--- /dev/null
+/*
+GoVPN -- simple secure free software virtual private network daemon
+Copyright (C) 2014-2016 Sergey Matveev <stargrave@stargrave.org>
+
+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 <http://www.gnu.org/licenses/>.
+*/
+
+package govpn
+
+import (
+ "crypto/subtle"
+ "encoding/binary"
+ "io"
+ "log"
+ "time"
+
+ "github.com/agl/ed25519"
+ "github.com/agl/ed25519/extra25519"
+ "github.com/dchest/blake2b"
+ "golang.org/x/crypto/curve25519"
+ "golang.org/x/crypto/salsa20"
+ "golang.org/x/crypto/xtea"
+)
+
+const (
+ RSize = 8
+ SSize = 32
+)
+
+type Handshake struct {
+ addr string
+ conn io.Writer
+ LastPing time.Time
+ Conf *PeerConf
+ dsaPubH *[ed25519.PublicKeySize]byte
+ key *[32]byte
+ rNonce *[RSize]byte
+ dhPriv *[32]byte // own private DH key
+ rServer *[RSize]byte // random string for authentication
+ rClient *[RSize]byte
+ sServer *[SSize]byte // secret string for main key calculation
+ sClient *[SSize]byte
+}
+
+func keyFromSecrets(server, client []byte) *[SSize]byte {
+ k := new([SSize]byte)
+ for i := 0; i < SSize; i++ {
+ k[i] = server[i] ^ client[i]
+ }
+ return k
+}
+
+// Zero handshake's memory state
+func (h *Handshake) Zero() {
+ if h.rNonce != nil {
+ SliceZero(h.rNonce[:])
+ }
+ if h.dhPriv != nil {
+ SliceZero(h.dhPriv[:])
+ }
+ if h.key != nil {
+ SliceZero(h.key[:])
+ }
+ if h.dsaPubH != nil {
+ SliceZero(h.dsaPubH[:])
+ }
+ if h.rServer != nil {
+ SliceZero(h.rServer[:])
+ }
+ if h.rClient != nil {
+ SliceZero(h.rClient[:])
+ }
+ if h.sServer != nil {
+ SliceZero(h.sServer[:])
+ }
+ if h.sClient != nil {
+ SliceZero(h.sClient[:])
+ }
+}
+
+func (h *Handshake) rNonceNext(count uint64) []byte {
+ nonce := make([]byte, RSize)
+ nonceCurrent, _ := binary.Uvarint(h.rNonce[:])
+ binary.PutUvarint(nonce, nonceCurrent+count)
+ return nonce
+}
+
+func dhKeypairGen() (*[32]byte, *[32]byte) {
+ priv := new([32]byte)
+ pub := new([32]byte)
+ repr := new([32]byte)
+ reprFound := false
+ for !reprFound {
+ if _, err := Rand.Read(priv[:]); err != nil {
+ log.Fatalln("Error reading random for DH private key:", err)
+ }
+ reprFound = extra25519.ScalarBaseMult(pub, repr, priv)
+ }
+ return priv, repr
+}
+
+func dhKeyGen(priv, pub *[32]byte) *[32]byte {
+ key := new([32]byte)
+ curve25519.ScalarMult(key, priv, pub)
+ hashed := blake2b.Sum256(key[:])
+ return &hashed
+}
+
+// Create new handshake state.
+func NewHandshake(addr string, conn io.Writer, conf *PeerConf) *Handshake {
+ state := Handshake{
+ addr: addr,
+ conn: conn,
+ LastPing: time.Now(),
+ Conf: conf,
+ }
+ state.dsaPubH = new([ed25519.PublicKeySize]byte)
+ copy(state.dsaPubH[:], state.Conf.Verifier.Pub[:])
+ hashed := blake2b.Sum256(state.dsaPubH[:])
+ state.dsaPubH = &hashed
+ return &state
+}
+
+// Generate ID tag from client identification and data.
+func idTag(id *PeerId, data []byte) []byte {
+ ciph, err := xtea.NewCipher(id[:])
+ if err != nil {
+ panic(err)
+ }
+ enc := make([]byte, xtea.BlockSize)
+ ciph.Encrypt(enc, data[:xtea.BlockSize])
+ return enc
+}
+
+// Start handshake's procedure from the client. It is the entry point
+// for starting the handshake procedure. // First handshake packet
+// will be sent immediately.
