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+ GNU GENERAL PUBLIC LICENSE
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+
+ END OF TERMS AND CONDITIONS
+
+ How to Apply These Terms to Your New Programs
+
+ If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+ To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+ <one line to give the program's name and a brief idea of what it does.>
+ Copyright (C) <year> <name of author>
+
+ 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/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+ If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+ <program> Copyright (C) <year> <name of author>
+ This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+ This is free software, and you are welcome to redistribute it
+ under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+ You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+ The GNU General Public License does not permit incorporating your program
+into proprietary programs. 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
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
--- /dev/null
+/*
+govpn -- high-performance secure virtual private network daemon
+Copyright (C) 2014 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 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
+}