added support for binary files

README.md

@@ -2,14 +2,20 @@
 
 Hides a string inside the least significant bit (LSB) of all colors of each pixel.
 
+## Build
+
+```
+go build -o stego stego.go
+```
+
 ## Hide
 
 ```
-./stego -in testdata/lenna.png -out testdata/stego.png -secret "hello world!"
+./stego -in testdata/lenna.png -secret testdata/lenna_256.png -out testdata/stego.png
 ```
 
 ## Reveal
 
 ```
-./stego -in testdata/stego.png
+./stego -in testdata/stego.png -out lenna_256.png
 ```

stego.go

@@ -3,6 +3,7 @@
 package main
 
 import (
+	"encoding/binary"
 	"errors"
 	"flag"
 	"fmt"
@@ -11,23 +12,49 @@ import (
 	_ "image/gif"
 	_ "image/jpeg"
 	"image/png"
+	"io/ioutil"
 	"os"
 )
 
+const offset = 4
+
+func encodeLen(l int) []byte {
+	b := make([]byte, offset)
+	binary.LittleEndian.PutUint32(b, uint32(l))
+	return b
+}
+
+func getLen(p image.Image) int {
+	z := make([]byte, offset)
+	for i := 0; i < offset; i++ {
+		pix := color.NRGBAModel.Convert(p.At(i, 0)).(color.NRGBA)
+		z[i] = (pix.R << 6)
+		z[i] |= (pix.G << 6) >> 2
+		z[i] |= (pix.B << 6) >> 4
+		z[i] |= (pix.A << 6) >> 6
+	}
+	return int(binary.LittleEndian.Uint32(z))
+}
+
 func unseal(p image.Image) (b []byte) {
 	rect := p.Bounds()
+	l := getLen(p)
+	c := 0
 	for i := 0; i < rect.Max.Y; i++ {
 		for j := 0; j < rect.Max.X; j++ {
+			if i == 0 && j == 0 {
+				j = offset
+			}
 			pix := color.NRGBAModel.Convert(p.At(j, i)).(color.NRGBA)
 			z := (pix.R << 6)
 			z |= (pix.G << 6) >> 2
 			z |= (pix.B << 6) >> 4
 			z |= (pix.A << 6) >> 6
-			if z == byte(0) {
-				b = append(b, '\n')
+			if c == l {
 				return
 			}
 			b = append(b, z)
+			c++
 		}
 	}
 	return
@@ -37,28 +64,22 @@ func seal(p image.Image, s []byte) (image.Image, error) {
 	rect := p.Bounds()
 	n := image.NewNRGBA(rect)
 	c := 0
-	max := (rect.Max.Y * rect.Max.X) - 1
-	if len(s) > max {
+	arr := append(encodeLen(len(s)), s...)
+	l := len(arr)
+	max := (rect.Max.Y * rect.Max.X)
+	if l > max {
 		return nil, errors.New("not enough space in image")
 	}
 	for i := 0; i < rect.Max.Y; i++ {
 		for j := 0; j < rect.Max.X; j++ {
 			pix := color.NRGBAModel.Convert(p.At(j, i)).(color.NRGBA)
-			if c < len(s) {
-				r := (pix.R &^ 3) | (s[c] >> 6)
-				g := (pix.G &^ 3) | (s[c]<<2)>>6
-				b := (pix.B &^ 3) | (s[c]<<4)>>6
-				a := (pix.A &^ 3) | (s[c]<<6)>>6
+			if c < l {
+				r := (pix.R &^ 3) | (arr[c] >> 6)
+				g := (pix.G &^ 3) | (arr[c]<<2)>>6
+				b := (pix.B &^ 3) | (arr[c]<<4)>>6
+				a := (pix.A &^ 3) | (arr[c]<<6)>>6
 				n.Set(j, i, color.NRGBA{r, g, b, a})
 				c++
-			} else if c == len(s) {
-				n.Set(j, i, color.NRGBA{
-					pix.R &^ 3,
-					pix.G &^ 3,
-					pix.B &^ 3,
-					pix.A &^ 3,
-				})
-				c++
 			} else {
 				n.Set(j, i, pix)
 			}
@@ -81,7 +102,7 @@ func errf(err error) {
 func main() {
 	flag.StringVar(&inFile, "in", "-", "input file (default: stdin)")
 	flag.StringVar(&outFile, "out", "-", "output file, always png (default: stdout)")
-	flag.StringVar(&secret, "secret", "", "secret to hide")
+	flag.StringVar(&secret, "secret", "", "secret file to hide")
 	flag.Parse()
 	var (
 		err error
@@ -94,12 +115,22 @@ func main() {
 			errf(err)
 		}
 	}
+	if outFile != "-" {
+		out, err = os.OpenFile(outFile, os.O_RDWR|os.O_CREATE, 0644)
+		if err != nil {
+			errf(err)
+		}
+	}
 	p, _, err := image.Decode(in)
 	if err != nil {
 		errf(err)
 	}
 	if secret != "" {
-		n, err := seal(p, []byte(secret))
+		b, err := ioutil.ReadFile(secret)
+		if err != nil {
+			errf(err)
+		}
+		n, err := seal(p, b)
 		if err != nil {
 			errf(err)
 		}