govpn.go

   1 /*
   2 govpn -- high-performance secure virtual private network daemon
   3 Copyright (C) 2014 Sergey Matveev <stargrave@stargrave.org>
   4
   5 This program is free software: you can redistribute it and/or modify
   6 it under the terms of the GNU General Public License as published by
   7 the Free Software Foundation, either version 3 of the License, or
   8 (at your option) any later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18 package main
  19
  20 import (
  21         "encoding/binary"
  22         "encoding/hex"
  23         "flag"
  24         "fmt"
  25         "log"
  26         "net"
  27         "time"
  28
  29         "code.google.com/p/go.crypto/poly1305"
  30         "code.google.com/p/go.crypto/salsa20"
  31         "code.google.com/p/gopacket"
  32         "code.google.com/p/gopacket/pcap"
  33 )
  34
  35 const (
  36         // NonceIncrServer is nonce increment value for server message
  37         NonceIncrServer = 1
  38         // NonceIncrClient is nonce increment value for client message
  39         NonceIncrClient = 2
  40         NonceSize       = 8
  41         AliveTimeout    = time.Second * 90
  42         // S20BS is Salsa20's internal blocksize in bytes
  43         S20BS           = 64
  44 )
  45
  46 type Peer struct {
  47         addr      *net.UDPAddr
  48         lastPing  time.Time
  49         key       *[32]byte // encryption key
  50         nonceOur  uint64    // nonce for our messages
  51         nonceRecv uint64    // latest received nonce from remote peer
  52 }
  53
  54 func (p *Peer) IsAlive() bool {
  55         if (p == nil) || (p.lastPing.Add(AliveTimeout).Before(time.Now())) {
  56                 return false
  57         }
  58         return true
  59 }
  60
  61 func (p *Peer) SetAlive() {
  62         p.lastPing = time.Now()
  63 }
  64
  65 type UDPPkt struct {
  66         addr *net.UDPAddr
  67         data []byte
  68 }
  69
  70 var (
  71         remoteAddr = flag.String("remote", "", "Remote server address")
  72         bindAddr   = flag.String("bind", "", "Bind to address")
  73         ifaceName  = flag.String("iface", "eth0", "Network interface")
  74         keyHex     = flag.String("key", "", "Authentication key")
  75         mtu        = flag.Int("mtu", 1500, "MTU")
  76 )
  77
  78 func main() {
  79         flag.Parse()
  80         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
  81
  82         // Key decoding
  83         if len(*keyHex) != 64 {
  84                 panic("Key is required argument (64 hex characters)")
  85         }
  86         keyDecoded, err := hex.DecodeString(*keyHex)
  87         if err != nil {
  88                 panic(err)
  89         }
  90         key := new([32]byte)
  91         copy(key[:], keyDecoded)
  92
  93         // Interface listening
  94         iface, err := pcap.OpenLive(*ifaceName, int32(*mtu), true, 0)
  95         if err != nil {
  96                 panic(err)
  97         }
  98         ethSink := gopacket.NewPacketSource(iface, iface.LinkType()).Packets()
  99         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
 100         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
 101
 102         // Network address parsing
 103         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) || (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 104                 panic("Either -bind or -remote must be specified only")
 105         }
 106
 107         var conn *net.UDPConn
 108         var remote *net.UDPAddr
 109
 110         serverMode := false
 111         nonceIncr := uint64(NonceIncrClient)
 112         bindTo := "0.0.0.0:0"
 113
 114         if len(*bindAddr) > 1 {
 115                 bindTo = *bindAddr
 116                 serverMode = true
 117                 nonceIncr = uint64(NonceIncrServer)
 118         }
 119
 120         bind, err := net.ResolveUDPAddr("udp", bindTo)
 121         if err != nil {
 122                 panic(err)
 123         }
 124         conn, err = net.ListenUDP("udp", bind)
 125         if err != nil {
 126                 panic(err)
 127         }
 128
 129         if len(*remoteAddr) > 1 {
 130                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 131                 if err != nil {
 132                         panic(err)
 133                 }
 134         }
 135
 136         udpSink := make(chan UDPPkt)
 137         go func(conn *net.UDPConn, sink chan<- UDPPkt) {
 138                 data := make([]byte, *mtu)
 139                 for {
 140                         n, addr, err := conn.ReadFromUDP(data)
 141                         if err != nil {
 142                                 fmt.Print("B")
 143                         }
 144                         sink <- UDPPkt{addr, data[:n]}
 145                 }
 146         }(conn, udpSink)
 147
 148         // Process packets
 149         var udpPkt UDPPkt
