# ᒣ⍑╎ϟ ╎ϟ リᒷᖋᒣ
## Description```We have reason to believe that Mortimer is rebuilding the Armageddon Machine. We managed to intercept a message sent from his personal computer. After consulting with the Oracle, we were only able to discover two things:
The tool used to encrypt messages (encrypt.py)All messages sent by Mortimer begin with Mortimer_McMire:
Can you decrypt the message?```
## Provided Files```- encrypt.py- message.enc```
## Writeup
Looking at `encrypt.py` we can see the encryption used for the plaintext. ```pyfrom Crypto.Cipher import AESimport binascii, os
key = b"3153153153153153"iv =  os.urandom(16)
plaintext = open('message.txt', 'rb').read().strip()
cipher = AES.new(key, AES.MODE_CBC, iv)
encrypted_flag = open('message.enc', 'wb')encrypted_flag.write(binascii.hexlify(cipher.encrypt(plaintext)))encrypted_flag.close()```
`message.enc` contains the output of `encrypt.py`. ```2a21c725b4c3a33f151be9dc694cb1cfd06ef74a3eccbf28e506bf22e8346998952895b6b35c8faa68fac52ed796694f62840c51884666321004535834dd16b1```
To get the flag we actually already have everything we need. - `key` - Key used for encryption and decryption, `b'3153153153153153'`.- `iv` - Initialization vector used for encryption algorithm (first 16 bytes of ciphertext), `b'2a21c725b4c3a33f'`.- `ciphertext` - Ciphertext containing the flag `151be9dc694cb1cfd06ef74a3eccbf28e506bf22e8346998952895b6b35c8faa68fac52ed796694f62840c51884666321004535834dd16b1`. 
Putting these things together in a solution script:```pyfrom Crypto.Cipher import AESimport binascii
key = b"3153153153153153"
with open('message.enc', 'rb') as file:    hex_data = file.read()
cipher_text_bytes = binascii.unhexlify(hex_data)
iv = cipher_text_bytes[:16]  # IV is first 16 bytes of ciphertextcipher_text = cipher_text_bytes[16:]  # The rest is the actual ciphertext
cipher = AES.new(key, AES.MODE_CBC, iv)
plain_text = cipher.decrypt(cipher_text)
print(plain_text.decode('utf-8'))```
Running the decryption script concludes this writeup. ```sh$ python3 decrypt.py         shctf{th1s_was_ju5t_a_big_d1str4ction}```