Spencer/PNG_CC
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2021-10-03 15:59:26 -04:00
parent 3a5862f32f
commit 6cae1ecc58
2 changed files with 36 additions and 5 deletions
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35
crc.c
View File

@@ -4,6 +4,7 @@
#include <stdlib.h>
#include <sodium.h>
#include "CRCLib.h"
#include "crc.h"
const long png_signature[8] = { 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a };
const long idat_signature = 1229209940;
@@ -34,7 +35,7 @@ int check_header_length(unsigned char *addr, long offset) {
return res;
}
unsigned long first_idat(char *addr) {
unsigned long first_idat(unsigned char *addr) {
int idat_found = 0;
unsigned long offset = 8;
int jump_offset = 0;
@@ -51,7 +52,7 @@ unsigned long first_idat(char *addr) {
return offset;
}
int total_idat(char *addr) {
int total_idat(unsigned char *addr) {
int iend_found = 0;
int found_idat = 0;
unsigned long offset = 8;
@@ -72,6 +73,15 @@ int total_idat(char *addr) {
return found_idat;
}
int update_file_crc(unsigned char *addr, unsigned long offset , unsigned int crc_num) {
int startCRC = 8 + offset + check_header_length(addr, offset);
unsigned char new_crc;
for(int i = 0; i < 4; i++) {
new_crc = crc_num >> (8*(3-i)) & 0xFF;
addr[startCRC+i] = new_crc;
}
}
int change_idat_content(unsigned char *addr, char *message, int accuracy, unsigned long offset) {
printf("Starting IDAT Tranform\n");
if(accuracy > 4) {
@@ -125,6 +135,8 @@ int change_idat_content(unsigned char *addr, char *message, int accuracy, unsign
printf("Full CRC: %08X\n", crcnum);
printf("Original: %02X\n", idat_data[j]);
printf("Change offset: %d to hex: %02X\n", j, temp_idat_data[j]);
addr[offset+8+j] = temp_idat_data[j];
update_file_crc(addr, offset, crcnum);
prop_found = 1;
}
}
@@ -132,12 +144,24 @@ int change_idat_content(unsigned char *addr, char *message, int accuracy, unsign
return 0;
}
int create_cc_file(unsigned char *addr, unsigned long file_length) {
FILE *fp;
fp = fopen("png2.png", "w");
if(fp == NULL) {
return EXIT_FAILURE;
}
for(int i = 0; i < file_length; i++){
fputc(addr[i], fp);
}
fclose(fp);
}
int main() {
FILE *fp;
unsigned int c;
//unsigned char myArray[838860];
unsigned char * myArray = NULL;
myArray = calloc(880388560, sizeof(char));
unsigned char* myArray = calloc(1000, sizeof(unsigned char));
unsigned long i = 0;
unsigned long offset = 0;
char message[1];
@@ -152,6 +176,7 @@ int main() {
fclose(fp);
offset = first_idat(myArray);
change_idat_content(myArray, message, 2, offset);
create_cc_file(myArray, i);
//int crcnum = crc(myArray, 19);
//printf("%08X\n", crcnum);
}

6
crc.h Normal file
View File

@@ -0,0 +1,6 @@
int check_file_header(char *addr);
int check_header_length(unsigned char *addr, long offset);
unsigned long first_idat(unsigned char *addr);
int total_idat(unsigned char *addr);
int change_idat_content(unsigned char *addr, char *message, int accuracy, unsigned long offset);