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The DHKE challenge.
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from Crypto.Cipher import AES | |
from Crypto.Util.number import long_to_bytes | |
import hashlib | |
import random | |
import socketserver | |
import signal | |
FLAG = "CTF{--REDACTED--}" | |
DEBUG_MSG = "DEBUG MSG - " | |
p = 0x509efab16c5e2772fa00fc180766b6e62c09bdbd65637793c70b6094f6a7bb8189172685d2bddf87564fe2a6bc596ce28867fd7bbc300fd241b8e3348df6a0b076a0b438824517e0a87c38946fa69511f4201505fca11bc08f257e7a4bb009b4f16b34b3c15ec63c55a9dac306f4daa6f4e8b31ae700eba47766d0d907e2b9633a957f19398151111a879563cbe719ddb4a4078dd4ba42ebbf15203d75a4ed3dcd126cb86937222d2ee8bddc973df44435f3f9335f062b7b68c3da300e88bf1013847af1203402a3147b6f7ddab422d29d56fc7dcb8ad7297b04ccc52f7bc5fdd90bf9e36d01902e0e16aa4c387294c1605c6859b40dad12ae28fdfd3250a2e9 | |
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() |
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