Obfuscate/randomize message nonces

[govpn.git] / govpn.go

diff --git a/govpn.go b/govpn.go
index 70d48d295a2a363df7a3756b344cb75243823bb4..6f662c60ca208d5d4a8bce9d69ce1dbc0382ae65 100644 (file)
--- a/govpn.go
+++ b/govpn.go
@@ -36,6 +36,7 @@ import (
 
        "golang.org/x/crypto/poly1305"
        "golang.org/x/crypto/salsa20"
+       "golang.org/x/crypto/xtea"
 )
 
 var (
@@ -68,10 +69,11 @@ type TAP interface {
 }
 
 type Peer struct {
-       addr      *net.UDPAddr
-       key       *[KeySize]byte // encryption key
-       nonceOur  uint64         // nonce for our messages
-       nonceRecv uint64         // latest received nonce from remote peer
+       addr        *net.UDPAddr
+       key         *[KeySize]byte // encryption key
+       nonceOur    uint64         // nonce for our messages
+       nonceRecv   uint64         // latest received nonce from remote peer
+       nonceCipher *xtea.Cipher   // nonce cipher
 }
 
 type UDPPkt struct {
@@ -278,12 +280,6 @@ func main() {
                                udpSinkReady <- true
                                continue
                        }
-                       nonceRecv, _ = binary.Uvarint(udpPktData[:8])
-                       if nonceRecv < peer.nonceRecv-noncediff {
-                               fmt.Print("R")
-                               udpSinkReady <- true
-                               continue
-                       }
                        copy(buf[:KeySize], emptyKey)
                        copy(tag[:], udpPktData[udpPkt.size-poly1305.TagSize:])
                        copy(buf[S20BS:], udpPktData[NonceSize:udpPkt.size-poly1305.TagSize])
@@ -299,6 +295,13 @@ func main() {
                                fmt.Print("T")
                                continue
                        }
+                       peer.nonceCipher.Decrypt(buf, udpPktData[:NonceSize])
+                       nonceRecv, _ = binary.Uvarint(buf[:NonceSize])
+                       if nonceRecv < peer.nonceRecv-noncediff {
+                               fmt.Print("R")
+                               udpSinkReady <- true
+                               continue
+                       }
                        udpSinkReady <- true
                        peer.nonceRecv = nonceRecv
                        timeouts = 0
@@ -321,8 +324,14 @@ func main() {
                                ethSinkReady <- true
                                continue
                        }
+
                        peer.nonceOur = peer.nonceOur + 2
+                       for i := 0; i < NonceSize; i++ {
+                               nonce[i] = '\x00'
+                       }
                        binary.PutUvarint(nonce, peer.nonceOur)
+                       peer.nonceCipher.Encrypt(nonce, nonce)
+
                        copy(buf[:KeySize], emptyKey)
                        if ethPktSize > -1 {
                                copy(buf[S20BS:], ethBuf[:ethPktSize])