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         "io"
  26         "io/ioutil"
  27         "log"
  28         "net"
  29         "time"
  30
  31         "code.google.com/p/go.crypto/poly1305"
  32         "code.google.com/p/go.crypto/salsa20"
  33 )
  34
  35 var (
  36         remoteAddr = flag.String("remote", "", "Remote server address")
  37         bindAddr   = flag.String("bind", "", "Bind to address")
  38         ifaceName  = flag.String("iface", "tap0", "TAP network interface")
  39         keyPath    = flag.String("key", "", "Path to authentication key file")
  40         mtu        = flag.Int("mtu", 1500, "MTU")
  41         timeout    = flag.Int("timeout", 60, "Timeout seconds")
  42         verbose    = flag.Bool("v", false, "Increase verbosity")
  43 )
  44
  45 const (
  46         NonceSize = 8
  47         KeySize   = 32
  48         // S20BS is Salsa20's internal blocksize in bytes
  49         S20BS = 64
  50 )
  51
  52 type TAP interface {
  53         io.Reader
  54         io.Writer
  55 }
  56
  57 type Peer struct {
  58         addr      *net.UDPAddr
  59         key       *[KeySize]byte // encryption key
  60         nonceOur  uint64         // nonce for our messages
  61         nonceRecv uint64         // latest received nonce from remote peer
  62 }
  63
  64 type UDPPkt struct {
  65         addr *net.UDPAddr
  66         size int
  67 }
  68
  69 func main() {
  70         flag.Parse()
  71         log.SetFlags(log.Ldate | log.Lmicroseconds | log.Lshortfile)
  72
  73         // Key decoding
  74         keyData, err := ioutil.ReadFile(*keyPath)
  75         if err != nil {
  76                 panic("Unable to read keyfile: " + err.Error())
  77         }
  78         if len(keyData) < 64 {
  79                 panic("Key must be 64 hex characters long")
  80         }
  81         keyDecoded, err := hex.DecodeString(string(keyData[0:64]))
  82         if err != nil {
  83                 panic("Unable to decode the key: " + err.Error())
  84         }
  85         key := new([KeySize]byte)
  86         copy(key[:], keyDecoded)
  87         keyDecoded = nil
  88         keyData = nil
  89
  90         // Interface listening
  91         maxIfacePktSize := *mtu - poly1305.TagSize - NonceSize
  92         log.Println("Max MTU", maxIfacePktSize, "on interface", *ifaceName)
  93         iface := NewTAP(*ifaceName)
  94         ethBuf := make([]byte, maxIfacePktSize)
  95         ethSink := make(chan int)
  96         ethSinkReady := make(chan bool)
  97         go func() {
  98                 for {
  99                         <-ethSinkReady
 100                         n, err := iface.Read(ethBuf)
 101                         if err != nil {
 102                                 panic(err)
 103                         }
 104                         ethSink <- n
 105                 }
 106         }()
 107         ethSinkReady <- true
 108
 109         // Network address parsing
 110         if (len(*bindAddr) > 1 && len(*remoteAddr) > 1) ||
 111                 (len(*bindAddr) == 0 && len(*remoteAddr) == 0) {
 112                 panic("Either -bind or -remote must be specified only")
 113         }
 114         var conn *net.UDPConn
 115         var remote *net.UDPAddr
 116         serverMode := false
 117         bindTo := "0.0.0.0:0"
 118
 119         if len(*bindAddr) > 1 {
 120                 bindTo = *bindAddr
 121                 serverMode = true
 122         }
 123
 124         bind, err := net.ResolveUDPAddr("udp", bindTo)
 125         if err != nil {
 126                 panic(err)
 127         }
 128         conn, err = net.ListenUDP("udp", bind)
 129         if err != nil {
 130                 panic(err)
 131         }
 132
 133         if len(*remoteAddr) > 1 {
 134                 remote, err = net.ResolveUDPAddr("udp", *remoteAddr)
 135                 if err != nil {
 136                         panic(err)
 137                 }
 138         }
 139
 140         udpBuf := make([]byte, *mtu)
 141         udpSink := make(chan *UDPPkt)
 142         udpSinkReady := make(chan bool)
 143         go func(conn *net.UDPConn) {
 144                 for {
 145                         <-udpSinkReady
 146                         conn.SetReadDeadline(time.Now().Add(time.Second))
 147                         n, addr, err := conn.ReadFromUDP(udpBuf)
 148                         if err != nil {
 149                                 if *verbose {
 150                                         fmt.Print("B")
 151                                 }
 152                                 udpSink <- nil
 153                         } else {
 154                                 udpSink <- &UDPPkt{addr, n}
 155                         }
 156                 }
 157         }(conn)
 158         udpSinkReady <- true
 159
 160         // Process packets
 161         var udpPkt *UDPPkt
 162         var udpPktData []byte
 163         var ethPktSize int
 164         var addr string
 165         var peer *Peer
 166         var p *Peer
 167
 168         timeouts := 0
 169         states := make(map[string]*Handshake)
 170         nonce := make([]byte, NonceSize)
 171         keyAuth := new([KeySize]byte)
 172         tag := new([poly1305.TagSize]byte)
 173         buf := make([]byte, *mtu+S20BS)
 174         emptyKey := make([]byte, KeySize)
 175         ethPkt := make([]byte, maxIfacePktSize)
 176         udpPktDataBuf := make([]byte, *mtu)
 177
 178         if !serverMode {
