c - 如何将 LSB 提取的数据转换为文本或二进制转换为文本

Question

更新************************ 作为引用，我包含了用于打开 PPM 图像的程序 - 将消息嵌入到图像中，然后保存带有嵌入文本的新图像。通过下面的函数，我希望额外添加该消息(隐藏在 LSB 中)，然后将其转换为文本以显示它。感谢您到目前为止的回复 - 我将开始测试它们，看看是否有任何效果。

<小时/>

我正在尝试编写一个函数来提取无符号字符值的 LSB - 将它们组合在一起以形成提取的消息。我知道需要从文件中提取多少个 LSB 的长度，但我在如何将其转换为消息时遇到了麻烦。

首先，我将前 8 位提取到一个 int 数组中 - 给了我一些诸如 00110000 之类的东西。现在我有一个包含该值的 INT 数组，我需要将其转换为单个字符来表示字母。但是，我认为我应该将所有 LSB 放入一个 messageLength * 7 的数组中，并以某种方式将该 int 数组转换为文本。它将在转换之前为我提供文本的二进制表示形式。也许他们有一种将一长串 1 和 0 转换为文本的方法？

unsigned char * extBits(PPMImage *img, int messageLen, unsigned char * decMsg)
{
    //int count = 2;
    int embCount = 0;
    int deM = messageLen * 7;
    int count = 0;
    unsigned char byte;
//  int mask;
//  unsigned char update;
//  unsigned char flipOne = 0x01;  //0x01
//  unsigned char flipZero = 0xFE;  //0x00
    unsigned char dMsg[deM];
    int byteArray[7];
    int takeByte = 0;
    unsigned char *extMsg;
    char c;

    for(int j = 0; j < 7; j++)
    {
        if(takeByte == 8)
        {
            //first letter extracted

            takeByte = 0;               
        }
        //byte = msgOne[j];
    //  byte = img->pixel[j];
        //encMsg[j] = byte;
        byte = img->pixel[j];
        //printf("byte: %c\n", byte); 
    //  printf("byte: %x\n", byte); 
        byte &= 1;
        //printf("byte after: %x\n", byte); 
        dMsg[j] = byte; 
        byteArray[j] = byte;
        data[j] = byteArray[j];
        printf("dMsg:%x ", dMsg[j]);        
    //  printf("pixel:%c \n", img->pixel[j]);       
        embCount++; 
        takeByte++;
    }
/*  
    for(int r=0;r<7;r++)
    {
        printf("\n%d\n", byteArray[r]);
    }   
    printf("count: %d", embCount);
    printf("%s ", dMsg);
*/
    return decMsg = dMsg;
}

嵌入程序********

//////////////////////////////////////////////////////////////
/*
    execute as ./emb -i <img2embed> -i <text file> -o <embedIMG>

*/
//////////////////////////////////////////////////////////////


#include<stdio.h>
#include<stdlib.h>
#include<string.h>


typedef struct {
    int x, y;
    unsigned char *pixel;
} PPMImage;

#define RGB_COMPONENT_COLOR 255

static PPMImage *readPPM(const char *filename)
{
    FILE * fp;
    PPMImage *img;
        int rgb_comp_color;
    int size = 0;
    fp = fopen(filename, "a+");

    fseek(fp, 0, SEEK_END);
    size = ftell(fp);
    fseek(fp, 0, SEEK_SET);

    unsigned char *buff;
    unsigned char stuff[16];
    int c;
    int x,y;
    buff = (unsigned char*) malloc(sizeof(unsigned char)*size +1);
    memset(buff, '\0', sizeof(unsigned char)*size+1);

        fgets(stuff, sizeof(stuff), fp);

    if (stuff[0] != 'P' || stuff[1] != '3') {
    fprintf(stderr, "Invalid image format (must be 'P3')\n");
    exit(1);
    }

    //alloc memory form image
    img = (PPMImage*)malloc(sizeof(PPMImage));
    if (!img) {
        fprintf(stderr, "Unable to allocate memory\n");
        exit(1);
    }

    c = getc(fp);
    while (c == '#') {
        while (getc(fp) != '\n') ;
        c = getc(fp);
    }

    ungetc(c, fp);

    if (fscanf(fp, "%d %d", &img->x, &img->y) != 2) {
        fprintf(stderr, "Invalid image size (error loading '%s')\n", filename);
        exit(1);
    }

    if (fscanf(fp, "%d", &rgb_comp_color) != 1) {
        fprintf(stderr, "Invalid rgb component (error loading '%s')\n", filename);
        exit(1);
    }
    if (rgb_comp_color!= RGB_COMPONENT_COLOR) {
        fprintf(stderr, "'%s' does not have 8-bits components\n",filename);
        exit(1);
    }

