2 GoVPN -- simple secure free software virtual private network daemon
3 Copyright (C) 2014-2015 Sergey Matveev <stargrave@stargrave.org>
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.
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.
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/>.
28 "github.com/agl/ed25519"
29 "github.com/agl/ed25519/extra25519"
30 "golang.org/x/crypto/curve25519"
31 "golang.org/x/crypto/salsa20"
32 "golang.org/x/crypto/salsa20/salsa"
33 "golang.org/x/crypto/xtea"
41 type Handshake struct {
46 dsaPubH *[ed25519.PublicKeySize]byte
49 dhPriv *[32]byte // own private DH key
50 rServer *[RSize]byte // random string for authentication
52 sServer *[SSize]byte // secret string for main key calculation
56 func keyFromSecrets(server, client []byte) *[SSize]byte {
58 for i := 0; i < SSize; i++ {
59 k[i] = server[i] ^ client[i]
64 // Apply HSalsa20 function for data. Used to hash public keys.
65 func HApply(data *[32]byte) {
66 salsa.HSalsa20(data, new([16]byte), data, &salsa.Sigma)
69 // Zero handshake's memory state
70 func (h *Handshake) Zero() {
72 sliceZero(h.rNonce[:])
75 sliceZero(h.dhPriv[:])
81 sliceZero(h.dsaPubH[:])
84 sliceZero(h.rServer[:])
87 sliceZero(h.rClient[:])
90 sliceZero(h.sServer[:])
93 sliceZero(h.sClient[:])
97 func (h *Handshake) rNonceNext(count uint64) []byte {
98 nonce := make([]byte, RSize)
99 nonceCurrent, _ := binary.Uvarint(h.rNonce[:])
100 binary.PutUvarint(nonce, nonceCurrent+count)
104 func randRead(b []byte) error {
107 _, err = rand.Read(b)
114 func dhKeypairGen() (*[32]byte, *[32]byte) {
115 priv := new([32]byte)
117 repr := new([32]byte)
120 if err := randRead(priv[:]); err != nil {
121 log.Fatalln("Error reading random for DH private key:", err)
123 reprFound = extra25519.ScalarBaseMult(pub, repr, priv)
128 func dhKeyGen(priv, pub *[32]byte) *[32]byte {
130 curve25519.ScalarMult(key, priv, pub)
135 // Create new handshake state.
136 func HandshakeNew(addr string, conn RemoteConn, conf *PeerConf) *Handshake {
140 LastPing: time.Now(),
143 state.dsaPubH = new([ed25519.PublicKeySize]byte)
144 copy(state.dsaPubH[:], state.Conf.DSAPub[:])
145 HApply(state.dsaPubH)
149 // Generate ID tag from client identification and data.
150 func idTag(id *PeerId, data []byte) []byte {
151 ciph, err := xtea.NewCipher(id[:])
155 enc := make([]byte, xtea.BlockSize)
156 ciph.Encrypt(enc, data[:xtea.BlockSize])
160 // Start handshake's procedure from the client. It is the entry point
161 // for starting the handshake procedure. // First handshake packet
162 // will be sent immediately.
163 func HandshakeStart(addr string, conn RemoteConn, conf *PeerConf) *Handshake {
164 state := HandshakeNew(addr, conn, conf)
165 var dhPubRepr *[32]byte
166 state.dhPriv, dhPubRepr = dhKeypairGen()
168 state.rNonce = new([RSize]byte)
169 if err := randRead(state.rNonce[:]); err != nil {
170 log.Fatalln("Error reading random for nonce:", err)
172 enc := make([]byte, 32)
173 salsa20.XORKeyStream(enc, dhPubRepr[:], state.rNonce[:], state.dsaPubH)
174 data := append(state.rNonce[:], enc...)
175 data = append(data, idTag(state.Conf.Id, state.rNonce[:])...)
176 state.conn.Write(data)
180 // Process handshake message on the server side.
181 // This function is intended to be called on server's side.
182 // If this is the final handshake message, then new Peer object
183 // will be created and used as a transport. If no mutually
184 // authenticated Peer is ready, then return nil.
