Steganography Encoder

-=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- (c) WidthPadding Industries 1987 0\|608\|0 -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=- -=+=-
SoCoder -> Snippet Home -> Variables

mike_g	Created : 11 August 2008 Language : Basic Steganography Encoder Hides information in plain sight
This snippet hides information withing a bitmap image. It uses only the standard library so the source can be compiled on its own w/o linking. Its a command line tool that accepts 2 arguments: the first is a bitmap file; the second either another bitmap, or a text file. If the second arg is not a bitmap it will run through each bit of data in the file flipping the least significant bit of the colour components of the pixels. The output is an image that appears the same, but has hidden info. To retreive the hidden info pass both the original image and the modified image as paramaters and it will output the original text file. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_EXT_LEN 5 typedef struct { unsigned char depth; unsigned char channels; int w, h; void* data; }Image; void GetExtension(const char* filename, char* ext); Image* LoadBMP(const char* filename); int SaveBMP(Image* image, const char* filename); void FreeImage(Image image); int Encode(const char bitmap, const char* textfile); int Decode(const char* bitmap1, const char* bitmap2); int main(int argc, char* argv[]) { if(argc != 3) { fprintf(stderr, "Usage:\n"); fprintf(stderr, "To encode: %s bitmap textfile\n", argv[0]); fprintf(stderr, "To decode: %s bitmap bitmap\n", argv[0]); return 1; } char ext[MAX_EXT_LEN+1]; GetExtension(argv[2], ext); if(strcmp(ext, "bmp") == 0) return Decode(argv[1], argv[2]); Encode(argv[1], argv[2]); return 0; } int Encode(const char* bitmap, const char* textfile) { Image ip = LoadBMP(bitmap); if(! ip) return 2; FILE fp = fopen(textfile, "r"); if(! fp) { fprintf(stderr, "Unable to open %s\n", textfile); FreeImage(ip); return 3; } //Get textfile size int i, text_bytes=0; while( (i=fgetc(fp)) != EOF ) text_bytes++; rewind(fp); //Check enough space on image for encoding int image_bytes = ip->w * ip->h * 3; int text_bits = text_bytes * 8; if(text_bits > image_bytes) { fprintf(stderr, "Aborted: Not enough pixels in %s to encode %s text\n", bitmap, textfile); FreeImage(ip); fclose(fp); return 4; } //Do encoding int byte, bit; unsigned char c, mask; unsigned char* ptr = ip->data; for(byte=0; byte<text_bytes; byte++) { c = fgetc(fp); mask = 128; for(bit=0; bit<8; bit++, mask>>=1, ptr++) if(mask & c)ptr^=1; } return SaveBMP(ip, "encoded.bmp"); } int Decode(const char bitmap1, const char* bitmap2) { Image a = LoadBMP(bitmap1); if(! a) return 5; Image b = LoadBMP(bitmap2); if(! b) { FreeImage(a); return 6; } //Chek images are of same size int a_size = a->wa->ha->channels; int b_size = b->wb->hb->channels; if(a_size != b_size) { FreeImage(a); FreeImage(b); fprintf(stderr, "Image files are not of same size\n"); return 7; } //Open a file for writing to FILE fp = fopen("decoded.txt", "w"); if(! fp) { FreeImage(a); FreeImage(b); fprintf(stderr, "Unable to open output file.