    //printf("x: %d y: %d\n", img->x, img->y);

    unsigned char buffer[1024];
    memset(buffer,0,1024);  
    fgets(buffer,1024,fp);

    fread(buff, 1, size, fp);   

    img->pixel = buff;
/*  
    for(int h = 0; h < 20; h++)
    {
        printf("%c", buff2[h]);

    }


    printf("%s", buff2);
*/
    fclose(fp);

    return img;

} 

void writePPM(const char *filename, unsigned char * img, int x, int y)
{
    FILE *fp;
    //open file for output
    fp = fopen(filename, "wb");
    if (!fp) {
        fprintf(stderr, "Unable to open file '%s'\n", filename);
        exit(1);
    }

    //write the header file
    //image format
    fprintf(fp, "P3\n");

    //comments
   // fprintf(fp, "# Created by %s\n",CREATOR);

    //image size
    fprintf(fp, "%d %d\n",x,y);

    // rgb component depth
    fprintf(fp, "%d\n",RGB_COMPONENT_COLOR);

    // pixel pixel
    fwrite(img,1, strlen(img), fp);
    fclose(fp);
}

//unsigned char * embBits(PPMImage *img, int messageLen, unsigned char*msgOne, unsigned char *encMsg)
int embBits(PPMImage *img, int messageLen, unsigned char*msgOne, int embLen)
{
    //int count = 2;
    int embCount = 0;
    int count = 0;
    unsigned char *eMsg;    
    unsigned char byte;
    int mask;
    unsigned char update;
    unsigned char flipOne = 0x01;  //0x01
    unsigned char flipZero = 0xFE;  //0x00

    for(int j = 0; j < messageLen; j++)
    {
        byte = msgOne[j];
        //encMsg[j] = byte;

        for(int k=7; 0 < k; k--)
        {
            update = byte;  

            update = update & (1<<k);
            //printf("pixel:%c\n", img->pixel[count]);      
            //printf("pixel+1:%c\n", img->pixel[count+1]);      
        //  printf("pixel+2:%c\n", img->pixel[count+2]);        
            if(update == 0)
            {
                // if i see 1   |=
                // if i see a 0 &=
                //img->pixel[count] = img->pixel[count] &= flipZero;        
                img->pixel[count+2] &= flipZero;        
            }   
            else
            {
                //flip bit
                //red
                    //check LSB and FLIP 
                //  img->pixel[count] = img->pixel[count] |= flipOne;       
                img->pixel[count+2] |= flipOne;     
            }       

            //mask--;   
            //eMsg[count] = img->pixel[count];
            //printf("count: %d\n", count);
            count = count + 3;
        }   
//      eMsg[j] = byte; 
    }

    //return encMsg = eMsg;
    //unsigned char *yes = "sucess";
    /*
    for(int a = 0; a < messageLen; a++)
    {
        printf("pixel: %c", img->pixel[a]);     
        printf("msg: %c\n", eMsg[a]);       
    //  eMsg[a] = img->pixel[a];
    }
*/

    embCount = count;   
    return embLen = embCount;
}

int main(int argc, char **argv){

    int messageLen;
    int i = 0; 
    PPMImage *img;
    int size = 0;
    FILE * fp;
    int testSize;
    fp = fopen(argv[4], "a+");

    fseek(fp, 0, SEEK_END);
    size = ftell(fp);
    fseek(fp, 0, SEEK_SET);

    unsigned char *buff;
    buff = (unsigned char*) malloc(sizeof(unsigned char)*size +1);
    memset(buff, '\0', sizeof(unsigned char)*size+1);
    fread(buff, 1, size, fp);

    fclose(fp);
//  printf("text encryption: %s\n", buff);
    testSize = strlen(buff);    
//  printf("Size of text %d\n", testSize);

    messageLen = strlen(buff); 

    img = readPPM(argv[2]);
/*
    int testing = strlen(img->pixel);
    for (int f=0;f<6;f++)
    {   
        //f2 = 1
        //f3 = 6
        printf("%c", img->pixel[f]);            
    }       
*/

//  printf("%c \n", img->pixel[2]);
//  printf("%c \n", img->pixel[5]);
    printf("\n");
//  unsigned char * encMsg;

    int encMsg = 0;         
    encMsg = embBits(img, messageLen, buff, encMsg);

//  printf("cipher msg:%s\n", img->pixel);
    printf("message length: %d\n", messageLen);
//  printf("cipher msg length: %d\n", encMsg);


    writePPM(argv[6], img->pixel, img->x, img->y);

    printf("Please press enter to complete\n");
    getchar();
}

Answer 1

我不知道您具体对文件做了什么，并将每个位分配给数组中的位置，但您可以打印存储在unsigned int中的二进制序列。尝试使用这样的东西...

#include <stdio.h>

int main() {
    unsigned int arr[] = {00110110, 00111100, 10111011};
    int i = sizeof(arr)/sizeof(arr[0]);
    while(i-->0) {
        printf("%c, ", arr[i]);
    }
    printf("\n");
}