The following 3 files take a PPM image and will encrypt or decrypt it when suppl
ID: 3750340 • Letter: T
Question
The following 3 files take a PPM image and will encrypt or decrypt it when supplied with a key. Find and fix the errors in the code. Each section will state if there may be an error contained.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
#include "stdio.h"
#include "stdlib.h"
#include "crypto.h"
int main(int argc, char const *argv[]) {
FILE* image_file = fopen(argv[1], "r");
FILE* key_file = fopen(argv[2], "r");
FILE* out_image = fopen(argv[3], "w");
// Read image
header_t header;
img_t img;
read_header(image_file, header);
read_image(image_file, &img, &header);
// Read secret key
int seed;
read_seed(key_file, *seed);
sp_rand(eed);
/** NO ERROR HERE **/
printf("Encrypt[1] or Decrypt[2]? ");
int choice;
while(true) {
scanf("%d",&choice);
if(choice == 1 || choice == 2) {
sym_crypt(out_image, &header, &img, choice);
break;
} else {
printf("Please enter 1 or 2 ");
}
}
/********************/
fclose(image_file);
fclose(key_file);
fclose(out_image);
return 0;
}
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
#include "crypto.h"
int P_RAND_SEED = 1;
/** NO ERRORS HERE! **/
void read_header(FILE* in_img, header_t* header) {
header->type = malloc(sizeof(char)*3);
fscanf(in_img, "%s ", header->type);
fscanf(in_img, "%d %d ", &header->w, &header->h);
fscanf(in_img, "%d ", &header->cs);
printf("Header: %s %d %d %d ", header->type, header->w, header->h, header->cs);
}
/********************/
/** Could be errors... **/
void read_image(FILE* input, img_t* image, header_t* header) {
int row, col;
image->data = malloc(sizeof(pixel_t*) * header.h);
for(row = 0; row < header->h; row++) {
image->data[row] = malloc(sizeof(pixel_t) * header->w * 3);
for(; col < header->w; col++) {
pixel_t pix
fscanf(input, "%c%c%c", &pix.r, &pix.g, &pix.b);
image.data[row][col] = pix;
}
}
}
/** NO ERRORS HERE! **/
void read_seed(FILE* seed_file, int* seed) {
fscanf(seed_file, "%d", seed);
}
/** Could be errors... **/
void sym_crypt(FILE* output, header_t* header, img_t* image, int mode) {
// Write header of PPM to files
/** NO ERRORS HERE! **/
fprintf(output, "%s %d %d %d ", header->type, header->w, header->h, header->cs);
/*********************/
// Encrypt or Decrypt!
// Could be errors...
int row, col;
switch (mode) {
case 1:
printf("Encrypt ", );
for(row = 0; row < header->h; row++) {
for(col = 0; col < header->w; col++) {
int swap_row = p_rand(row*row) % header.h;
int swap_col = p_rand(col*col) % header->w;
pixel_t swap = image->data[row][col];
image->data[row][col] = image->data[swap_row][swap_col];
image->data[swap_row][swap_col] = swap;
}
} break;
case 2:
printf("Decrypt ");
for(row = header->h-1; row >= 0; row--) {
for(; col >= 0; col--) {
int swap_row = p_rand(row*row) % header->h;
int swap_col = p_rand(col*col) % header->w;
pixel_t swap = image->data[row][col];
image->data[row][col] = image->data[swap_row][swap_col];
image->data[swap_row][swap_col] = swap;
}
} break;
default: break;
}
/** NO ERRORS HERE! **/
for(row = 0; row < header->h; row++) {
for(col = 0; col < header->w; col++) {
pixel_t pix = image->data[row][col];
fprintf(output, "%c%c%c", pix.r, pix.g, pix.b);
}
}
/********************/
}
/** NO ERRORS HERE! **/
void sp_rand(unsigned int seed) {
P_RAND_SEED = seed;
}
/********************/
/** NO ERRORS HERE! **/
unsigned int p_rand(unsigned int init) {
return (P_RAND_SEED*init) % INT_MAX;
}
/********************/
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
#ifndef CRYPTO_H
#define CRYPTO_H value
#include "stdio.h"
#include "stdlib.h"
#include "limits.h"
#include "stdbool.h"
extern int P_RAND_SEED;
typedef struct header_t {
char* type;
int w, h, cs;
} header_t;
typedef struct pixel_t {
unsigned char r,g,b;
} pixel_t;
typedef struct img_t {
pixel_t** data;
} img_t;
void read_header(FILE* in_img, header_t* header);
void read_image(FILE* in_img, img_t* image, header_t* header);
void read_seed(FILE* seed_file, int* seed);
void sym_crypt(FILE* out_img, header_t* header, img_t* image, int mode);
// Dumb random number generator
void sp_rand(unsigned int seed);
unsigned int p_rand(unsigned int init);
#endif
Explanation / Answer
Answer:
