Android-in-the-Middle

source.py

from Crypto.Cipher import AES
from Crypto.Util.number import long_to_bytes
import hashlib
import random
import socketserver
import signal


FLAG = "HTBREDACTED"
DEBUG_MSG = "DEBUG MSG - "
p = 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
g = 2


class Handler(socketserver.BaseRequestHandler):
    def handle(self):
        signal.alarm(0)
        main(self.request)


class ReusableTCPServer(socketserver.ForkingMixIn, socketserver.TCPServer):
    pass


def sendMessage(s, msg):
    s.send(msg.encode())


def recieveMessage(s, msg):
    sendMessage(s, msg)
    return s.recv(4096).decode().strip()


def decrypt(encrypted, shared_secret):
    key = hashlib.md5(long_to_bytes(shared_secret)).digest()
    cipher = AES.new(key, AES.MODE_ECB)
    message = cipher.decrypt(encrypted)
    return message


def main(s):
    sendMessage(s, DEBUG_MSG + "Generating The Global DH Parameters\n")
    sendMessage(s, DEBUG_MSG + f"g = {g}, p = {p}\n")
    sendMessage(s, DEBUG_MSG + "Calculation Complete\n\n")

    sendMessage(s, DEBUG_MSG + "Generating The Public Key of CPU...\n")
    c = random.randrange(2, p - 1)
    C = pow(g, c, p)
    sendMessage(s, DEBUG_MSG + "Calculation Complete\n")
    sendMessage(s, DEBUG_MSG + "Public Key is: ???\n\n")

    M = recieveMessage(s, "Enter The Public Key of The Memory: ")

    try:
        M = int(M)
    except:
        sendMessage(s, DEBUG_MSG + "Unexpected Error Occured\n")
        exit()

    sendMessage(s, "\n" + DEBUG_MSG + "The CPU Calculates The Shared Secret\n")
    shared_secret = pow(M, c, p)
    sendMessage(s, DEBUG_MSG + "Calculation Complete\n\n")

    encrypted_sequence = recieveMessage(
        s, "Enter The Encrypted Initialization Sequence: ")

    try:
        encrypted_sequence = bytes.fromhex(encrypted_sequence)
        assert len(encrypted_sequence) % 16 == 0
    except:
        sendMessage(s, DEBUG_MSG + "Unexpected Error Occured\n")
        exit()

    sequence = decrypt(encrypted_sequence, shared_secret)

    if sequence == b"Initialization Sequence - Code 0":
        sendMessage(s, "\n" + DEBUG_MSG +
                    "Reseting The Protocol With The New Shared Key\n")
        sendMessage(s, DEBUG_MSG + f"{FLAG}")
    else:
        exit()


if __name__ == '__main__':
    socketserver.TCPServer.allow_reuse_address = True
    server = ReusableTCPServer(("0.0.0.0", 1337), Handler)
    server.serve_forever()

Dengan input M = 0, diperoleh decript key yang selalu sama

sehingga diperoleh ide penyelesaian

key = <input_user_0>

decrypted_message = AES.ECB(key).encrypt('Initialization Sequence - Code 0')
encrypted_message = AES.ECB(key).decrypt('<decrypted_message>')

flag.py

from Crypto.Cipher import AES
from Crypto.Util.number import long_to_bytes
import hashlib
import random
from base64 import b64encode

# M = 0
# shared_secret = pow(M, c, p)

shared_secret = 0
key = hashlib.md5(long_to_bytes(shared_secret)).digest()
print(key)
print(b64encode(key))

# dengan bantuan
# https://gchq.github.io/CyberChef/#recipe=AES_Encrypt(%7B'option':'Base64','string':'k7iFrf4NoInN9jSQT9WfcQ%3D%3D'%7D,%7B'option':'Hex','string':''%7D,'ECB','Raw','Hex',%7B'option':'Hex','string':''%7D)AES_Decrypt(%7B'option':'Base64','string':'k7iFrf4NoInN9jSQT9WfcQ%3D%3D'%7D,%7B'option':'Hex','string':''%7D,'ECB','Hex','Raw',%7B'option':'Hex','string':''%7D,%7B'option':'Hex','string':''%7D/disabled)&input=SW5pdGlhbGl6YXRpb24gU2VxdWVuY2UgLSBDb2RlIDA
# catatan, hasil operasi cyberchef dengan python berbeda sedikit, tapi dapat dikondisikan
# diperoleh

enc = bytes.fromhex("1af761314a07bf79f31aeb53bc9e1335e1749e1142b326d82a3c29ac37a042bf")

cipher = AES.new(key, AES.MODE_ECB)
message = cipher.decrypt(enc)

print(message)

# jawaban 
# Enter The Public Key of The Memory: 0
# Enter The Encrypted Initialization Sequence: 1af761314a07bf79f31aeb53bc9e1335e1749e1142b326d82a3c29ac37a042bf

$ nc <ip_target> <port>

...
Enter The Public Key of The Memory: 0
...
Enter The Encrypted Initialization Sequence: 1af761314a07bf79f31aeb53bc9e1335e1749e1142b326d82a3c29ac37a042bf
...

flag HTB{7h15_p2070c0l_15_pr0tec73d_8y_D@nb3er_c0pyr1gh7_1aws}