ALL the CTFS of Crypto2025 finally

crypto-simmetric/decrypt_it_if_you_are_fast_enough/attack.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+import os
+import random
+from time import time
+from pwn import *
+
+HOST = "130.192.5.212"
+PORT = "6562"
+server = remote(HOST, PORT)
+example_flag = "5377d37d23d8b447c3ad04300eaf24d033fceb109ebf764876103b150ff7693f16d220d1a56b2043f503c2fd5ebd"
+lenFlag = len(bytes.fromhex(example_flag))
+sleepT = 0.1
+print(server.recv(1024))
+sleep(sleepT)
+server.send(b'y\n')
+sleep(sleepT)
+print(server.recv(1024))
+sleep(sleepT)
+payload = b'A'*lenFlag
+server.send(payload)
+server.send(b'\n')
+
+seed = int(time.time())
+payload_enc = server.recv(1024)
+server.send(b'f\n')
+flag_enc = server.recv(1024)
+print(f"Payload:{payload_enc.split(b'\n')[0]} flagEnc:{flag_enc.split(b'\n')[0]}")
+payload_enc = bytes.fromhex(payload_enc.split(b'\n')[0].decode())
+flag_enc = bytes.fromhex(flag_enc.split(b'\n')[0].decode())
+
+ks = [ p ^ pe for p,pe in zip(payload,payload_enc)]
+flag = [ f ^ k for f,k in zip(flag_enc,ks)]
+print(bytes(flag))
+# The script sometimes fail if it goes to fast, just rerun it

crypto-simmetric/decrypt_it_if_you_are_fast_enough/chall.py

@@ -0,0 +1,31 @@
+import os
+import random
+from time import time
+from Crypto.Cipher import ChaCha20
+from Crypto.Util.number import long_to_bytes
+from secret import flag
+
+key = os.urandom(32)
+
+
+def encrypt(msg):
+    random.seed(int(time()))
+    cipher = ChaCha20.new(
+        key=key, nonce=long_to_bytes(random.getrandbits(12*8)))
+    return cipher.encrypt(msg.encode())
+
+
+def main():
+
+    confirm = input("Want to encrypt? (y/n/f)")
+    while confirm.lower() != 'n':
+        if confirm.lower() == 'y':
+            msg = input("> ")
+            print(encrypt(msg).hex())
+        elif confirm.lower() == 'f':
+            print(encrypt(flag).hex())
+        confirm = input("Want to encrypt something else? (y/n/f)")
+
+
+if __name__ == '__main__':
+    main()