Intro to Reversing 2 - localo

Category: Reverse Engineering
Difficulty: Baby
Author: 0x4d5a
Dependencies: Intro to Reversing 1


This is a introductory challenge for beginners which are eager to learn reverse engineering on linux. The three stages of this challenge will increase in difficulty. But for a gentle introduction, we have you covered: Check out the video of LiveOverflow or follow the authors step by step guide to solve the first part of the challenge.

Once you solved the challenge locally, grab your real flag at: nc 9601

Note: Create a dummy flag file in the working directory of the rev1 challenge. The real flag will be provided on the server


The author provided again a simple password checker. If the password is correct we get the flag.


  1. Throw the binary in the Ghidra-Decompiler
undefined8 main(void)
  int is_pass;
  ssize_t len;
  long in_FS_OFFSET;
  int i;
  char input [40];
  long local_10;
  local_10 = *(long *)(in_FS_OFFSET + 0x28);
  puts("Give me your password: ");
  len = read(0,input,0x1f);
  input[(int)len + -1] = '\0';
  i = 0;
  while (i < (int)len + -1) {
    input[i] = input[i] + -0x77;
    i = i + 1;
  is_pass = strcmp(input,&password);
  if (is_pass == 0) {
    puts("Thats the right password!");
    printf("Flag: %s",flagBuffer);
  else {
    puts("Thats not the password!");
  if (local_10 != *(long *)(in_FS_OFFSET + 0x28)) {
                    /* WARNING: Subroutine does not return */
  return 0;
  1. Use ROT 119 base 256 on the byte array of the password use in the strcmp. As the function uses ROT -0x77 (decimal: 119) on our input. We can get the bytes by clicking on password in Ghidra.

    Python is here quite handy.
data = [0xFC,0xFD,0xEA,0xC0,0xBA,0xEC,0xE8,0xFD,0xFB,0xBD,0xF7,0xBE,0xEF,0xB9,0xFB,0xF6,0xBD,0xC0,0xBA,0xB9,0xF7,0xE8,0xF2,0xFD,0xE8,0xF2,0xFC]
print("".join(map(lambda x: chr((x+119)&0xFF),data)))

> sta71c_tr4n5f0rm4710n_it_is
  1. Get the flag:
$ nc 9601
Give me your password:
Thats the right password!
Flag: CSCG{1s_th4t_wh4t_they_c4ll_on3way_transf0rmati0n?}