FAQ

1) Why is RSA faster on a Mega core then an 8515 ?
2) Why do is the AVRCryptoLib only for the Mega core ?

1) Why is RSA faster on a Mega core then an 8515 ?

The 8515 does not have a MUL instruction that makes the difference it also make the code a bit smaller. 

2) Why do is the AVRCryptoLib only for the Mega core

The mega core is the only core that is develop, but you can compile it for the older cores.