FlexiADKG: Asynchronous Distributed Key Generation with configurable access structures and constant round complexity

Distributed Key Generation (DKG) enables threshold cryptographic key establishment without trusted third parties. Adapting DKG to asynchronous networks (ADKG) presents challenges. This paper addresses two critical limitations: (i) fixed thresholds , where each set of t+1 participants is identical, lacking the flexible configurations needed for asynchronous environments; and (ii) high complexity , stemming from parallel asynchronous binary agreement (ABA) instances during consensus. We propose FlexiADKG, an ADKG protocol achieving configurable threshold structures via vector space secret sharing, enabling heterogeneous authorization policies based on node attributes. We further present FlexiADKG+, an enhanced construction supporting composite access structures by unifying multiple authorization policies into a single MSP instance. Both protocols replace n parallel ABA instances with signature-free multivalued validated Byzantine agreement (MVBA), reducing round complexity from O(logn) to O(1). Implementation on geographically distributed AWS infrastructure demonstrates performance advantages: FlexiADKG achieves 61% runtime and 53% bandwidth consumption on average compared to state-of-the-art ADKG (SP’22), while FlexiADKG+ maintains practical efficiency with additional expressiveness for composite access structures. We provide formal security proofs validating all claimed properties for both constructions.