added default.nix and various ctf examples

ctf-solutions/bean_counter.py

@@ -0,0 +1,92 @@
+'''
+Solution for https://cryptohack.org/courses/symmetric/bean_counter/
+'''
+
+import os
+import requests
+from math import ceil
+
+from Crypto.Cipher import AES
+
+from imp.math.util import xor_bytes
+
+class StepUpCounter(object):
+    def __init__(self, step_up=False):
+        self.value = os.urandom(16).hex()
+        self.step = 1
+        self.stup = step_up
+
+    def increment(self):
+        if self.stup:
+            self.newIV = hex(int(self.value, 16) + self.step)
+        else:
+            self.newIV = hex(int(self.value, 16) - self.stup)
+        self.value = self.newIV[2:len(self.newIV)]
+        return bytes.fromhex(self.value.zfill(32))
+
+    def __repr__(self):
+        self.increment()
+        return self.value
+
+'''
+NOTE: Since step_up is used ONLY as false, we can simplify:  
+class StepUpCounter(object):
+    def __init__(self):
+        self.value = os.urandom(16).hex()
+
+    # SAME AS DOING NOTHING
+    def increment(self):
+        return self.value()
+
+    def __repr__(self):
+        return self.value
+'''
+
+URL = 'https://aes.cryptohack.org/bean_counter'
+
+def get_encrypted() -> bytes:
+    resp = requests.get(f'{URL}/encrypt/')
+    encrypted = bytes.fromhex(resp.json()['encrypted'])
+    return encrypted
+
+PNG_HEADER = [
+    '89', '50', '4e', '47', 
+    '0d', '0a', '1a', '0a', 
+    '00', '00', '00', '0d', 
+    '49', '48', '44', '52'
+]
+
+def main() -> None:
+    # NOTE: the counter is constant!
+    ctr = StepUpCounter()
+    # init = ctr.increment()
+    # init_val = ctr.value
+    # for i in range(2560000):
+    #     if ctr.increment() != init:
+    #         print('Counter Changed')
+    #         print(i)
+    #         break
+    #     elif ctr.value != init_val:
+    #         print('valued changed')
+    #         print(i)
+    #         break
+            
+    # PNGs *should* have a constant header, we will use the first 16 bytes
+    # to determine what the counter value must be set to
+    encrypted = get_encrypted()
+    png_header = bytes.fromhex(''.join(PNG_HEADER))
+    ctr_value = xor_bytes(encrypted[:16], png_header)
+    # apply the counter value to the entire encrypted image (in blocks of 16 bytes)
+    BLOCK_SIZE = 16
+    with open('bean_flag.png', 'wb') as f:
+        for i in range(ceil(len(encrypted) / BLOCK_SIZE)):
+            block = encrypted[i*BLOCK_SIZE : (i+1)*BLOCK_SIZE]
+            # NOTE: the block we get is not guaranteed to be block size (ie if at end)
+            plaintext_block = xor_bytes(block, ctr_value[:len(block)])
+            f.write(plaintext_block)
+
+if __name__ == '__main__':
+    try:
+        main()
+    except (KeyboardInterrupt, EOFError):
+        print('\n[!] Interrupt')

