xs/hkexnet/hkexnet.go

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// hkexnet.go - net.Conn compatible channel setup with encrypted/HMAC
// negotiation
// Copyright (c) 2017-2018 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)
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package hkexnet
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// TODO:
// If key exchange algs other than the experimental HerraduraKEx are to
// be supported, the Dial() and Accept() methods should take a kex param,
// specifying which to use; and the client/server negotiation must then
// prefix the channel setup with this param over the wire in order to decide
// which is in use.
//
// 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).
// Implementation of HKEx-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).
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import (
"bytes"
"crypto/cipher"
"encoding/binary"
"encoding/hex"
"errors"
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"fmt"
"hash"
"io"
"log"
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"math/big"
"math/rand"
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"net"
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"strings"
"sync"
"time"
"blitter.com/go/hkexsh/herradurakex"
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)
// KEx type - sent from client to server in order to specify which
// algo shall be used (eg., HerraduraKEx, [TODO: others...])
type KEX uint8
const (
KEX_HERRADURA = iota // this MUST be first for default if omitted in ctor
KEX_FOO
//KEX_DH
//KEX_ETC
)
// const CSExtendedCode - extended (>255 UNIX exit status) codes
// This indicate channel-related or internal errors
const (
CSEBadAuth = 1024 // Failed login password
CSETruncCSO // No CSOExitStatus in payload
CSEStillOpen // Channel closed unexpectedly
CSEExecFail // cmd.Start() (exec) failed
CSEPtyExecFail // pty.Start() (exec w/pty) failed
)
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
CSOChaff // Dummy packet, do not pass beyond decryption
)
const MAX_PAYLOAD_LEN = 4*1024*1024*1024 - 1
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/*---------------------------------------------------------------------*/
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type (
WinSize struct {
Rows uint16
Cols uint16
}
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// 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
enabled bool
msecsMin uint //msecs min interval
msecsMax uint //msecs max interval
szMax uint // max size in bytes
}
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// Conn is a HKex connection - a superset of net.Conn
Conn struct {
kex KEX // KEX alg (typedef uint8)
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m *sync.Mutex
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)
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WinCh chan WinSize
Rows uint16
Cols uint16
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chaff ChaffConfig
closeStat *uint32 // close status (CSOExitStatus)
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r cipher.Stream //read cipherStream
rm hash.Hash
w cipher.Stream //write cipherStream
wm hash.Hash
dBuf *bytes.Buffer //decrypt buffer for Read()
}
)
func (hc Conn) GetStatus() uint32 {
return *hc.closeStat
}
func (hc *Conn) SetStatus(stat uint32) {
*hc.closeStat = stat
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//fmt.Println("closeStat:", *hc.closeStat)
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
}
func (hc *Conn) applyConnExtensions(extensions ...string) {
for _, s := range extensions {
switch s {
case "KEX_HERRADURA":
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 "C_AES_256":
log.Println("[extension arg = C_AES_256]")
hc.cipheropts &= (0xFFFFFF00)
hc.cipheropts |= CAlgAES256
break
case "C_TWOFISH_128":
log.Println("[extension arg = C_TWOFISH_128]")
hc.cipheropts &= (0xFFFFFF00)
hc.cipheropts |= CAlgTwofish128
break
case "C_BLOWFISH_64":
log.Println("[extension arg = C_BLOWFISH_64]")
hc.cipheropts &= (0xFFFFFF00)
hc.cipheropts |= CAlgBlowfish64
break
case "H_SHA256":
log.Println("[extension arg = H_SHA256]")
hc.cipheropts &= (0xFFFF00FF)
hc.cipheropts |= (HmacSHA256 << 8)
break
default:
log.Printf("[Dial ext \"%s\" ignored]\n", s)
break
}
}
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}
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
//
// Can be called like net.Dial(), defaulting to C_AES_256/H_SHA256,
// or additional option arguments can be passed amongst the following:
//
// "C_AES_256" | "C_TWOFISH_128"
//
// "H_SHA256"
func Dial(protocol string, ipport string, extensions ...string) (hc *Conn, err error) {
// Open raw Conn c
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c, err := net.Dial(protocol, ipport)
if err != nil {
return nil, err
}
// Init hkexnet.Conn hc over net.Conn c
// NOTE: kex default of KEX_HERRADURA may be overridden by
// future extension args to applyConnExtensions(), which is
// called prior to Dial()
hc = &Conn{m: &sync.Mutex{}, c: c, closeStat: new(uint32), h: hkex.New(0, 0), dBuf: new(bytes.Buffer)}
hc.applyConnExtensions(extensions...)
