diff --git a/xs/xs.go b/xs/xs.go
index e941b4c..dc440d2 100755
--- a/xs/xs.go
+++ b/xs/xs.go
@@ -702,6 +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
 		copySrc       []byte
 		copyDst       string
 		copyQuiet     bool
@@ -745,8 +746,9 @@ func main() { //nolint: funlen, gocyclo
       KEX_FRODOKEM_976AES
       KEX_FRODOKEM_976SHAKE`)
 	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(&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)")
 	//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
@@ -973,6 +975,9 @@ func main() { //nolint: funlen, gocyclo
 		exitWithStatus(XSNetDialFailed)
 	}
 
+	if remodulate {
+		conn.SetOpts(xsnet.CORemodulateShields)
+	}
 	conn.RekeyHelper(rekeySecs)
 	defer conn.ShutdownRekey()
 
diff --git a/xsd/xsd.go b/xsd/xsd.go
index e7081c1..b682141 100755
--- a/xsd/xsd.go
+++ b/xsd/xsd.go
@@ -530,12 +530,14 @@ 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 useSystemPasswd bool
 
 	flag.BoolVar(&vopt, "v", false, "show version")
 	flag.UintVar(&rekeySecs, "r", 300, "rekey interval in `secs`")
-	flag.StringVar(&laddr, "l", ":2000", "interface[:port] to listen") //nolint:gomnd,lll
+	flag.BoolVar(&remodulate, "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")
 	flag.BoolVar(&chaffEnabled, "e", true, "enable chaff pkts")
@@ -702,6 +704,9 @@ func main() { //nolint:funlen,gocyclo
 			} else {
 				log.Println("Accepted client")
 
+				if remodulate {
+					conn.SetOpts(xsnet.CORemodulateShields)
+				}
 				conn.RekeyHelper(rekeySecs)
 
 				// Set up chaffing to client
diff --git a/xsnet/chan.go b/xsnet/chan.go
index 40babee..4b4e82d 100644
--- a/xsnet/chan.go
+++ b/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
-   a cipherStream and hash
- */
+// Choose a cipher and hmac alg from supported sets, given two uint8 values
+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
diff --git a/xsnet/consts.go b/xsnet/consts.go
index b491a87..ae2740c 100644
--- a/xsnet/consts.go
+++ b/xsnet/consts.go
@@ -122,5 +122,12 @@ 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
diff --git a/xsnet/net.go b/xsnet/net.go
index 3a6789d..8253886 100644
--- a/xsnet/net.go
+++ b/xsnet/net.go
@@ -1351,6 +1351,9 @@ 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.cipheropts = getNewStreamAlgs(rekeyData[0], rekeyData[1])
+				}
 				hc.r, hc.rm, err = hc.getStream(rekeyData)
 			case CSOTermSize:
 				fmt.Sscanf(string(payloadBytes), "%d %d", &hc.Rows, &hc.Cols)
@@ -1615,6 +1618,9 @@ 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()