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import os
import string
import random
import socketserver
import signal
from hashlib import sha256
from ocb.aes import AES
from ocb import OCB
FLAG =
BLOCKSIZE = 16
MENU = br"""
[1] Encrypt
[2] Decrypt
[3] Get Flag
[4] Exit
"""
class Task(socketserver.BaseRequestHandler):
def _recvall(self):
pass
def send(self, msg, newline=True):
pass
def recv(self, prompt=b'> '):
pass
def recvhex(self, prompt=b'> '):
pass
def proof_of_work(self):
pass
def timeout_handler(self, signum, frame):
pass
def encrypt(self, nonce, message, associate_data=b''):
assert nonce not in self.NONCEs
self.NONCEs.add(nonce)
self.ocb.setNonce(nonce)
tag, cipher = self.ocb.encrypt(bytearray(message), bytearray(associate_data))
return (bytes(cipher), bytes(tag))
def decrypt(self, nonce, cipher, tag, associate_data=b''):
self.ocb.setNonce(nonce)
authenticated, message = self.ocb.decrypt(
*map(bytearray, (associate_data, cipher, tag))
)
if not authenticated:
raise ValueError('REJECT')
return bytes(message)
def handle(self):
signal.signal(signal.SIGALRM, self.timeout_handler)
signal.alarm(60)
if not self.proof_of_work():
return
aes = AES(128)
self.ocb = OCB(aes)
KEY = os.urandom(BLOCKSIZE)
self.ocb.setKey(KEY)
self.NONCEs = set()
while True:
USERNAME = self.recv(prompt=b'Enter username > ')
if len(USERNAME) > BLOCKSIZE:
self.send(b"I can't remember long names")
continue
if USERNAME == b'Alice':
self.send(b'Name already used')
continue
break
signal.alarm(60)
while True:
self.send(MENU, newline=False)
try:
choice = int(self.recv(prompt=b'Enter option > '))
if choice == 1:
nonce = self.recvhex(prompt=b'Enter nonce > ')
message = self.recvhex(prompt=b'Enter message > ')
associate_data = b'from ' + USERNAME
ciphertext, tag = self.encrypt(nonce, message, associate_data)
self.send(str.encode(f"ciphertext: {ciphertext.hex()}"))
self.send(str.encode(f"tag: {tag.hex()}"))
elif choice == 2:
nonce = self.recvhex(prompt=b'Enter nonce > ')
ciphertext = self.recvhex(prompt=b'Enter ciphertext > ')
tag = self.recvhex(prompt=b'Enter tag > ')
associate_data = self.recvhex(prompt=b'Enter associate data > ')
message = self.decrypt(nonce, ciphertext, tag, associate_data)
self.send(str.encode(f"message: {message.hex()}"))
elif choice == 3:
nonce = self.recvhex(prompt=b'Enter nonce > ')
ciphertext = self.recvhex(prompt=b'Enter ciphertext > ')
tag = self.recvhex(prompt=b'Enter tag > ')
associate_data = b'from Alice'
message = self.decrypt(nonce, ciphertext, tag, associate_data)
if message == b'please_give_me_the_flag':
self.send(FLAG)
elif choice == 4:
break
else:
break
except:
self.send(b'Error!')
break
signal.alarm(0)
self.send(b'Bye!')
self.request.close()
class ForkedServer(socketserver.ForkingMixIn, socketserver.TCPServer):
pass
if __name__ == "__main__":
HOST, PORT = '0.0.0.0', 10000
print(HOST, PORT)
server = ForkedServer((HOST, PORT), Task)
server.allow_reuse_address = True
server.serve_forever()
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