Answering kbs972;
There are restrictions on release of cetain types of encryption information here in the U.S.A. that are controlled by ITAR. Some reference designs show generic methods for achieving the desired effect. Some companies my not be allow to export that information, but may be able to provide it within the country you are located, based on how they apply for, and release that information to you.
Sasushi1;
Dallas Semiconductor was aquired by Maxim Semi, and may still offer the product listed above. Check with them - the one wire interface is pretty good, and only takes 1 I/O pin (as the name implies).
As kbs972 very corretly points out, you will not be able to protect (encrypt) the .rbt file as the Cyclone device has no means of decrypting it.
Good luck with your efforts.