Fixes to negotiate/accept cipher remodulation

xs/xs.go

@@ -702,7 +702,7 @@ func main() { //nolint: funlen, gocyclo
 		cmdStr        string
 		tunSpecStr    string // lport1:rport1[,lport2:rport2,...]
 		rekeySecs     uint
-		remodulate    bool // true: when rekeying, switch to random cipher/hmac alg
+		remodRequested    bool // true: when rekeying, switch to random cipher/hmac alg
 		copySrc       []byte
 		copyDst       string
 		copyQuiet     bool
@@ -748,7 +748,7 @@ func main() { //nolint: funlen, gocyclo
 	flag.StringVar(&kcpMode, "K", "unused", "KCP `alg`, one of [KCP_NONE | KCP_AES | KCP_BLOWFISH | KCP_CAST5 | KCP_SM4 | KCP_SALSA20 | KCP_SIMPLEXOR | KCP_TEA | KCP_3DES | KCP_TWOFISH | KCP_XTEA] to use KCP (github.com/xtaci/kcp-go) reliable UDP instead of TCP") //nolint:lll
 	flag.UintVar(&port, "p", 2000, "``port")                                                                                                                                                                                                                            //nolint:gomnd,lll
 	flag.UintVar(&rekeySecs, "r", 300, "rekey interval in `secs`")
-	flag.BoolVar(&remodulate, "R", false, "Borg Countermeasures (remodulate cipher/hmac alg on each rekey)")
+	flag.BoolVar(&remodRequested, "R", false, "Borg Countermeasures (remodulate cipher/hmac alg on each rekey)")
 	//nolint:gocritic,nolintlint // flag.StringVar(&authCookie, "a", "", "auth cookie")
 	flag.BoolVar(&chaffEnabled, "e", true, "enable chaff pkts")
 	flag.UintVar(&chaffFreqMin, "f", 100, "chaff pkt freq min `msecs`")  //nolint:gomnd
@@ -969,15 +969,18 @@ func main() { //nolint: funlen, gocyclo
 	if kcpMode != "unused" {
 		proto = "kcp"
 	}
-	conn, err := xsnet.Dial(proto, server, cipherAlg, hmacAlg, kexAlg, kcpMode)
+	
+	remodExtArg := ""
+	if remodRequested {
+		remodExtArg = "-R"
+	}
+	// Pass opt to Dial() via extensions arg
+	conn, err := xsnet.Dial(proto, server, cipherAlg, hmacAlg, kexAlg, kcpMode, remodExtArg)
 	if err != nil {
 		fmt.Println(err)
 		exitWithStatus(XSNetDialFailed)
 	}
 
-	if remodulate {
-		conn.SetOpts(xsnet.CORemodulateShields)
-	}
 	conn.RekeyHelper(rekeySecs)
 	defer conn.ShutdownRekey()
 

xsd/xsd.go

@@ -530,13 +530,13 @@ func main() { //nolint:funlen,gocyclo
 	var dbg bool
 	var laddr string
 	var rekeySecs uint
-	var remodulate bool // true: when rekeying, switch to random cipher/hmac alg
+	var remodSupported bool // true: when rekeying, switch to random cipher/hmac alg
 
 	var useSystemPasswd bool
 
 	flag.BoolVar(&vopt, "v", false, "show version")
 	flag.UintVar(&rekeySecs, "r", 300, "rekey interval in `secs`")
-	flag.BoolVar(&remodulate, "R", false, "Borg Countermeasures (remodulate cipher/hmac alg on each rekey)")
+	flag.BoolVar(&remodSupported, "R", false, "Borg Countermeasures (remodulate cipher/hmac alg on each rekey)")
 	flag.StringVar(&laddr, "l", ":2000", "interface[:port] to listen")                                                                                                                                                                                                         //nolint:gomnd,lll
 	flag.StringVar(&kcpMode, "K", "unused", `set to one of ["KCP_NONE","KCP_AES", "KCP_BLOWFISH", "KCP_CAST5", "KCP_SM4", "KCP_SALSA20", "KCP_SIMPLEXOR", "KCP_TEA", "KCP_3DES", "KCP_TWOFISH", "KCP_XTEA"] to use KCP (github.com/xtaci/kcp-go) reliable UDP instead of TCP`) //nolint:lll
 	flag.BoolVar(&useSysLogin, "L", false, "use system login")
@@ -704,8 +704,21 @@ func main() { //nolint:funlen,gocyclo
 			} else {
 				log.Println("Accepted client")
 
