20,360 research outputs found
Extended Nested Dual System Groups, Revisited
The notion of extended nested dual system groups (ENDSG) was recently proposed by Hofheinz et al. [PKC 2015] for constructing almost-tight identity based encryptions (IBE) in the multi-instance, multi-ciphertext (MIMC) setting. However only a composite-order instantiation was proposed and more efficient prime-order instantiations are absent. The paper fills the blank by presenting two constructions.
We revise the definition of ENDSG and realize it using prime-order bilinear groups based on Chen and Wee\u27s prime-order instantiation of nested dual system groups [CRYPTO 2013]. This yields the first almost-tight IBE in the prime-order setting achieving weak adaptive security in MIMC scenario under the -linear (-Lin) assumption. We further enhanced the revised ENDSG to capture stronger security notions for IBE, including -weak adaptive security and full adaptive security. We show that our prime-order instantiation is readily -weak adaptive secure and full adaptive secure without introducing extra assumption.
We then try to find better solution by fine-tuning ENDSG again and realizing it using the technique of Chen, Gay, and Wee [EUROCRYPT 2015]. This leads to an almost-tight secure IBE in the same setting with better performance than our first result, but the security relies on a non-standard assumption, -linear assumption with auxiliary input (-LinAI) for an even positive integer . However we note that, the -LinAI assumption is implied by the external decisional linear (XDLIN) assumption. This concrete instantiation could also be realized using symmetric bilinear groups under standard decisional linear assumption
A New Class of MDS Erasure Codes Based on Graphs
Maximum distance separable (MDS) array codes are XOR-based optimal erasure
codes that are particularly suitable for use in disk arrays. This paper
develops an innovative method to build MDS array codes from an elegant class of
nested graphs, termed \textit{complete-graph-of-rings (CGR)}. We discuss a
systematic and concrete way to transfer these graphs to array codes, unveil an
interesting relation between the proposed map and the renowned perfect
1-factorization, and show that the proposed CGR codes subsume B-codes as their
"contracted" codes. These new codes, termed \textit{CGR codes}, and their dual
codes are simple to describe, and require minimal encoding and decoding
complexity.Comment: in Proceeding of IEEE Global Communications Conference (GLOBECOM
Hierarchy Theory of Evolution and the Extended Evolutionary Synthesis: Some Epistemic Bridges, Some Conceptual Rifts
Contemporary evolutionary biology comprises a plural landscape of multiple co-existent conceptual frameworks and strenuous voices that disagree on the nature and scope of evolutionary theory. Since the mid-eighties, some of these conceptual frameworks have denounced the ontologies of the Modern Synthesis and of the updated Standard Theory of Evolution as unfinished or even flawed. In this paper, we analyze and compare two of those conceptual frameworks, namely Niles Eldredge’s Hierarchy Theory of Evolution (with its extended ontology of evolutionary entities) and the Extended Evolutionary Synthesis (with its proposal of an extended ontology of evolutionary processes), in an attempt to map some epistemic bridges (e.g. compatible views of causation; niche construction) and some conceptual rifts (e.g. extra-genetic inheritance; different perspectives on macroevolution; contrasting standpoints held in the “externalism–internalism” debate) that exist between them. This paper seeks to encourage theoretical, philosophical and historiographical discussions about pluralism or the possible unification of contemporary evolutionary biology
Conformal Carroll groups
Conformal extensions of Levy-Leblond's Carroll group, based on geometric
properties analogous to those of Newton-Cartan space-time are proposed. The
extensions are labelled by an integer . This framework includes and extends
our recent study of the Bondi-Metzner-Sachs (BMS) and Newman-Unti (NU) groups.
The relation to Conformal Galilei groups is clarified. Conformal Carroll
symmetry is illustrated by "Carrollian photons". Motion both in the
Newton-Cartan and Carroll spaces may be related to that of strings in the
Bargmann space.Comment: 31 pages, no figures. Minor misprints corrected and clarifications
added. To be published in J. Phys.
Cosmic branes and asymptotic structure
Superrotations of asymptotically flat spacetimes in four dimensions can be
interpreted in terms of including cosmic strings within the phase space of
allowed solutions. In this paper we explore the implications of the inclusion
of cosmic branes on the asymptotic structure of vacuum spacetimes in dimension
d > 4. We first show that only cosmic (d-3)-branes are Riemann flat in the
neighbourhood of the brane, and therefore only branes of such dimension passing
through the celestial sphere can respect asymptotic local flatness. We derive
the asymptotically locally flat boundary conditions associated with including
cosmic branes in the phase space of solutions. We find the asymptotic expansion
of vacuum spacetimes in d=5 with such boundary conditions; the expansion is
polyhomogenous, with logarithmic terms arising at subleading orders in the
expansion. The asymptotically locally flat boundary conditions identified here
are associated with an extended asymptotic symmetry group, which may be
relevant to soft scattering theorems and memory effects.Comment: 52 pages; v2, minor additions, published versio
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