xs/xsnet/net.go

// xsnet.go - net.Conn compatible channel setup with encrypted/HMAC
// negotiation

// Copyright (c) 2017-2020 Russell Magee
// Licensed under the terms of the MIT license (see LICENSE.mit in this
// distribution)
//
// golang implementation by Russ Magee (rmagee_at_gmail.com)

package xsnet

// Implementation of key-exchange-wrapped versions of the golang standard
// net package interfaces, allowing clients and servers to simply replace
// 'net.Dial' and 'net.Listen' with 'hkex.Dial' and 'hkex.Listen'
// (though some extra methods are implemented and must be used
//  for things outside of the scope of plain sockets).

// DESIGN PRINCIPLE: There shall be no protocol features which enable
// downgrade attacks. The server shall have final authority to accept or
// reject any and all proposed KEx and connection parameters proposed by
// clients at setup. Action on denial shall be a simple server disconnect
// with possibly a status code sent so client can determine why connection
// was denied (compare to how failed auth is communicated to client).

import (
	"bytes"
	"crypto/cipher"
	crand "crypto/rand"
	"encoding/binary"
	"encoding/hex"
	"errors"
	"fmt"
	"hash"
	"io"
	"io/ioutil"
	"log"
	"math/big"
	"math/rand"
	"net"
	"strings"
	"sync"
	"syscall"
	"time"

	hkex "blitter.com/go/herradurakex"
	"blitter.com/go/kyber"
	"blitter.com/go/newhope"
	"blitter.com/go/xs/logger"
	frodo "github.com/kuking/go-frodokem"
)

/*---------------------------------------------------------------------*/
const PAD_SZ = 32     // max size of padding applied to each packet
const HMAC_CHK_SZ = 8 // leading bytes of HMAC to xmit for verification

type (
	WinSize struct {
		Rows uint16
		Cols uint16
	}

	// chaffconfig captures attributes used to send chaff packets betwixt
	// client and server connections, to obscure true traffic timing and
	// patterns
	// see: https://en.wikipedia.org/wiki/chaff_(countermeasure)
	ChaffConfig struct {
		shutdown bool //set to inform chaffHelper to shut down
		msecsMin uint //msecs min interval
		msecsMax uint //msecs max interval
		szMax    uint // max size in bytes
	}

	// Conn is a connection wrapping net.Conn with KEX & session state
	Conn struct {
		kex KEXAlg // KEX/KEM proposal (client -> server)

		m *sync.Mutex // (internal)
		c *net.Conn   // which also implements io.Reader, io.Writer, ...

		logCipherText  bool // somewhat expensive, for debugging
		logPlainText   bool // INSECURE and somewhat expensive, for debugging
		logTunActivity bool

		cipheropts uint32 // post-KEx cipher/hmac options
		opts       uint32 // post-KEx protocol options (caller-defined)
		WinCh      chan WinSize
		Rows       uint16
		Cols       uint16

		keepalive uint // if this reaches zero, conn is considered dead
		rekey     uint // if nonzero, rekeying interval in seconds
		Pproc     int  // proc ID of command run on this conn
		chaff     ChaffConfig
		tuns      *map[uint16](*TunEndpoint)

		closeStat *CSOType      // close status (CSOExitStatus)
		r         cipher.Stream //read cipherStream
		rm        hash.Hash
		w         cipher.Stream //write cipherStream
		wm        hash.Hash
		dBuf      *bytes.Buffer //decrypt buffer for Read()
	}
)

var (
	Log *logger.Writer // reg. syslog output (no -d)
)

// Return string (suitable as map key) for a tunnel endpoint
func (t *TunEndpoint) String() string {
	return fmt.Sprintf("[%d:%s:%d]", t.Lport, t.Peer, t.Rport)
}

func (k *KEXAlg) String() string {
	switch *k {
	case KEX_HERRADURA256:
		return "KEX_HERRADURA256"
	case KEX_HERRADURA512:
		return "KEX_HERRADURA512"
	case KEX_HERRADURA1024:
		return "KEX_HERRADURA1024"
	case KEX_HERRADURA2048:
		return "KEX_HERRADURA2048"
	case KEX_KYBER512:
		return "KEX_KYBER512"
	case KEX_KYBER768:
		return "KEX_KYBER768"
	case KEX_KYBER1024:
		return "KEX_KYBER1024"
	case KEX_NEWHOPE:
		return "KEX_NEWHOPE"
	case KEX_NEWHOPE_SIMPLE:
		return "KEX_NEWHOPE_SIMPLE"
	case KEX_FRODOKEM_1344AES:
		return "KEX_FRODOKEM_1344AES"
	case KEX_FRODOKEM_1344SHAKE:
		return "KEX_FRODOKEM_1344SHAKE"
	case KEX_FRODOKEM_976AES:
		return "KEX_FRODOKEM_976AES"
	case KEX_FRODOKEM_976SHAKE:
		return "KEX_FRODOKEM_976SHAKE"
	default:
		return "KEX_ERR_UNK"
	}
}

func (hc *Conn) CAlg() CSCipherAlg {
	return CSCipherAlg(hc.cipheropts & 0x0FF)
}

func (c *CSCipherAlg) String() string {
	switch *c & 0x0FF {
	case CAlgAES256:
		return "C_AES_256"
	case CAlgTwofish128:
		return "C_TWOFISH_128"
	case CAlgBlowfish64:
		return "C_BLOWFISH_64"
	case CAlgCryptMT1:
		return "C_CRYPTMT1"
	case CAlgHopscotch:
		return "C_HOPSCOTCH"
	case CAlgChaCha20_12:
		return "C_CHACHA20_12"
	default:
		return "C_ERR_UNK"
	}
}

func (hc *Conn) HAlg() CSHmacAlg {
	return CSHmacAlg((hc.cipheropts >> 8) & 0x0FF)
}

func (h *CSHmacAlg) String() string {
	switch *h & 0x0FF {
	case HmacSHA256:
		return "H_SHA256"
	case HmacSHA512:
		return "H_SHA512"
	default:
		return "H_ERR_UNK"
	}
}

func _initLogging(d bool, c string, f logger.Priority) {
	if Log == nil {
		Log, _ = logger.New(f, fmt.Sprintf("%s:xsnet", c))
	}
	if d {
		log.SetFlags(0) // syslog will have date,time
		log.SetOutput(Log)
	} else {
		log.SetOutput(ioutil.Discard)
	}
}

func Init(d bool, c string, f logger.Priority) {
	_initLogging(d, c, f)
}

func (hc *Conn) Lock() {
	hc.m.Lock()
}

func (hc *Conn) Unlock() {
	hc.m.Unlock()
}

func (hc *Conn) KEX() KEXAlg {
	return hc.kex
}

func (hc *Conn) GetStatus() CSOType {
	return *hc.closeStat
}

func (hc *Conn) SetStatus(stat CSOType) {
	*hc.closeStat = stat
	log.Println("closeStat:", *hc.closeStat)
}

// ConnOpts returns the cipher/hmac options value, which is sent to the
// peer but is not itself part of the KEx.
//
// (Used for protocol-level negotiations after KEx such as
// cipher/HMAC algorithm options etc.)
func (hc *Conn) ConnOpts() uint32 {
	return hc.cipheropts
}

// SetConnOpts sets the cipher/hmac options value, which is sent to the
// peer as part of KEx but not part of the KEx itself.
//
// opts - bitfields for cipher and hmac alg. to use after KEx
func (hc *Conn) SetConnOpts(copts uint32) {
	hc.cipheropts = copts
}

// Opts returns the protocol options value, which is sent to the peer
// but is not itself part of the KEx or connection (cipher/hmac) setup.
//
// 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 {
	return hc.opts
}