+func HandshakeStart(addr string, conn io.Writer, conf *PeerConf) *Handshake {
+ state := NewHandshake(addr, conn, conf)
+ var dhPubRepr *[32]byte
+ state.dhPriv, dhPubRepr = dhKeypairGen()
+
+ state.rNonce = new([RSize]byte)
+ if _, err := Rand.Read(state.rNonce[:]); err != nil {
+ log.Fatalln("Error reading random for nonce:", err)
+ }
+ var enc []byte
+ if conf.Noise {
+ enc = make([]byte, conf.MTU-xtea.BlockSize-RSize)
+ } else {
+ enc = make([]byte, 32)
+ }
+ copy(enc, dhPubRepr[:])
+ if conf.Encless {
+ var err error
+ enc, err = EnclessEncode(state.dsaPubH, state.rNonce[:], enc)
+ if err != err {
+ panic(err)
+ }
+ } else {
+ salsa20.XORKeyStream(enc, enc, state.rNonce[:], state.dsaPubH)
+ }
+ data := append(state.rNonce[:], enc...)
+ data = append(data, idTag(state.Conf.Id, state.rNonce[:])...)
+ state.conn.Write(data)
+ return state
+}
+
+// Process handshake message on the server side.
+// This function is intended to be called on server's side.
+// If this is the final handshake message, then new Peer object
+// will be created and used as a transport. If no mutually
+// authenticated Peer is ready, then return nil.
+func (h *Handshake) Server(data []byte) *Peer {
+ // R + ENC(H(DSAPub), R, El(CDHPub)) + IDtag
+ if h.rNonce == nil && ((!h.Conf.Encless && len(data) >= 48) ||
+ (h.Conf.Encless && len(data) == EnclessEnlargeSize+h.Conf.MTU)) {
+ h.rNonce = new([RSize]byte)
+ copy(h.rNonce[:], data[:RSize])
+
+ // Decrypt remote public key
+ cDHRepr := new([32]byte)
+ if h.Conf.Encless {
+ out, err := EnclessDecode(
+ h.dsaPubH,
+ h.rNonce[:],
+ data[RSize:len(data)-xtea.BlockSize],
+ )
+ if err != nil {
+ log.Println("Unable to decode packet from", h.addr, err)
+ return nil
+ }
+ copy(cDHRepr[:], out)
+ } else {
+ salsa20.XORKeyStream(
+ cDHRepr[:],
+ data[RSize:RSize+32],
+ h.rNonce[:],
+ h.dsaPubH,
+ )
+ }
+
+ // Generate DH keypair
+ var dhPubRepr *[32]byte
+ h.dhPriv, dhPubRepr = dhKeypairGen()
+
+ // Compute shared key
+ cDH := new([32]byte)
+ extra25519.RepresentativeToPublicKey(cDH, cDHRepr)
+ h.key = dhKeyGen(h.dhPriv, cDH)
+
+ var encPub []byte
+ var err error
+ if h.Conf.Encless {
+ encPub = make([]byte, h.Conf.MTU)
+ copy(encPub, dhPubRepr[:])
+ encPub, err = EnclessEncode(h.dsaPubH, h.rNonceNext(1), encPub)
+ if err != nil {
+ panic(err)
+ }
+ } else {
+ encPub = make([]byte, 32)
+ salsa20.XORKeyStream(encPub, dhPubRepr[:], h.rNonceNext(1), h.dsaPubH)
+ }
+
+ // Generate R* and encrypt them
+ h.rServer = new([RSize]byte)
+ if _, err = Rand.Read(h.rServer[:]); err != nil {
+ log.Fatalln("Error reading random for R:", err)
+ }
+ h.sServer = new([SSize]byte)
+ if _, err = Rand.Read(h.sServer[:]); err != nil {
+ log.Fatalln("Error reading random for S:", err)
+ }
+ var encRs []byte
+ if h.Conf.Noise && !h.Conf.Encless {
+ encRs = make([]byte, h.Conf.MTU-len(encPub)-xtea.BlockSize)
+ } else if h.Conf.Encless {
+ encRs = make([]byte, h.Conf.MTU-xtea.BlockSize)
+ } else {
+ encRs = make([]byte, RSize+SSize)
+ }
+ copy(encRs, append(h.rServer[:], h.sServer[:]...))