ctf-solutions/flipping_cookie.py

@@ -0,0 +1,55 @@
+'''
+Solution to https://cryptohack.org/courses/symmetric/flipping_cookie/ 
+'''
+
+import requests
+from datetime import datetime, timedelta
+
+URL = 'https://aes.cryptohack.org/flipping_cookie'
+
+# NOTE: assumes A and B are equal length
+def xor_bytes(A: bytes, B: bytes) -> bytes:
+    return b''.join([(a ^ b).to_bytes() for (a, b) in zip(A, B)])
+def xor_str(A: str, B: str) -> str:
+    return ''.join([chr(ord(a) ^ ord(b)) for (a, b) in zip(A, B)])
+
+def gen_expiry() -> str:
+    return (datetime.today() + timedelta(days=1)).strftime("%s")
+
+def get_cookie() -> tuple[bytes, bytes]:
+    resp = requests.get(f'{URL}/get_cookie/')
+    cookie = resp.json()['cookie']
+    iv = bytes.fromhex(cookie[:32])
+    ciphertext = bytes.fromhex(cookie[32:])
+    return iv, ciphertext
+
+
+def main() -> None:
+    # cookie flipping preprocessing step
+    admin_len = len('admin=')
+    expiry_len = len(';expiry=') + len(gen_expiry())
+    admin_mask = '\x00' * admin_len
+    expiry_mask = '\x00' * expiry_len
+    # we aim to replace "admin=False;" with "admin=True;;"
+    # NOTE: double semicolon ("True;;") is intentional
+    # NOTE: and the server won't ever realise it happened!
+    deletion = admin_mask  + 'False' + expiry_mask
+    insertion = admin_mask + 'True;' + expiry_mask
+    # determine the value that replaces deletion with insertion
+    cookie_flip = xor_str(deletion, insertion)
+
+    # get our new cookie and apply the cookie flip!
+    iv, ciphertext = get_cookie()
+    flipped_iv = xor_bytes(cookie_flip.encode(), iv)
+
+    print('Flipped Cookie:')
+    print('IV:', flipped_iv.hex())
+    print('Body:', ciphertext.hex())
+
+    
+    
+        
+    
+
+if __name__ == '__main__':
+    main()

ctf-solutions/symmetry.py

@@ -0,0 +1,39 @@
+'''
+Solution to https://cryptohack.org/courses/symmetric/symmetry/ 
+'''
+
+import os
+import requests
+
+from imp.math.util import xor_bytes, xor_str
+
+URL = 'https://aes.cryptohack.org/symmetry'
+
+def get_encrypted_flag() -> tuple[bytes, bytes]:
+    resp = requests.get(f'{URL}/encrypt_flag/')
+    ciphertext = resp.json()['ciphertext']
+    iv = bytes.fromhex(ciphertext[:32])
+    flag = bytes.fromhex(ciphertext[32:])
+    return iv, flag
+
+def encrypt(plaintext: bytes, iv: bytes) -> bytes:
+    plaintext, iv = plaintext.hex(), iv.hex()
+    resp = requests.get(f'{URL}/encrypt/{plaintext}/{iv}')
+    return bytes.fromhex(resp.json()['ciphertext'])
+
+def main() -> None:
+    iv, flag = get_encrypted_flag()
+    # generate a random plaintext of equal length to the flag
+    random_plaintext = os.urandom(len(flag))
+    random_ciphertext = encrypt(random_plaintext, iv)
+    # XOR random plaintext with corresponding ciphertext to
+    # get the set generated by IV under the keyed AES permutation
+    aes_orbit = xor_bytes(random_plaintext, random_ciphertext)
+    # XOR this orbit with the flag to get the hexed flag plaintext
+    flag_plaintext = xor_bytes(flag, aes_orbit)
+    print('Flag:', flag_plaintext.decode())
+    
+    print('IV:', iv.hex())
+
+if __name__ == '__main__':
+    main()

default.nix

@@ -0,0 +1,10 @@
+let
+  sources = import ./nix/sources.nix;
+  pkgs = import sources.nixpkgs {};
+  # Let all API attributes like "poetry2nix.mkPoetryApplication"
+  # use the packages and versions (python3, poetry etc.) from our pinned nixpkgs above
+  # under the hood:
+  poetry2nix = import sources.poetry2nix {inherit pkgs;};
+  myPythonApp = poetry2nix.mkPoetryApplication {projectDir = ./.;};
+in
+  myPythonApp

examples/cryptohack-ecboracle.py

@@ -34,7 +34,7 @@ def encrypt(b: bytes) -> bytes:
     return bytes.fromhex(resp['ciphertext'])
 
 def main() -> None:
-    paddingoracle.crack(encrypt, pad, CHARSET, 64, batch_size=2, debug=True)
+    paddingoracle.crack(encrypt, pad, CHARSET, 16, batch_size=20, debug=True)