// SetOpts sets the protocol options value, which is sent to the peer
// but is not itself part of the KEx or connection (cipher/hmac) setup.
//
// Consumers of this lib may use this for protocol-level options not part
// of the KEx of encryption info used by the connection.
//
// opts - a uint32, caller-defined
func (hc *Conn) SetOpts(opts uint32) {
	hc.opts = opts
}

// Return a new xsnet.Conn
//
// Note this is internal: use Dial() or Accept()
func _new(kexAlg KEXAlg, conn *net.Conn) (hc *Conn, e error) {
	// Set up stuff common to all KEx/KEM types
	hc = &Conn{kex: kexAlg,
		m:         &sync.Mutex{},
		c:         conn,
		closeStat: new(CSOType),
		WinCh:     make(chan WinSize, 1),
		dBuf:      new(bytes.Buffer)}
	tempMap := make(map[uint16]*TunEndpoint)
	hc.tuns = &tempMap

	// Set up KEx/KEM-specifics
	switch kexAlg {
	case KEX_HERRADURA256:
		fallthrough
	case KEX_HERRADURA512:
		fallthrough
	case KEX_HERRADURA1024:
		fallthrough
	case KEX_HERRADURA2048:
		fallthrough
	case KEX_KYBER512:
		fallthrough
	case KEX_KYBER768:
		fallthrough
	case KEX_KYBER1024:
		fallthrough
	case KEX_NEWHOPE:
		fallthrough
	case KEX_NEWHOPE_SIMPLE:
		fallthrough
	case KEX_FRODOKEM_1344AES:
		fallthrough
	case KEX_FRODOKEM_1344SHAKE:
		fallthrough
	case KEX_FRODOKEM_976AES:
		fallthrough
	case KEX_FRODOKEM_976SHAKE:
		//log.Printf("[KEx alg %d is valid]\n", kexAlg)
	default:
		// UNREACHABLE: _getkexalgnum() guarantees a valid KEX value
		hc.kex = KEX_HERRADURA512
		log.Printf("[KEx alg %d ?? defaults to %d]\n", kexAlg, hc.kex)
	}

	//hc.logCipherText = true // !!! DEBUGGING ONLY !!! NEVER DEPLOY this uncommented !!!
	return
}

// applyConnExtensions processes optional Dial() negotiation
// parameters. See also getkexalgnum().
//
// # Currently defined extension values
//
// # KEx algs
//
// KEX_HERRADURA256 KEX_HERRADURA512 KEX_HERRADURA1024 KEX_HERRADURA2048
//
// KEX_KYBER512 KEX_KYBER768 KEX_KYBER1024
//
// KEX_NEWHOPE KEX_NEWHOPE_SIMPLE
//
// # Session (symmetric) crypto
//
// C_AES_256 C_TWOFISH_128 C_BLOWFISH_128 C_CRYPTMT1 C_CHACHA20_12 C_HOPSCOTCH
//
// # Session HMACs
//
// H_SHA256 H_SHA512
func (hc *Conn) applyConnExtensions(extensions ...string) {
	for _, s := range extensions {
		switch s {
		case "C_AES_256":
			log.Println("[extension arg = C_AES_256]")
			hc.cipheropts &= (0xFFFFFF00)
			hc.cipheropts |= CAlgAES256
		case "C_TWOFISH_128":
			log.Println("[extension arg = C_TWOFISH_128]")
			hc.cipheropts &= (0xFFFFFF00)
			hc.cipheropts |= CAlgTwofish128
		case "C_BLOWFISH_64":
			log.Println("[extension arg = C_BLOWFISH_64]")
			hc.cipheropts &= (0xFFFFFF00)
			hc.cipheropts |= CAlgBlowfish64
		case "C_CRYPTMT1":
			log.Println("[extension arg = C_CRYPTMT1]")
			hc.cipheropts &= (0xFFFFFF00)
			hc.cipheropts |= CAlgCryptMT1
		case "C_HOPSCOTCH":
			log.Println("[extension arg = C_HOPSCOTCH]")
			hc.cipheropts &= (0xFFFFFF00)
			hc.cipheropts |= CAlgHopscotch
		case "C_CHACHA20_12":
			log.Println("[extension arg = C_CHACHA20_12]")
			hc.cipheropts &= (0xFFFFFF00)
			hc.cipheropts |= CAlgChaCha20_12
		case "H_SHA256":
			log.Println("[extension arg = H_SHA256]")
			hc.cipheropts &= (0xFFFF00FF)
			hc.cipheropts |= (HmacSHA256 << 8)
		case "H_SHA512":
			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)
		}
	}
}

func getkexalgnum(extensions ...string) (k KEXAlg) {
	k = KEX_HERRADURA512 // default
	for _, s := range extensions {
		switch s {
		case "KEX_HERRADURA256":
			k = KEX_HERRADURA256
			break //out of for
		case "KEX_HERRADURA512":
			k = KEX_HERRADURA512
			break //out of for
		case "KEX_HERRADURA1024":
			k = KEX_HERRADURA1024
			break //out of for
		case "KEX_HERRADURA2048":
			k = KEX_HERRADURA2048
			break //out of for
		case "KEX_KYBER512":
			k = KEX_KYBER512
			break //out of for
		case "KEX_KYBER768":
			k = KEX_KYBER768
			break //out of for
		case "KEX_KYBER1024":
			k = KEX_KYBER1024
			break //out of for
		case "KEX_NEWHOPE":
			k = KEX_NEWHOPE
			break //out of for
		case "KEX_NEWHOPE_SIMPLE":
			k = KEX_NEWHOPE_SIMPLE
			break //out of for
		case "KEX_FRODOKEM_1344AES":
			k = KEX_FRODOKEM_1344AES
			break //out of for
		case "KEX_FRODOKEM_1344SHAKE":
			k = KEX_FRODOKEM_1344SHAKE
			break //out of for
		case "KEX_FRODOKEM_976AES":
			k = KEX_FRODOKEM_976AES
			break //out of for
		case "KEX_FRODOKEM_976SHAKE":
			k = KEX_FRODOKEM_976SHAKE
			break //out of for
		}
	}
	return
}

func FrodoKEMDialSetup(c io.ReadWriter, hc *Conn) (err error) {
	// Send xsnet.Conn parameters to remote side

	// Alice, step 1: Generate a key pair.
	var kem frodo.FrodoKEM

	switch hc.kex {
	case KEX_FRODOKEM_1344AES:
		kem = frodo.Frodo1344AES()
	case KEX_FRODOKEM_1344SHAKE:
		kem = frodo.Frodo1344SHAKE()
	case KEX_FRODOKEM_976AES:
		kem = frodo.Frodo976AES()
	default:
		kem = frodo.Frodo976SHAKE()
	}
	pubA, secA := kem.Keygen() // pA

	// Alice, step 2: Send the public key (na,ea) to Bob
	n, err := fmt.Fprintf(c, "0x%x\n", pubA)
	if err != nil {
		panic(err)
	}
	if n < len(pubA) {
		panic(errors.New("incomplete Fprintf() of pubA"))
	}

	// (... and send cipher, connection opts)
	fmt.Fprintf(c, "0x%x:0x%x\n", hc.cipheropts, hc.opts)

	// [Bob does the same and sends use a public key (nb, eb)
	pubB_bigint := big.NewInt(0)
	_, err = fmt.Fscanf(c, "0x%x\n", pubB_bigint)
	pubB := pubB_bigint.Bytes()

	// (... and sends us cipher, connection opts)
	_, err = fmt.Fscanf(c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	if err != nil {
		return err
	}

	// Alice, step 3: Create ctAtoB, shareA
	ctAtoB, shareA, err := kem.Encapsulate(pubB)
	if err != nil {
		return err
	}

	// Alice, step 4: Send ctAtoB to Bob
	fmt.Fprintf(c, "0x%x\n", ctAtoB)

