A New Protocol for Conditional Disclosure of Secrets and Its Applications

  • Authors:
  • Sven Laur;Helger Lipmaa

  • Affiliations:
  • Helsinki University of Technology, Finland;University College London, UK

  • Venue:
  • ACNS '07 Proceedings of the 5th international conference on Applied Cryptography and Network Security
  • Year:
  • 2007

Quantified Score

Hi-index 0.00

Visualization

Abstract

Many protocols that are based on homomorphic encryption are private only if a client submits inputs from a limited range $\mathcal{S}$. Conditional disclosure of secrets (CDS) helps to overcome this restriction. In a CDS protocol for a set $\mathcal{S}$, the client obtains server's secret if and only if the client's inputs belong to $\mathcal{S}$ and thus the server can guard itself against malformed queries. We extend the existing CDS protocols to work over additively homomorphic cryptosystems for every set from NP/poly. The new construction is modular and easy to apply. As an example, we derive a new oblivious transfer protocol with log-squared communication and a millionaire's protocol with logarithmic communication. We also implement private, universally verifiable and robust multi-candidate electronic voting so that all voters only transmit an encryption of their vote. The only hardness assumption in all these protocols is that the underlying public-key cryptosystem is IND-CPA secure and the plaintext order does not have small factors.