# Encryption Switching Protocols

3 CASCADE - Construction and Analysis of Systems for Confidentiality and Authenticity of Data and Entities
DI-ENS - Département d'informatique de l'École normale supérieure, Inria Paris-Rocquencourt, CNRS - Centre National de la Recherche Scientifique : UMR 8548
4 Groupe Crypto
ICTEAM - Institute of Information and Communication Technologies, Electronics and Applied Mathematics
Abstract : We formally define the primitive of encryption switching protocol (ESP), allowing to switch between two encryption schemes. Intuitively, this two-party protocol converts given ciphertexts from one scheme into ciphertexts of the same messages under the other scheme, for any polynomial number of switches, in any direction. Although ESP is a special kind of two-party computation protocol, it turns out that ESP implies general two-party computation (2-PC) under natural conditions. In particular, our new paradigm is tailored to the evaluation of functions over rings. Indeed, assuming the compatibility of two additively and multiplicatively homomorphic encryption schemes, switching ciphertexts makes it possible to efficiently reconcile the two internal laws. Since no such pair of public-key encryption schemes appeared in the literature, except for the non-interactive case of fully homomorphic encryption which still remains prohibitive in practice, we build the first multiplicatively homomorphic ElGamal-like encryption scheme over $(\mathbb {Z}_n,\times )$ as a complement to the Paillier encryption scheme over $(\mathbb {Z}_n,+)$, where n is a strong RSA modulus. Eventually, we also instantiate secure ESPs between the two schemes, in front of malicious adversaries. This enhancement relies on a new technique called refreshable twin ciphertext pool, which we show being of independent interest. We additionally prove this is enough to argue the security of our general 2-PC protocol against malicious adversaries.
Keywords :
Type de document :
Communication dans un congrès
Matthew Robshaw ; Jonathan Katz Crypto 2016 - 36th Annual International Cryptology Conference, Aug 2016, Santa Barbara, United States. Springer, CRYPTO 2016, Aug 2016, Santa Barbara, United States. Springer, Volume 9814 pp 308-338, 2016, Advances in Cryptology - CRYPTO 2016, 2016, 〈10.1007/978-3-662-53018-4_12〉

https://hal.inria.fr/hal-01407341
Contributeur : Geoffroy Couteau <>
Soumis le : jeudi 1 décembre 2016 - 23:57:52
Dernière modification le : jeudi 11 janvier 2018 - 06:22:10

### Citation

Geoffroy Couteau, Thomas Peters, David Pointcheval. Encryption Switching Protocols. Matthew Robshaw ; Jonathan Katz Crypto 2016 - 36th Annual International Cryptology Conference, Aug 2016, Santa Barbara, United States. Springer, CRYPTO 2016, Aug 2016, Santa Barbara, United States. Springer, Volume 9814 pp 308-338, 2016, Advances in Cryptology - CRYPTO 2016, 2016, 〈10.1007/978-3-662-53018-4_12〉. 〈hal-01407341〉

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