chall.py

# challenge source code
# Env: Python 3.10

import os
from Crypto.Util.number import long_to_bytes, bytes_to_long
from Crypto.Util.Padding import pad, unpad
from magic_box import *

banner = """
Traveler, choose one God to talk with.
1. Negligent God
2. Softhearted God
3. Harsh God
Other. exit()
"""


def Negligent_God():
    print("Who are u?")
    your_name = input("> name: ")
    your_pass = your_name + "Open the door!"

    print("Uh, I don't care who you are. Just show me your magic power.")
    algo = input("> algo: ")
    mode = input("> mode: ")

    assert algo in algos
    assert mode in modes

    if algo == "AES":
        blocksize = 16
    else:
        blocksize = 8

    keys = bytes.fromhex(input("> hex keys: "))
    magic_box = Magic_box(algo, mode, keys)

    if magic_box.auto_enc(pad(your_pass.encode(), blocksize)) == pad(your_pass.encode(), blocksize):
        print("Well done")
        print(open("./flag1", "r").read())
    else:
        print("I'm sorry, maybe something is wrong with your name? Um, I just say it casually.")


def Softhearted_God():
    print("Who are u?")
    your_name = input("> name: ")

    print("Oh, what a poor guy from another world. You are allowed to show me your magic power block by block.")
    algo = input("> algo: ")
    mode = input("> mode: ")

    assert algo in algos
    assert mode in modes

    block_num = 10

    if algo == "AES":
        blocksize = 16
    else:
        blocksize = 8

    your_pass = os.urandom(block_num*blocksize)
    print(f"[+] you_pass : {your_pass.hex()}")

    for i in range(block_num):
        print(f"[+] rounds {i}")

        keys = bytes.fromhex(input("> hex keys: "))
        magic_box = Magic_box(algo, mode, keys)

        if magic_box.auto_enc(your_pass)[i*blocksize:(i+1)*blocksize] != your_pass[i*blocksize:(i+1)*blocksize]:
            print("You're not a pure guy from another world!")
            return

    print("Well done")
    print(open("./flag2", "r").read())


def Harsh_God():
    print("Treat no exceptions. You're not allowed to select the keys directly.")
    print("Anyway, this time I want to encrypt the message twice.")

    your_name = input("> name: ")
    algo = input("> algo: ")
    mode = input("> mode: ")

    assert algo in algos
    assert mode in modes

    if algo == "AES":
        blocksize = 16
    else:
        blocksize = 8

    your_pass = bytes.fromhex(input("> hex msg (at least 16 bytes): "))

    assert len(your_pass) >= 16 and len(your_pass) % blocksize == 0, "Invalid msg length"

    your_key = long_to_bytes(crc128(your_pass), 16)[:blocksize]

    if mode != "ECB":
        iv = os.urandom(blocksize)
        magic_box = Magic_box(algo, mode, your_key+iv)
    else:
        magic_box = Magic_box(algo, mode, your_key)

    if magic_box.auto_enc(magic_box.auto_enc(your_pass)) == your_pass:
        print("What a miracle!")
        print(open("./flag3", "r").read())
    else:
        print("Out, Right Now!")


if __name__ == "__main__":
    while True:
        print(banner)
    
        try:
            choice = int(input("> choice: "))
        except:
            print("Must be a digit number")
            continue
        
        if choice == 1:
            Negligent_God()
        elif choice == 2:
            Softhearted_God()
        elif choice == 3:
            Harsh_God()
        else:
            print("Byebye!")
            exit()