Privately Outsourcing Exponentiation to a Single Server: Cryptanalysis and Optimal Constructions - Inria - Institut national de recherche en sciences et technologies du numérique Access content directly
Conference Papers Year : 2016

Privately Outsourcing Exponentiation to a Single Server: Cryptanalysis and Optimal Constructions

Abstract

We address the problem of speeding up group computations in cryptography using a single untrusted computational resource. We analyze the security of an efficient protocol for securely outsourcing multi-exponentiations proposed at ESORICS 2014. We show that this scheme does not achieve the claimed security guarantees and we present practical polynomial-time attacks on the delegation protocol which allow the untrusted helper to recover part (or the whole) of the device secret inputs. We then provide simple constructions for outsourcing group exponentiations in different settings (e.g. public/secret, fixed/variable bases and public/secret exponents). Finally, we prove that our attacks on the ESORICS 2014 protocol are unavoidable if one wants to use a single untrusted computational resource and to limit the computational cost of the limited device to a constant number of (generic) group operations. In particular, we show that our constructions are actually optimal in terms of operations in the underlying group.

Dates and versions

hal-01375817 , version 1 (03-10-2016)

Identifiers

Cite

Céline Chevalier, Fabien Laguillaumie, Damien Vergnaud. Privately Outsourcing Exponentiation to a Single Server: Cryptanalysis and Optimal Constructions. Computer Security - ESORICS 2016, Sep 2016, Heraklion, Greece. pp.261-278, ⟨10.1007/978-3-319-45744-4_13⟩. ⟨hal-01375817⟩
147 View
0 Download

Altmetric

Share

Gmail Facebook X LinkedIn More