SECCON 2019 QUALS

seccon2019-coffee_break.py

from Crypto.Cipher import AES
import base64


def encrypt(text):
    key = "SECCON"
    s = ''
    for i in range(len(text)):
        s += chr((((ord(text[i]) - 0x20) + (ord(key[i % len(key)]) - 0x20)) % (0x7e - 0x20 + 1)) + 0x20)
    return s

key2 = "seccon2019"
cipher = AES.new(key2 + chr(0x00) * (16 - (len(key2) % 16)), AES.MODE_ECB)

ctext = "FyRyZNBO2MG6ncd3hEkC/yeYKUseI/CxYoZiIeV2fe/Jmtwx+WbWmU1gtMX9m905"

dec1 = base64.b64decode(ctext)
dec2 = cipher.decrypt(dec1).decode("ascii")

chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_{}"

def search(memo):
    for c in chars:
        enc = encrypt(memo + c)
        if enc in dec2:
            print(memo + c)
            search(memo + c)

search("SECCON{")