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// TODO: Factor out ALL params following this to helpers for
// specific KEx algs
fmt.Fprintf(c, "%02x\n", hc.kex)
// --
*hc.closeStat = CSEStillOpen // open or prematurely-closed status
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// 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")
}
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return
}
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// Close a hkex.Conn
func (hc *Conn) Close() (err error) {
hc.DisableChaff()
s := make([]byte, 4)
binary.BigEndian.PutUint32(s, *hc.closeStat)
hc.WritePacket(s, CSOExitStatus)
err = hc.c.Close()
log.Println("[Conn Closing]")
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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)
}
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/*---------------------------------------------------------------------*/
// HKExListener is a Listener conforming to net.Listener
//
// See go doc net.Listener
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type HKExListener struct {
l net.Listener
}
// Listen for a connection
//
// See go doc net.Listen
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func Listen(protocol string, ipport string) (hl HKExListener, e error) {
l, err := net.Listen(protocol, ipport)
if err != nil {
return HKExListener{nil}, err
}
log.Println("[Listening]")
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hl.l = l
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 {
log.Println("[Listener Closed]")
return hl.l.Close()
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}
// Addr returns a the listener's network address.
//
// See go doc net.Listener.Addr
func (hl HKExListener) Addr() net.Addr {
return hl.l.Addr()
}
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// Accept a client connection, conforming to net.Listener.Accept()
//
// See go doc net.Listener.Accept
func (hl *HKExListener) Accept() (hc Conn, err error) {
// Open raw Conn c
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c, err := hl.l.Accept()
if err != nil {
hc := Conn{m: &sync.Mutex{}, c: nil, h: nil, closeStat: new(uint32), cipheropts: 0, opts: 0,
r: nil, w: nil}
return hc, err
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}
log.Println("[Accepted]")
hc = Conn{ /*kex: from client,*/ m: &sync.Mutex{}, c: c, h: hkex.New(0, 0), closeStat: new(uint32), WinCh: make(chan WinSize, 1),
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dBuf: new(bytes.Buffer)}
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// TODO: Factor out ALL params following this to helpers for
// specific KEx algs
var kexAlg uint8
_, err = fmt.Fscanln(c, &kexAlg)
if err != nil {
return hc, err
}
log.Printf("[Client proposed KEx alg: %v]\n", kexAlg)
// --
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")
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}
return
}
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/*---------------------------------------------------------------------*/
// Read into a byte slice
//
// See go doc io.Reader
func (hc Conn) Read(b []byte) (n int, err error) {
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//log.Printf("[Decrypting...]\r\n")
for {
//log.Printf("hc.dBuf.Len(): %d\n", hc.dBuf.Len())
if hc.dBuf.Len() > 0 /* len(b) */ {
break
}
var ctrlStatOp uint8
var hmacIn [4]uint8
var payloadLen uint32
// Read ctrl/status opcode (CSOHmacInvalid on hmac mismatch)
err = binary.Read(hc.c, binary.BigEndian, &ctrlStatOp)
log.Printf("[ctrlStatOp: %v]\n", ctrlStatOp)
if ctrlStatOp == CSOHmacInvalid {
// Other side indicated channel tampering, close channel
hc.Close()
return 1, errors.New("** ALERT - remote end detected HMAC mismatch - possible channel tampering **")
}
// Read the hmac and payload len first
err = binary.Read(hc.c, binary.BigEndian, &hmacIn)
// Normal client 'exit' from interactive session will cause
// (on server side) err.Error() == "<iface/addr info ...>: use of closed network connection"
if err != nil {
if !strings.HasSuffix(err.Error(), "use of closed network connection") {
//fmt.Println("[1]unexpected Read() err:", err)
log.Println("[1]unexpected Read() err:", err)
} else {
//fmt.Println("[Client hung up]")
log.Println("[Client hung up]")
}
return 0, err
}
err = binary.Read(hc.c, binary.BigEndian, &payloadLen)
if err != nil {
if err.Error() != "EOF" {
log.Println("[2]unexpected Read() err:", err)
}
}
if payloadLen > MAX_PAYLOAD_LEN {
log.Printf("[Insane payloadLen:%v]\n", payloadLen)
hc.Close()