	// Alice, step 5: Receive ctBtoA from Bob
	ctBtoA_bigint := big.NewInt(0)
	_, err = fmt.Fscanf(c, "0x%x\n", ctBtoA_bigint)
	ctBtoA := ctBtoA_bigint.Bytes()

	// Alice, step 6: compute Bob's share
	shareB, err := kem.Dencapsulate(secA, ctBtoA)
	sessionKey := append(shareA, shareB...)

	hc.r, hc.rm, err = hc.getStream(sessionKey)
	hc.w, hc.wm, err = hc.getStream(sessionKey)
	return
}

func NewHopeDialSetup(c io.ReadWriter, hc *Conn) (err error) {
	// Send xsnet.Conn parameters to remote side

	// Alice, step 1: Generate a key pair.
	privKeyAlice, pubKeyAlice, err := newhope.GenerateKeyPairAlice(crand.Reader)
	if err != nil {
		panic(err)
	}

	// Alice, step 2: Send the public key to Bob
	fmt.Fprintf(c, "0x%x\n0x%x:0x%x\n", pubKeyAlice.Send,
		hc.cipheropts, hc.opts)

	// [Bob does step 1-3], from which we read Bob's pubkey
	publicKeyBob := big.NewInt(0)
	fmt.Fscanf(c, "0x%x\n", publicKeyBob)
	var pubKeyBob newhope.PublicKeyBob
	for i := range pubKeyBob.Send {
		pubKeyBob.Send[i] = publicKeyBob.Bytes()[i]
	}
	//log.Printf("[Got server pubKey[]:%v]\n", pubKeyBob)

	// Read cipheropts, session opts
	_, err = fmt.Fscanf(c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	if err != nil {
		return err
	}

	// Alice, step 3: Derive shared secret
	// (NOTE: actual over-wire exchange was already done above. This is
	//  the math voodoo 'exchange' done after receiving data from Bob.)
	aliceSharedSecret, err := newhope.KeyExchangeAlice(&pubKeyBob, privKeyAlice)
	if err != nil {
		panic(err)
	}

	hc.r, hc.rm, err = hc.getStream(aliceSharedSecret)
	hc.w, hc.wm, err = hc.getStream(aliceSharedSecret)
	return
}

func NewHopeSimpleDialSetup(c io.ReadWriter, hc *Conn) (err error) {
	// Send xsnet.Conn parameters to remote side

	// Alice, step 1: Generate a key pair.
	privKeyAlice, pubKeyAlice, err := newhope.GenerateKeyPairSimpleAlice(crand.Reader)
	if err != nil {
		panic(err)
	}

	// Alice, step 2: Send the public key to Bob
	fmt.Fprintf(c, "0x%x\n0x%x:0x%x\n", pubKeyAlice.Send,
		hc.cipheropts, hc.opts)

	// [Bob does step 1-3], from which we read Bob's pubkey
	publicKeyBob := big.NewInt(0)
	fmt.Fscanf(c, "0x%x\n", publicKeyBob)
	var pubKeyBob newhope.PublicKeySimpleBob
	for i := range pubKeyBob.Send {
		pubKeyBob.Send[i] = publicKeyBob.Bytes()[i]
	}
	//log.Printf("[Got server pubKey[]:%v]\n", pubKeyBob)

	// Read cipheropts, session opts
	_, err = fmt.Fscanf(c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	if err != nil {
		return err
	}

	// Alice, step 3: Derive shared secret
	// (NOTE: actual over-wire exchange was already done above. This is
	//  the math voodoo 'exchange' done after receiving data from Bob.)
	aliceSharedSecret, err := newhope.KeyExchangeSimpleAlice(&pubKeyBob, privKeyAlice)
	if err != nil {
		panic(err)
	}

	hc.r, hc.rm, err = hc.getStream(aliceSharedSecret)
	hc.w, hc.wm, err = hc.getStream(aliceSharedSecret)
	return
}

func KyberDialSetup(c io.ReadWriter /*net.Conn*/, hc *Conn) (err error) {
	// Send xsnet.Conn parameters to remote side

	// Alice, step 1: Generate a key pair.
	var alicePublicKey *kyber.PublicKey
	var alicePrivateKey *kyber.PrivateKey
	switch hc.kex {
	case KEX_KYBER512:
		alicePublicKey, alicePrivateKey, err = kyber.Kyber512.GenerateKeyPair(crand.Reader)
	case KEX_KYBER768:
		alicePublicKey, alicePrivateKey, err = kyber.Kyber768.GenerateKeyPair(crand.Reader)
	case KEX_KYBER1024:
		alicePublicKey, alicePrivateKey, err = kyber.Kyber1024.GenerateKeyPair(crand.Reader)
	default:
		alicePublicKey, alicePrivateKey, err = kyber.Kyber768.GenerateKeyPair(crand.Reader)
	}

	if err != nil {
		panic(err)
	}

	// Alice, step 2: Send the public key to Bob
	fmt.Fprintf(c, "0x%x\n0x%x:0x%x\n", alicePublicKey.Bytes(),
		hc.cipheropts, hc.opts)

	// [Bob, step 1-3], from which we read cipher text
	pubKeyB := make([]byte, 4096)
	fmt.Fscanf(c, "0x%x\n", &pubKeyB)
	//if err != nil {
	//	return err
	//}
	//log.Printf("[Got server pubKeyB[]:%v]\n", pubKeyB)

	// Read cipheropts, session opts
	_, err = fmt.Fscanf(c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	if err != nil {
		return err
	}

	// Alice, step 3: Decrypt the KEM cipher text.
	aliceSharedSecret := alicePrivateKey.KEMDecrypt(pubKeyB)

	hc.r, hc.rm, err = hc.getStream(aliceSharedSecret)
	hc.w, hc.wm, err = hc.getStream(aliceSharedSecret)
	return
}

func HKExDialSetup(c io.ReadWriter /*net.Conn*/, hc *Conn) (err error) {
	var h *hkex.HerraduraKEx
	switch hc.kex {
	case KEX_HERRADURA256:
		h = hkex.New(256, 64)
	case KEX_HERRADURA512:
		h = hkex.New(512, 128)
	case KEX_HERRADURA1024:
		h = hkex.New(1024, 256)
	case KEX_HERRADURA2048:
		h = hkex.New(2048, 512)
	default:
		h = hkex.New(256, 64)
	}

	// Send xsnet.Conn parameters to remote side
	// d is value for Herradura key exchange
	fmt.Fprintf(c, "0x%s\n0x%x:0x%x\n", h.D().Text(16),
		hc.cipheropts, hc.opts)

	// Read peer D over net.Conn (c)
	d := big.NewInt(0)
	_, err = fmt.Fscanln(c, d)
	if err != nil {
		return err
	}
	_, err = fmt.Fscanf(c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	if err != nil {
		return err
	}

	h.SetPeerD(d)
	log.Printf("** local D:%s\n", h.D().Text(16))
	log.Printf("**(c)** peer D:%s\n", h.PeerD().Text(16))
	h.ComputeFA()
	log.Printf("**(c)** FA:%s\n", h.FA())

	hc.r, hc.rm, err = hc.getStream(h.FA().Bytes())
	hc.w, hc.wm, err = hc.getStream(h.FA().Bytes())
	return
}

func FrodoKEMAcceptSetup(c *net.Conn, hc *Conn) (err error) {
	// Bob, step 1: Generate a key pair.
	var kem frodo.FrodoKEM

	switch hc.kex {
	case KEX_FRODOKEM_1344AES:
		kem = frodo.Frodo1344AES()
	case KEX_FRODOKEM_1344SHAKE:
		kem = frodo.Frodo1344SHAKE()
	case KEX_FRODOKEM_976AES:
		kem = frodo.Frodo976AES()
	default:
		kem = frodo.Frodo976SHAKE()
	}
	pubB, secB := kem.Keygen()