-				if remodulate {
+				// Only enable cipher alg changes on re-key if we were told
-					conn.SetOpts(xsnet.CORemodulateShields)
+				// to support it (launching xsd with -R), *and* the client
+				// proposes to use it.
+				if !remodSupported {
+					if (conn.Opts() & xsnet.CORemodulateShields) != 0 {
+						logger.LogDebug("[client proposed -R, but we don't support it.]")
+						conn.Close()
+						continue
+					}
+				} else {
+					if conn.Opts()&xsnet.CORemodulateShields != 0 {
+						logger.LogDebug("[cipher remodulation active]")
+					} else {
+						logger.LogDebug("[cipher remodulation inactive]")
+					}
 				}
 				conn.RekeyHelper(rekeySecs)
 

xsnet/net.go

@@ -241,7 +241,7 @@ func (hc *Conn) SetConnOpts(copts uint32) {
 //
 // Consumers of this lib may use this for protocol-level options not part
 // of the KEx or encryption info used by the connection.
-func (hc Conn) Opts() uint32 {
+func (hc *Conn) Opts() uint32 {
 	return hc.opts
 }
 
@@ -363,8 +363,11 @@ func (hc *Conn) applyConnExtensions(extensions ...string) {
 			log.Println("[extension arg = H_SHA512]")
 			hc.cipheropts &= (0xFFFF00FF)
 			hc.cipheropts |= (HmacSHA512 << 8)
-			//default:
+		case "-R":
-			//	log.Printf("[Dial ext \"%s\" ignored]\n", s)
+			log.Println("[extension arg = -R]")
+			hc.opts |= CORemodulateShields
+		//default:
+		//	log.Printf("[Dial ext \"%s\" ignored]\n", s)
 		}
 	}
 }
@@ -1351,7 +1354,7 @@ func (hc *Conn) Read(b []byte) (n int, err error) {
 				//logger.LogDebug(fmt.Sprintf("[Got rekey [%02x %02x %02x ...]\n",
 				//	payloadBytes[0], payloadBytes[1], payloadBytes[2]))
 				rekeyData := payloadBytes
-				if hc.opts&CORemodulateShields != 0 {
+				if (hc.opts & CORemodulateShields) != 0 {
 					hc.cipheropts = getNewStreamAlgs(rekeyData[0], rekeyData[1])
 				}
 				hc.r, hc.rm, err = hc.getStream(rekeyData)
@@ -1615,10 +1618,10 @@ func (hc *Conn) RekeyHelper(intervalSecs uint) {
 				_, err := crand.Read(rekeyData)
 				//logger.LogDebug(fmt.Sprintf("[rekey [%02x %02x %02x ...]\n",
 				//	rekeyData[0], rekeyData[1], rekeyData[2]))
-				//logger.LogDebug("[+rekeyHelper]")
+				logger.LogDebug("[+rekeyHelper]")
 				_, err = hc.WritePacket(rekeyData, CSORekey)
 				hc.Lock()
-				if hc.opts&CORemodulateShields != 0 {
+				if (hc.opts & CORemodulateShields) != 0 {
 					hc.cipheropts = getNewStreamAlgs(rekeyData[0], rekeyData[1])
 				}
 				hc.w, hc.wm, err = hc.getStream(rekeyData)