te

cscg25/crypto/intro1/exploit.py

@@ -0,0 +1,45 @@
+from pwn import *
+import binascii
+
+
+p = remote("a96a15c9c5222abacb014e80-1024-intro-crypto-1.challenge.cscg.live", 1337, ssl=True)# Define functions for convenience
+
+def recv_until(delim):
+    return p.recvuntil(delim)
+
+def interact():
+    p.interactive()
+
+def send_payload(payload):
+    p.sendline(payload)
+
+def xor(bytes1, bytes2):
+    return bytes([b1 ^ b2 for b1, b2 in zip(bytes1, bytes2)])
+
+
+# Example interaction
+recv_until(b":")
+payload = b"41" * 74
+send_payload(payload)
+
+encrypted_plaintext = []
+
+for _ in range(255):
+    data = binascii.unhexlify(recv_until(b"\n").replace(b"\n",b"").split(b" ")[-1])
+    encrypted_plaintext.append(data)
+
+payload = b"\x41" * 74
+
+print(payload)
+
+keystreams = [xor(enc, payload) for enc in encrypted_plaintext]
+
+enc_flag = binascii.unhexlify(recv_until(b"\n").replace(b"\n",b"").split(b" ")[-1])
+print(enc_flag)
+
+dec_flags = [xor(keystream, enc_flag) for keystream in keystreams]
+
+for flag in dec_flags:
+        if b'CSCG{' in flag:
+            print(flag)
+

cscg25/crypto/intro1/main.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env pypy3
+
+import os
+from pydoc import plain
+from sys import byteorder
+from Crypto.Cipher import AES
+from Crypto.Util import Counter
+import hashlib
+
+# Create a secret.py file with a variable `FLAG` for local testing :)
+from secret import FLAG
+
+secret_key = os.urandom(16)
+
+def encrypt(plaintext, counter):
+    m = hashlib.sha256()
+    m.update(counter.to_bytes(8, byteorder="big"))
+
+    alg = AES.new(secret_key, AES.MODE_CTR, nonce=m.digest()[0:8])
+    ciphertext = alg.encrypt(plaintext)
+
+    return ciphertext.hex()
+
+def xor(bytes1, bytes2):
+    return bytes([b1 ^ b2 for b1, b2 in zip(bytes1, bytes2)])
+
+def main():
+    print("DES is broken, long live the secure AES encryption!")
+    print("Give me a plaintext and I'll encrypt it a few times for you. For more security of course!")
+
+    try:
+        plaintext = bytes.fromhex("41" * 512)
+        print(plaintext)
+    except ValueError:
+        print("Please enter a hex string next time.")
+        exit(0)
+    
+    encrypted_plaintext = []
+
+    for i in range(0, 255):
+        crypt = encrypt(plaintext, i)
+        encrypted_plaintext.append(bytes.fromhex(crypt))
+        print(f"Ciphertext {i:03d}: {crypt}")
+
+    keystreams = [xor(enc, plaintext) for enc in encrypted_plaintext]
+
+    enc_flag = encrypt(FLAG.encode("ascii"), int.from_bytes(os.urandom(1), byteorder="big"))
+    
+    print("Flag:", enc_flag)
+
+    dec_flags = [xor(keystream, bytes.fromhex(enc_flag)) for keystream in keystreams]
+
+    for flag in dec_flags:
+        if b'cscg' in flag:
+            print(flag)
+
+
+
+if __name__ == "__main__":
+    main()

cscg25/crypto/intro1/secret.py

@@ -0,0 +1 @@
+FLAG = "cscg{a1b2c3d4e5f67890abcdef1234567890abcdef1234567890abcdef1234}"