How to shuffle in public

  • Authors:
  • Ben Adida;Douglas Wikström

  • Affiliations:
  • MIT, Computer Science and Artificial Intelligence Laboratory;ETH Zürich, Department of Computer Science

  • Venue:
  • TCC'07 Proceedings of the 4th conference on Theory of cryptography
  • Year:
  • 2007

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Abstract

We show how to obfuscate a secret shuffle of ciphertexts: shuffling becomes a public operation. Given a trusted party that samples and obfuscates a shuffle before any ciphertexts are received, this reduces the problem of constructing a mix-net to verifiable joint decryption. We construct public-key obfuscations of a decryption shuffle based on the Boneh-Goh-Nissim (BGN) cryptosystem and a re-encryption shuffle based on the Paillier cryptosystem. Both allow efficient distributed verifiable decryption. Finally, we give a distributed protocol for sampling and obfuscating each of the above shuffles and show how it can be used in a trivial way to construct a universally composable mix-net. Our constructions are practical when the number of senders N is small, yet large enough to handle a number of practical cases, e.g. N = 350 in the BGN case and N = 2000 in the Paillier case.