\n"); return 7; } // Do decoding int max_byte = a_size / 8; int byte, bit; unsigned char ap = a->data; unsigned char* bp = b->data; unsigned char out, mask; for(byte=0; byte<max_byte; byte++) { out = 0; mask = 128; for(bit=0; bit<8; bit++, ap++, bp++, mask>>=1) { if(ap != bp) out \|= mask; } if(out == 0) break; fwrite(&out, 1, 1, fp); } fclose(fp); return 0; } void GetExtension(const char* filename, char* ext) { int len = strlen(filename); int a, b=0, dot_found = 0; //Loop backwards to the last dot for(a=len; a>= 0; a--) { if(filename[a] == '.') { dot_found = 1; break; } } a++; if(dot_found) //Copy extension { for(; a<len && b<=MAX_EXT_LEN; a++, b++) ext[b] = filename[a]; } ext[b] = '\0'; } Image* LoadBMP(const char* filename) { FILE fp = fopen(filename, "rb"); if(!fp) { fprintf(stderr, "Error Opening BMP File: %s File Could Not Be Opened.\n", filename); return NULL; } char signature[2]; fread(signature, 1, 2, fp); if(signature[0]!='B' \|\| signature[1]!='M') { fprintf(stderr, "Error Opening BMP File: %s Invalid Signature: %s\n", filename, signature); fclose(fp); return NULL; } // GET IMAGE PROPERTIES int width, height; short depth; fseek(fp, 16, SEEK_CUR); fread(&width, 4, 1, fp); fread(&height, 4, 1, fp); fseek(fp, 2, SEEK_CUR); fread(&depth, 2, 1, fp); if(depth != 24) { fprintf(stderr, "Error Opening BMP File: %s Loader Only Supports 24bit Bitmaps\n", filename); fclose(fp); return NULL; } // CREATE AND INIT IMAGE BUFFER Image image = malloc(sizeof(Image)); if(!image) { fprintf(stderr, "Error Loading %s: Unable To Allocate Space For Image\n", filename); fclose(fp); return NULL; } image->data = malloc(width * height * 3); if(! image->data) { fprintf(stderr, "Error Loading %s: Unable To Allocate Space For Image Data\n", filename); free(image); fclose(fp); return NULL; } image->data = memset(image->data, 0, (width * height * 3)); image->h = height; image->w = width; image->depth = 24; image->channels = 3; // LOAD IMAGE DATA unsigned char ptr = image->data; ptr+=(widthheight3)-(width3); int rows, cols, elem; fseek(fp, 54, SEEK_SET); //rows inverted so not upside down for(rows=0; rows<height; rows++, ptr-=(width6)) for(cols=0; cols<width; cols++) for(elem=0; elem<3; elem++, ptr++) fread(ptr, 1, 1, fp); fclose(fp); return image; } //Writes unpaletted 24bit bitmaps only int SaveBMP(Image image, const char* filename) { FILE fp = fopen(filename, "wb"); if(! fp) return 1; if(! image) return 2; if(image->channels < 3) return 3; int pixel_num = image->wimage->h; int data_size = pixel_num3; int file_size = data_size + 54; int start_add = 54, header_size = 40; int zero = 0, planes = 1, bpp = 24; fwrite("BM", 2, 1, fp); fwrite(&file_size, 4, 1, fp); fwrite(&zero, 4, 1, fp); fwrite(&start_add, 4, 1, fp); //This is probably wrong fwrite(&header_size, 4, 1, fp); // Size of header fwrite(&image->w, 4, 1, fp); fwrite(&image->h, 4, 1, fp); fwrite(&planes, 2, 1, fp); //number of planes must be 1 fwrite(&bpp, 2, 1, fp); // BPP fwrite(&zero, 4, 1, fp); // No comprssion fwrite(&data_size, 4, 1, fp); fwrite(&zero, 4, 4, fp); //Stuff we dont care about int row, col, row_size = image->wimage->channels; int alpha_skip = image->channels-3; unsigned char ip = (unsigned char)image->data; ip += (row_sizeimage->h) - row_size; for(row=0; row<image->h; row++, ip -= (row_size2)) for(col=0; col<image->w; col++) { fwrite(ip, 1, 1, fp); ip++; fwrite(ip, 1, 1, fp); ip++; fwrite(ip, 1, 1, fp); ip++; ip += alpha_skip; } return 0; } void FreeImage(Image *image) { free(image->data); free(image); } --v

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