CTFs and solutions

decrypt-the-flag/chall.py

@@ -0,0 +1,34 @@
+import random
+from Cryptodome.Cipher import ChaCha20
+from Cryptodome.Util.number import long_to_bytes
+#from secret import flag, randkey
+
+nonce = -1
+flag = 'Z'*46
+randkey= b'A'*32
+def encrypt_and_update(msg, nonce):
+    print(f"Encrypting with NONCE:{nonce}")
+    cipher = ChaCha20.new(key=randkey, nonce=long_to_bytes(nonce))
+    nonce = random.getrandbits(12*8)
+    return cipher.encrypt(msg.encode())
+
+
+def main():
+    seed = int(input(
+        "Hi, our system doesn't support analogic entropy... so please give a value to initialize me!\n> "))
+    random.seed(seed)
+    nonce = random.getrandbits(12*8)
+
+    print("OK! I can now give you the encrypted secret!")
+    print(encrypt_and_update(flag, nonce).hex())
+
+    confirm = input("Do you want to encrypt something else? (y/n)")
+    while confirm.lower() != 'n':
+        if confirm.lower() == 'y':
+            msg = input("What is the message? ")
+            print(encrypt_and_update(msg, nonce).hex())
+        confirm = input("Do you want to encrypt something else? (y/n)")
+
+
+if __name__ == '__main__':
+    main()