+ if h.Conf.Encless {
+ encRs, err = EnclessEncode(h.key, h.rNonce[:], encRs)
+ if err != nil {
+ panic(err)
+ }
+ } else {
+ salsa20.XORKeyStream(encRs, encRs, h.rNonce[:], h.key)
+ }
+
+ // Send that to client
+ h.conn.Write(append(encPub, append(encRs, idTag(h.Conf.Id, encPub)...)...))
+ h.LastPing = time.Now()
+ } else
+ // ENC(K, R+1, RS + RC + SC + Sign(DSAPriv, K)) + IDtag
+ if h.rClient == nil && ((!h.Conf.Encless && len(data) >= 120) ||
+ (h.Conf.Encless && len(data) == EnclessEnlargeSize+h.Conf.MTU)) {
+ var dec []byte
+ var err error
+ if h.Conf.Encless {
+ dec, err = EnclessDecode(
+ h.key,
+ h.rNonceNext(1),
+ data[:len(data)-xtea.BlockSize],
+ )
+ if err != nil {
+ log.Println("Unable to decode packet from", h.addr, err)
+ return nil
+ }
+ dec = dec[:RSize+RSize+SSize+ed25519.SignatureSize]
+ } else {
+ dec = make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
+ salsa20.XORKeyStream(
+ dec,
+ data[:RSize+RSize+SSize+ed25519.SignatureSize],
+ h.rNonceNext(1),
+ h.key,
+ )
+ }
+ if subtle.ConstantTimeCompare(dec[:RSize], h.rServer[:]) != 1 {
+ log.Println("Invalid server's random number with", h.addr)
+ return nil
+ }
+ sign := new([ed25519.SignatureSize]byte)
+ copy(sign[:], dec[RSize+RSize+SSize:])
+ if !ed25519.Verify(h.Conf.Verifier.Pub, h.key[:], sign) {
+ log.Println("Invalid signature from", h.addr)
+ return nil
+ }
+
+ // Send final answer to client
+ var enc []byte
+ if h.Conf.Noise {
+ enc = make([]byte, h.Conf.MTU-xtea.BlockSize)
+ } else {
+ enc = make([]byte, RSize)
+ }
+ copy(enc, dec[RSize:RSize+RSize])
+ if h.Conf.Encless {
+ enc, err = EnclessEncode(h.key, h.rNonceNext(2), enc)
+ if err != nil {
+ panic(err)
+ }
+ } else {
+ salsa20.XORKeyStream(enc, enc, h.rNonceNext(2), h.key)
+ }
+ h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
+
+ // Switch peer
+ peer := newPeer(
+ false,
+ h.addr,
+ h.conn,
+ h.Conf,
+ keyFromSecrets(h.sServer[:], dec[RSize+RSize:RSize+RSize+SSize]))
+ h.LastPing = time.Now()
+ return peer
+ } else {
+ log.Println("Invalid handshake message from", h.addr)
+ }
+ return nil
+}
+
+// Process handshake message on the client side.
+// This function is intended to be called on client's side.
+// If this is the final handshake message, then new Peer object
+// will be created and used as a transport. If no mutually
+// authenticated Peer is ready, then return nil.
