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value: it has to be updated every time another element is added to the accumulator, and it cannot be used with outdated accumulator values.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 blockchainbased 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to be updated a small number of times, and old-accumulator compatibility, which means that a witness can be used with outdated accumulator values.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.