AES

문제코드

from Crypto.Cipher import AES
import random


def padding(plaintext):
    block_size = 32
    if len(plaintext) % block_size != 0:
        plaintext += b'\x00' * (block_size - (len(plaintext) % block_size))
    return plaintext


def make_key():
    key = b''
    for i in range(16):
        key += str(random.randrange(0, 2)).encode('utf-8')
    return key


FLAG = b'~~~~~~~~~~~~~~~'
FLAG = padding(FLAG)
key = make_key()

cipher = AES.new(key, AES.MODE_ECB)
ciphertext = cipher.encrypt(FLAG)

print(ciphertext)

 

decryption_code

from Crypto.Cipher import AES

def find_key(i):
    key =b''
    key += str(format(i,'b')).encode('utf-8').zfill(16)
    return key

ciphertext=b'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'
for i in range(65536):
    key = find_key(i)
    print(key)
    cipher = AES.new(key, AES.MODE_ECB)
    plaintext = cipher.decrypt(ciphertext)
    if b'DSU' in plaintext:
        print("Find plain text:  "+plaintext.decode('utf-8'))
        break