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Secure multiparty computation systems are commonly built form a small set of primitive components. Composability of security notions has a central role in the analysis of such systems, since it allows us to deduce security properties of complex protocols from the properties of its components. We show that the standard notions of universally composable security are overly restrictive in this context and can lead to protocols with sub-optimal performance. As a remedy, we introduce a weaker notion of privacy that is satisfied by simpler protocols and is preserved by composition. After that we fix a passive security model and show how to convert a private protocol into a universally composable protocol. As a result, we obtain modular security proofs without performance penalties.

We consider the problem of a client who outsources the computation of a function $f$ over an input $x$ to a server, who returns $y=f(x)$. The client wants to be assured of the correctness of the computation and wants to preserve confidentiality of the input $x$ and possibly of the function $f$ as well. Moreover, the client wants to invest substantially less effort in verifying the correctness of the result than it would require to compute $f$ from scratch.

This is the problem of secure outsourced computation over encrypted data. Most of the work on outsourced computation in the literature focuses on either privacy of the data, using {\\em Fully Homomorphic Encryption (FHE)}, or the integrity of the computation. No general security definition for protocols achieving both privacy and integrity appears in the literature. Previous definitions only deal with a very limited security model where the server is not allowed to

issue {\\em verification queries} to the client: i.e. it is not allowed to ``see\'\' if the client accepts or rejects the value $y$.

In this paper we present:

-- A formal definition of {\\em private and secure} outsourced computation {\\em in the presence of verification queries};

-- A protocol based on FHE that achieves the above definition for arbitrary poly-time computations;

-- Some additional protocols for the computation of {\\em ad-hoc} functions (such as the computation of polynomials and linear

combinations) over encrypted data. These protocols do not use the power of FHE, and therefore are much more efficient than the generic approach. We point out that some existing protocols in the literature for these tasks become insecure in the presence of verification queries, while our protocols can be proven in the stronger security model where verification queries are allowed.

2014-03-17

The ANR \\\"SIMPATIC: SIM and PAiring Theory for Information and Communications security\\\" will recruit one post-doc position for the academic year 2014-2015.

The successful applicant will be a member of the Computer Science (LIASD) laboratory at Paris 8 University, France.

The position is open for one year, and may exceptionnally be renewed for a second year. If necessary, the starting date can be arranged as convenient.

The partners involved in the SIMPATIC project are the crypto teams of the Laboratoire d\\\'Informatique de l\\\'ENS Paris, of IMB (Bordeaux), of University Paris 8 (LAGA and LIASD), of University of Caen, Oberthur, INVIA, ST (Le Mans) and Orange Labs (Caen). Further information about the SIMPATIC project can be found on its webpage http://simpatic.orange-labs.fr/ .

Preference will be given to condidates whose profile is adapted to one of the following priorities of the project:

(i) The study of suitable pairing-friendly curves, both theoretical and algorithmic aspects. Candidates should therefore have a good background in relevant number theory and algebraic geometry. Some experience in software implementation (for example in Pari, Magma, Sage, ...) would be useful.

(ii) The secure implementation of efficient arithmetic suitable for SIMs and other small supports. Candidates are expected to have a good potential in theoretical cryptography.

(iii) The study of side channel attack in pairing based cryptography, both theoretical and practical. Candidates are expected to have a good potential in theoretical cryptography. He/she will be expected to interact with members of Oberthur.

Candidates must hold a PhD thesis or equivalent in mathematics or computer science, together with a strong research record.

From August 19 to August 23

Location: Santa Barbara, USA

More Information: http://www.iacr.org/conferences/

From August 20 to August 24

Location: Santa Barbara, USA

More Information: http://www.iacr.org/conferences/

From August 14 to August 18

Location: Santa Barbara, USA

More Information: http://www.iacr.org/conferences/

From August 16 to August 20

Location: Santa Barbara, USA

More Information: http://www.iacr.org/conferences/

This paper presents a fast implementation to compute the scalar multiplication of elliptic curve points based on a ``General-Purpose computing on Graphics Processing Units\'\' (GPGPU) approach. A GPU implementation using Dan Bernstein\'s Curve25519, an elliptic curve over a 255-bit prime field complying with the new 128-bit security level, computes the scalar multiplication in less than a microsecond on AMD\'s R9 290X GPU. The presented methods and implementation considerations can be applied to any parallel architecture.

2014-03-16