International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Updating the Parameters of a Threshold Scheme by Minimal Broadcast

S. G. Barwick
W.-A. Jackson
K. M. Martin
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Abstract: Threshold schemes allow secret data to be protected amongst a set of participants in such a way that only a pre-specified threshold of participants can reconstruct the secret from private information (shares) distributed to them on system setup using secure channels. We consider the general problem of designing unconditionally secure threshold schemes whose defining parameters (the threshold and the number of participants) can later be changed by using only public channel broadcast messages. In this paper we are interested in the efficiency of such threshold schemes, and seek to minimise storage costs (size of shares) as well as optimise performance in low bandwidth environments by minimising the size of necessary broadcast messages. We prove a number of lower bounds on the smallest size of broadcast message necessary to make general changes to the parameters of a threshold scheme in which each participant already holds shares of minimal size. We establish the tightness of these bounds by demonstrating optimal schemes.
  title={Updating the Parameters of a Threshold Scheme by Minimal Broadcast},
  booktitle={IACR Eprint archive},
  keywords={Cryptology, secret sharing schemes, threshold schemes,},
  note={ 12622 received 22 Jul 2004},
  author={S. G. Barwick and W.-A. Jackson and K. M. Martin},