diff --git a/RNS/Cryptography/AES.py b/RNS/Cryptography/AES.py
index 2689509..f3130b4 100644
--- a/RNS/Cryptography/AES.py
+++ b/RNS/Cryptography/AES.py
@@ -36,15 +36,48 @@ if cp.PROVIDER == cp.PROVIDER_INTERNAL:
     
 elif cp.PROVIDER == cp.PROVIDER_PYCA:
     from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
-
-    if pu.cryptography_old_api():
-        from cryptography.hazmat.backends import default_backend
+    if pu.cryptography_old_api(): from cryptography.hazmat.backends import default_backend
 
 
 class AES_128_CBC:
-
     @staticmethod
     def encrypt(plaintext, key, iv):
+        if len(key) != 16: raise ValueError(f"Invalid key length {len(key)*8} for {self}")
+        if cp.PROVIDER == cp.PROVIDER_INTERNAL:
+            cipher = AES(key)
+            return cipher.encrypt(plaintext, iv)
+
+        elif cp.PROVIDER == cp.PROVIDER_PYCA:
+            if not pu.cryptography_old_api():
+                cipher = Cipher(algorithms.AES(key), modes.CBC(iv))
+            else:
+                cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
+
+            encryptor = cipher.encryptor()
+            ciphertext = encryptor.update(plaintext) + encryptor.finalize()
+            return ciphertext
+
+    @staticmethod
+    def decrypt(ciphertext, key, iv):
+        if len(key) != 16: raise ValueError(f"Invalid key length {len(key)*8} for {self}")
+        if cp.PROVIDER == cp.PROVIDER_INTERNAL:
+            cipher = AES(key)
+            return cipher.decrypt(ciphertext, iv)
+
+        elif cp.PROVIDER == cp.PROVIDER_PYCA:
+            if not pu.cryptography_old_api():
+                cipher = Cipher(algorithms.AES(key), modes.CBC(iv))
+            else:
+                cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=default_backend())
+
+            decryptor = cipher.decryptor()
+            plaintext = decryptor.update(ciphertext) + decryptor.finalize()
+            return plaintext
+
+class AES_256_CBC:
+    @staticmethod
+    def encrypt(plaintext, key, iv):
+        if len(key) != 32: raise ValueError(f"Invalid key length {len(key)*8} for {self}")
         if cp.PROVIDER == cp.PROVIDER_INTERNAL:
             cipher = AES(key)
             return cipher.encrypt(plaintext, iv)
@@ -61,6 +94,7 @@ class AES_128_CBC:
 
     @staticmethod
     def decrypt(ciphertext, key, iv):
+        if len(key) != 32: raise ValueError(f"Invalid key length {len(key)*8} for {self}")
         if cp.PROVIDER == cp.PROVIDER_INTERNAL:
             cipher = AES(key)
             return cipher.decrypt(ciphertext, iv)