287,338 research outputs found
Dualities and signatures of G++ invariant theories
The G++ content of the formulation of gravity and M-theories as very-extended
Kac-Moody invariant theories is further analysed. The different exotic phases
of all the G_B++ theories, which admit exact solutions describing intersecting
branes smeared in all directions but one, are derived. This is achieved by
analysing for all G++ the signatures which are related to the conventional one
(1,D-1) by `dualities' generated by the Weyl reflections.Comment: 26 pages, 3 figure
The fundamental group and torsion group of Beauville surfaces
We give a survey on the fundamental group of surfaces isogenous to a higher
product. If the surfaces are regular, e.g. if they are Beauville surfaces, the
first homology group is a finite group. We present a MAGMA script which
calculates the first homology groups of regular surfaces isogenous to a
product.Comment: 14 pages; MAGMA script included; v2: minor corrections, final version
to appear in the Proceedings of the Conference "Beauville Surfaces and
Groups", Newcastle University (UK), 7-9th June 201
A New Cryptosystem Based On Hidden Order Groups
Let be a cyclic multiplicative group of order . It is known that the
Diffie-Hellman problem is random self-reducible in with respect to a
fixed generator if is known. That is, given and
having oracle access to a `Diffie-Hellman Problem' solver with fixed generator
, it is possible to compute in polynomial time (see
theorem 3.2). On the other hand, it is not known if such a reduction exists
when is unknown (see conjuncture 3.1). We exploit this ``gap'' to
construct a cryptosystem based on hidden order groups and present a practical
implementation of a novel cryptographic primitive called an \emph{Oracle Strong
Associative One-Way Function} (O-SAOWF). O-SAOWFs have applications in
multiparty protocols. We demonstrate this by presenting a key agreement
protocol for dynamic ad-hoc groups.Comment: removed examples for multiparty key agreement and join protocols,
since they are redundan
Security of discrete log cryptosystems in the random oracle and the generic model
We introduce novel security proofs that use combinatorial counting arguments rather than reductions to the discrete logarithm or to the Diffie-Hellman problem. Our security results are sharp and clean with no polynomial reduction times involved. We consider a combination of the random oracle model and the generic model. This corresponds to assuming an ideal hash function H given by an oracle and an ideal group of prime order q, where the binary encoding of the group elements is useless for cryptographic attacks In this model, we first show that Schnorr signatures are secure against the one-more signature forgery : A generic adversary performing t generic steps including l sequential interactions with the signer cannot produce l+1 signatures with a better probability than (t 2)/q. We also characterize the different power of sequential and of parallel attacks. Secondly, we prove signed ElGamal encryption is secure against the adaptive chosen ciphertext attack, in which an attacker can arbitrarily use a decryption oracle except for the challenge ciphertext. Moreover, signed ElGamal encryption is secure against the one-more decryption attack: A generic adversary performing t generic steps including l interactions with the decryption oracle cannot distinguish the plaintexts of l + 1 ciphertexts from random strings with a probability exceeding (t 2)/q
Fuzzy Interval-Valued Multi Criteria Based Decision Making for Ranking Features in Multi-Modal 3D Face Recognition
Soodamani Ramalingam, 'Fuzzy interval-valued multi criteria based decision making for ranking features in multi-modal 3D face recognition', Fuzzy Sets and Systems, In Press version available online 13 June 2017. This is an Open Access paper, made available under the Creative Commons license CC BY 4.0 https://creativecommons.org/licenses/by/4.0/This paper describes an application of multi-criteria decision making (MCDM) for multi-modal fusion of features in a 3D face recognition system. A decision making process is outlined that is based on the performance of multi-modal features in a face recognition task involving a set of 3D face databases. In particular, the fuzzy interval valued MCDM technique called TOPSIS is applied for ranking and deciding on the best choice of multi-modal features at the decision stage. It provides a formal mechanism of benchmarking their performances against a set of criteria. The technique demonstrates its ability in scaling up the multi-modal features.Peer reviewedProo
Reducible conformal holonomy in any metric signature and application to twistor spinors in low dimension
We prove that given a pseudo-Riemannian conformal structure whose conformal
holonomy representation fixes a totally lightlike subspace of arbitrary
dimension, there is, wrt. a local metric in the conformal class defined off a
singular set, a parallel, totally lightlike distribution on the tangent bundle
which contains the image of the Ricci-tensor. This generalizes results obtained
for invariant lightlike lines and planes and closes a gap in the understanding
of the geometric meaning of reducibly acting conformal holonomy groups. We show
how this result naturally applies to the classification of geometries admitting
twistor spinors in some low-dimensional split signatures when they are
described using conformal spin tractor calculus. Together with already known
results about generic distributions in dimensions 5 and 6 we obtain a complete
geometric description of local geometries admitting real twistor spinors in
signatures (3,2) and (3,3). In contrast to the generic case where generic
geometric distributions play an important role, the underlying geometries in
the non-generic case without zeroes turn out to admit integrable distributions.Comment: 15 page
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