Paper 2026/2588

Eras MPC: Granular Preprocessing and Abort Recovery with Dynamic Committees

Abstract

MPC with dynamic committees achieves scalability by having small committees execute each round of the computation, instead of involving all parties in the entire execution. However, achieving Guaranteed Output Delivery in efficient information theoretical protocols requires larger honest majority committees, limiting scalability. Moreover, using preprocessed correlated randomness to speed up the computation is prohibitively expensive due to the cost of transferring such randomness to parties that have not yet joined the execution. We propose Eras MPC, a model where small dishonest majority computation committees execute one or more rounds of the computation with the help of honest majority preprocessing and checkpointing committees. The computation is carried out in "Eras", which are sets of shorter epochs. In the beginning of each Era's first epoch, a preprocessing committee generates correlated randomness for the computation epochs to be executed by different computation committees. In the end of an Era, checkpoint committees verify the current state of the computation, save this state if it is valid and provide the latest valid state to the next Era. We show an Eras MPC protocol where the preprocessing is carried out using an honest majority MPC protocol to generate authenticated Beaver triples, requiring only enough rounds of interaction to perform two subsequent batches of multiplications. The computation is done via the SPDZ online phase executed in each epoch by a small dishonest majority committee. Finally, intermediate state is checkpointed by verifying the validity of wire shares and saving wire values in $4$ rounds, each executed by a different honest majority checkpoint committee.