17,536 research outputs found
Quantum interference and Coulomb interaction in arrays of tunnel junctions
We study the electronic properties of an array of small metallic grains
connected by tunnel junctions. Such an array serves as a model for a granular
metal. Previous theoretical studies of junction arrays were based on models of
quantum dissipation which did not take into account the diffusive motion of
electrons within the grains. We demonstrate that these models break down at
sufficiently low temperatures: for a correct description of the screening
properties of a granular metal at low energies the diffusive nature of the
electronic motion within the grains is crucial. We present both a diagrammatic
and a functional integral approach to analyse the properties of junction
arrays. In particular, a new effective action is obtained which enables us to
describe the array at arbitrary temperature. In the low temperature limit, our
theory yields the correct, dynamically screened Coulomb interaction of a normal
metal, whereas at high temperatures the standard description in terms of
quantum dissipation is recovered.Comment: 14 pages, 7 figure
SU(2) and SU(1,1) algebra eigenstates: A unified analytic approach to coherent and intelligent states
We introduce the concept of algebra eigenstates which are defined for an
arbitrary Lie group as eigenstates of elements of the corresponding complex Lie
algebra. We show that this concept unifies different definitions of coherent
states associated with a dynamical symmetry group. On the one hand, algebra
eigenstates include different sets of Perelomov's generalized coherent states.
On the other hand, intelligent states (which are squeezed states for a system
of general symmetry) also form a subset of algebra eigenstates. We develop the
general formalism and apply it to the SU(2) and SU(1,1) simple Lie groups.
Complete solutions to the general eigenvalue problem are found in the both
cases, by a method that employs analytic representations of the algebra
eigenstates. This analytic method also enables us to obtain exact closed
expressions for quantum statistical properties of an arbitrary algebra
eigenstate. Important special cases such as standard coherent states and
intelligent states are examined and relations between them are studied by using
their analytic representations.Comment: LaTeX, 24 pages, 1 figure (compressed PostScript, available at
http://www.technion.ac.il/~brif/abstracts/AES.html ). More information on
http://www.technion.ac.il/~brif/science.htm
Small Scale AES Toolbox: Algebraic and Propositional Formulas, Circuit-Implementations and Fault Equations
Cryptography is one of the key technologies ensuring security in the digital
domain. As such, its primitives and implementations have been extensively analyzed both
from a theoretical, cryptoanalytical perspective, as well as regarding their capabilities to
remain secure in the face of various attacks.
One of the most common ciphers, the Advanced Encryption Standard (AES) (thus far)
appears to be secure in the absence of an active attacker. To allow for the testing and
development of new attacks or countermeasures a small scale version of the AES with a
variable number of rounds, number of rows, number of columns and data word size, and a
complexity ranging from trivial up to the original AES was developed.
In this paper we present a collection of various implementations of the relevant small scale
AES versions based on hardware (VHDL and gate-level), algebraic representations (Sage
and CoCoA) and their translations into propositional formulas (in CNF). Additionally, we
present fault attack equations for each version.
Having all these resources available in a single and well structured package allows researchers
to combine these different sources of information which might reveal new patterns or solving
strategies. Additionally, the fine granularity of difficulty between the different small scale
AES versions allows for the assessment of new attacks or the comparison of different attacks
High-level Cryptographic Abstractions
The interfaces exposed by commonly used cryptographic libraries are clumsy,
complicated, and assume an understanding of cryptographic algorithms. The
challenge is to design high-level abstractions that require minimum knowledge
and effort to use while also allowing maximum control when needed.
This paper proposes such high-level abstractions consisting of simple
cryptographic primitives and full declarative configuration. These abstractions
can be implemented on top of any cryptographic library in any language. We have
implemented these abstractions in Python, and used them to write a wide variety
of well-known security protocols, including Signal, Kerberos, and TLS.
We show that programs using our abstractions are much smaller and easier to
write than using low-level libraries, where size of security protocols
implemented is reduced by about a third on average. We show our implementation
incurs a small overhead, less than 5 microseconds for shared key operations and
less than 341 microseconds (< 1%) for public key operations. We also show our
abstractions are safe against main types of cryptographic misuse reported in
the literature
Efficient Implementation on Low-Cost SoC-FPGAs of TLSv1.2 Protocol with ECC_AES Support for Secure IoT Coordinators
Security management for IoT applications is a critical research field, especially when taking into account the performance variation over the very different IoT devices. In this paper, we present high-performance client/server coordinators on low-cost SoC-FPGA devices for secure IoT data collection. Security is ensured by using the Transport Layer Security (TLS) protocol based on the TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 cipher suite. The hardware architecture of the proposed coordinators is based on SW/HW co-design, implementing within the hardware accelerator core Elliptic Curve Scalar Multiplication (ECSM), which is the core operation of Elliptic Curve Cryptosystems (ECC). Meanwhile, the control of the overall TLS scheme is performed in software by an ARM Cortex-A9 microprocessor. In fact, the implementation of the ECC accelerator core around an ARM microprocessor allows not only the improvement of ECSM execution but also the performance enhancement of the overall cryptosystem. The integration of the ARM processor enables to exploit the possibility of embedded Linux features for high system flexibility. As a result, the proposed ECC accelerator requires limited area, with only 3395 LUTs on the Zynq device used to perform high-speed, 233-bit ECSMs in 413 µs, with a 50 MHz clock. Moreover, the generation of a 384-bit TLS handshake secret key between client and server coordinators requires 67.5 ms on a low cost Zynq 7Z007S device
MIMO-aided near-capacity turbo transceivers: taxonomy and performance versus complexity
In this treatise, we firstly review the associated Multiple-Input Multiple-Output (MIMO) system theory and review the family of hard-decision and soft-decision based detection algorithms in the context of Spatial Division Multiplexing (SDM) systems. Our discussions culminate in the introduction of a range of powerful novel MIMO detectors, such as for example Markov Chain assisted Minimum Bit-Error Rate (MC-MBER) detectors, which are capable of reliably operating in the challenging high-importance rank-deficient scenarios, where there are more transmitters than receivers and hence the resultant channel-matrix becomes non-invertible. As a result, conventional detectors would exhibit a high residual error floor. We then invoke the Soft-Input Soft-Output (SISO) MIMO detectors for creating turbo-detected two- or three-stage concatenated SDM schemes and investigate their attainable performance in the light of their computational complexity. Finally, we introduce the powerful design tools of EXtrinsic Information Transfer (EXIT)-charts and characterize the achievable performance of the diverse near- capacity SISO detectors with the aid of EXIT charts
- …