The better way I was thinking about last night is to hash from a serial number,date.etc.
generating your 128 bit key,then you can use a symetric cipher such as aes in cbc mode or blowfish even.Trouble is you are going to spend more time trouble is you are going to spend more time doing the decrytion than anything else.Or you do it in hardware with an fpga,128 bit blowfish in cbc mode is equivelent to 168 bit triple des and is a lot faster.There is no known crack for blowfish so brute force would take on average 100x10^21 years at one key test per microsecond.Which is conciderably longer than current estimates for the age of the universe.