MD5 function in SQLite

I am trying to port some sql from MySQL to SQLite, however we use mysql's md5() function, which doesn't exist in sqlite.

I've seen references to people recompiling sqlite to include this function, and i think it's possible to include user defined functions in sqlite (right?). So how do I go about adding md5() to sqlite? I'd rather not have to recompile the sqlite installed by my package manager, is it possible to have md5 without doing this?