From 8bd8176f7f7d88dc1b9a93a8cb90fd9ee399c141 Mon Sep 17 00:00:00 2001 From: Sergey Matveev Date: Wed, 30 Jul 2014 10:52:43 +0400 Subject: [PATCH] Initial commit Signed-off-by: Sergey Matveev --- AUTHORS | 1 + COPYING | 674 +++++++++++++++++++++++++++++++++++++++++++++++++++ README | 191 +++++++++++++++ govpn.go | 241 ++++++++++++++++++ handshake.go | 263 ++++++++++++++++++++ 5 files changed, 1370 insertions(+) create mode 100644 AUTHORS create mode 100644 COPYING create mode 100644 README create mode 100644 govpn.go create mode 100644 handshake.go diff --git a/AUTHORS b/AUTHORS new file mode 100644 index 0000000..f047789 --- /dev/null +++ b/AUTHORS @@ -0,0 +1 @@ +* Sergey Matveev diff --git a/COPYING b/COPYING new file mode 100644 index 0000000..9a2708d --- /dev/null +++ b/COPYING @@ -0,0 +1,674 @@ + GNU GENERAL PUBLIC LICENSE + Version 3, 29 June 2007 + + Copyright (C) 2007 Free Software Foundation, Inc. + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The GNU General Public License is a free, copyleft license for +software and other kinds of works. + + The licenses for most software and other practical works are designed +to take away your freedom to share and change the works. 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If your program is a subroutine library, you +may consider it more useful to permit linking proprietary applications with +the library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. But first, please read +. diff --git a/README b/README new file mode 100644 index 0000000..42c9fa1 --- /dev/null +++ b/README @@ -0,0 +1,191 @@ + GoVPN + ===== +SYNOPSIS + +govpn is simple high-performance secure virtual private network daemon. +It uses DH-EKE for mutual zero-knowledge authentication and +authenticated encrypted transport. + +DESCRIPTION + +All packets captured on network interface are encrypted, authenticated +and sent to remote server, that writes them to his interface, and vice +versa. Client and server use pre-shared authentication key (PSK). +Because of stateless UDP nature, after some timeout of inactivity peers +forget about each other and have to retry handshake process again. As a +rule, there are enough time-to-time traffic in ordinary Ethernet +networks to heartbeat connection. + +Handshake is used to mutually authenticate peers, exchange common secret +per-session encryption key and checks UDP transport availability. + +Because of UDP and authentication overhead: each packet grows in size +during transmission, so you have to lower you maximum transmission unit +(MTU) on network interface. + +High security and high performance are the goals for that daemon. It +uses fast cryptography algorithms with 128bit security margin, strong +mutual zero-knowledge authentication and perfect-forward secrecy +property. An attacker can not know anything from captured traffic, even +if pre-shared key is compromised. + +COMPARISON TO OpenVPN + +* Higher performance +* Perfect-forward secrecy (if long-term pre-shared keys are compromised, + no captured traffic can be decrypted anyway) +* Mutual two-side authentication (noone will send real network interface + data unless the other side is authenticated) +* Zero-knowledge authentication (pre-shared key is not transmitted in + any form between the peers, not even it's hash value) +* Fast handshake + +CONSOLE OUTPUT LEGEND + +B -- bad UDP packet (some system error) +T -- bad tag on packet (MiTM, unordered packet) +[HS?] -- unknown handshake