Adi Shamir

In this paper we show how to divide data D into n pieces in such a way that D is easily reconstructable from any k pieces, but even complete knowledge of k - 1 pieces reveals absolutely no information about D. This technique enables the construction of robust key management schemes for cryptographic systems that can function securely and reliably even when misfortunes destroy half the pieces and security breaches expose all but one of the remaining pieces.

The classical fixedpoint approach toward recursive programs suggests choosing the “least defined fixedpoint” as the most appropriate solution to a recursive program. A new approach is described which introduces an “optimal fixedpoint,” which, in contrast to the least defined fixedpoint, embodies the maximal amount of valuable information embedded in the program. The practical implications of this approach are discussed and techniques for proving properties of optimal fixedpoints are given. The presentation is informal, with emphasis on examples.