initial commit

stego.go

@@ -0,0 +1,116 @@
+// Copyright (C) 2018 Marius Schellenberger
+
+package main
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"image"
+	"image/color"
+	_ "image/gif"
+	_ "image/jpeg"
+	"image/png"
+	"os"
+)
+
+func unseal(p image.Image) (b []byte) {
+	rect := p.Bounds()
+	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)
+			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')
+				return
+			}
+			b = append(b, z)
+		}
+	}
+	return
+}
+
+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 {
+		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
+				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)
+			}
+		}
+	}
+	return n, nil
+}
+
+var (
+	inFile  string
+	outFile string
+	secret  string
+)
+
+func errf(err error) {
+	fmt.Fprintln(os.Stderr, err)
+	os.Exit(1)
+}
+
+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.Parse()
+	var (
+		err error
+		in  = os.Stdin
+		out = os.Stdout
+	)
+	if inFile != "-" {
+		in, err = os.Open(inFile)
+		if err != nil {
+			errf(err)
+		}
+	}
+	p, _, err := image.Decode(in)
+	if err != nil {
+		errf(err)
+	}
+	if secret != "" {
+		n, err := seal(p, []byte(secret))
+		if err != nil {
+			errf(err)
+		}
+		err = png.Encode(out, n)
+		if err != nil {
+			errf(err)
+		}
+		return
+	}
+	_, err = out.Write(unseal(p))
+	if err != nil {
+		errf(err)
+	}
+}