message +w -- successful write to remote peer +r -- successful read from remote peer +[HS1], [HS2], [HS3], [HS4] -- handshake packet stage +[rS?] -- invalid server's random authentication number received (MiTM, bad PSK) +[rC?] -- invalid client's random authentication number received (MiTM, bad PSK) +[S?] -- invalid handshake stage is trying to perform (MiTM, duplicate packet) +[OK] -- handshake's stage passed + +TECHNICAL INTERNALS + +Encryption: Salsa20 +Message authentication: Poly1305 +Password authenticated key agreement: Curve25519 based DH-EKE +Packet overhead: 24 bytes per packet +Handshake overhead: 4 UDP (2 from client, 2 from server) packets, + 232 bytes total payload + + Transport protocol + + SERIAL + ENC(KEY, SERIAL, DATA) + AUTH(SERIAL + ENC_DATA) + +where SERIAL is message serial number. Odds are reserved for +client->server, evens are for server->client. SERIAL is used as a nonce +for DATA encryption: encryption key is different during each handshake, +so (key, nonce) pair is always used once. + +We generate Salsa20's output using this key and nonce for each message: +* first 256 bits are used as a one-time key for Poly1305 authentication +* next 256 bits of output are ignored +* and all remaining ones XORed with the data, encrypting it + + Handshake protocol + ┌──────┐ ┌──────┐ + │Client│ │Server│ + └──┬───┘ └──┬───┘ + │────┐ + │ │ R=rand(64bit); CPrivKey=rand(256bit) + │<───┘ + │ │ + │ R, enc(PSK, R, CPubKey) │ + │ ────────────────────────────────────────> + │ │ + │ │────┐ + │ │ │ SPrivKey=rand(256bit) + │ │<───┘ + │ │ + │ │────┐ + │ │ │ K=DH(SPrivKey, CPubKey) + │ │<───┘ + │ │ + │ │────┐ + │ │ │ RS=rand(64bit); SS=rand(256bit) + │ │<───┘ + │ │ + │ enc(PSK, R+1, SPubKey); enc(K, R, RS+SS)│ + │ <──────────────────────────────────────── + │ │ + │────┐ │ + │ │ K=DH(CPrivKey, SPubKey) │ + │<───┘ │ + │ │ + │────┐ │ + │ │ RC=rand(64bit); SC=rand(256bit) │ + │<───┘ │ + │ │ + │ enc(K, R+1, RS+RC+SC) │ + │ ────────────────────────────────────────> + │ │ + │ │────┐ + │ │ │ compare(RS) + │ │<───┘ + │ │ + │ │────┐ + │ │ │ MasterKey=SS XOR SC + │ │<───┘ + │ │ + │ enc(K, 0x00, RC) │ + │ <──────────────────────────────────────── + │ │ + │────┐ │ + │ │ compare(RC) │ + │<───┘ │ + │ │ + │────┐ │ + │ │ MasterKey=SS XOR SC │ + │<───┘ │ + ┌──┴───┐ ┌──┴───┐ + │Client│ │Server│ + └──────┘ └──────┘ + +* client generates CPubKey, random 64bit R that is used as a nonce + for encryption +* R + enc(PSK, R, CPubKey) + NULLs -> Server [56 bytes] +* server remembers clients address, decrypt CPubKey, generates + SPrivKey/SPubKey, computes common shared key K (based on + CPubKey and SPrivKey), generates 64bit random number RS and + 256bit random SS. PSK-encryption uses incremented R (from previous + message) for nonce +* enc(PSK, SPubKey) + enc(K, RS + SS) + NULLs -> Client [88 bytes] +* client decrypt SPubKey, computes K, decrypts RS, SS with key K, + remembers SS, generates 64bit random number RC and 256bit random SC, +* enc(K, RS + RC + SC) + NULLs -> Server [64 bytes] +* server decrypt RS, RC, SC with key K, compares RS with it's own one + send before, computes final main encryption key S = SS XOR SC +* ENC(K, RC) + NULLs -> Client [24 bytes] +* server switches to the new client +* client decrypts RC and compares with it's own generated one, computes + final main encryption key S + +Where PSK is 256bit pre-shared key, NULLs are 16 null-bytes. R* are +required for handshake randomization and two-way authentication. K