CTFs and solutions

fool-the-oracle-v3/chall.py

@@ -0,0 +1,42 @@
+from Crypto.Cipher import AES
+from Crypto.Util.Padding import pad, unpad
+from Crypto.Random import get_random_bytes
+from random import randint
+from secret import flag
+
+assert (len(flag) == len("CRYPTO25{}") + 36)
+
+key = get_random_bytes(24)
+padding = get_random_bytes(randint(1, 15))
+flag = flag.encode()
+
+
+def encrypt() -> bytes:
+    data = bytes.fromhex(input("> ").strip())
+    payload = padding + data + flag
+
+    cipher = AES.new(key=key, mode=AES.MODE_ECB)
+    print(cipher.encrypt(pad(payload, AES.block_size)).hex())
+
+
+def main():
+    menu = \
+        "What do you want to do?\n" + \
+        "quit - quit the program\n" + \
+        "enc - encrypt something\n" + \
+        "help - show this menu again\n" + \
+        "> "
+
+    while True:
+        cmd = input(menu).strip()
+
+        if cmd == "quit":
+            break
+        elif cmd == "help":
+            continue
+        elif cmd == "enc":
+            encrypt()
+
+
+if __name__ == '__main__':
+    main()