分野別セミナー

Abstract: Functional encryption is now receiving a lot of attention. However, the topic of functional encryption was preceded by functional secret sharing (SIAM Journal on Discrete Mathematics, 2000).
In this lecture, we explain some of the motivations behind functional secret sharing. We note that in functional secret sharing, we have, as in normal secret sharing, a dealer. However, after the participants received shares from the dealer, a function f will be chosen and the participants will be asked to evaluate f(secret), without any help of the dealer.
Two approaches are surveyed. The first one is non-interactive in the sense that the participants need to broadcast some partial evaluation of f(secret). Since broadcast is used, these partial evaluations should not facilitate a non-authorized set to compute f'(secret), except if f'(secret) follows logically from f(secret). The second approach is interactive in which stricter privacy requirements can be enforced. Most of our solutions are reusable.
We conclude with giving open problems.