	// [Alice sends use a public key (na, ea)
	pubA_bigint := big.NewInt(0)
	_, err = fmt.Fscanf(*c, "0x%x\n", pubA_bigint)
	pubA := pubA_bigint.Bytes()

	// (... and sends us cipher, connection opts)
	_, err = fmt.Fscanf(*c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	if err != nil {
		return err
	}

	// Bob, step 2: Send the public key (nb,eb) to Alice
	n, err := fmt.Fprintf(*c, "0x%x\n", pubB)
	if err != nil {
		panic(err)
	}
	if n < len(pubB) {
		panic(errors.New("incomplete Fprintf() of pubB"))
	}

	// (... and send cipher, connection opts)
	fmt.Fprintf(*c, "0x%x:0x%x\n", hc.cipheropts, hc.opts)

	// Bob, step 3: Create ctBtoA, shareB
	ctBtoA, shareB, err := kem.Encapsulate(pubA)
	if err != nil {
		return err
	}

	// Bob, step 4: Send ctBtoA to Alice
	fmt.Fprintf(*c, "0x%x\n", ctBtoA)

	// Bob, step 5: Receive ctAtoB from Alice
	ctAtoB_bigint := big.NewInt(0)
	_, err = fmt.Fscanf(*c, "0x%x\n", ctAtoB_bigint)
	ctAtoB := ctAtoB_bigint.Bytes()

	// Alice, step 6: compute Bob's share
	shareA, err := kem.Dencapsulate(secB, ctAtoB)
	sessionKey := append(shareA, shareB...)

	hc.r, hc.rm, err = hc.getStream(sessionKey)
	hc.w, hc.wm, err = hc.getStream(sessionKey)
	return
}

func NewHopeAcceptSetup(c *net.Conn, hc *Conn) (err error) {
	// Bob, step 1: Deserialize Alice's public key from the binary encoding.
	alicePublicKey := big.NewInt(0)
	_, err = fmt.Fscanln(*c, alicePublicKey)
	//log.Printf("[Got client pubKey:0x%x\n]", alicePublicKey)
	if err != nil {
		return err
	}

	var pubKeyAlice newhope.PublicKeyAlice
	for i := range pubKeyAlice.Send {
		pubKeyAlice.Send[i] = alicePublicKey.Bytes()[i]
	}

	_, err = fmt.Fscanf(*c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	log.Printf("[Got cipheropts, opts:%v, %v]", hc.cipheropts, hc.opts)
	if err != nil {
		return err
	}

	// Bob, step 2: Generate the KEM cipher text and shared secret.
	pubKeyBob, bobSharedSecret, err := newhope.KeyExchangeBob(crand.Reader, &pubKeyAlice)
	if err != nil {
		panic(err)
	}

	// Bob, step 3: Send the cipher text to Alice.
	fmt.Fprintf(*c, "0x%x\n0x%x:0x%x\n", pubKeyBob.Send,
		hc.cipheropts, hc.opts)

	hc.r, hc.rm, err = hc.getStream(bobSharedSecret)
	hc.w, hc.wm, err = hc.getStream(bobSharedSecret)
	return
}

func NewHopeSimpleAcceptSetup(c *net.Conn, hc *Conn) (err error) {
	// Bob, step 1: Deserialize Alice's public key from the binary encoding.
	alicePublicKey := big.NewInt(0)
	_, err = fmt.Fscanln(*c, alicePublicKey)
	//log.Printf("[Got client pubKey:0x%x\n]", alicePublicKey)
	if err != nil {
		return err
	}

	var pubKeyAlice newhope.PublicKeySimpleAlice
	for i := range pubKeyAlice.Send {
		pubKeyAlice.Send[i] = alicePublicKey.Bytes()[i]
	}

	_, err = fmt.Fscanf(*c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	log.Printf("[Got cipheropts, opts:%v, %v]", hc.cipheropts, hc.opts)
	if err != nil {
		return err
	}

	// Bob, step 2: Generate the KEM cipher text and shared secret.
	pubKeyBob, bobSharedSecret, err := newhope.KeyExchangeSimpleBob(crand.Reader, &pubKeyAlice)
	if err != nil {
		panic(err)
	}

	// Bob, step 3: Send the cipher text to Alice.
	fmt.Fprintf(*c, "0x%x\n0x%x:0x%x\n", pubKeyBob.Send,
		hc.cipheropts, hc.opts)

	hc.r, hc.rm, err = hc.getStream(bobSharedSecret)
	hc.w, hc.wm, err = hc.getStream(bobSharedSecret)
	return
}

func KyberAcceptSetup(c *net.Conn, hc *Conn) (err error) {
	// Bob, step 1: Deserialize Alice's public key from the binary encoding.
	alicePublicKey := big.NewInt(0)
	_, err = fmt.Fscanln(*c, alicePublicKey)
	//log.Printf("[Got client pubKey:0x%x\n]", alicePublicKey)
	if err != nil {
		return err
	}
	_, err = fmt.Fscanf(*c, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	log.Printf("[Got cipheropts, opts:%v, %v]", hc.cipheropts, hc.opts)
	if err != nil {
		return err
	}

	var peerPublicKey *kyber.PublicKey
	switch hc.kex {
	case KEX_KYBER512:
		peerPublicKey, err = kyber.Kyber512.PublicKeyFromBytes(alicePublicKey.Bytes())
	case KEX_KYBER768:
		peerPublicKey, err = kyber.Kyber768.PublicKeyFromBytes(alicePublicKey.Bytes())
	case KEX_KYBER1024:
		peerPublicKey, err = kyber.Kyber1024.PublicKeyFromBytes(alicePublicKey.Bytes())
	default:
		peerPublicKey, err = kyber.Kyber768.PublicKeyFromBytes(alicePublicKey.Bytes())
	}

	if err != nil {
		panic(err)
	}

	// Bob, step 2: Generate the KEM cipher text and shared secret.
	cipherText, bobSharedSecret, err := peerPublicKey.KEMEncrypt(crand.Reader)
	if err != nil {
		panic(err)
	}

	// Bob, step 3: Send the cipher text to Alice.
	fmt.Fprintf(*c, "0x%x\n0x%x:0x%x\n", cipherText,
		hc.cipheropts, hc.opts)

	hc.r, hc.rm, err = hc.getStream(bobSharedSecret)
	hc.w, hc.wm, err = hc.getStream(bobSharedSecret)
	return
}

func HKExAcceptSetup(c *net.Conn, hc *Conn) (err error) {
	var h *hkex.HerraduraKEx
	switch hc.kex {
	case KEX_HERRADURA256:
		h = hkex.New(256, 64)
	case KEX_HERRADURA512:
		h = hkex.New(512, 128)
	case KEX_HERRADURA1024:
		h = hkex.New(1024, 256)
	case KEX_HERRADURA2048:
		h = hkex.New(2048, 512)
	default:
		h = hkex.New(256, 64)
	}

	// Read in xsnet.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, "0x%x:0x%x\n",
		&hc.cipheropts, &hc.opts)
	log.Printf("[Got cipheropts, opts:%v, %v]", hc.cipheropts, hc.opts)
	if err != nil {
		return err
	}
	h.SetPeerD(d)
	log.Printf("** D:%s\n", h.D().Text(16))
	log.Printf("**(s)** peerD:%s\n", h.PeerD().Text(16))
	h.ComputeFA()
	log.Printf("**(s)** FA:%s\n", h.FA())

	// Send D and cipheropts/conn_opts to peer
	fmt.Fprintf(*c, "0x%s\n0x%x:0x%x\n", h.D().Text(16),
		hc.cipheropts, hc.opts)

	hc.r, hc.rm, err = hc.getStream(h.FA().Bytes())
	hc.w, hc.wm, err = hc.getStream(h.FA().Bytes())
	return
}

