diff --git a/hkexnet/hkexnet.go b/hkexnet/hkexnet.go
index 4337502..0c2505f 100644
--- a/hkexnet/hkexnet.go
+++ b/hkexnet/hkexnet.go
@@ -54,7 +54,7 @@ type KEX uint8
 
 const (
 	KEX_HERRADURA = iota // this MUST be first for default if omitted in ctor
-	//KEX_FOO
+	KEX_FOO
 	//KEX_DH
 	//KEX_ETC
 )
@@ -73,7 +73,7 @@ const (
 	CSONone        = iota // No error, normal packet
 	CSOHmacInvalid        // HMAC mismatch detected on remote end
 	CSOTermSize           // set term size (rows:cols)
-	CSOExitStatus         // Remote cmd exit status (TODO)
+	CSOExitStatus         // Remote cmd exit status
 	CSOChaff              // Dummy packet, do not pass beyond decryption
 )
 
@@ -101,12 +101,12 @@ type (
 
 	// Conn is a HKex connection - a superset of net.Conn
 	Conn struct {
-		kex        KEX
+		kex        KEX // KEX alg (typedef uint8)
 		m          *sync.Mutex
-		c          net.Conn // which also implements io.Reader, io.Writer, ...
-		h          *hkex.HerraduraKEx
-		cipheropts uint32 // post-KEx cipher/hmac options
-		opts       uint32 // post-KEx protocol options (caller-defined)
+		c          net.Conn           // which also implements io.Reader, io.Writer, ...
+		h          *hkex.HerraduraKEx // TODO: make an interface?
+		cipheropts uint32             // post-KEx cipher/hmac options
+		opts       uint32             // post-KEx protocol options (caller-defined)
 		WinCh      chan WinSize
 		Rows       uint16
 		Cols       uint16
@@ -176,10 +176,10 @@ func (hc *Conn) applyConnExtensions(extensions ...string) {
 			log.Println("[extension arg = KEX_HERRADURA]")
 			hc.kex = KEX_HERRADURA
 			break
-		//case "KEX_FOO":
-		//	log.Println("[extension arg = KEX_FOO]")
-		//	hc.kex = KEX_FOO
-		//	break
+		case "KEX_FOO":
+			log.Println("[extension arg = KEX_FOO]")
+			hc.kex = KEX_FOO
+			break
 		case "C_AES_256":
 			log.Println("[extension arg = C_AES_256]")
 			hc.cipheropts &= (0xFFFFFF00)
@@ -207,6 +207,65 @@ func (hc *Conn) applyConnExtensions(extensions ...string) {
 	}
 }
 
+func HKExDialSetup(c net.Conn, hc *Conn) (err error) {
+	// Send hkexnet.Conn parameters to remote side
+	// d is value for Herradura key exchange
+	fmt.Fprintf(c, "0x%s\n%08x:%08x\n", hc.h.D().Text(16),
+		hc.cipheropts, hc.opts)
+
+	d := big.NewInt(0)
+	_, err = fmt.Fscanln(c, d)
+	if err != nil {
+		return err
+	}
+	// Read peer D over net.Conn (c)
+	_, err = fmt.Fscanf(c, "%08x:%08x\n",
+		&hc.cipheropts, &hc.opts)
+	if err != nil {
+		return err
+	}
+
+	hc.h.SetPeerD(d)
+	log.Printf("** local D:%s\n", hc.h.D().Text(16))
+	log.Printf("**(c)** peer D:%s\n", hc.h.PeerD().Text(16))
+	hc.h.ComputeFA()
+	log.Printf("**(c)** FA:%s\n", hc.h.FA())
+
+	hc.r, hc.rm, err = hc.getStream(hc.h.FA())
+	hc.w, hc.wm, err = hc.getStream(hc.h.FA())
+	return
+}
+
+func HKExAcceptSetup(c net.Conn, hc *Conn) (err error) {
+	// Read in hkexnet.Conn parameters over raw Conn c
+	// d is value for Herradura key exchange
+	d := big.NewInt(0)
+	_, err = fmt.Fscanln(c, d)
+	log.Printf("[Got d:%v]", d)
+	if err != nil {
+		return err
+	}
+	_, err = fmt.Fscanf(c, "%08x:%08x\n",
+		&hc.cipheropts, &hc.opts)
+	log.Printf("[Got cipheropts, opts:%v, %v]", hc.cipheropts, hc.opts)
+	if err != nil {
+		return err
+	}
+	hc.h.SetPeerD(d)
+	log.Printf("** D:%s\n", hc.h.D().Text(16))
+	log.Printf("**(s)** peerD:%s\n", hc.h.PeerD().Text(16))
+	hc.h.ComputeFA()
+	log.Printf("**(s)** FA:%s\n", hc.h.FA())
+
+	// Send D and cipheropts/conn_opts to peer
+	fmt.Fprintf(c, "0x%s\n%08x:%08x\n", hc.h.D().Text(16),
+		hc.cipheropts, hc.opts)
+
+	hc.r, hc.rm, err = hc.getStream(hc.h.FA())
+	hc.w, hc.wm, err = hc.getStream(hc.h.FA())
+	return
+}
+
 // Dial as net.Dial(), but with implicit key exchange to set up secure
 // channel on connect
 //
@@ -234,32 +293,25 @@ func Dial(protocol string, ipport string, extensions ...string) (hc *Conn, err e
 	fmt.Fprintf(c, "%02x\n", hc.kex)
 	// --
 