 150         var ethPkt gopacket.Packet
 151         var addr string
 152         var peer Peer
 153         var p *Peer
 154         var buf []byte
 155
 156         states := make(map[string]*Handshake)
 157         nonce := make([]byte, NonceSize)
 158         keyAuth := new([32]byte)
 159         tag := new([poly1305.TagSize]byte)
 160
 161         if !serverMode {
 162                 log.Println("starting handshake with", *remoteAddr)
 163                 states[remote.String()] = HandshakeStart(conn, remote, key)
 164         }
 165
 166         for {
 167                 buf = make([]byte, *mtu+S20BS)
 168                 select {
 169                 case udpPkt = <-udpSink:
 170                         if isValidHandshakePkt(udpPkt.data) {
 171                                 addr = udpPkt.addr.String()
 172                                 state, exists := states[addr]
 173                                 if serverMode {
 174                                         if !exists {
 175                                                 state = &Handshake{addr: udpPkt.addr}
 176                                                 states[addr] = state
 177                                         }
 178                                         p = state.Server(conn, key, udpPkt.data)
 179                                 } else {
 180                                         if !exists {
 181                                                 fmt.Print("[HS?]")
 182                                                 continue
 183                                         }
 184                                         p = state.Client(conn, key, udpPkt.data)
 185                                 }
 186                                 if p != nil {
 187                                         fmt.Print("[HS-OK]")
 188                                         peer = *p
 189                                         delete(states, addr)
 190                                 }
 191                                 continue
 192                         }
 193                         if !peer.IsAlive() {
 194                                 continue
 195                         }
 196                         nonceRecv, _ := binary.Uvarint(udpPkt.data[:8])
 197                         if peer.nonceRecv >= nonceRecv {
 198                                 continue
 199                         }
 200                         copy(tag[:], udpPkt.data[len(udpPkt.data)-poly1305.TagSize:])
 201                         copy(buf[S20BS:], udpPkt.data[NonceSize:len(udpPkt.data)-poly1305.TagSize])
 202                         salsa20.XORKeyStream(
 203                                 buf[:S20BS+len(udpPkt.data)-poly1305.TagSize],
 204                                 buf[:S20BS+len(udpPkt.data)-poly1305.TagSize],
 205                                 udpPkt.data[:NonceSize],
 206                                 peer.key,
 207                         )
 208                         copy(keyAuth[:], buf[:32])
 209                         if !poly1305.Verify(tag, udpPkt.data[:len(udpPkt.data)-poly1305.TagSize], keyAuth) {
 210                                 fmt.Print("T")
 211                                 continue
 212                         }
 213                         peer.nonceRecv = nonceRecv
 214                         peer.SetAlive()
 215                         if err := iface.WritePacketData(buf[S20BS : S20BS+len(udpPkt.data)-NonceSize-poly1305.TagSize]); err != nil {
 216                                 log.Println("Error writing to iface")
 217                         }
 218                         fmt.Print("r")
 219                 case ethPkt = <-ethSink:
 220                         if len(ethPkt.Data()) > maxIfacePktSize {
 221                                 panic("Too large packet on interface")
 222                         }
 223                         if !peer.IsAlive() {
 224                                 continue
 225                         }
 226                         peer.nonceOur = peer.nonceOur + nonceIncr
 227                         pktData := ethPkt.Data()
 228                         binary.PutUvarint(nonce, peer.nonceOur)
 229                         copy(buf[S20BS:], pktData)
 230                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 231                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 232                         copy(keyAuth[:], buf[:32])
 233                         poly1305.Sum(tag, buf[S20BS-NonceSize:S20BS+len(pktData)], keyAuth)
 234                         _, err := conn.WriteTo(append(buf[S20BS-NonceSize:S20BS+len(pktData)], tag[:]...), peer.addr)
 235                         if err != nil {
 236                                 log.Println("Error sending UDP", err)
 237                         }
 238                         fmt.Print("w")
 239                 }
 240         }
 241 }