 179                 states[remote.String()] = HandshakeStart(conn, remote, key)
 180         }
 181
 182         finished := false
 183         for {
 184                 if finished {
 185                         break
 186                 }
 187                 select {
 188                 case udpPkt = <-udpSink:
 189                         timeouts++
 190                         if !serverMode && timeouts >= *timeout {
 191                                 finished = true
 192                         }
 193                         if udpPkt == nil {
 194                                 udpSinkReady <- true
 195                                 continue
 196                         }
 197                         copy(udpPktDataBuf, udpBuf[:udpPkt.size])
 198                         udpSinkReady <- true
 199                         udpPktData = udpPktDataBuf[:udpPkt.size]
 200                         if isValidHandshakePkt(udpPktData) {
 201                                 addr = udpPkt.addr.String()
 202                                 state, exists := states[addr]
 203                                 if serverMode {
 204                                         if !exists {
 205                                                 state = &Handshake{addr: udpPkt.addr}
 206                                                 states[addr] = state
 207                                         }
 208                                         p = state.Server(conn, key, udpPktData)
 209                                 } else {
 210                                         if !exists {
 211                                                 fmt.Print("[HS?]")
 212                                                 continue
 213                                         }
 214                                         p = state.Client(conn, key, udpPktData)
 215                                 }
 216                                 if p != nil {
 217                                         fmt.Print("[HS-OK]")
 218                                         peer = p
 219                                         delete(states, addr)
 220                                 }
 221                                 continue
 222                         }
 223                         if peer == nil {
 224                                 continue
 225                         }
 226                         nonceRecv, _ := binary.Uvarint(udpPktData[:8])
 227                         if peer.nonceRecv >= nonceRecv {
 228                                 fmt.Print("R")
 229                                 continue
 230                         }
 231                         copy(buf[:KeySize], emptyKey)
 232                         copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
 233                         copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
 234                         salsa20.XORKeyStream(
 235                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 236                                 buf[:S20BS+udpPkt.size-poly1305.TagSize],
 237                                 udpPktData[:NonceSize],
 238                                 peer.key,
 239                         )
 240                         copy(keyAuth[:], buf[:KeySize])
 241                         if !poly1305.Verify(tag, udpPktData[:udpPkt.size-poly1305.TagSize], keyAuth) {
 242                                 fmt.Print("T")
 243                                 continue
 244                         }
 245                         peer.nonceRecv = nonceRecv
 246                         timeouts = 0
 247                         if _, err := iface.Write(buf[S20BS : S20BS+udpPkt.size-NonceSize-poly1305.TagSize]); err != nil {
 248                                 log.Println("Error writing to iface: ", err)
 249                         }
 250                         if *verbose {
 251                                 fmt.Print("r")
 252                         }
 253                 case ethPktSize = <-ethSink:
 254                         if ethPktSize > maxIfacePktSize {
 255                                 panic("Too large packet on interface")
 256                         }
 257                         if peer == nil {
 258                                 ethSinkReady <- true
 259                                 continue
 260                         }
 261                         copy(ethPkt, ethBuf[:ethPktSize])
 262                         ethSinkReady <- true
 263                         peer.nonceOur = peer.nonceOur + 2
 264                         binary.PutUvarint(nonce, peer.nonceOur)
 265                         copy(buf[:KeySize], emptyKey)
 266                         copy(buf[S20BS:], ethPkt[:ethPktSize])
 267                         salsa20.XORKeyStream(buf, buf, nonce, peer.key)
 268                         copy(buf[S20BS-NonceSize:S20BS], nonce)
 269                         copy(keyAuth[:], buf[:KeySize])
 270                         dataToSend := buf[S20BS-NonceSize : S20BS+ethPktSize]
 271                         poly1305.Sum(tag, dataToSend, keyAuth)
 272                         if _, err := conn.WriteTo(append(dataToSend, tag[:]...), peer.addr); err != nil {
 273                                 log.Println("Error sending UDP", err)
 274                         }
 275                         if *verbose {
 276                                 fmt.Print("w")
 277                         }
 278                 }
 279         }
 280 }