The OpenSSL support in MagLev is currently the basic support needed to
get md5 working and to get encrypted cookies in rails working (a few
other things may work as well). It was not an exhaustive
implementation. MagLev uses FFI to wrap the underlying libcrypto (see
lib/ruby/1.8/maglev/openssl/ffi).
You might be able to back-port some of the Cipher work from the 1.9
branch: E.g., see:
https://github.com/MagLev/maglev/blob/master-1.9/lib/ruby/1.9/maglev/openssl/cipher.rb
which appears to support aes-256-cbc. Perhaps Tim knows more?