The go language implementation writes important data to images
- 2020-05-30 20:19:34
- OfStack
Principle: the binary form of data is written to the low end of the binary data in the image red channel
Only output in png format is supported
Write data
go run shadow.go -in="c.jpg" -data="hide me" -out="out.png"
Read the data
go run shadow.go -in="out.png"
package main
import (
"errors"
"flag"
"fmt"
"image"
"image/color"
_ "image/jpeg"
"image/png"
"log"
"math"
"os"
)
var FLAG = [4]byte{0x13, 0x14, 0x52, 0x00} //shadow flag.
//byte to 8 bits
func Byte2bits(b byte) (a [8]byte) {
var c uint8 = 7
var i uint8
for i = 0; i < 8; i++ {
a[i] = b >> (c - i) & 1
}
return
}
//8 bits to byte.
func Bits2Byte(a [8]byte) (b byte) {
for i := 0; i < 8; i++ {
b += a[i] * uint8(math.Pow(2, float64(7-i)))
}
return
}
//uint32 to 4 bytes.
func Uint32ToBytes(i uint32) (b [4]byte) {
b[0] = uint8(i >> 24)
b[1] = uint8(i >> 16 & 0xffff)
b[2] = uint8(i >> 8 & 0xff)
b[3] = uint8(i & 0xff)
return
}
//4 bytes to uint32.
func Bytes2Uint32(b [4]byte) (i uint32) {
var j uint32
for ; j < 4; j++ {
i += uint32(b[j]) << (24 - j*8)
}
return
}
func BuildShadowHeader(length uint32) (b [8]byte) {
var i int
for ; i < 4; i++ {
b[i] = FLAG[i]
}
a := Uint32ToBytes(length)
for ; i < 8; i++ {
b[i] = a[i-4]
}
return
}
func WriteShadow(b []byte, im image.Image) (out image.Image, err error) {
max := im.Bounds().Max.X*im.Bounds().Max.Y/8 - 64
b_len := len(b)
if len(b) > max {
return nil, errors.New("image does not have enough space for shadow.")
}
head := BuildShadowHeader(uint32(b_len))
var bb byte
var bs [8]byte
var i int
out, err = SetImage(im, func(index, x, y int, in, out image.Image) {
rgba := readRGBAColor(im.At(x, y))
if index < b_len*8+64 {
if index < 64 {
bb = head[index/8]
} else {
bb = b[index/8-8]
}
bs = Byte2bits(bb)
i = index % 8
if bs[i] != rgba.R&1 {
if bs[i] == 0 {
rgba.R -= 1
} else {
rgba.R += 1
}
}
}
if v := out.(*image.RGBA); v != nil {
v.SetRGBA(x, y, rgba)
}
})
if err != nil {
return nil, err
}
return
}
func ReadShadowData(im image.Image) (b []byte, err error) {
head, err := ReadShadowHeader(im)
if err != nil {
return nil, err
}
length := int(ReadShadowLength(head))
var bk []byte = make([]byte, length*8)
b = make([]byte, length)
_, err = SetImage(im, func(index, x, y int, in, out image.Image) {
if index >= 64 && index < length*8+64 {
R := readRGBAColor(im.At(x, y)).R
bk[index-64] = uint8(R & 1)
}
})
var bb [8]byte
var bs []byte
for i := 0; i < length; i++ {
bs = bk[8*i : 8*(i+1)]
for j := 0; j < 8; j++ {
bb[j] = bs[j]
}
b[i] = Bits2Byte(bb)
}
return
}
func ReadShadowHeader(im image.Image) (b [8]byte, err error) {
var bm [64]byte
_, err = SetImage(im, func(index, x, y int, in, out image.Image) {
rgba := readRGBAColor(im.At(x, y))
if index < 64 {
bm[index] = uint8(rgba.R & 1)
}
})
if err != nil {
return
}
var bb [8]byte
var bs []byte
for i := 0; i < 8; i++ {
bs = bm[8*i : 8*(i+1)]
for j := 0; j < 8; j++ {
bb[j] = bs[j]
}
b[i] = Bits2Byte(bb)
}
return
}
func ReadShadowFlag(b [8]byte) (a [4]byte) {
for i := 0; i < 4; i++ {
a[i] = b[i]
}
return
}
func ReadShadowLength(b [8]byte) uint32 {
var bb [4]byte
for i := 4; i < 8; i++ {
bb[i-4] = b[i]
}
return Bytes2Uint32(bb)
}
func OpenImage(path string) (image.Image, error) {
im_read, err := os.Open(path)
defer im_read.Close()
if err != nil {
return nil, err
}
im, _, err := image.Decode(im_read)
if err != nil {
return nil, err
}
return im, nil
}
//modify image
func SetImage(im image.Image, f func(index, x, y int, in, out image.Image)) (out image.Image, err error) {
if f == nil {
return im, nil
}
index := 0
bounds := im.Bounds()
out = image.NewRGBA(bounds)
var m *image.RGBA = out.(*image.RGBA)
for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
for x := bounds.Min.X; x < bounds.Max.X; x++ {
m.Set(x, y, im.At(x, y))
f(index, x, y, im, out)
index += 1
}
}
return out, nil
}
//conert any color to RABGA color.
func readRGBAColor(from_color color.Color) color.RGBA {
return color.RGBAModel.Convert(from_color).(color.RGBA)
}
//only write to jpeg formats.
func WriteImage(path string, im image.Image) error {
out, err := os.OpenFile(path, os.O_CREATE, os.ModePerm)
defer out.Close()
if err != nil {
return err
}
err = png.Encode(out, im)
if err != nil {
return err
}
return nil
}
var read_in string
var write_out string
var data string
func init() {
flag.StringVar(&read_in, "in", "", "image path read in.")
flag.StringVar(&write_out, "out", "out.jpg", "image path write out.")
flag.StringVar(&data, "data", "", "data to shadow.")
}
func errHandle(err error) {
if err != nil {
log.Fatal(err)
}
}
func main() {
flag.Parse()
if read_in == "" {
fmt.Println("Options:")
flag.PrintDefaults()
return
}
im, err := OpenImage(read_in)
errHandle(err)
if data != "" {
out, err := WriteShadow([]byte(data), im)
errHandle(err)
err = WriteImage(write_out, out)
errHandle(err)
} else {
head, err := ReadShadowHeader(im)
errHandle(err)
_flag := ReadShadowFlag(head)
if _flag != FLAG {
fmt.Println("image doesn't have shadow data.")
return
}
data, err := ReadShadowData(im)
errHandle(err)
fmt.Println("shadow:", string(data))
}
}
That's all for this article, I hope you enjoy it.