A distributed key generation (DKG) protocol is a central component in distributed cryptosystems. It allows a group of participants to jointly generate a pair of keys (private key and public key) without assuming any trusted participant. The public key is output in clear but only authorised subgroups of participants are able to reconstruct or use the private key. Existing literature on DKG protocols assumes equal authority for participants. In this study, the authors consider the problem of DKG in groups with hierarchical structure where the authorised subsets can be defined by a hierarchical threshold access structure. They first propose a verifiable hierarchical threshold secret sharing protocol. On the basis of this construction, they then propose a new DKG protocol with hierarchical threshold access structure for discrete-logarithm-based cryptosystems. It is shown that the proposed protocols satisfy all the security requirements.
