EXPERIMENT_ID: 003

Steganography Tool

CONCEPT

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

OBJECTIVE

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

CONSTRAINTS

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 main23import (4	"encoding/binary"5	"fmt"6	"image"7	"image/color"8	"image/png"9	"os"10)1112func 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...)1617	idx := 018	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 nil22			}23			c := img.NRGBAAt(x, y)24			bytePos, bitPos := idx/8, uint(7-idx%8)25			bit := (bits[bytePos] >> bitPos) & 126			c.R = (c.R & 0xFE) | bit27			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}3334func main() {35	f, _ := os.Open("cover.png")36	defer f.Close()37	src, _ := png.Decode(f)3839	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	}4546	_ = embed(dst, []byte("HIDDEN_MESSAGE"))4748	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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