// Dial as net.Dial(), but with implicit key exchange to set up secure
// channel on connect
//
//	Can be called like net.Dial(), defaulting to C_AES_256/H_SHA256,
//	or additional extensions can be passed amongst the following:
//
//	"C_AES_256" | "C_TWOFISH_128" | ...
//
//	"H_SHA256" | "H_SHA512" | ...
//
// See go doc -u xsnet.applyConnExtensions
func Dial(protocol string, ipport string, extensions ...string) (hc Conn, err error) {
	if Log == nil {
		Init(false, "client", logger.LOG_DAEMON|logger.LOG_DEBUG)
	}

	var c net.Conn
	if protocol == "kcp" {
		c, err = kcpDial(ipport, extensions)
		if err != nil {
			return Conn{}, err
		}
	} else {
		// Open raw Conn c
		c, err = net.Dial(protocol, ipport)
		if err != nil {
			return Conn{}, err
		}
	}
	// Init xsnet.Conn hc over net.Conn c
	ret, err := _new(getkexalgnum(extensions...), &c)
	if err != nil {
		return Conn{}, err
	}
	hc = *ret

	// Client has full control over Conn extensions. It's the server's
	// responsibility to accept or reject the proposed parameters.
	hc.applyConnExtensions(extensions...)

	// Perform Key Exchange according to client-request algorithm
	fmt.Fprintf(c, "%02x\n", hc.kex)
	switch hc.kex {
	case KEX_HERRADURA256:
		fallthrough
	case KEX_HERRADURA512:
		fallthrough
	case KEX_HERRADURA1024:
		fallthrough
	case KEX_HERRADURA2048:
		log.Printf("[Setting up for KEX_HERRADURA %d]\n", hc.kex)
		if HKExDialSetup(c, &hc) != nil {
			return Conn{}, nil
		}
	case KEX_KYBER512:
		fallthrough
	case KEX_KYBER768:
		fallthrough
	case KEX_KYBER1024:
		log.Printf("[Setting up for KEX_KYBER %d]\n", hc.kex)
		if KyberDialSetup(c, &hc) != nil {
			return Conn{}, nil
		}
	case KEX_NEWHOPE:
		log.Printf("[Setting up for KEX_NEWHOPE %d]\n", hc.kex)
		if NewHopeDialSetup(c, &hc) != nil {
			return Conn{}, nil
		}
	case KEX_NEWHOPE_SIMPLE:
		log.Printf("[Setting up for KEX_NEWHOPE_SIMPLE %d]\n", hc.kex)
		if NewHopeSimpleDialSetup(c, &hc) != nil {
			return Conn{}, nil
		}
	case KEX_FRODOKEM_1344AES:
		fallthrough
	case KEX_FRODOKEM_1344SHAKE:
		fallthrough
	case KEX_FRODOKEM_976AES:
		fallthrough
	case KEX_FRODOKEM_976SHAKE:
		log.Printf("[Setting up for KEX_FRODOKEM %d]\n", hc.kex)
		if FrodoKEMDialSetup(c, &hc) != nil {
			return Conn{}, nil
		}
	default:
		return Conn{}, err
	}
	return
}

// Close a hkex.Conn
func (hc *Conn) Close() (err error) {
	hc.ShutdownChaff()
	s := make([]byte, 4)
	binary.BigEndian.PutUint32(s, uint32(*hc.closeStat))
	log.Printf("** Writing closeStat %d at Close()\n", *hc.closeStat)
	//(*hc.c).SetWriteDeadline(time.Now().Add(500 * time.Millisecond))
	hc.WritePacket(s, CSOExitStatus)

	// HACK: Bug #22,#33: Need to wait for rcvr to get final data
	// TODO: Find a way to explicitly check if any outgoing data is pending

	//Ensure socket has sent all data to client prior to closing
	//NOTE: This is not ideal, as it would be better to somehow
	//determine if there is any pending outgoing (write) data to the
	//underlying socket (TCP/KCP) prior to closing; however Go's net pkg
	//completely hides lower-level stuff. net.Conn.Close() according to
	//docs sends written data in the background, so how best to determine
	//all data has been sent? -rlm 2022-10-04
	time.Sleep(10 * time.Millisecond) //nolint:gomnd

	err = (*hc.c).Close()
	logger.LogDebug(fmt.Sprintln("[Conn Closing]"))
	return
}

// LocalAddr returns the local network address.
func (hc *Conn) LocalAddr() net.Addr {
	return (*hc.c).LocalAddr()
}

// RemoteAddr returns the remote network address.
func (hc *Conn) RemoteAddr() net.Addr {
	return (*hc.c).RemoteAddr()
}

// SetDeadline sets the read and write deadlines associated
// with the connection. It is equivalent to calling both
// SetReadDeadline and SetWriteDeadline.
//
// A deadline is an absolute time after which I/O operations
// fail with a timeout (see type Error) instead of
// blocking. The deadline applies to all future and pending
// I/O, not just the immediately following call to Read or
// Write. After a deadline has been exceeded, the connection
// can be refreshed by setting a deadline in the future.
//
// An idle timeout can be implemented by repeatedly extending
// the deadline after successful Read or Write calls.
//
// A zero value for t means I/O operations will not time out.
func (hc *Conn) SetDeadline(t time.Time) error {
	return (*hc.c).SetDeadline(t)
}

// SetWriteDeadline sets the deadline for future Write calls
// and any currently-blocked Write call.
// Even if write times out, it may return n > 0, indicating that
// some of the data was successfully written.
// A zero value for t means Write will not time out.
func (hc *Conn) SetWriteDeadline(t time.Time) error {
	return (*hc.c).SetWriteDeadline(t)
}

// SetReadDeadline sets the deadline for future Read calls
// and any currently-blocked Read call.
// A zero value for t means Read will not time out.
func (hc *Conn) SetReadDeadline(t time.Time) error {
	return (*hc.c).SetReadDeadline(t)
}

/*---------------------------------------------------------------------*/

// HKExListener is a Listener conforming to net.Listener
//
// See go doc net.Listener
type HKExListener struct {
	l     net.Listener
	proto string
}

// Listen for a connection
//
// See go doc net.Listen
func Listen(proto string, ipport string, extensions ...string) (hl HKExListener, e error) {
	if Log == nil {
		Init(false, "server", logger.LOG_DAEMON|logger.LOG_DEBUG)
	}

	var lErr error
	var l net.Listener

	if proto == "kcp" {
		l, lErr = kcpListen(ipport, extensions)
	} else {
		l, lErr = net.Listen(proto, ipport)
	}
	if lErr != nil {
		return HKExListener{nil, proto}, lErr
	}
	logger.LogDebug(fmt.Sprintf("[Listening (proto '%s') on %s]\n", proto, ipport))
	hl.l = l
	hl.proto = proto
	return
}

// Close a hkex Listener - closes the Listener.
// Any blocked Accept operations will be unblocked and return errors.
//
// See go doc net.Listener.Close
func (hl HKExListener) Close() error {
	logger.LogDebug(fmt.Sprintln("[Listener Closed]"))
	return hl.l.Close()
}

// Addr returns the listener's network address.
//
// See go doc net.Listener.Addr
func (hl HKExListener) Addr() net.Addr {
	return hl.l.Addr()
}

