNonce...))...)) // token = crypto.Sha3(shared-secret) sessionToken = crypto.Sha3(sharedSecret) // aes-secret = crypto.Sha3(ecdhe-shared-secret || shared-secret) var aesSecret = crypto.Sha3(append(dhSharedSecret, sharedSecret...)) // # destroy shared-secret // mac-secret = crypto.Sha3(ecdhe-shared-secret || aes-secret) var macSecret = crypto.Sha3(append(dhSharedSecret, aesSecret...)) // # destroy ecdhe-shared-secret // egress-mac = crypto.Sha3(mac-secret^nonce || auth) var egressMac = crypto.Sha3(append(Xor(macSecret, respNonce), auth...)) // # destroy nonce // ingress-mac = crypto.Sha3(mac-secret^initiator-nonce || auth), var ingressMac = crypto.Sha3(append(Xor(macSecret, initNonce), auth...)) // # destroy remote-nonce rw = &secretRW{ aesSecret: aesSecret, macSecret: macSecret, egressMac: egressMac, ingressMac: ingressMac, } return } // should use cipher.xorBytes from crypto/cipher/xor.go for fast xor 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 }