1. There are no errors in source file containing main function.
2. There are also no errors in crypto.h header file.
3. There are errors in the source file containing definitions of functions of crypto.h header file. Errors have been removed. See the updated code below:
--------------------------------------------------
#include "crypto.h"
int P_RAND_SEED = 1;
/** NO ERRORS HERE! **/
void read_header(FILE* in_img, header_t* header) {
header->type = malloc(sizeof(char) * 3);
fscanf(in_img, "%s ", header->type);
fscanf(in_img, "%d %d ", &header->w, &header->h);
fscanf(in_img, "%d ", &header->cs);
printf("Header: %s %d %d %d ", header->type, header->w, header->h,
header->cs);
}
/********************/
/** Could be errors... **/
void read_image(FILE* input, img_t* image, header_t* header) {
int row, col;
image->data = malloc(sizeof(pixel_t*) * header.h);
for (row = 0; row < header->h; row++) {
image->data[row] = malloc(sizeof(pixel_t) * header->w * 3);
for (col=0; col < header->w; col++) {
pixel_t pix;
fscanf(input, "%c%c%c", &pix.r, &pix.g, &pix.b);
image.data[row][col] = pix;
}
}
}
/** NO ERRORS HERE! **/
void read_seed(FILE* seed_file, int* seed) {
fscanf(seed_file, "%d", seed);
}
/** Could be errors... **/
void sym_crypt(FILE* output, header_t* header, img_t* image, int mode) {
// Write header of PPM to files
/** NO ERRORS HERE! **/
fprintf(output, "%s %d %d %d ", header->type, header->w, header->h,header->cs);
/*********************/
// Encrypt or Decrypt!
// Could be errors...
int row, col;
switch (mode) {
case 1:
printf("Encrypt ");
for (row = 0; row < header->h; row++) {
for (col = 0; col < header->w; col++) {
int swap_row = p_rand(row * row) % header.h;
int swap_col = p_rand(col * col) % header->w;
pixel_t swap = image->data[row][col];
image->data[row][col] = image->data[swap_row][swap_col];
image->data[swap_row][swap_col] = swap;
}
}
break;
case 2:
printf("Decrypt ");
for (row = header->h - 1; row >= 0; row--) {
for (col=header->w; col >= 0; col--) {
int swap_row = p_rand(row * row) % header->h;
int swap_col = p_rand(col * col) % header->w;
pixel_t swap = image->data[row][col];
image->data[row][col] = image->data[swap_row][swap_col];
image->data[swap_row][swap_col] = swap;
}
}
break;
default:
break;
}
/** NO ERRORS HERE! **/
for (row = 0; row < header->h; row++) {
for (col = 0; col < header->w; col++) {
pixel_t pix = image->data[row][col];
fprintf(output, "%c%c%c", pix.r, pix.g, pix.b);
}
}
/********************/
}
/** NO ERRORS HERE! **/
void sp_rand(unsigned int seed) {
P_RAND_SEED = seed;
}
/********************/
/** NO ERRORS HERE! **/
unsigned int p_rand(unsigned int init) {
return (P_RAND_SEED * init) % INT_MAX;
}
/********************/
---------------------------------------