// Accept a client connection, conforming to net.Listener.Accept()
//
// See go doc net.Listener.Accept
func (hl *HKExListener) Accept() (hc Conn, err error) {
	var c net.Conn
	if hl.proto == "kcp" {
		c, err = hl.AcceptKCP()
		if err != nil {
			return Conn{}, err
		}
		logger.LogDebug(fmt.Sprintln("[kcp.Listener Accepted]"))
	} else {
		// Open raw Conn c
		c, err = hl.l.Accept()
		if err != nil {
			return Conn{}, err
		}

		logger.LogDebug(fmt.Sprintf("[net.Listener Accepted %v]\n", c.RemoteAddr()))
	}
	// Read KEx alg proposed by client
	var kexAlg KEXAlg
	//! NB. Was using fmt.FScanln() here, but integers with a leading zero
	//  were being mis-scanned? (is it an octal thing? Investigate.)
	_, err = fmt.Fscanf(c, "%02x\n", &kexAlg)
	if err != nil {
		return Conn{}, err
	}
	log.Printf("[Client proposed KEx alg: %v]\n", kexAlg)
	// --

	ret, err := _new(kexAlg, &c)
	if err != nil {
		return Conn{}, err
	}
	hc = *ret

	switch hc.kex {
	case KEX_HERRADURA256:
		fallthrough
	case KEX_HERRADURA512:
		fallthrough
	case KEX_HERRADURA1024:
		fallthrough
	case KEX_HERRADURA2048:
		log.Printf("[Setting up for KEX_HERRADURA %d]\n", hc.kex)
		if HKExAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_KYBER512:
		fallthrough
	case KEX_KYBER768:
		fallthrough
	case KEX_KYBER1024:
		log.Printf("[Setting up for KEX_KYBER %d]\n", hc.kex)
		if KyberAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_NEWHOPE:
		log.Printf("[Setting up for KEX_NEWHOPE %d]\n", hc.kex)
		if NewHopeAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_NEWHOPE_SIMPLE:
		log.Printf("[Setting up for KEX_NEWHOPE_SIMPLE %d]\n", hc.kex)
		if NewHopeSimpleAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_FRODOKEM_1344AES:
		log.Printf("[Setting up for KEX_FRODOKEM_1344AES %d]\n", hc.kex)
		if FrodoKEMAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_FRODOKEM_1344SHAKE:
		log.Printf("[Setting up for KEX_FRODOKEM_1344SHAKE %d]\n", hc.kex)
		if FrodoKEMAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_FRODOKEM_976AES:
		log.Printf("[Setting up for KEX_FRODOKEM_976AES %d]\n", hc.kex)
		if FrodoKEMAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	case KEX_FRODOKEM_976SHAKE:
		log.Printf("[Setting up for KEX_FRODOKEM_976SHAKE %d]\n", hc.kex)
		if FrodoKEMAcceptSetup(&c, &hc) != nil {
			return Conn{}, err
		}
	default:
		return Conn{}, err
	}

	log.Println("[hc.Accept successful]")
	return hc, err
}

/*---------------------------------------------------------------------*/

// Read into a byte slice
//
// In addition to regular io.Reader behaviour this does demultiplexing of
// secured terminal comms and (if defined) tunnel traffic and session control
// packet processing.
//
// See go doc io.Reader
func (hc *Conn) Read(b []byte) (n int, err error) {
	for {
		if hc.dBuf.Len() > 0 {
			break
		}

		var ctrlStatOp uint8
		var hmacIn [HMAC_CHK_SZ]uint8
		var payloadLen uint32

		//------------- Read ctrl/status opcode --------------------
		// Read ctrl/status opcode (CSOHmacInvalid on hmac mismatch)
		err = binary.Read(*hc.c, binary.BigEndian, &ctrlStatOp)
		if err != nil {
			if err.Error() == "EOF" {
				return 0, io.EOF
			}
			if strings.HasSuffix(err.Error(), "use of closed network connection") {
				logger.LogDebug(fmt.Sprintln("[Client hung up(1)]"))
				//!rlm hc.SetStatus(CSENone) //FIXME: re-examine this (exit 9 w/o it - 2023-11-05)
				return 0, io.EOF
			}
			etxt := fmt.Sprintf("** Failed read:%s (%s) **", "ctrlStatOp", err)
			logger.LogDebug(etxt)
			return 0, errors.New(etxt)
		}
		log.Printf("[ctrlStatOp: %v]\n", ctrlStatOp)
		if ctrlStatOp == CSOHmacInvalid {
			// Other side indicated channel tampering, close channel
			hc.Close()
			return 0, errors.New("** ALERT - remote end detected HMAC mismatch - possible channel tampering **")
		}
		//----------------------------------------------------------

		//------------------ Read HMAC len  ------------------------
		// Read the hmac and payload len first
		err = binary.Read(*hc.c, binary.BigEndian, &hmacIn)
		if err != nil {
			if err.Error() == "EOF" {
				return 0, io.EOF
			}
			if strings.HasSuffix(err.Error(), "use of closed network connection") {
				logger.LogDebug(fmt.Sprintln("[Client hung up(2)]"))
				return 0, io.EOF
			}
			etxt := fmt.Sprintf("** Failed read:%s (%s) **", "HMAC", err)
			logger.LogDebug(etxt)
			return 0, errors.New(etxt)
		}
		//----------------------------------------------------------

		//------------------ Read Payload len  ---------------------
		err = binary.Read(*hc.c, binary.BigEndian, &payloadLen)
		if err != nil {
			if err.Error() == "EOF" {
				return 0, io.EOF
			}
			if strings.HasSuffix(err.Error(), "use of closed network connection") {
				logger.LogDebug(fmt.Sprintln("[Client hung up(3)]"))
				return 0, io.EOF
			}
			etxt := fmt.Sprintf("** Failed read:%s (%s) **", "payloadLen", err)
			logger.LogDebug(etxt)
			return 0, errors.New(etxt)
		}
		//----------------------------------------------------------

		if payloadLen > MAX_PAYLOAD_LEN {
			logger.LogDebug(fmt.Sprintf("[Insane payloadLen:%v]\n", payloadLen))
			hc.Close()
			return 1, errors.New("Insane payloadLen")
		}

		//-------------------- Read Payload ------------------------
		var payloadBytes = make([]byte, payloadLen)
		n, err = io.ReadFull(*hc.c, payloadBytes)
		if err != nil {
			if err.Error() == "EOF" {
				return 0, io.EOF
			}
			if strings.HasSuffix(err.Error(), "use of closed network connection") {
				logger.LogDebug(fmt.Sprintln("[Client hung up(4)]"))
				return 0, io.EOF
			}
			etxt := fmt.Sprintf("** Failed read:%s (%s) **", "payloadBytes", err)
			logger.LogDebug(etxt)
			return 0, errors.New(etxt)
		}
		//----------------------------------------------------------

		if hc.logCipherText {
			log.Printf("  <:ctext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))
		}
		//fmt.Printf("  <:ctext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))

		//---------------- Verify Payload via HMAC -----------------
		hc.rm.Write(payloadBytes) // Calc hmac on received data
		hTmp := hc.rm.Sum(nil)[0:HMAC_CHK_SZ]
		//log.Printf("<%04x) HMAC:(i)%s (c)%02x\r\n", decryptN, hex.EncodeToString([]byte(hmacIn[0:])), hTmp)

		// Log alert if hmac didn't match, corrupted channel
		if !bytes.Equal(hTmp, []byte(hmacIn[0:])) /*|| hmacIn[0] > 0xf8*/ {
			logger.LogDebug(fmt.Sprintln("** ALERT - detected HMAC mismatch, possible channel tampering **"))
			_, _ = (*hc.c).Write([]byte{CSOHmacInvalid})
		}
		//----------------------------------------------------------

