معرف التجربة: 003

Steganography Tool

CONCEPT

LSB (Least Significant Bit) image steganography in Go. Embeds a length-prefixed payload into the red channel of PNG pixels.

الهدف

Implement a covert channel by modifying the least significant bits of image pixel data, then verify extraction round-trips cleanly.

القيود

Payload size limited to (width × height) / 8 bytes. Not robust against JPEG re-encoding or image resizing.

Go Cryptography Image Processing

src/main.go

1package main
2
3import (
4	"encoding/binary"
5	"fmt"
6	"image"
7	"image/color"
8	"image/png"
9	"os"
10)
11
12func embed(img *image.NRGBA, payload []byte) error {
13	header := make([]byte, 4)
14	binary.BigEndian.PutUint32(header, uint32(len(payload)))
15	bits := append(header, payload...)
16
17	idx := 0
18	for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
19		for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
20			if idx >= len(bits)*8 {
21				return nil
22			}
23			c := img.NRGBAAt(x, y)
24			bytePos, bitPos := idx/8, uint(7-idx%8)
25			bit := (bits[bytePos] >> bitPos) & 1
26			c.R = (c.R & 0xFE) | bit
27			img.SetNRGBA(x, y, color.NRGBA{R: c.R, G: c.G, B: c.B, A: c.A})
28			idx++
29		}
30	}
31	return fmt.Errorf("image too small for payload")
32}
33
34func main() {
35	f, _ := os.Open("cover.png")
36	defer f.Close()
37	src, _ := png.Decode(f)
38
39	dst := image.NewNRGBA(src.Bounds())
40	for y := dst.Bounds().Min.Y; y < dst.Bounds().Max.Y; y++ {
41		for x := dst.Bounds().Min.X; x < dst.Bounds().Max.X; x++ {
42			dst.Set(x, y, src.At(x, y))
43		}
44	}
45
46	_ = embed(dst, []byte("CLASSIFIED_PAYLOAD"))
47
48	out, _ := os.Create("stego.png")
49	defer out.Close()
50	png.Encode(out, dst)
51	fmt.Println("Done — payload embedded into stego.png")
52}

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