slight update

week05/easy/server.py

@@ -0,0 +1,111 @@
+import asyncio
+import base64
+import hmac
+import logging
+import random
+import subprocess
+from asyncio import StreamReader, StreamWriter
+
+from Crypto.Cipher import AES
+from Crypto.Hash import CMAC
+
+from pwn_utils import utils
+
+log = logging.getLogger(__name__)
+clients = {}  # task -> (reader, writer)
+
+KEY = b'1337133713371337'
+
+
+def pkcs7(message: bytes, block_size: int = 16) -> bytes:
+    gap_size = block_size - (len(message) % block_size)
+    return message + bytes([gap_size] * gap_size)
+
+
+def calc_cbc_mac(message: bytes, iv: bytes, key: bytes) -> bytes:
+    cipher = AES.new(key, AES.MODE_CBC, iv)
+    message = pkcs7(message)
+    last_block = cipher.encrypt(message)[-16:]
+    return last_block
+
+
+def calc_hmac(message: bytes, key: bytes) -> bytes:
+    return hmac.new(key, message, digestmod='sha256').digest()
+
+
+def calc_cmac(message: bytes, key: bytes) -> bytes:
+    c = CMAC.new(key, ciphermod=AES)
+    c.update(message)
+    return c.digest()
+
+
+def check_challenge(challenge: bytes, hmac: bytes, cbc_mac: bytes, cmac: bytes) -> bool:
+    return (
+        hmac == calc_hmac(challenge, KEY)
+        and cbc_mac == calc_cbc_mac(challenge, b'\x00' * 16, KEY)
+        and cmac == calc_cmac(challenge, KEY)
+    )
+
+
+async def handle_client(client_reader: StreamReader, client_writer: StreamWriter):
+    try:
+        remote = client_writer.get_extra_info('peername')
+        if remote is None:
+            log.error('Could not get ip of client')
+            return
+        remote = '%s:%s' % (remote[0], remote[1])
+        log.info('new connection from: %s' % remote)
+    except Exception as e:
+        log.error('EXCEPTION (get peername): %s (%s)' % (e, type(e)))
+        return
+
+    try:
+        challenge = random.randbytes(35)
+        client_writer.write(challenge.hex().encode() + b'\n')
+        answer = await utils.read_line_safe(client_reader)
+        match answer.split(';'):
+            case [hmac, cbc_mac, cmac]:
+                hmac = base64.b64decode(hmac)
+                cbc_mac = base64.b64decode(cbc_mac)
+                cmac = base64.b64decode(cmac)
+                if check_challenge(challenge, hmac, cbc_mac, cmac):
+                    client_writer.write(subprocess.check_output('flag'))
+                else:
+                    client_writer.write(b'Invalid MACs!')
+            case _:
+                client_writer.write(b'Invalid input!')
+
+    except Exception as e:
+        utils.log_error(e, client_writer)
+
+
+def accept_client(client_reader: StreamReader, client_writer: StreamWriter):
+    task = asyncio.Task(handle_client(client_reader, client_writer))
+    clients[task] = (client_reader, client_writer)
+
+    def client_done(task):
+        del clients[task]
+        client_writer.close()
+        log.info('connection closed')
+
+    task.add_done_callback(client_done)
+
+
+def main():
+    # start server
+    loop = asyncio.get_event_loop()
+    f = asyncio.start_server(accept_client, host=None, port=20105)
+    log.info('Server waiting for connections')
+    loop.run_until_complete(f)
+    loop.run_forever()
+
+
+if __name__ == '__main__':
+    logging.basicConfig(
+        level=logging.INFO,
+        format='%(asctime)s %(levelname)s [%(module)s:%(lineno)d] %(message)s',
+    )
+
+    # "INFO:asyncio:poll took 25.960 seconds" is annyoing
+    logging.getLogger('asyncio').setLevel(logging.WARNING)
+    main()