Add optional cipher/hmac algo remodulate on rekey

Makefile

@@ -1,4 +1,4 @@
-VERSION := 0.9.6
+VERSION := 0.9.7
 .PHONY: lint vis clean common client server passwd\
  subpkgs install uninstall reinstall scc
  

xs/xs.go

@@ -702,6 +702,7 @@ func main() { //nolint: funlen, gocyclo
 		cmdStr        string
 		tunSpecStr    string // lport1:rport1[,lport2:rport2,...]
 		rekeySecs     uint
+		remodRequested    bool // true: when rekeying, switch to random cipher/hmac alg
 		copySrc       []byte
 		copyDst       string
 		copyQuiet     bool
@@ -747,6 +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(&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
@@ -967,7 +969,13 @@ func main() { //nolint: funlen, gocyclo
 	if kcpMode != "unused" {
 		proto = "kcp"
 	}
-	conn, err := xsnet.Dial(proto, server, cipherAlg, hmacAlg, kexAlg, kcpMode)
+	
+	remodExtArg := ""
+	if remodRequested {
+		remodExtArg = "OPT_REMOD"
+	}
+	// 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)

xsd/xsd.go

@@ -530,11 +530,13 @@ func main() { //nolint:funlen,gocyclo
 	var dbg bool
 	var laddr string
 	var rekeySecs uint
+	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(&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")
@@ -702,6 +704,22 @@ func main() { //nolint:funlen,gocyclo
 			} else {
 				log.Println("Accepted client")
 
+				// Only enable cipher alg changes on re-key if we were told
+				// 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 cipher/hmac remod, but we don't support it.]")
+						conn.Close()
+						continue
+					}
+				} else {
+					if conn.Opts()&xsnet.CORemodulateShields != 0 {
+						logger.LogDebug("[cipher/hmac remodulation active]")
+					} else {
+						logger.LogDebug("[cipher/hmac remodulation inactive]")
+					}
+				}
 				conn.RekeyHelper(rekeySecs)
 
 				// Set up chaffing to client

xsnet/chan.go

@@ -22,6 +22,7 @@ import (
 
 	"blitter.com/go/cryptmt"
 	"blitter.com/go/hopscotch"
+	"blitter.com/go/xs/logger"
 	"github.com/aead/chacha20/chacha"
 	"golang.org/x/crypto/blowfish"
 	"golang.org/x/crypto/twofish"
@@ -57,9 +58,19 @@ func expandKeyMat(keymat []byte, blocksize int) []byte {
 	return keymat
 }
 
-/* (Re-)initialize the keystream and hmac state for an xsnet.Conn, returning
+// Choose a cipher and hmac alg from supported sets, given two uint8 values
-   a cipherStream and hash
+func getNewStreamAlgs(cb uint8, hb uint8) (config uint32) {
- */
+	// Get new cipher and hash algs (clamped to valid values) based on
+	// the input rekeying data
+	c := (cb % CAlgNoneDisallowed)
+	h := (hb % HmacNoneDisallowed)
+	config = uint32(h<<8) | uint32(c)
+	logger.LogDebug(fmt.Sprintf("[Chose new algs [%d:%d]", h, c))
+	return
+}
+
+// (Re-)initialize the keystream and hmac state for an xsnet.Conn, returning
+// a cipherStream and hash
 func (hc *Conn) getStream(keymat []byte) (rc cipher.Stream, mc hash.Hash, err error) {
 	var key []byte
 	var block cipher.Block

xsnet/consts.go

@@ -122,5 +122,19 @@ const (
 	HmacNoneDisallowed
 )
 
+// Conn opts outside of basic kex/cipher/hmac connect config
+const (
+	CONone              = iota
+	CORemodulateShields // if set, rekeying also reselects random cipher/hmac alg
+)
+
+type COValue uint32
+
 // Available HMACs for hkex.Conn
 type CSHmacAlg uint32
+
+// Some bounds-checking consts
+const (
+	REKEY_SECS_MIN       = 1
+	CHAFF_FREQ_MSECS_MIN = 1
+)