		//------------------- Decrypt Payload ----------------------
		db := bytes.NewBuffer(payloadBytes[:n]) //copying payloadBytes to db
		// The StreamReader acts like a pipe, decrypting
		// whatever is available and forwarding the result
		// to the parameter of Read() as a normal io.Reader
		rs := &cipher.StreamReader{S: hc.r, R: db}
		// The caller isn't necessarily reading the full payload so we need
		// to decrypt to an intermediate buffer, draining it on demand of caller
		decryptN, err := rs.Read(payloadBytes)
		//----------------------------------------------------------

		if hc.logPlainText {
			log.Printf("  <:ptext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))
		}
		if err != nil {
			log.Println("xsnet.Read():", err)
			//panic(err)
		} else {
			//------------ Discard Padding ---------------------
			// Padding: Read padSide, padLen, (padding | d) or (d | padding)
			padSide := payloadBytes[0]
			padLen := payloadBytes[1]

			payloadBytes = payloadBytes[2:]
			if padSide == 0 {
				payloadBytes = payloadBytes[padLen:]
			} else {
				payloadBytes = payloadBytes[0 : len(payloadBytes)-int(padLen)]
			}
			//--------------------------------------------------

			switch ctrlStatOp {
			case CSOChaff:
				// Throw away pkt if it's chaff (ie., caller to Read() won't see this data)
				log.Printf("[Chaff pkt, discarded (len %d)]\n", decryptN)
			case CSOKeepAlive:
				//logger.LogDebug(fmt.Sprintf("[got keepAlive pkt, discarded (len %d)]\n", decryptN))
				// payload of keepalive (2 bytes) is not currently used (0x55aa fixed)
				_ = binary.BigEndian.Uint16(payloadBytes[0:2])
				hc.ResetKeepAlive()
			case CSORekey:
				// rekey
				//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)
				log.Printf("[TermSize pkt: rows %v cols %v]\n", hc.Rows, hc.Cols)
				hc.WinCh <- WinSize{hc.Rows, hc.Cols}
			case CSOExitStatus:
				if len(payloadBytes) > 0 {
					hc.SetStatus(CSOType(binary.BigEndian.Uint32(payloadBytes)))
				} else {
					logger.LogDebug(fmt.Sprintln("[truncated payload, cannot determine CSOExitStatus]"))
					hc.SetStatus(CSETruncCSO)
				}
				hc.Close()
			case CSOTunSetup:
				// server side tunnel setup in response to client
				lport := binary.BigEndian.Uint16(payloadBytes[0:2])
				rport := binary.BigEndian.Uint16(payloadBytes[2:4])
				if _, ok := (*hc.tuns)[rport]; !ok {
					// tunnel first-time open
					logger.LogDebug(fmt.Sprintf("[Server] Got Initial CSOTunSetup [%d:%d]", lport, rport))
					hc.StartServerTunnel(lport, rport)
				} else {
					logger.LogDebug(fmt.Sprintf("[Server] Got CSOTunSetup [%d:%d]", lport, rport))
				}
				(*hc.tuns)[rport].Ctl <- 'd' // Dial() rport
			case CSOTunSetupAck:
				lport := binary.BigEndian.Uint16(payloadBytes[0:2])
				rport := binary.BigEndian.Uint16(payloadBytes[2:4])
				if _, ok := (*hc.tuns)[rport]; !ok {
					// tunnel first-time open
					logger.LogDebug(fmt.Sprintf("[Client] Got Initial CSOTunSetupAck [%d:%d]", lport, rport))
					hc.StartClientTunnel(lport, rport)
				} else {
					logger.LogDebug(fmt.Sprintf("[Client] Got CSOTunSetupAck [%d:%d]", lport, rport))
				}
				(*hc.tuns)[rport].Ctl <- 'a' // Listen() for lport connection
			case CSOTunRefused:
				// client side receiving CSOTunRefused means the remote side
				// could not dial() rport. So we cannot yet listen()
				// for client-side on lport.
				lport := binary.BigEndian.Uint16(payloadBytes[0:2])
				rport := binary.BigEndian.Uint16(payloadBytes[2:4])
				logger.LogDebug(fmt.Sprintf("[Client] Got CSOTunRefused [%d:%d]", lport, rport))
				if _, ok := (*hc.tuns)[rport]; ok {
					hc.MarkTunDead(rport)
				} else {
					logger.LogDebug(fmt.Sprintf("[Client] CSOTunRefused on already-closed tun [%d:%d]", lport, rport))
				}
			case CSOTunDisconn:
				// server side's rport has disconnected (server lost)
				lport := binary.BigEndian.Uint16(payloadBytes[0:2])
				rport := binary.BigEndian.Uint16(payloadBytes[2:4])
				logger.LogDebug(fmt.Sprintf("[Client] Got CSOTunDisconn [%d:%d]", lport, rport))
				if _, ok := (*hc.tuns)[rport]; ok {
					hc.MarkTunDead(rport)
				} else {
					logger.LogDebug(fmt.Sprintf("[Client] CSOTunDisconn on already-closed tun [%d:%d]", lport, rport))
				}
			case CSOTunHangup:
				// client side's lport has hung up
				lport := binary.BigEndian.Uint16(payloadBytes[0:2])
				rport := binary.BigEndian.Uint16(payloadBytes[2:4])
				logger.LogDebug(fmt.Sprintf("[Server] Got CSOTunHangup [%d:%d]", lport, rport))
				if _, ok := (*hc.tuns)[rport]; ok {
					hc.MarkTunDead(rport)
				} else {
					logger.LogDebug(fmt.Sprintf("[Server] CSOTunHangup to already-closed tun [%d:%d]", lport, rport))
				}
			case CSOTunData:
				lport := binary.BigEndian.Uint16(payloadBytes[0:2])
				rport := binary.BigEndian.Uint16(payloadBytes[2:4])
				//fmt.Printf("[Got CSOTunData: [lport %d:rport %d] data:%v\n", lport, rport, payloadBytes[4:])
				if _, ok := (*hc.tuns)[rport]; ok {
					if hc.logTunActivity {
						logger.LogDebug(fmt.Sprintf("[Writing data to rport [%d:%d]", lport, rport))
					}
					(*hc.tuns)[rport].Data <- payloadBytes[4:]
					hc.ResetTunnelAge(rport)
				} else {
					logger.LogDebug(fmt.Sprintf("[Attempt to write data to closed tun [%d:%d]", lport, rport))
				}
			case CSOTunKeepAlive:
				// client side has sent keepalive for tunnels -- if client
				// dies or exits unexpectedly the absence of this will
				// let the server know to hang up on Dial()ed server rports.
				_ = binary.BigEndian.Uint16(payloadBytes[0:2])
				//logger.LogDebug(fmt.Sprintf("[Server] Got CSOTunKeepAlive"))
				// though CSOTunKeepAlive sends an endp (uint16), we don't use it,
				// preferring to refresh *all* tunnels on the message.
				// (?rlm 2023-11-04 -- TODO: verify this, it's been a while.)
				for _, t := range *hc.tuns {
					hc.Lock()
					t.KeepAlive = 0
					hc.Unlock()
				}
			case CSONone:
				hc.dBuf.Write(payloadBytes)
			default:
				logger.LogDebug(fmt.Sprintf("[Unknown CSOType:%d]", ctrlStatOp))
			}
		}
	}

	retN := hc.dBuf.Len()
	if retN > len(b) {
		retN = len(b)
	}

	log.Printf("Read() got %d bytes\n", retN)

	copy(b, hc.dBuf.Next(retN))
	return retN, nil
}

// Write a byte slice
//
// See go doc io.Writer
func (hc *Conn) Write(b []byte) (n int, err error) {
	//logger.LogDebug("[+Write]")
	n, err = hc.WritePacket(b, CSONone)
	//logger.LogDebug("[-Write]")
	return n, err
}

// Write a byte slice with specified ctrlStatOp byte
func (hc *Conn) WritePacket(b []byte, ctrlStatOp byte) (n int, err error) {
	hc.Lock()
	defer hc.Unlock()

