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diff --git a/lib/Crypto/Cipher/__init__.py b/lib/Crypto/Cipher/__init__.py
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+#
+# A block cipher is instantiated as a combination of:
+# 1. A base cipher (such as AES)
+# 2. A mode of operation (such as CBC)
+#
+# Both items are implemented as C modules.
+#
+# The API of #1 is (replace "AES" with the name of the actual cipher):
+# - AES_start_operaion(key) --> base_cipher_state
+# - AES_encrypt(base_cipher_state, in, out, length)
+# - AES_decrypt(base_cipher_state, in, out, length)
+# - AES_stop_operation(base_cipher_state)
+#
+# Where base_cipher_state is AES_State, a struct with BlockBase (set of
+# pointers to encrypt/decrypt/stop) followed by cipher-specific data.
+#
+# The API of #2 is (replace "CBC" with the name of the actual mode):
+# - CBC_start_operation(base_cipher_state) --> mode_state
+# - CBC_encrypt(mode_state, in, out, length)
+# - CBC_decrypt(mode_state, in, out, length)
+# - CBC_stop_operation(mode_state)
+#
+# where mode_state is a a pointer to base_cipher_state plus mode-specific data.
+
+import os
+
+from Crypto.Cipher._mode_ecb import _create_ecb_cipher
+from Crypto.Cipher._mode_cbc import _create_cbc_cipher
+from Crypto.Cipher._mode_cfb import _create_cfb_cipher
+from Crypto.Cipher._mode_ofb import _create_ofb_cipher
+from Crypto.Cipher._mode_ctr import _create_ctr_cipher
+from Crypto.Cipher._mode_openpgp import _create_openpgp_cipher
+from Crypto.Cipher._mode_ccm import _create_ccm_cipher
+from Crypto.Cipher._mode_eax import _create_eax_cipher
+from Crypto.Cipher._mode_siv import _create_siv_cipher
+from Crypto.Cipher._mode_gcm import _create_gcm_cipher
+from Crypto.Cipher._mode_ocb import _create_ocb_cipher
+
+_modes = { 1:_create_ecb_cipher,
+           2:_create_cbc_cipher,
+           3:_create_cfb_cipher,
+           5:_create_ofb_cipher,
+           6:_create_ctr_cipher,
+           7:_create_openpgp_cipher,
+           9:_create_eax_cipher
+           }
+
+_extra_modes = { 8:_create_ccm_cipher,
+                10:_create_siv_cipher,
+                11:_create_gcm_cipher,
+                12:_create_ocb_cipher
+                }
+
+def _create_cipher(factory, key, mode, *args, **kwargs):
+
+    kwargs["key"] = key
+
+    modes = dict(_modes)
+    if kwargs.pop("add_aes_modes", False):
+        modes.update(_extra_modes)
+    if not mode in modes:
+        raise ValueError("Mode not supported")
+
+    if args:
+        if mode in (8, 9, 10, 11, 12):
+            if len(args) > 1:
+                raise TypeError("Too many arguments for this mode")
+            kwargs["nonce"] = args[0]
+        elif mode in (2, 3, 5, 7):
+            if len(args) > 1:
+                raise TypeError("Too many arguments for this mode")
+            kwargs["IV"] = args[0]
+        elif mode == 6:
+            if len(args) > 0:
+                raise TypeError("Too many arguments for this mode")
+        elif mode == 1:
+            raise TypeError("IV is not meaningful for the ECB mode")
+
+    return modes[mode](factory, **kwargs)