Well, Softcams are full of encryption routines for actually decrypting Emm's/ECM's so it would seem reasonably logical to use those routines to encrypt any keys. You'll likely have a choice of RSA, DES, IDEA or maybe a comination of all of them.
To do this, of course, you would need to modify the softcam source code so that would give you your chance to also embed your new encrypted keys into the actual code