key +is used only during handshake. NULLs are required to differentiate +common transport protocol messages from handshake ones. DH public keys +can be trivially derived from private ones. + + +RELATED DOCUMENTS + +* http://cr.yp.to/ecdh.html +* http://cr.yp.to/snuffle.html +* http://cr.yp.to/mac.html +* http://grouper.ieee.org/groups/1363/passwdPK/contributions/jablon.pdf +* Applied Cryptography (C) 1996 Bruce Schneier + +TODO + +* Move decryption and encryption processes into goroutines +* Add identity management (client can send it's identification, server has + on-disk id↔key plaintext database) +* Implement alternative Secure Remote Password protocol (it is much slower, + technically has more code, but human memorized passwords can be used + instead of keys) + +LICENCE + +This program is free software: you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation, either version 3 of the License, or +any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. diff --git a/govpn.go b/govpn.go new file mode 100644 index 0000000..e49f81c --- /dev/null +++ b/govpn.go @@ -0,0 +1,241 @@ +/* +govpn -- high-performance secure virtual private network daemon +Copyright (C) 2014 Sergey Matveev + +This program is free software: you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation, either version 3 of the License, or +(at your option) any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program. If not, see . +*/ +package main + +import ( + "encoding/binary" + "encoding/hex" + "flag" + "fmt" + "log" + "net" + "time" + + "code.google.com/p/go.crypto/poly1305" + "code.google.com/p/go.crypto/salsa20" + "code.google.com/p/gopacket" + "code.google.com/p/gopacket/pcap" +) + +const ( + // NonceIncrServer is nonce increment value for server message + NonceIncrServer = 1 + // NonceIncrClient is nonce increment value for client message + NonceIncrClient = 2 + NonceSize = 8 + AliveTimeout = time.Second * 90 + // S20BS is Salsa20's internal blocksize in bytes + S20BS = 64 +) + +type Peer struct { + addr *net.UDPAddr + lastPing time.Time + key *[32]byte // encryption key + nonceOur uint64 // nonce for our messages + nonceRecv uint64 // latest received nonce from remote peer +} + +func (p *Peer) IsAlive() bool { + if (p == nil) || (p.lastPing.Add(AliveTimeout).Before(time.Now())) { + return false + } + return true +} + +func (p *Peer) SetAlive() { + p.lastPing = time.Now() +} + +type UDPPkt struct { + addr *net.UDPAddr + data []byte +} + +var ( + remoteAddr = flag.String("remote", "", "Remote server address") + bindAddr = flag.String("bind", "", "Bind to address") + ifaceName = flag.String("iface", "eth0", "Network interface") + keyHex = flag.String("key", "", "Authentication key") + mtu = flag.Int("mtu", 1500, "MTU") +) + +func main() { + flag.Parse() + log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile) + + // Key decoding + if len(*keyHex) != 64 { + panic("Key is required argument (64 hex characters)") + } + keyDecoded, err := hex.DecodeString(*keyHex) + if err != nil { + panic(err) + } + key := new([32]byte) + copy(key[:], keyDecoded) + + // Interface listening + iface, err := pcap.OpenLive(*ifaceName, int32(*mtu), true, 0) + if err != nil { + panic(err) + } + ethSink := gopacket.NewPacketSource(iface, iface.LinkType()).Packets() + maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize + log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName) + + // Network address parsing + if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) || (len(*bindAddr) == 0 && len(*remoteAddr) == 0) { + panic("Either -bind or -remote must be specified only") + } + + var conn *net.UDPConn + var remote *net.UDPAddr + + serverMode := false + nonceIncr := uint64(NonceIncrClient) + bindTo := "0.0.0.0:0" + + if len(*bindAddr) > 1 { + bindTo = *bindAddr + serverMode = true + nonceIncr = uint64(NonceIncrServer) + } + + bind, err := net.ResolveUDPAddr("udp", bindTo) + if err != nil { + panic(err) + } + conn, err = net.ListenUDP("udp", bind) + if err != nil { + panic(err) + } + + if len(*remoteAddr) > 1 { + remote, err = net.ResolveUDPAddr("udp", *remoteAddr) + if err != nil { + panic(err) + } + } + + udpSink := make(chan UDPPkt) + go func(conn *net.UDPConn, sink chan<- UDPPkt) { + data := make([]byte, *mtu) + for { + n, addr, err := conn.ReadFromUDP(data) + if err != nil { + fmt.Print("B") + } + sink <- UDPPkt{addr, data[:n]} + } + }(conn, udpSink) + + // Process packets + var udpPkt UDPPkt + var ethPkt gopacket.Packet + var addr string + var peer Peer + var p *Peer + var buf []byte + + states := make(map[string]*Handshake) + nonce := make([]byte, NonceSize) + keyAuth := new([32]byte) + tag := new([poly1305.TagSize]byte) + + if !serverMode { + log.Println("starting handshake with", *remoteAddr) + states[remote.String()] = HandshakeStart(conn, remote, key) + } + + for { + buf = make([]byte, *mtu+S20BS) + select { + case udpPkt = <-udpSink: + if isValidHandshakePkt(udpPkt.data) { + addr = udpPkt.addr.String() + state, exists := states[addr] + if serverMode { + if !exists { + state = &Handshake{addr: udpPkt.addr} + states[addr] = state + } + p = state.Server(conn, key, udpPkt.data) + } else { + if !exists { + fmt.Print("[HS?]") + continue + } + p = state.Client(conn, key, udpPkt.data) + } + if p != nil { + fmt.Print("[HS-OK]") + peer = *p + delete(states, addr) + } + continue + } + if !peer.IsAlive() { + continue + } + nonceRecv, _ := binary.Uvarint(udpPkt.data[:8]) + if peer.nonceRecv >= nonceRecv { + continue + } + copy(tag[:], udpPkt.data[len(udpPkt.data)-poly1305.TagSize:]) + copy(buf[S20BS:], udpPkt.data[NonceSize:len(udpPkt.data)-poly1305.TagSize]) + salsa20.XORKeyStream( + buf[:S20BS+len(udpPkt.data)-poly1305.TagSize], + buf[:S20BS+len(udpPkt.data)-poly1305.TagSize], + udpPkt.data[:NonceSize], + peer.key, + ) + copy(keyAuth[:], buf[:32]) + if !poly1305.Verify(tag, udpPkt.data[:len(udpPkt.data)-poly1305.TagSize], keyAuth) { + fmt.Print("T") + continue + } + peer.nonceRecv = nonceRecv + peer.SetAlive() + if err := iface.WritePacketData(buf[S20BS : S20BS+len(udpPkt.data)-NonceSize-poly1305.TagSize]); err != nil { + log.Println("Error writing to iface") + } + fmt.Print("r") + case ethPkt = <-ethSink: + if len(ethPkt.Data()) > maxIfacePktSize { + panic("Too large packet on interface") + } + if !peer.IsAlive() { + continue + } + peer.nonceOur = peer.nonceOur + nonceIncr + pktData := ethPkt.Data() + binary.PutUvarint(nonce, peer.nonceOur) + copy(buf[S20BS:], pktData) + salsa20.XORKeyStream(buf, buf, nonce, peer.key) + copy(buf[S20BS-NonceSize:S20BS], nonce) + copy(keyAuth[:], buf[:32]) + poly1305.Sum(tag, buf[S20BS-NonceSize:S20BS+len(pktData)], keyAuth) + _, err := conn.WriteTo(append(buf[S20BS-NonceSize:S20BS+len(pktData)], tag[:]...), peer.addr) + if err != nil { + log.Println("Error sending UDP", err) + } + fmt.Print("w") + } + } +} diff --git a/handshake.go b/handshake.go new file mode 100644 index 0000000..331e4e6 --- /dev/null +++ b/handshake.go @@ -0,0 +1,263 @@ +/* +govpn -- high-performance secure virtual private network daemon +Copyright (C) 2014 Sergey Matveev + +This program is free software: you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation, either version 3 of the License, or +(at your option) any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program. If not, see . +*/ +package main + +import ( + "crypto/rand" + "crypto/subtle" + "encoding/binary" + "fmt" + "net" + "time" + + "code.google.com/p/go.crypto/curve25519" + "code.google.com/p/go.crypto/poly1305" + "code.google.com/p/go.crypto/salsa20" + "code.google.com/p/go.crypto/salsa20/salsa" +) + +type Handshake struct { + addr *net.UDPAddr + lastPing time.Time + rNonce *[8]byte + dhPriv *[32]byte // own private DH key + key *[32]byte // handshake encryption key + rServer *[8]byte // random string for authentication + rClient *[8]byte + sServer *[32]byte // secret string for main key calculation + sClient *[32]byte +} + +func KeyFromSecrets(server, client []byte) *[32]byte { + k := new([32]byte) + for i := 0; i < 32; i++ { + k[i] = server[i] ^ client[i] + } + return k +} + +// Check if it is valid handshake-related message +// Minimal size and last 16 zero bytes +func isValidHandshakePkt(pkt []byte) bool { + if len(pkt) < 24 { + return false + } + for i := len(pkt) - poly1305.TagSize; i < len(pkt); i++ { + if pkt[i] != '\x00' { + return false + } + } + return true +} + +func (h *Handshake) rNonceNext() []byte { + nonce := make([]byte, 8) + nonceCurrent, _ := binary.Uvarint(h.rNonce[:]) + binary.PutUvarint(nonce, nonceCurrent+1) + return nonce +} + +func dhPrivGen() *[32]byte { + dh := new([32]byte) + if _, err := rand.Read(dh[:]); err != nil { + panic("Can not read random for DH private key") + } + // This bitwise operations are required by Curve25519 whitepaper + dh[0] = dh[0] & (255 - 128 - 64 - 32) // clear first three bits + dh[31] = dh[31] & (255 - 1) // clear last bit + dh[31] = dh[31] | 2 // set pre-last bit + return dh +} + +func dhKeyGen(priv, pub *[32]byte) *[32]byte { + key := new([32]byte) + curve25519.ScalarMult(key, priv, pub) + salsa.HSalsa20(key, new([16]byte), key, &salsa.Sigma) + return key +} + +func HandshakeStart(conn *net.UDPConn, addr *net.UDPAddr, key *[32]byte) *Handshake { + state := Handshake{} + state.addr = addr + state.lastPing = time.Now() + + state.dhPriv = dhPrivGen() + dhPub := new([32]byte) + curve25519.ScalarBaseMult(dhPub, state.dhPriv) + + state.rNonce = new([8]byte) + if _, err := rand.Read(state.rNonce[:]); err != nil { + panic("Can not read random for handshake nonce") + } + enc := make([]byte, 32) + salsa20.XORKeyStream(enc, dhPub[:], state.rNonce[:], key) + + if _, err := conn.WriteTo( + append(state.rNonce[:], + append(enc, make([]byte, poly1305.TagSize)...)...), addr); err != nil { + panic(err) + } + return &state +} + +func (h *Handshake) Server(conn *net.UDPConn, key *[32]byte, data []byte) *Peer { + switch len(data) { + case 56: // R + ENC(PSK, dh_client_pub) + NULLs + fmt.Print("[HS1]") + if h.rNonce != nil { + fmt.Print("[S?]") + return nil + } + + // Generate private DH key + h.dhPriv = dhPrivGen() + dhPub := new([32]byte) + curve25519.ScalarBaseMult(dhPub, h.dhPriv) + + // Decrypt remote public key and compute shared key + dec := new([32]byte) + salsa20.XORKeyStream(dec[:], data[8:8+32], data[:8], key) + h.key = dhKeyGen(h.dhPriv, dec) + + // Compute nonce and encrypt our public key + h.rNonce = new([8]byte) + copy(h.rNonce[:], data[:8]) + + encPub := make([]byte, 32) + salsa20.XORKeyStream(encPub, dhPub[:], h.rNonceNext(), key) + + // Generate R* and encrypt them + h.rServer = new([8]byte) + if _, err := rand.Read(h.rServer[:]); err != nil { + panic("Can not read random for handshake random key") + } + h.sServer = new([32]byte) + if _, err := rand.Read(h.sServer[:]); err != nil { + panic("Can not read random for handshake shared key") + } + encRs := make([]byte, 8+32) + salsa20.XORKeyStream(encRs, append(h.rServer[:], h.sServer[:]...), h.rNonce[:], h.key) + + // Send that to client + if _, err := conn.WriteTo( + append(encPub, + append(encRs, make([]byte, poly1305.TagSize)...)...), h.addr); err != nil { + panic(err) + } + fmt.Print("[OK]") + case 64: // ENC(K, RS + RC + SC) + NULLs + fmt.Print("[HS3]") + if (h.rNonce == nil) || (h.rClient != nil) { + fmt.Print("[S?]") + return nil + } + + // Decrypt Rs compare rServer + decRs := make([]byte, 8+8+32) + salsa20.XORKeyStream(decRs, data[:8+8+32], h.rNonceNext(), h.key) + if res := subtle.ConstantTimeCompare(decRs[:8], h.rServer[:]); res != 1 { + fmt.Print("[rS?]") + return nil + } + + // Send final answer to client + enc := make([]byte, 8) + salsa20.XORKeyStream(enc, decRs[8:8+8], make([]byte, 8), h.key) + if _, err := conn.WriteTo(append(enc, make([]byte, poly1305.TagSize)...), h.addr); err != nil { + panic(err) + } + + // Switch peer + peer := Peer{addr: h.addr, nonceOur: 0, nonceRecv: 0} + peer.SetAlive() + peer.key = KeyFromSecrets(h.sServer[:], decRs[8+8:]) + fmt.Print("[OK]") + return &peer + default: + fmt.Print("[HS?]") + } + return nil +} + +func (h *Handshake) Client(conn *net.UDPConn, key *[32]byte, data []byte) *Peer { + switch len(data) { + case 88: // ENC(PSK, dh_server_pub) + ENC(K, RS + SS) + NULLs + fmt.Print("[HS2]") + if h.key != nil { + fmt.Print("[S?]") + return nil + } + + // Decrypt remote public key and compute shared key + dec := new([32]byte) + salsa20.XORKeyStream(dec[:], data[:32], h.rNonceNext(), key) + h.key = dhKeyGen(h.dhPriv, dec) + + // Decrypt Rs + decRs := make([]byte, 8+32) + salsa20.XORKeyStream(decRs, data[32:32+8+32], h.rNonce[:], h.key) + h.rServer = new([8]byte) + copy(h.rServer[:], decRs[:8]) + h.sServer = new([32]byte) + copy(h.sServer[:], decRs[8:]) + + // Generate R* and encrypt them + h.rClient = new([8]byte) + if _, err := rand.Read(h.rClient[:]); err != nil { + panic("Can not read random for handshake random key") + } + h.sClient = new([32]byte) + if _, err := rand.Read(h.sClient[:]); err != nil { + panic("Can not read random for handshake shared key") + } + encRs := make([]byte, 8+8+32) + salsa20.XORKeyStream(encRs, + append(h.rServer[:], + append(h.rClient[:], h.sClient[:]...)...), h.rNonceNext(), h.key) + + // Send that to server + if _, err := conn.WriteTo(append(encRs, make([]byte, poly1305.TagSize)...), h.addr); err != nil { + panic(err) + } + fmt.Print("[OK]") + case 24: // ENC(K, RC) + NULLs + fmt.Print("[HS4]") + if h.key == nil { + fmt.Print("[S?]") + return nil + } + + // Decrypt rClient + dec := make([]byte, 8) + salsa20.XORKeyStream(dec, data[:8], make([]byte, 8), h.key) + if res := subtle.ConstantTimeCompare(dec, h.rClient[:]); res != 1 { + fmt.Print("[rC?]") + return nil + } + + // Switch peer + peer := Peer{addr: h.addr, nonceOur: 0, nonceRecv: 0} + peer.SetAlive() + peer.key = KeyFromSecrets(h.sServer[:], h.sClient[:]) + fmt.Print("[OK]") + return &peer + default: + fmt.Print("[HS?]") + } + return nil +} -- 2.44.0