Defcon 23 :: OpenCTF 2015 - Absence (200)

I loved this challenge, it exactly my cup of tea in the lands of obscurity.

Here's the code provided in the challenge:

#include           
 
void one(char k)          
{ 
  unsigned int i, bytes[]={0x0a,0x5d,0x2c,0x0b,0x37,0x38,0x04,0x05,0x1f,0x4c,0x05,0x1f,0x4c,0x02,0x03,0x18,0x4c,0x18,0x04,0x09,0x4c,0x0f,0x03,0x08,0x09,0x4c,0x15,0x03,0x19,0x4b,0x1e,0x09,0x4c};       
 
  for(i=0; i<32; i++)       
 printf("%c",(char)bytes[i]^k);
  printf("\n");          
} 
            
 
char two(char c)          
{ 
  return (c^0x32)-7;        
} 
            
 
void main(int argc, char** argv)         
{ 
  // lo0kin-fo
  one(two('A'));          
} 
  

First I tried compiling it and looking at the output. When doing this we get the following:

f1@g[This is not the code you're 

Cool, starts with a lead! That's nice!
After trying to change the 'A' value on line 22, to see if it changed the output, I got nothing and moved on to look for other clues.
Playing around in vim, one act I occasionally play with is pressing $ to go to the end of the line and skimming through the code by hitting each end point. In this case, there were a few spaces after one of the lines. With a past in heavy code reviews, this made me a little uneasy inside, so I decided to do another quick check:

/\t

With that we get wayy too many tab characters in irregular places:

This immediately redirects my thoughts to Whitespace, the programming language. If you're unfamiliar with whitespace, you can check out an example program here - http://www.99-bottles-of-beer.net/language-whitespace-154.html
The gist is that it's a language completely comprised of spaces, tabs, and linefeeds.

Because it's whitespace, and not the most supported in the world, I decided to do something I rarely find myself doing - finding an online compiler. In this case, there was a great one with a gomod example of whitespace found here - http://www.tutorialspoint.com/execute_whitespace_online.php (If anyone knows of good offline *nix whitespace compilers, please leave them in the comments section below!)

 lo0kin-fo]

This resulted in the full flag:

f1@g[This is not the code you're lo0kin-fo]