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 (6)

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
6 CEA - Commissariat à l'énergie atomique et aux énergies alternatives

In typical applications of homomorphic encryption, the rst 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 specically considers that rst step, i.e. the problem of transmitting c as eciently 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 c0 = (HEpk(k); Ek(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 oered 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 rmly established for over a decade, and the new variant Kreyvium have an excellent performance.

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. CryptoAction Symposium 2016, Apr 2016, Budapest, Hungary. ⟨hal-01401328⟩