+func (h *Handshake) Client(data []byte) *Peer {
+ // ENC(H(DSAPub), R+1, El(SDHPub)) + ENC(K, R, RS + SS) + IDtag
+ if h.rServer == nil && h.key == nil &&
+ ((!h.Conf.Encless && len(data) >= 80) ||
+ (h.Conf.Encless && len(data) == 2*(EnclessEnlargeSize+h.Conf.MTU))) {
+ // Decrypt remote public key
+ sDHRepr := new([32]byte)
+ var tmp []byte
+ var err error
+ if h.Conf.Encless {
+ tmp, err = EnclessDecode(
+ h.dsaPubH,
+ h.rNonceNext(1),
+ data[:len(data)/2],
+ )
+ if err != nil {
+ log.Println("Unable to decode packet from", h.addr, err)
+ return nil
+ }
+ copy(sDHRepr[:], tmp[:32])
+ } else {
+ salsa20.XORKeyStream(
+ sDHRepr[:],
+ data[:32],
+ h.rNonceNext(1),
+ h.dsaPubH,
+ )
+ }
+
+ // Compute shared key
+ sDH := new([32]byte)
+ extra25519.RepresentativeToPublicKey(sDH, sDHRepr)
+ h.key = dhKeyGen(h.dhPriv, sDH)
+
+ // Decrypt Rs
+ h.rServer = new([RSize]byte)
+ h.sServer = new([SSize]byte)
+ if h.Conf.Encless {
+ tmp, err = EnclessDecode(
+ h.key,
+ h.rNonce[:],
+ data[len(data)/2:len(data)-xtea.BlockSize],
+ )
+ if err != nil {
+ log.Println("Unable to decode packet from", h.addr, err)
+ return nil
+ }
+ copy(h.rServer[:], tmp[:RSize])
+ copy(h.sServer[:], tmp[RSize:RSize+SSize])
+ } else {
+ decRs := make([]byte, RSize+SSize)
+ salsa20.XORKeyStream(
+ decRs,
+ data[SSize:SSize+RSize+SSize],
+ h.rNonce[:],
+ h.key,
+ )
+ copy(h.rServer[:], decRs[:RSize])
+ copy(h.sServer[:], decRs[RSize:])
+ }
+
+ // Generate R* and signature and encrypt them
+ h.rClient = new([RSize]byte)
+ if _, err = Rand.Read(h.rClient[:]); err != nil {
+ log.Fatalln("Error reading random for R:", err)
+ }
+ h.sClient = new([SSize]byte)
+ if _, err = Rand.Read(h.sClient[:]); err != nil {
+ log.Fatalln("Error reading random for S:", err)
+ }
+ sign := ed25519.Sign(h.Conf.DSAPriv, h.key[:])
+
+ var enc []byte
+ if h.Conf.Noise {
+ enc = make([]byte, h.Conf.MTU-xtea.BlockSize)
+ } else {
+ enc = make([]byte, RSize+RSize+SSize+ed25519.SignatureSize)
+ }
+ copy(enc, h.rServer[:])
+ copy(enc[RSize:], h.rClient[:])
+ copy(enc[RSize+RSize:], h.sClient[:])
+ copy(enc[RSize+RSize+SSize:], sign[:])
+ if h.Conf.Encless {
+ enc, err = EnclessEncode(h.key, h.rNonceNext(1), enc)
+ if err != nil {
+ panic(err)
+ }
+ } else {
+ salsa20.XORKeyStream(enc, enc, h.rNonceNext(1), h.key)
+ }
+
+ // Send that to server
+ h.conn.Write(append(enc, idTag(h.Conf.Id, enc)...))
+ h.LastPing = time.Now()
+ } else
+ // ENC(K, R+2, RC) + IDtag
+ if h.key != nil && ((!h.Conf.Encless && len(data) >= 16) ||
+ (h.Conf.Encless && len(data) == EnclessEnlargeSize+h.Conf.MTU)) {
+ var err error
+ // Decrypt rClient
+ var dec []byte
+ if h.Conf.Encless {
+ dec, err = EnclessDecode(
+ h.key,
+ h.rNonceNext(2),
+ data[:len(data)-xtea.BlockSize],
+ )
+ if err != nil {
+ log.Println("Unable to decode packet from", h.addr, err)
+ return nil
+ }
+ dec = dec[:RSize]
+ } else {
+ dec = make([]byte, RSize)
+ salsa20.XORKeyStream(dec, data[:RSize], h.rNonceNext(2), h.key)
+ }
+ if subtle.ConstantTimeCompare(dec, h.rClient[:]) != 1 {
+ log.Println("Invalid client's random number with", h.addr)
+ return nil
+ }
+
+ // Switch peer
+ peer := newPeer(
+ true,
+ h.addr,
+ h.conn,
+ h.Conf,
+ keyFromSecrets(h.sServer[:], h.sClient[:]),
+ )
+ h.LastPing = time.Now()
+ return peer
+ } else {
+ log.Println("Invalid handshake stage from", h.addr)
+ }
+ return nil
+}