challenge.c

#include <stdlib.h>
#include <string.h>

int main(int argc, char* *argv)
{
  // FOR STREAM VIEWERS
  // A buddy of mine into security/cryptography challenged me to this
  // "very easy" problem.
  // Now I'm making a friend of mine and YOU guys try and solve the same
  // challenge

  // 1. The challenge is to figure out what this program is doing
  // 2. Then we need to find out what the answer is for what the program is doing

  // Things we know - ahoward1024
  // length of input has to be the same length as the address of a

  int len;
  unsigned ii;
  const unsigned long long a = 0x4017111a1b1d29;
  char b = (0x11 + 0x52) ^ 34;
  char *c = (char*)&a;
  char *d;

  if (argc != 2) {
    return -1;
  }

  len = strlen(argv[1]);
  d = argv[1];

  if (len != strlen(c)) {
    return -1;
  }

  for (ii=0; ii<len; ii++) {
    if ((*d ^ b) == *c) {
      b = *d;
      d++; 
      c++;
    } else {
      return -1;
    }
  }

  puts("congratz\n");
  return 0;
}