[Saegon]

The goal is to reverse engineer the program and find out what password is.
What's interesting is that to decrypt some string you simply encrypt it again. I tried to print out each value of key in encrypt(input_data, password), but the compiler complains about indentation. Also, how can I input password as arg[4] when I don't know what it is. The problem included some file that I cannot upload.
It's true that I could probably look up the answer, but I'd rather solve as much of the problem that I can by myself.

Here is the code:

Code

#!/usr/bin/python

import sys

"""
Daedalus Corporation encryption script.
"""

def xor(input_data, key):
    result = ""
    for ch in input_data:
      result += chr(ord(ch) ^ key)

    return result

def encrypt(input_data, password):
    key = 0
    for ch in password:
      key ^= ((2 * ord(ch) + 3) & 0xff)

    return xor(input_data, key)

def decrypt(input_data, password):
    return encrypt(input_data, password)

def usage():
    print("Usage: %s [encrypt/decrypt] [in_file] [out_file] [password]" % sys.argv[0])
    exit()

def main():
    if len(sys.argv) < 5:
      usage()

    input_data = open(sys.argv[2], 'r').read()
    result_data = ""

    if sys.argv[1] == "encrypt":
      result_data = encrypt(input_data, sys.argv[4])
    elif sys.argv[1] == "decrypt":
      result_data = decrypt(input_data, sys.argv[4])
    else:
      usage()

    out_file = open(sys.argv[3], 'w')
    out_file.write(result_data)
    out_file.close()

main()

[Shiv]

Code

def encrypt(input_data, password):
    key = 0
    for ch in password:
      key ^= ((2 * ord(ch) + 3) & 0xff)

    return xor(input_data, key)

key will always be between 0-255, you just have to skip the function encrypt and test all 256 possibilities for key directly in the xor function