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

Anne Canteaut (1) , Sergiu Carpov (2) , Caroline Fontaine (3, 4) , Tancrède Lepoint (5) , María Naya-Plasencia (1) , Pascal Paillier (5) , Renaud Sirdey (2)

1 SECRET - Security, Cryptology and Transmissions
2 LIST (CEA) - Laboratoire d'Intégration des Systèmes et des Technologies
3 Lab-STICC_TB_CID_SFIIS
4 ITI - Département Image et Traitement Information
5 CryptoExperts

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 = HEpk(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′ = (HEpk(k), Ek(m)) that Charlie decompresses homomorphically into the original c using a decryption circuit CE−1 . In this paper, we revisit that paradigm in light of its concrete implemen- tation 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 pro- pose 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.

Mots clés: Stream Ciphers; Homomorphic cryptography; Trivium

Domaines: Cryptographie et sécurité [cs.CR]

Anne Canteaut, Sergiu Carpov, Caroline Fontaine, Tancrède Lepoint, María Naya-Plasencia, et al.. Stream ciphers: A Practical Solution for Efficient Homomorphic-Ciphertext Compression. FSE 2016 : 23rd International Conference on Fast Software Encryption, Mar 2016, Bochum, Germany. pp.313-333, ⟨10.1007/978-3-662-52993-5_16⟩. ⟨hal-01280479⟩