Upgrade basic AES block cipher

include/boost/crypt2/aes/cipher_mode.hpp

@@ -0,0 +1,17 @@
+// Copyright 2025 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#ifndef BOOST_CIPHER_MODE_HPP
+#define BOOST_CIPHER_MODE_HPP
+
+namespace boost::crypt::aes {
+
+enum class cipher_mode
+{
+    ecb,        // Electronic Codebook
+};
+
+} // namespace boost::crypt::aes
+
+#endif //BOOST_CIPHER_MODE_HPP