week06

week06/hard/client.py

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+#!/usr/bin/env python3
+import random
+import socket
+
+# Kerckhoff’s principle for the win
+# here are all the crypto primitives Alice and Bob are using
+from insecurelib import KDRV256, HMAC, encrypt, decrypt
+
+# Fill in the right target here
+HOST = 'this.is.not.a.valid.domain'  # TODO
+PORT1 = 20008
+PORT2 = 20108
+
+
+# note the numbers you encounter may be small for demonstration purposes.
+# Anyway, please do NOT brute force.
+
+
+# debug the data sent over the secure channel
+# we don't know the key, there is not much to debug here, ...
+def debug_secure_channel(s1, s2, data: str):
+    data = data.rstrip('\n')  # remove trailing newline
+    if len(data) >= 1024:
+        print(f"from {s1} to {s2}: '{data[:1024]}...'")
+    else:
+        print(f"from {s1} to {s2}: '{data}...'")
+
+    iv, ciphertext, mac = data.split(',')
+    assert len(iv) == 16 * 2  # a hexlified byte is two bytes long, the IV should be 16 bytes
+    assert (
+        len(ciphertext) % (16 * 2) == 0
+    )  # a hexlified byte is two bytes long, AES block size is 128 bit (16 byte)
+    assert (
+        len(mac) == 16 * 2
+    )  # a quite short MAC. Hint: you still don't want to brute force it!
+
+
+def main():
+    # We connect to Alice and Bob and relay their messages.
+    # They send all their communication over us. How convenient :-)
+    # Dolev-Yao attacker model without any low-level effort.
+
+    s1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s1.connect((HOST, PORT1))
+    s1f = s1.makefile('rw')  # file abstraction for the sockets
+
+    s2 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s2.connect((HOST, PORT2))
+    s2f = s2.makefile('rw')
+
+    # A -> B: p,g,X
+    data = s1f.readline().rstrip('\n')
+    print(f"from s1 to s2: '{data}'")
+    p, g, X = map(int, data.split(','))
+
+    # TODO: get the flag
+
+    s1f.close()
+    s2f.close()
+    s1.close()
+    s2.close()
+
+
+if __name__ == '__main__':
+    main()