185 func (h *Handshake) Server(data []byte) *Peer {
186 // R + ENC(H(DSAPub), R, El(CDHPub)) + IDtag
187 if len(data) == 48 && h.rNonce == nil {
188 // Generate DH keypair
189 var dhPubRepr *[32]byte
190 h.dhPriv, dhPubRepr = dhKeypairGen()
192 h.rNonce = new([RSize]byte)
193 copy(h.rNonce[:], data[:RSize])
195 // Decrypt remote public key and compute shared key
196 cDHRepr := new([32]byte)
197 salsa20.XORKeyStream(
199 data[RSize:RSize+32],
204 extra25519.RepresentativeToPublicKey(cDH, cDHRepr)
205 h.key = dhKeyGen(h.dhPriv, cDH)
207 encPub := make([]byte, 32)
208 salsa20.XORKeyStream(encPub, dhPubRepr[:], h.rNonceNext(1), h.dsaPubH)
210 // Generate R* and encrypt them
211 h.rServer = new([RSize]byte)
212 if err := randRead(h.rServer[:]); err != nil {
213 log.Fatalln("Error reading random for R:", err)
215 h.sServer = new([SSize]byte)
216 if err := randRead(h.sServer[:]); err != nil {
217 log.Fatalln("Error reading random for S:", err)
219 encRs := make([]byte, RSize+SSize)
220 salsa20.XORKeyStream(encRs, append(h.rServer[:], h.sServer[:]...), h.rNonce[:], h.key)
222 // Send that to client
223 h.conn.Write(append(encPub, append(encRs, idTag(h.Conf.Id, encPub)...)...))
224 h.LastPing = time.Now()
226 // ENC(K, R+1, RS + RC + SC + Sign(DSAPriv, K)) + IDtag
227 if len(data) == 120 && h.rClient == nil {
228 // Decrypted Rs compare rServer
229 dec := make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
230 salsa20.XORKeyStream(
232 data[:RSize+RSize+SSize+ed25519.SignatureSize],
236 if subtle.ConstantTimeCompare(dec[:RSize], h.rServer[:]) != 1 {
237 log.Println("Invalid server's random number with", h.addr)
240 sign := new([ed25519.SignatureSize]byte)
241 copy(sign[:], dec[RSize+RSize+SSize:])
242 if !ed25519.Verify(h.Conf.DSAPub, h.key[:], sign) {
243 log.Println("Invalid signature from", h.addr)
247 // Send final answer to client
248 enc := make([]byte, RSize)
249 salsa20.XORKeyStream(enc, dec[RSize:RSize+RSize], h.rNonceNext(2), h.key)
250 h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
258 keyFromSecrets(h.sServer[:], dec[RSize+RSize:RSize+RSize+SSize]))
259 h.LastPing = time.Now()
262 log.Println("Invalid handshake message from", h.addr)
267 // Process handshake message on the client side.
268 // This function is intended to be called on client's side.
269 // If this is the final handshake message, then new Peer object
270 // will be created and used as a transport. If no mutually
271 // authenticated Peer is ready, then return nil.
272 func (h *Handshake) Client(data []byte) *Peer {
274 case 80: // ENC(H(DSAPub), R+1, El(SDHPub)) + ENC(K, R, RS + SS) + IDtag
276 log.Println("Invalid handshake stage from", h.addr)
280 // Decrypt remote public key and compute shared key
281 sDHRepr := new([32]byte)
282 salsa20.XORKeyStream(sDHRepr[:], data[:32], h.rNonceNext(1), h.dsaPubH)
284 extra25519.RepresentativeToPublicKey(sDH, sDHRepr)
285 h.key = dhKeyGen(h.dhPriv, sDH)
288 decRs := make([]byte, RSize+SSize)
289 salsa20.XORKeyStream(decRs, data[SSize:32+RSize+SSize], h.rNonce[:], h.key)
290 h.rServer = new([RSize]byte)
291 copy(h.rServer[:], decRs[:RSize])
292 h.sServer = new([SSize]byte)
293 copy(h.sServer[:], decRs[RSize:])
295 // Generate R* and signature and encrypt them
296 h.rClient = new([RSize]byte)
297 if err := randRead(h.rClient[:]); err != nil {
298 log.Fatalln("Error reading random for R:", err)
300 h.sClient = new([SSize]byte)
301 if err := randRead(h.sClient[:]); err != nil {
302 log.Fatalln("Error reading random for S:", err)
304 sign := ed25519.Sign(h.Conf.DSAPriv, h.key[:])
306 enc := make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
307 salsa20.XORKeyStream(enc,
310 append(h.sClient[:], sign[:]...)...)...), h.rNonceNext(1), h.key)
312 // Send that to server
313 h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
314 h.LastPing = time.Now()
315 case 16: // ENC(K, R+2, RC) + IDtag
317 log.Println("Invalid handshake stage from", h.addr)
322 dec := make([]byte, RSize)
323 salsa20.XORKeyStream(dec, data[:RSize], h.rNonceNext(2), h.key)
324 if subtle.ConstantTimeCompare(dec, h.rClient[:]) != 1 {
325 log.Println("Invalid client's random number with", h.addr)
335 keyFromSecrets(h.sServer[:], h.sClient[:]),
337 h.LastPing = time.Now()
340 log.Println("Invalid handshake message from", h.addr)