Perhaps you should take one (or two) steps back and tell us what you are trying to achieve with encrypting a (long) filename?

I see little or no benefit from a security point of view. Once an attacker has gained access to your file-system, having the filenames encrypted will then buy you little or no extra protection. Or perhaps you might wish to save the encrypted filenames into a database and thus "break" the link between the data in the database and the physical files on disk? Again, you will be better served by having your database and the access to it well protected and secured.

Not knowing anything more detailed about what you are trying to achieve, it strikes me as "protection through obfuscation" which is always the wrong way to do it. But I may be mistaken and you are trying to do something totally different, so please enlighten us.

The absolutely best way to encrypt anything is of course the use of a "one time pad" with a key length longer than the message. There are no known ways, brute force or otherwise, to reliably decrypt such a message.