perlgoon:

Crypt::Cipher::AES docs show a keysize method, so perhaps you could encrypt your data with it and compare it to the value you get with Crypt::CBC. Then when you find a configuration that matches, you can check the keysize. (Note: I don't use encryption modules, so I don't know if this may be helpful or not.)

...roboticus

When your only tool is a hammer, all problems look like your thumb.