Cryptology ePrint Archive: Report 2015/113

Stream ciphers: A Practical Solution for Efficient Homomorphic-Ciphertext Compression

Anne Canteaut and Sergiu Carpov and Caroline Fontaine and Tancrède Lepoint and María Naya-Plasencia and Pascal Paillier and Renaud Sirdey

Abstract: In typical applications of homomorphic encryption, the first step consists for Alice to encrypt some plaintext m under Bob’s public key pk and to send the ciphertext c = HE_pk(m) to some third-party evaluator Charlie. This paper specifically considers that first step, i.e. the problem of transmitting c as efficiently as possible from Alice to Charlie. As previously noted, a form of compression is achieved using hybrid encryption. Given a symmetric encryption scheme E, Alice picks a random key k and sends a much smaller ciphertext c′ = (HE_pk(k), E_k(m)) that Charlie decompresses homomorphically into the original c using a decryption circuit C_E^{−1}.

In this paper, we revisit that paradigm in light of its concrete implementation constraints; in particular E is chosen to be an additive IV-based stream cipher. We investigate the performances offered in this context by Trivium, which belongs to the eSTREAM portfolio, and we also propose a variant with 128-bit security: Kreyvium. We show that Trivium, whose security has been firmly established for over a decade, and the new variant Kreyvium have an excellent performance.

Category / Keywords: Stream Ciphers, Homomorphic cryptography, Ciphertext compression, Trivium

Date: received 13 Feb 2015, last revised 29 Nov 2015

Contact author: tancrede lepoint at cryptoexperts com

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Version: 20151129:105759 (All versions of this report)

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