WIP: dynamic chaff modes ('roulette' not working)

xs/xs.go

@@ -1047,7 +1047,7 @@ func main() {
 		rec.SetStatus(255)
 	} else {
 		//=== Set up chaffing to server
-		conn.SetupChaff(chaffFreqMin, chaffFreqMax, chaffBytesMax) // enable client->server chaffing
+		conn.SetupChaff(xsnet.ChaffConfigRoulette, chaffFreqMin, chaffFreqMax, chaffBytesMax) // enable client->server chaffing
 		if chaffEnabled {
 			// #gv:s/label=\"main\$2\"/label=\"deferCloseChaff\"/
 			// TODO:.gv:main:2:deferCloseChaff

xsd/xsd.go

@@ -663,7 +663,7 @@ func main() {
 				// Set up chaffing to client
 				// Will only start when runShellAs() is called
 				// after stdin/stdout are hooked up
-				conn.SetupChaff(chaffFreqMin, chaffFreqMax, chaffBytesMax) // configure server->client chaffing
+				conn.SetupChaff(xsnet.ChaffConfigRand, chaffFreqMin, chaffFreqMax, chaffBytesMax) // configure server->client chaffing
 
 				// Handle the connection in a new goroutine.
 				// The loop then returns to accepting, so that

xsnet/consts.go

@@ -58,6 +58,15 @@ const (
 // This indicate channel-related or internal errors
 type CSExtendedCode uint32
 
+// Chaffing config modes
+const (
+	ChaffConfigRand = iota
+	ChaffConfigCorpusA  // cycle (random reset point on wrap) through 'corpusA' text
+	ChaffConfigRoulette // NOTE: MUST BE LAST in this enum. Cycle randomly amongst all other modes :p
+)
+
+type ChaffMode uint8
+
 // Channel Status/Op bytes - packet types
 const (
 	// Main connection/session control

xsnet/net.go

@@ -65,6 +65,7 @@ type (
 	ChaffConfig struct {
 		shutdown bool //set to inform chaffHelper to shut down
 		enabled  bool
+		mode     ChaffMode
 		msecsMin uint //msecs min interval
 		msecsMax uint //msecs max interval
 		szMax    uint // max size in bytes
@@ -1556,30 +1557,80 @@ func (hc *Conn) ShutdownChaff() {
 	log.Println("Chaffing SHUTDOWN")
 }
 
-func (hc *Conn) SetupChaff(msecsMin uint, msecsMax uint, szMax uint) {
+func (hc *Conn) SetupChaff(mode ChaffMode, msecsMin uint, msecsMax uint, szMax uint) {
+	switch mode {
+	case ChaffConfigRand:
+		hc.chaff.mode = mode
+	case ChaffConfigCorpusA:
+		hc.chaff.mode = mode
+	case ChaffConfigRoulette:
+		hc.chaff.mode = mode
+	default:
+		hc.chaff.mode = ChaffConfigRand
+	}
 	hc.chaff.msecsMin = msecsMin //move these to params of chaffHelper() ?
 	hc.chaff.msecsMax = msecsMax
 	hc.chaff.szMax = szMax
 }
 
+func randBytes(sz uint) (r []byte) {
+	r = make([]byte, rand.Intn(int(sz)))
+	_, _ = rand.Read(r)
+	return r
+}
+
+func fillBufferWithText(fillerMat string, sz uint) (r []byte) {
+	r = make([]byte, sz)
+	fromIdx := 0
+	fillIdx := uint(0)
+	for fillIdx < sz {
+		if fromIdx == len(fillerMat) {
+			fromIdx = /* 0 */ rand.Intn(len(fillerMat))
+		}
+		r[fillIdx] = fillerMat[fromIdx]
+		fillIdx++
+		fromIdx++
+	}
+	return r
+}
+
+func ChaffStrategy(mode ChaffMode) (s ChaffMode) {
+	if mode == ChaffConfigRoulette {
+		s = ChaffMode(int(rand.Intn(ChaffConfigRoulette)))
+	}
+	fmt.Printf("strategy:%v\n", s)
+	return
+}
+
 // Helper routine to spawn a chaffing goroutine for each Conn
 func (hc *Conn) chaffHelper() {
 	go func() {
 		for {
 			var nextDuration int
 			if hc.chaff.enabled {
-				var bufTmp []byte
-				bufTmp = make([]byte, rand.Intn(int(hc.chaff.szMax)))
 				min := int(hc.chaff.msecsMin)
 				nextDuration = rand.Intn(int(hc.chaff.msecsMax)-min) + min
-				_, _ = rand.Read(bufTmp)
+
+				var bufTmp []byte
+				strat := ChaffStrategy(hc.chaff.mode)
+
+				switch strat {
+				case ChaffConfigCorpusA:
+					bufTmp = fillBufferWithText(corpusTextA, hc.chaff.szMax)
+				case ChaffConfigRand:
+				default:
+					bufTmp = randBytes(hc.chaff.szMax)
+				}
+
 				_, err := hc.WritePacket(bufTmp, CSOChaff)
 				if err != nil {
 					log.Println("[ *** error - chaffHelper quitting *** ]")
 					hc.chaff.enabled = false
 					break
 				}
+
 			}
+
 			time.Sleep(time.Duration(nextDuration) * time.Millisecond)
 			if hc.chaff.shutdown {
 				log.Println("*** chaffHelper shutting down")
@@ -1589,3 +1640,18 @@ func (hc *Conn) chaffHelper() {
 		}
 	}()
 }
+
+const (
+	corpusTextA = `cd $HOME
+ls dev
+cd dev
+vi 00README.txt
+cat "The quick brown fox jumps over the lazy cryptographer." && cd /var && rm -rf *
+## This is random 'corpusA' text material which should be disregarded. If you are 
+attempting to decode a live or recorded xs session you should note that this chaff 
+text will probably give you no end of difficulties, and that is by design. Have you 
+considered your life path? Snooping on other individuals, either domestic or foreign, 
+is an ethically questionable career and you may be doing more harm than good to democracy, 
+international relations, and general welfare of humanity. Consider buying a nice quiet 
+cabin somewhere by a lake, growing food and spending time with those you love.`
+)