return 1, errors.New("Insane payloadLen")
}
var payloadBytes = make([]byte, payloadLen)
n, err = io.ReadFull(hc.c, payloadBytes)
// Normal client 'exit' from interactive session will cause
// (on server side) err.Error() == "<iface/addr info ...>: use of closed network connection"
if err != nil && err.Error() != "EOF" {
if !strings.HasSuffix(err.Error(), "use of closed network connection") {
log.Println("[3]unexpected Read() err:", err)
} else {
log.Println("[Client hung up]")
}
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}
log.Printf(" <:ctext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))
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 ot an intermediate buffer, draining it on demand of caller
decryptN, err := rs.Read(payloadBytes)
log.Printf(" <-ptext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))
if err != nil {
//fmt.Print(err)
//panic(err)
} else {
// Throw away pkt if it's chaff (ie., caller to Read() won't see this data)
if ctrlStatOp == CSOChaff {
log.Printf("[Chaff pkt, discarded (len %d)]\n", decryptN)
} else if ctrlStatOp == 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}
} else if ctrlStatOp == CSOExitStatus {
if len(payloadBytes) > 0 {
hc.SetStatus(binary.BigEndian.Uint32(payloadBytes))
//!// If remote end is closing with an error, reply we're closing ours
//!if hc.GetStatus() != 0 {
//! log.Print("CSOExitStatus:", hc.GetStatus())
hc.Close()
//!}
} else {
log.Println("[truncated payload, cannot determine CSOExitStatus]")
*hc.closeStat = CSETruncCSO
}
} else {
hc.dBuf.Write(payloadBytes)
//log.Printf("hc.dBuf: %s\n", hex.Dump(hc.dBuf.Bytes()))
}
// Re-calculate hmac, compare with received value
hc.rm.Write(payloadBytes)
hTmp := hc.rm.Sum(nil)[0:4]
log.Printf("<%04x) HMAC:(i)%s (c)%02x\r\n", decryptN, hex.EncodeToString([]byte(hmacIn[0:])), hTmp)
if *hc.closeStat == CSETruncCSO {
log.Println("[cannot verify HMAC]")
} else {
// Log alert if hmac didn't match, corrupted channel
if !bytes.Equal(hTmp, []byte(hmacIn[0:])) /*|| hmacIn[0] > 0xf8*/ {
fmt.Println("** ALERT - detected HMAC mismatch, possible channel tampering **")
_, _ = hc.c.Write([]byte{CSOHmacInvalid})
}
}
}
}
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
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}
// Write a byte slice
//
// See go doc io.Writer
func (hc Conn) Write(b []byte) (n int, err error) {
n, err = hc.WritePacket(b, CSONone)
return n, err
}
// Write a byte slice with specified ctrlStatusOp byte
func (hc *Conn) WritePacket(b []byte, op byte) (n int, err error) {
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//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
// struct that must be protected to serialize main and
// chaff data written to it.
//
// Would be nice to determine if the mutex scope
// could be tightened.
hc.m.Lock()
//fmt.Printf("--== TOTAL payloadLen (b):%d\n", len(b))
payloadLen = uint32(len(b))
//!fmt.Printf(" --== payloadLen:%d\n", payloadLen)
log.Printf(" :>ptext:\r\n%s\r\n", hex.Dump(b[0:payloadLen]))
// Calculate hmac on payload
hc.wm.Write(b[0:payloadLen])
hmacOut = hc.wm.Sum(nil)[0:4]
log.Printf(" (%04x> HMAC(o):%s\r\n", payloadLen, hex.EncodeToString(hmacOut))
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}
_, err = ws.Write(b[0:payloadLen])
if err != nil {
panic(err)
}
log.Printf(" ->ctext:\r\n%s\r\n", hex.Dump(wb.Bytes()))
ctrlStatOp := op
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!")
}
hc.m.Unlock()
if err != nil {
log.Println(err)
}
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return
}
func (hc *Conn) EnableChaff() {
hc.chaff.shutdown = false
hc.chaff.enabled = true
log.Println("Chaffing ENABLED")
hc.chaffHelper()
}
func (hc *Conn) DisableChaff() {
hc.chaff.enabled = false
log.Println("Chaffing DISABLED")
}
func (hc *Conn) ShutdownChaff() {
hc.chaff.shutdown = true
log.Println("Chaffing SHUTDOWN")
}
func (hc *Conn) SetupChaff(msecsMin uint, msecsMax uint, szMax uint) {
hc.chaff.msecsMin = msecsMin //move these to params of chaffHelper() ?
hc.chaff.msecsMax = msecsMax
hc.chaff.szMax = szMax
}
// Helper routine to spawn a chaffing goroutine for each Conn
func (hc *Conn) chaffHelper() {
go func() {
for {
var nextDuration int
if hc.chaff.enabled {
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)
_, err := hc.WritePacket(bufTmp, CSOChaff)
if err != nil {
log.Println("[ *** error - chaffHelper quitting *** ]")
hc.chaff.enabled = false
break
}
}
time.Sleep(time.Duration(nextDuration) * time.Millisecond)
if hc.chaff.shutdown {
log.Println("*** chaffHelper shutting down")
break
}
}
}()
}