356 research outputs found
2-manifold recognition is in logspace
We prove that the homeomorphism problem for 2 manifolds can be decided in logspace. The proof relies on Reingold's logspace solution to the undirected s, t-connectivity problem in graphs
On the Security of the Algebraic Eraser Tag Authentication Protocol
The Algebraic Eraser has been gaining prominence as SecureRF, the company
commercializing the algorithm, increases its marketing reach. The scheme is
claimed to be well-suited to IoT applications but a lack of detail in available
documentation has hampered peer-review. Recently more details of the system
have emerged after a tag authentication protocol built using the Algebraic
Eraser was proposed for standardization in ISO/IEC SC31 and SecureRF provided
an open public description of the protocol. In this paper we describe a range
of attacks on this protocol that include very efficient and practical tag
impersonation as well as partial, and total, tag secret key recovery. Most of
these results have been practically verified, they contrast with the 80-bit
security that is claimed for the protocol, and they emphasize the importance of
independent public review for any cryptographic proposal.Comment: 21 pages. Minor changes. Final version accepted for ACNS 201
2-manifold recognition is in logspace
We prove that the homeomorphism problem for 2-manifolds can be decided in logspace. The proof relies on Reingold's logspace solution to the undirected -connectivity problem in graphs
Quantum Dot Potentials: Symanzik Scaling, Resurgent Expansions and Quantum Dynamics
This article is concerned with a special class of the ``double-well-like''
potentials that occur naturally in the analysis of finite quantum systems.
Special attention is paid, in particular, to the so-called Fokker-Planck
potential, which has a particular property: the perturbation series for the
ground-state energy vanishes to all orders in the coupling parameter, but the
actual ground-state energy is positive and dominated by instanton
configurations of the form exp(-a/g), where a is the instanton action. The
instanton effects are most naturally taken into account within the modified
Bohr-Sommerfeld quantization conditions whose expansion leads to the
generalized perturbative expansions (so-called resurgent expansions) for the
energy values of the Fokker-Planck potential. Until now, these resurgent
expansions have been mainly applied for small values of coupling parameter g,
while much less attention has been paid to the strong-coupling regime. In this
contribution, we compare the energy values, obtained by directly resumming
generalized Bohr-Sommerfeld quantization conditions, to the strong-coupling
expansion, for which we determine the first few expansion coefficients in
powers of g^(-2/3). Detailed calculations are performed for a wide range of
coupling parameters g and indicate a considerable overlap between the regions
of validity of the weak-coupling resurgent series and of the strong-coupling
expansion. Apart from the analysis of the energy spectrum of the Fokker-Planck
Hamiltonian, we also briefly discuss the computation of its eigenfunctions.
These eigenfunctions may be utilized for the numerical integration of the
(single-particle) time-dependent Schroedinger equation and, hence, for studying
the dynamical evolution of the wavepackets in the double-well-like potentials.Comment: 13 pages; RevTe
A Practical Cryptanalysis of the Algebraic Eraser
Anshel, Anshel, Goldfeld and Lemieaux introduced the Colored Burau Key
Agreement Protocol (CBKAP) as the concrete instantiation of their Algebraic
Eraser scheme. This scheme, based on techniques from permutation groups, matrix
groups and braid groups, is designed for lightweight environments such as RFID
tags and other IoT applications. It is proposed as an underlying technology for
ISO/IEC 29167-20. SecureRF, the company owning the trademark Algebraic Eraser,
has presented the scheme to the IRTF with a view towards standardisation.
We present a novel cryptanalysis of this scheme. For parameter sizes
corresponding to claimed 128-bit security, our implementation recovers the
shared key using less than 8 CPU hours, and less than 64MB of memory.Comment: 15 pages. Updated references, with brief comments added. Minor typos
corrected. Final version, accepted for CRYPTO 201
Formal comparison of SUSY in the nuclear U(6/2) model and in quantum field theory
A nuclear physics example of the U(6/2) supersymmetry group is considered. It
is shown that this group contains a supersymmetric subgroup with a structure
similar to the SUSY model of the quantum field theory (QFT). A comparison of
two models help to clarify the relation between the supersymmetry schemes of
QFT and of nuclear physics. Using this similarity a relation between the
numbers of the bosonic and fermionic states similar to the fundamental relation
in QFT is obtained. For those supermultiplets with at least two fermions the
number of the bosonic and fermionic states are equal as in QFT.Comment: 11 pages and one eps-figure. Phys.Rev.C (1999) in pres
Solvable three-state model of a driven double-well potential and coherent destruction of tunneling
A simple model for a particle in a double well is derived from discretizing its configuration space. The model contains as many free parameters as the original system and it respects all the existing symmetries. In the presence of an external periodic force both the continuous system and the discrete model are shown to possess a generalized time-reversal symmetry in addition to the known generalized parity. The impact of the driving force on the spectrum of the Floquet operator is studied. In particular, the occurrence of degenerate quasienergies causing coherent destruction of tunneling is discussed—to a large extent analytically—for arbitrary driving frequencies and barrier heights
Efficacy and Safety of Baclofen for Alcohol Dependence: A Randomized, Double-Blind, Placebo-Controlled Trial
Recent clinical trials and case-reports indicate that baclofen, a GABAB agonist, may have efficacy for alcohol dependence. Baclofen has been shown to enhance abstinence, to reduce drinking quantity, to reduce craving, and to reduce anxiety in alcohol dependent individuals in two placebo-controlled trials in Italy. However, the clinical trial data with baclofen is limited. The purpose of the present study was to test the efficacy and tolerability of baclofen in alcohol dependence in the United States
Transport of Streptococcus pneumoniae Capsular Polysaccharide in MHC Class II Tubules
Bacterial capsular polysaccharides are virulence factors and are considered T cell–independent antigens. However, the capsular polysaccharide Sp1 from Streptococcus pneumoniae serotype 1 has been shown to activate CD4(+) T cells in a major histocompatibility complex (MHC) class II–dependent manner. The mechanism of carbohydrate presentation to CD4(+) T cells is unknown. We show in live murine dendritic cells (DCs) that Sp1 translocates from lysosomal compartments to the plasma membrane in MHCII-positive tubules. Sp1 cell surface presentation results in reduction of self-peptide presentation without alteration of the MHCII self peptide repertoire. In DM-deficient mice, retrograde transport of Sp1/MHCII complexes resulting in T cell–dependent immune responses to the polysaccharide in vitro and in vivo is significantly reduced. The results demonstrate the capacity of a bacterial capsular polysaccharide antigen to use DC tubules as a vehicle for its transport as an MHCII/saccharide complex to the cell surface for the induction of T cell activation. Furthermore, retrograde transport requires the functional role of DM in self peptide–carbohydrate exchange. These observations open new opportunities for the design of vaccines against microbial encapsulated pathogens
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