Huge: Yes. Hack: No :-) It's the inline crypt implementation (gives additional 25% performance)
A Crypt_Base class, for better code maintain and double code-reducing, is (probably) planed which will move this inline-crypt code (and also the same inline-crypt code in Rijndael.php), besides other double code, to a generic base method which all ciphers then are able to use, so no double code will be there anymore.

This is the current result of the discussion between Terra, Patrick and myself (via Email... where we was discussing about the DES.php performance Update from Patrick)

Terra, Patrick... we should discuss the Crypt_Base issue here in github... so that Bantu is also informed.