	//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")
	}

	//Padding prior to encryption
	padSz := rand.Intn(PAD_SZ-1) + 1 /*(rand.Intn(PAD_SZ) / 2) + (PAD_SZ / 2)*/
	padLen := padSz - ((len(b) + padSz) % padSz)
	if padLen == padSz {
		// No padding required
		padLen = 0
	}

	padBytes := make([]byte, padLen)
	rand.Read(padBytes)
	// For a little more confusion let's support padding either before
	// or after the payload.
	padSide := rand.Intn(2)
	if padSide == 0 {
		b = append([]byte{byte(padSide)}, append([]byte{byte(padLen)}, append(padBytes, b...)...)...)
	} else {
		b = append([]byte{byte(padSide)}, append([]byte{byte(padLen)}, append(b, padBytes...)...)...)
	}

	payloadLen = uint32(len(b))
	if hc.logPlainText {
		log.Printf("  >:ptext:\r\n%s\r\n", hex.Dump(b[0:payloadLen]))
	}

	// NOTE releases prior to v0.9 used Authenticate-then-Encrypt,
	// which in block modes is insecure; however
	// 1) we use exclusively XOR-stream modes with random padding,
	// 2) are padding randomly either before or after the real payload, and
	// 3) the padding side indicator value itself is part of the ciphertext
	// ... thus are not subject to oracle attacks of the type used on SSL
	// (described in (Krawczyk 2001/2014,
	// https://link.springer.com/content/pdf/10.1007%2F3-540-44647-8_19.pdf)
	//
	// Nevertheless, to address any future concerns v0.9 onwards switches to
	// Encrypt-then-Auth and breaks interop with earlier versions.
	// -rlm 2020-12-15

	var wb bytes.Buffer
	// The StreamWriter acts like a pipe, forwarding whatever is
	// written to it through the cipher, encrypting as it goes
	ws := &cipher.StreamWriter{S: hc.w, W: &wb}
	wN, err := ws.Write(b[0:payloadLen])
	if err != nil {
		panic(err)
	}
	if wN < int(payloadLen) {
		panic("truncated Write to cipher *****")
	}

	if hc.logCipherText {
		log.Printf("  >:ctext:\r\n%s\r\n", hex.Dump(wb.Bytes()))
	}
	//fmt.Printf("  >:ctext:\r\n%s\r\n", hex.Dump(wb.Bytes()))

	// Calculate hmac on cipher payload
	hc.wm.Write(wb.Bytes())
	hmacOut = hc.wm.Sum(nil)[0:HMAC_CHK_SZ] //finalize
	//log.Printf("  (%08x> HMAC(o):%s\r\n", payloadLen, hex.EncodeToString(hmacOut))

	err = binary.Write(*hc.c, binary.BigEndian, &ctrlStatOp)
	if err == nil {
		// Write hmac LSB, payloadLen followed by payload
		err = binary.Write(*hc.c, binary.BigEndian, hmacOut)
		if err == nil {
			err = binary.Write(*hc.c, binary.BigEndian, payloadLen)
			if err == nil {
				n, err = (*hc.c).Write(wb.Bytes())
			} else {
				//fmt.Println("[c]WriteError!")
			}
		} else {
			//fmt.Println("[b]WriteError!")
		}
	} else {
		//fmt.Println("[a]WriteError!")
	}

	if err != nil {
		log.Println(err)
	}

	// We must 'lie' to caller indicating the length of THEIR
	// data written (ie., not including the padding and padding headers)
	retN := n - 2 - int(padLen)
	if retN <= 0 {
		retN = 0
	}
	return retN, err
}

func (hc *Conn) StartupChaff() {
	hc.chaff.shutdown = false
	log.Println("Chaffing ENABLED")
	hc.chaffHelper()
}

func (hc *Conn) ShutdownChaff() {
	hc.Lock()
	hc.chaff.shutdown = true
	hc.Unlock()
	log.Println("Chaffing SHUTDOWN")
}

func (hc *Conn) SetupChaff(msecsMin uint, msecsMax uint, szMax uint) {
	// 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
	}
	if hc.chaff.msecsMax > CHAFF_FREQ_MSECS_MAX {
		hc.chaff.msecsMax = CHAFF_FREQ_MSECS_MAX
	}
	hc.Unlock()

	hc.chaff.msecsMin = msecsMin //move these to params of chaffHelper() ?
	hc.chaff.msecsMax = msecsMax
	hc.chaff.szMax = szMax
}

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
	}
	if intervalSecs > REKEY_SECS_MAX {
		intervalSecs = REKEY_SECS_MAX
	}

	go func() {
		hc.Lock()
		hc.rekey = intervalSecs
		hc.Unlock()

		for {
			hc.Lock()
			rekey := hc.rekey
			hc.Unlock()

			if rekey != 0 {
				jitter := rand.Intn(int(rekey)) / 4
				rekey = rekey - uint(jitter)
				if rekey < 1 {
					rekey = 1
				}

				//logger.LogDebug(fmt.Sprintf("[rekeyHelper Loop]\n"))
				time.Sleep(time.Duration(rekey) * time.Second)

				// Send rekey to other end
				rekeyData := make([]byte, 64)
				_, err := crand.Read(rekeyData)
				//logger.LogDebug(fmt.Sprintf("[rekey [%02x %02x %02x ...]\n",
				//	rekeyData[0], rekeyData[1], rekeyData[2]))
				//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()
				if err != nil {
					log.Printf("[rekey WritePacket err! (%v) rekey dying ...]\n", err)
					return
				}
			} else {
				return
			}
		}
	}()
}

// Helper routine to spawn a chaffing goroutine for each Conn
func (hc *Conn) chaffHelper() {
	go func() {
		var nextDuration int
		for {
			//logger.LogDebug(fmt.Sprintf("[chaffHelper Loop]\n"))
			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)
				nextDuration = rand.Intn(int(hc.chaff.msecsMax)-min) + min
				_, _ = rand.Read(bufTmp)
				//logger.LogDebug("[+chaffHelper]")
				_, err := hc.WritePacket(bufTmp, CSOChaff)
				//logger.LogDebug("[-chaffHelper]")
				if err != nil {
					log.Println("[ *** error - chaffHelper shutting down *** ]")
					hc.Lock()
					hc.chaff.shutdown = true
					hc.Unlock()
					break
				}
			} else {
				log.Println("[ *** chaffHelper shutting down *** ]")
				break
			}
			time.Sleep(time.Duration(nextDuration) * time.Millisecond)
		}
	}()
}

func (hc *Conn) StartupKeepAlive() {
	hc.ResetKeepAlive()
	log.Println("KeepAlive ENABLED")
	hc.keepaliveHelper()
}

func (hc *Conn) ShutdownKeepAlive() {
	log.Println("Conn SHUTDOWN")
	hc.Close()
}

func (hc *Conn) ResetKeepAlive() {
	hc.Lock()
	hc.keepalive = 3
	hc.Unlock()
	log.Println("KeepAlive RESET")
}

// Helper routine to spawn a keepalive goroutine for each Conn
func (hc *Conn) keepaliveHelper() {
	go func() {
		for {
			nextDuration := 10000
			bufTmp := []byte{0x55, 0xaa}
			//logger.LogDebug("[+keepaliveHelper]")
			_, err := hc.WritePacket(bufTmp, CSOKeepAlive)
			//logger.LogDebug("[-keepaliveHelper]")
			//logger.LogDebug(fmt.Sprintf("[keepalive]\n"))
			if err != nil {
				logger.LogDebug(fmt.Sprintf("[ *** error - keepaliveHelper quitting *** ]\n"))
				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 {
			//	hc.keepalive = 0
			//}

			if hc.keepalive == 0 {
				logger.LogDebug(fmt.Sprintf("*** keepaliveHelper shutting down\n"))
				hc.SetStatus(CSEConnDead)
				hc.ShutdownKeepAlive()
				if hc.Pproc != 0 {
					//fmt.Printf("[pid %d needs to be killed]\n", hc.Pproc)
					syscall.Kill(hc.Pproc, syscall.SIGABRT) //nolint:errcheck
				}
				break
			}
		}
	}()
}