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124//==============================================================================
// Stash: DECODE.C
// Part of the Stash project.
//
// Created: 03/01/03
// Updated: 05/28/03
//
// Copyright (C) 2003 Peter Kieltyka
//==============================================================================
#include "stash.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "prng/prng.h"
#include "md5/global.h"
#include "md5/md5.h"
/*
d = (d & ~(1 << (7-b))) | ((s & 1) << (7-b));
assigns 'd' the LSB of 's' at bit location 'b' (0 => b <= 7, 0 = LSB)
*/
#define DECODE_BIT(d,s,b) ((d&~(1<<(7-b)))|((s&1)<<(7-b)))
void decode_file(FILE *, FILE *);
int decode_data(unsigned char *, int, unsigned char *, int, int);
float get_speed(clock_t,clock_t);
int decode_steg(char *file_input, char *file_output, unsigned char *key) {
FILE *fpi, *fpo;
unsigned char digest[16];
//clock_t c1, c2;
// Open files
if((fpi = fopen(file_input, "rb")) == NULL) {
fprintf(stderr, "Cannot open input file!\n");
return(-1);
}
if((fpo = fopen(file_output, "wb")) == NULL) {
fprintf(stderr, "Cannot open output file!\n");
return(-1);
}
// Get MD5 Checksum of key
MD5String(key, digest);
// Seed the PRNG with the md5 checksum of the key
prng_seed(digest);
// Decode
//c1 = clock();
decode_file(fpi, fpo);
//c2 = clock();
//printf("%f\n", get_speed(c1,c2));
//system("PAUSE");
// Close files
fclose(fpi);
fclose(fpo);
return(0);
}
void decode_file(FILE *fpi, FILE *fpo) {
size_t n, x;
unsigned long len;
unsigned char cont[CONTSIZE], data[DATASIZE];
struct stash_hdr shdr = {0};
// Skip restricted area
(void)fseek(fpi, STARTBYTE, SEEK_SET);
// Get header
n = fread(data, 1, sizeof(struct stash_hdr)<<3, fpi);
decode_data((unsigned char *)&shdr, sizeof(struct stash_hdr), data, (int)n, 0);
// Decode data
len = shdr.len;
while(len > 0) {
if(len >= DATASIZE)
x = DATASIZE;
else
x = len;
n = fread(cont, 1, x<<3, fpi);
decode_data(data, (int)n>>3, cont, (int)n, 1);
fwrite(data, 1, (int)x, fpo);
len -= (unsigned long)x;
}
return;
}
int decode_data(unsigned char *dst, int dst_len,
unsigned char *src, int src_len, int rand)
{
int i, b, x;
if((dst_len<<3) != src_len)
return(-1);
// rand
if(rand == 1)
prng_array_unshuffle(src, (unsigned int)src_len);
// Set destination bits
x=0;
memset(dst, 0, dst_len);
for(i=0; i<dst_len; i++) {
for(b=0; b<8; b++) {
dst[i] = DECODE_BIT(dst[i], src[x], b);
x++;
}
}
return(0);
}