solved easy

week05/hard/server.py

@@ -0,0 +1,124 @@
+import asyncio
+import base64
+import logging
+import random
+import subprocess
+from asyncio import StreamReader, StreamWriter
+
+from Crypto.Cipher import AES
+
+from pwn_utils import utils
+
+log = logging.getLogger(__name__)
+clients = {}  # task -> (reader, writer)
+
+KEY = random.randbytes(16)
+FACT_STORE = {
+    1: 'Rumors say that the most important secret is secret number 1337',
+    2: 'The 6 security goals are Confidentiality, Integrity, Availability, Authenticity, Accountability and Controlled Access.',
+    3: 'One of the first Computer Worms was the Morris Worm in 1988 (https://en.wikipedia.org/wiki/Morris_worm).',
+    4: 'Cloudflare uses a wall of lava lamps to generate randomness (https://blog.cloudflare.com/lavarand-in-production-the-nitty-gritty-technical-details/).',
+}
+
+SECRET_STORE = {
+    42: 'Answer to the Ultimate Question of Life, The Universe, and Everything',
+}
+
+
+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 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 handle_message(message: bytes, iv: bytes, mac: bytes) -> str:
+    kvs = [term.split(b'=') for term in message.split(b'&')]
+    args = {key: value for key, value in kvs}
+    type = args.get(b'type', b'')
+    number = int(args.get(b'number', b'0'))
+
+    expected_mac = cbc_mac(message, iv, KEY)
+    if expected_mac != mac:
+        if type == b'secrets':
+            # don't give any info for secrets
+            return 'MAC verification failed'
+        return f'MAC verification failed: expected {expected_mac.hex()}, got {mac.hex()}'
+    if type == b'funfact':
+        return FACT_STORE.get(number, 'No funfact available')
+    if type == b'secrets':
+        if number == 1337:
+            return subprocess.check_output('flag').decode()
+        return SECRET_STORE.get(number, 'No secret available')
+    return 'Unknown type'
+
+
+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:
+        while True:
+            message = await utils.read_line_safe(client_reader)
+            if message is None:
+                return
+            match message.split(';'):
+                case [m, iv, mac]:
+                    m = base64.b64decode(m)
+                    iv = base64.b64decode(iv)
+                    mac = base64.b64decode(mac)
+                    answer = handle_message(m, iv, mac)
+                    client_writer.write((answer + '\n').encode())
+                    continue
+                case _:
+                    client_writer.write(
+                        'Invalid message, expected format "message;iv;mac"\n'.encode()
+                    )
+    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=20205)
+    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()