Efficient Asynchronous Accumulators for Distributed PKI.

Cryptographic accumulators are a tool for compact set representation and secure set membership proofs. When an element is added to a set by means of an accumulator, a membership witness is generated. This witness can later be used to prove the membership of the element. Typically, the membership witness has to be synchronized with the accumulator value: it has to be updated every time another element is added to the accumulator, and it cannot be used with outdated accumulator values. However, in many distributed applications such as blockchain-based public key infrastructures, requiring strict synchronization is prohibitive. We define low update frequency, which means that a witness only needs to be updated a small number of times, and old-accumulator compatibility, which means that a witness can be used with outdated accumulator values. Finally, we propose an accumulator that achieves both of those properties.