From 4d85236d16b0df486e75d3cca1cdf626b746b56d Mon Sep 17 00:00:00 2001
From: Russ Magee <rmagee@gmail.com>
Date: Wed, 2 May 2018 12:28:56 -0700
Subject: [PATCH] Chaffing slight improvements (rand size, timing). TODO: Move
 into hkexsh.Conn

---
 hkexnet.go       | 48 ++++++++++++++++++++++++++++++++++++++++++-
 hkexsh/hkexsh.go | 53 ++++++++----------------------------------------
 2 files changed, 56 insertions(+), 45 deletions(-)

diff --git a/hkexnet.go b/hkexnet.go
index f714ab7..faef277 100644
--- a/hkexnet.go
+++ b/hkexnet.go
@@ -25,6 +25,7 @@ import (
 	"math/big"
 	"net"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -391,7 +392,7 @@ func (c Conn) Read(b []byte) (n int, err error) {
 
 		// Throw away pkt if it's chaff (ie., caller to Read() won't see this data)
 		if ctrlStatOp == CSOChaff {
-			log.Printf("[Chaff pkt, discarded]\n")
+			log.Printf("[Chaff pkt, discarded (len %d)]\n", decryptN)
 		} else if ctrlStatOp == CSOTermSize {
 			fmt.Sscanf(string(payloadBytes), "%d %d", &c.Rows, &c.Cols)
 			log.Printf("[TermSize pkt: rows %v cols %v]\n", c.Rows, c.Cols)
@@ -478,3 +479,48 @@ func (c Conn) WritePacket(b []byte, op byte) (n int, err error) {
 	}
 	return
 }
+
+// hkexsh.Copy() is a modified version of io.Copy() with locking,
+// on a passed-in mutex, around the actual call to Write() to permit
+// multiple producers to write hkexsh buffers to the same destination.
+//
+// (Used to generate chaff during sessions)
+func Copy(m *sync.Mutex, dst io.Writer, src io.Reader) (written int64, err error) {
+	//	// If the reader has a WriteTo method, use it to do the copy.
+	//	// Avoids an allocation and a copy.
+	//	if wt, ok := src.(io.WriterTo); ok {
+	//		return wt.WriteTo(dst)
+	//	}
+	//	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
+	//	if rt, ok := dst.(io.ReaderFrom); ok {
+	//		return rt.ReadFrom(src)
+	//	}
+
+	buf := make([]byte, 32*1024)
+	for {
+		nr, er := src.Read(buf)
+		if nr > 0 {
+			m.Lock()
+			nw, ew := dst.Write(buf[0:nr])
+			m.Unlock()
+			if nw > 0 {
+				written += int64(nw)
+			}
+			if ew != nil {
+				err = ew
+				break
+			}
+			if nr != nw {
+				err = io.ErrShortWrite
+				break
+			}
+		}
+		if er != nil {
+			if er != io.EOF {
+				err = er
+			}
+			break
+		}
+	}
+	return written, err
+}
diff --git a/hkexsh/hkexsh.go b/hkexsh/hkexsh.go
index df0ff77..ec423be 100644
--- a/hkexsh/hkexsh.go
+++ b/hkexsh/hkexsh.go
@@ -13,6 +13,7 @@ import (
 	"io"
 	"io/ioutil"
 	"log"
+	"math/rand"
 	"os"
 	"os/exec"
 	"os/signal"
@@ -220,15 +221,19 @@ func main() {
 		ch <- syscall.SIGWINCH // Initial resize.
 
 		// client chaffing goroutine
+		// TODO: Consider making this a feature of hkexsh.Conn itself
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-
 			for {
 				m.Lock()
-				conn.WritePacket([]byte("CHAFF"), hkexsh.CSOChaff)
+				chaff := make([]byte, rand.Intn(512))
+				nextDurationMin := 1000 //ms
+				nextDuration := rand.Intn(5000-nextDurationMin) + nextDurationMin
+				_, _ = rand.Read(chaff)
+				conn.WritePacket(chaff, hkexsh.CSOChaff)
 				m.Unlock()
-				time.Sleep(10 * time.Millisecond)
+				time.Sleep(time.Duration(nextDuration) * time.Millisecond)
 			}
 		}()
 
@@ -241,7 +246,7 @@ func main() {
 			// exit with outerr == nil
 			//!_, outerr := io.Copy(conn, os.Stdin)
 			_, outerr := func(m *sync.Mutex, conn *hkexsh.Conn, r io.Reader) (w int64, e error) {
-				return safeCopy(m, conn, r)
+				return hkexsh.Copy(m, conn, r)
 			}(m, conn, os.Stdin)
 
 			if outerr != nil {
@@ -260,43 +265,3 @@ func main() {
 	// Wait until both stdin and stdout goroutines finish
 	wg.Wait()
 }
-
-func safeCopy(m *sync.Mutex, dst io.Writer, src io.Reader) (written int64, err error) {
-	//	// If the reader has a WriteTo method, use it to do the copy.
-	//	// Avoids an allocation and a copy.
-	//	if wt, ok := src.(io.WriterTo); ok {
-	//		return wt.WriteTo(dst)
-	//	}
-	//	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
-	//	if rt, ok := dst.(io.ReaderFrom); ok {
-	//		return rt.ReadFrom(src)
-	//	}
-
-	buf := make([]byte, 32*1024)
-	for {
-		nr, er := src.Read(buf)
-		if nr > 0 {
-			m.Lock()
-			nw, ew := dst.Write(buf[0:nr])
-			m.Unlock()
-			if nw > 0 {
-				written += int64(nw)
-			}
-			if ew != nil {
-				err = ew
-				break
-			}
-			if nr != nw {
-				err = io.ErrShortWrite
-				break
-			}
-		}
-		if er != nil {
-			if er != io.EOF {
-				err = er
-			}
-			break
-		}
-	}
-	return written, err
-}