-	// Send hkexnet.Conn parameters to remote side
-	// d is value for Herradura key exchange
-	fmt.Fprintf(c, "0x%s\n%08x:%08x\n", hc.h.D().Text(16),
-		hc.cipheropts, hc.opts)
-
-	d := big.NewInt(0)
-	_, err = fmt.Fscanln(c, d)
-	if err != nil {
-		return nil, err
-	}
-	// Read peer D over net.Conn (c)
-	_, err = fmt.Fscanf(c, "%08x:%08x\n",
-		&hc.cipheropts, &hc.opts)
-	if err != nil {
-		return nil, err
-	}
-
-	hc.h.SetPeerD(d)
-	log.Printf("** local D:%s\n", hc.h.D().Text(16))
-	log.Printf("**(c)** peer D:%s\n", hc.h.PeerD().Text(16))
-	hc.h.ComputeFA()
-	log.Printf("**(c)** FA:%s\n", hc.h.FA())
-
-	hc.r, hc.rm, err = hc.getStream(hc.h.FA())
-	hc.w, hc.wm, err = hc.getStream(hc.h.FA())
 	*hc.closeStat = CSEStillOpen // open or prematurely-closed status
+
+	// Perform Key Exchange according to client-request algorithm
+	switch hc.kex {
+	case KEX_HERRADURA:
+		if HKExDialSetup(c, hc) != nil {
+			return hc, nil
+		}
+	case KEX_FOO:
+		// For testing: set up as HKEx anyway, but server via Accept() should
+		// reject as invalid.
+		//if FooKExDialSetup(c, hc) != nil {
+		if HKExDialSetup(c, hc) != nil {
+			return hc, nil
+		}
+	default:
+		log.Printf("Invalid kex alg (%d), rejecting\n", hc.kex)
+		return nil, errors.New("Invalid kex alg")
+	}
 	return
 }
 
@@ -380,35 +432,19 @@ func (hl *HKExListener) Accept() (hc Conn, err error) {
 	if err != nil {
 		return hc, err
 	}
-	log.Printf("[KEx alg: %v]\n", kexAlg)
+	log.Printf("[Client proposed KEx alg: %v]\n", kexAlg)
 	// --
 
-	// Read in hkexnet.Conn parameters over raw Conn c
-	// d is value for Herradura key exchange
-	d := big.NewInt(0)
-	_, err = fmt.Fscanln(c, d)
-	log.Printf("[Got d:%v]", d)
-	if err != nil {
-		return hc, err
+	switch kexAlg {
+	case KEX_HERRADURA:
+		log.Printf("[KEx alg %d accepted]\n", kexAlg)
+		if HKExAcceptSetup(c, &hc) != nil {
+			return hc, nil
+		}
+	default:
+		log.Printf("[KEx alg %d rejected]\n", kexAlg)
+		return hc, errors.New("KEx rejected")
 	}
-	_, err = fmt.Fscanf(c, "%08x:%08x\n",
-		&hc.cipheropts, &hc.opts)
-	log.Printf("[Got cipheropts, opts:%v, %v]", hc.cipheropts, hc.opts)
-	if err != nil {
-		return hc, err
-	}
-	hc.h.SetPeerD(d)
-	log.Printf("** D:%s\n", hc.h.D().Text(16))
-	log.Printf("**(s)** peerD:%s\n", hc.h.PeerD().Text(16))
-	hc.h.ComputeFA()
-	log.Printf("**(s)** FA:%s\n", hc.h.FA())
-
-	// Send D and cipheropts/conn_opts to peer
-	fmt.Fprintf(c, "0x%s\n%08x:%08x\n", hc.h.D().Text(16),
-		hc.cipheropts, hc.opts)
-
-	hc.r, hc.rm, err = hc.getStream(hc.h.FA())
-	hc.w, hc.wm, err = hc.getStream(hc.h.FA())
 	return
 }
 
@@ -559,7 +595,11 @@ func (hc *Conn) WritePacket(b []byte, op byte) (n int, err error) {
 	//log.Printf("[Encrypting...]\r\n")
 	var hmacOut []uint8
 	var payloadLen uint32
-
+	
+	if hc.m == nil || hc.wm == nil {
+			return 0, errors.New("Secure chan not ready for writing")
+	}
+	
 	// N.B. Originally this Lock() surrounded only the
 	// calls to binary.Write(hc.c ..) however there appears
 	// to be some other unshareable state in the Conn