keygenme-py is a Reverse Engineering puzle worth 30 points.

The puzzle does not come with a description, but provides source code for a small game written in Python named keygenme-trial.py.

This game is far from complete and is only 243 lines of Python. Reading the source, it is clear that the check_key function is the key to obtaining the flag. This code is taking positional values from the SHA256 hex digest of the username this software was licensed to. 

 def check_key(key, username_trial):      global key_full_template_trial      if len(key) != len(key_full_template_trial):         return False     else:         # Check static base key part --v         i = 0         for c in key_part_static1_trial:             if key[i] != c:                 return False              i += 1          # TODO : test performance on toolbox container         # Check dynamic part --v         if key[i] != hashlib.sha256(username_trial).hexdigest()[4]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[5]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[3]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[6]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[2]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[7]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[1]:             return False         else:             i += 1          if key[i] != hashlib.sha256(username_trial).hexdigest()[8]:             return False            return True

At the top of the source code, it has the expected template for the key, which is in picoCTF{} flag format. Writing a key generator for this software was straightforward:

 #!/usr/bin/env python3  import hashlib  username = b"YOUR_USERNAME_HERE" key_prefix = "picoCTF{1n_7h3_|<3y_of_"  user_hash = hashlib.sha256(username).hexdigest()  key_prefix += user_hash[4] key_prefix += user_hash[5] key_prefix += user_hash[3] key_prefix += user_hash[6] key_prefix += user_hash[2] key_prefix += user_hash[7] key_prefix += user_hash[1] key_prefix += user_hash[8] key_prefix += "}"  print(key_prefix)

Running this key generator yielded the correct flag.