Protostar/Net 2

If you get stuck, you can watch the solution and explanation here:

Solving network level 1 with socket programming in python.

This code tests the ability to add up 4 unsigned 32-bit integers. Hint: Keep in mind that it wraps.

This level is at /opt/protostar/bin/net2


#include "../common/common.c"

#define NAME "net2"
#define UID 997
#define GID 997
#define PORT 2997

void run()
  unsigned int quad[4];
  int i;
  unsigned int result, wanted;

  result = 0;
  for(i = 0; i < 4; i++) {
      quad[i] = random();
      result += quad[i];

      if(write(0, &(quad[i]), sizeof(result)) != sizeof(result)) {
          errx(1, ":(\n");

  if(read(0, &wanted, sizeof(result)) != sizeof(result)) {
      errx(1, ":<\n");

  if(result == wanted) {
      printf("you added them correctly\n");
  } else {
      printf("sorry, try again. invalid\n");

int main(int argc, char **argv, char **envp)
  int fd;
  char *username;

  /* Run the process as a daemon */
  background_process(NAME, UID, GID); 
  /* Wait for socket activity and return */
  fd = serve_forever(PORT);

  /* Set the client socket to STDIN, STDOUT, and STDERR */

  /* Don't do this :> */


See also

Before we continue with the network challenges, let's first introduce the TCP protocol properly. Using netcat and wireshark to understand it.

This is a mirror. Copyright and original can be found here: