I think the idea is that you should be able to reconstruct the data fully from any X of Y configured shards of the data (and keys). You can do this with multi-signature keys and reed-solomon codes for the data. There may be some smart way to combine the two that exists. Anybody know of an algorithm that would accomplish this? I vaguely remember reading a paper using Goppa codes that worked likes this, but google-fu is failing this morning.