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
 }
 
@@ -363,6 +363,9 @@ func (hc *Conn) applyConnExtensions(extensions ...string) {
 			log.Println("[extension arg = H_SHA512]")
 			hc.cipheropts &= (0xFFFF00FF)
 			hc.cipheropts |= (HmacSHA512 << 8)
+		case "OPT_REMOD":
+			log.Println("[extension arg = OPT_REMOD]")
+			hc.opts |= CORemodulateShields
 			//default:
 			//	log.Printf("[Dial ext \"%s\" ignored]\n", s)
 		}
@@ -1351,6 +1354,11 @@ 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 {
+					hc.Lock()
+					hc.cipheropts = getNewStreamAlgs(rekeyData[0], rekeyData[1])
+					hc.Unlock()
+				}
 				hc.r, hc.rm, err = hc.getStream(rekeyData)
 			case CSOTermSize:
 				fmt.Sscanf(string(payloadBytes), "%d %d", &hc.Rows, &hc.Cols)
@@ -1585,7 +1593,9 @@ func (hc *Conn) StartupChaff() {
 }
 
 func (hc *Conn) ShutdownChaff() {
+	hc.Lock()
 	hc.chaff.shutdown = true
+	hc.Unlock()
 	log.Println("Chaffing SHUTDOWN")
 }
 
@@ -1596,16 +1606,28 @@ func (hc *Conn) SetupChaff(msecsMin uint, msecsMax uint, szMax uint) {
 }
 
 func (hc *Conn) ShutdownRekey() {
+	hc.Lock()
 	hc.rekey = 0
+	hc.Unlock()
 }
 
 func (hc *Conn) RekeyHelper(intervalSecs uint) {
+	if intervalSecs < REKEY_SECS_MIN {
+		intervalSecs = REKEY_SECS_MIN
+	}
+
 	go func() {
+		hc.Lock()
 		hc.rekey = intervalSecs
+		hc.Unlock()
+
 		for {
-			if hc.rekey != 0 {
+			hc.Lock()
+			rekey := hc.rekey
+			hc.Unlock()
+			if rekey != 0 {
 				//logger.LogDebug(fmt.Sprintf("[rekeyHelper Loop]\n"))
-				time.Sleep(time.Duration(hc.rekey) * time.Second)
+				time.Sleep(time.Duration(rekey) * time.Second)
 
 				// Send rekey to other end
 				rekeyData := make([]byte, 64)
@@ -1615,6 +1637,9 @@ func (hc *Conn) RekeyHelper(intervalSecs uint) {
 				//logger.LogDebug("[+rekeyHelper]")
 				_, err = hc.WritePacket(rekeyData, CSORekey)
 				hc.Lock()
+				if (hc.opts & CORemodulateShields) != 0 {
+					hc.cipheropts = getNewStreamAlgs(rekeyData[0], rekeyData[1])
+				}
 				hc.w, hc.wm, err = hc.getStream(rekeyData)
 				//logger.LogDebug("[-rekeyHelper]")
 				hc.Unlock()
@@ -1631,11 +1656,21 @@ func (hc *Conn) RekeyHelper(intervalSecs uint) {
 
 // Helper routine to spawn a chaffing goroutine for each Conn
 func (hc *Conn) chaffHelper() {
+	// Enforce bounds on chaff frequency and pkt size
+	hc.Lock()
+	if hc.chaff.msecsMin < CHAFF_FREQ_MSECS_MIN {
+		hc.chaff.msecsMin = CHAFF_FREQ_MSECS_MIN
+	}
+	hc.Unlock()
+
 	go func() {
 		var nextDuration int
 		for {
 			//logger.LogDebug(fmt.Sprintf("[chaffHelper Loop]\n"))
-			if !hc.chaff.shutdown {
+			hc.Lock()
+			shutdown := hc.chaff.shutdown
+			hc.Unlock()
+			if !shutdown {
 				var bufTmp []byte
 				bufTmp = make([]byte, rand.Intn(int(hc.chaff.szMax)))
 				min := int(hc.chaff.msecsMin)
@@ -1646,7 +1681,9 @@ func (hc *Conn) chaffHelper() {
 				//logger.LogDebug("[-chaffHelper]")
 				if err != nil {
 					log.Println("[ *** error - chaffHelper shutting down *** ]")
+					hc.Lock()
 					hc.chaff.shutdown = true
+					hc.Unlock()
 					break
 				}
 			} else {
@@ -1670,7 +1707,9 @@ func (hc *Conn) ShutdownKeepAlive() {
 }
 
 func (hc *Conn) ResetKeepAlive() {
+	hc.Lock()
 	hc.keepalive = 3
+	hc.Unlock()
 	log.Println("KeepAlive RESET")
 }
 
@@ -1689,7 +1728,9 @@ func (hc *Conn) keepaliveHelper() {
 				break
 			}
 			time.Sleep(time.Duration(nextDuration) * time.Millisecond)
+			hc.Lock()
 			hc.keepalive -= 1
+			hc.Unlock()
 			//logger.LogDebug(fmt.Sprintf("[keepAlive is now %d]\n", hc.keepalive))
 
 			//if rand.Intn(8) == 0 {