22,024 research outputs found
Sequential Circuit Design for Embedded Cryptographic Applications Resilient to Adversarial Faults
In the relatively young field of fault-tolerant cryptography, the main research effort has focused exclusively on the protection of the data path of cryptographic circuits. To date, however, we have not found any work that aims at protecting the control logic of these circuits against fault attacks, which thus remains the proverbial Achillesâ heel. Motivated by a hypothetical yet realistic fault analysis attack that, in principle, could be mounted against any modular exponentiation engine, even one with appropriate data path protection, we set out to close this remaining gap. In this paper, we present guidelines for the design of multifault-resilient sequential control logic based on standard Error-Detecting Codes (EDCs) with large minimum distance. We introduce a metric that measures the effectiveness of the error detection technique in terms of the effort the attacker has to make in relation to the area overhead spent in
implementing the EDC. Our comparison shows that the proposed EDC-based technique provides superior performance when compared against regular N-modular redundancy techniques. Furthermore, our technique scales well and does not affect the critical path delay
Classical simulatability, entanglement breaking, and quantum computation thresholds
We investigate the amount of noise required to turn a universal quantum gate
set into one that can be efficiently modelled classically. This question is
useful for providing upper bounds on fault tolerant thresholds, and for
understanding the nature of the quantum/classical computational transition. We
refine some previously known upper bounds using two different strategies. The
first one involves the introduction of bi-entangling operations, a class of
classically simulatable machines that can generate at most bipartite
entanglement. Using this class we show that it is possible to sharpen
previously obtained upper bounds in certain cases. As an example, we show that
under depolarizing noise on the controlled-not gate, the previously known upper
bound of 74% can be sharpened to around 67%. Another interesting consequence is
that measurement based schemes cannot work using only 2-qubit non-degenerate
projections. In the second strand of the work we utilize the Gottesman-Knill
theorem on the classically efficient simulation of Clifford group operations.
The bounds attained for the pi/8 gate using this approach can be as low as 15%
for general single gate noise, and 30% for dephasing noise.Comment: 12 pages, 3 figures. v2: small typos changed, no change to result
Fault-Tolerant Control of a Flux-switching Permanent Magnet Synchronous Machine
Je jasnĂ©, ĆŸe nejĂșspÄĆĄnÄjĆĄĂ konstrukce zahrnuje postup vĂcefĂĄzovĂ©ho ĆĂzenĂ, ve kterĂ©m kaĆŸdĂĄ fĂĄze mĆŻĆŸe bĂœt povaĆŸovĂĄna za samostatnĂœ modul. Provoz kterĂ©koliv z jednotek musĂ mĂt minimĂĄlnĂ vliv na ostatnĂ, a to tak, ĆŸe v pĆĂpadÄ selhĂĄnĂ jednĂ© jednotky ostatnĂ mohou bĂœt v provozu neovlivnÄny. ModulĂĄrnĂ ĆeĆĄenĂ vyĆŸaduje minimĂĄlnĂ elektrickĂ©, magnetickĂ© a tepelnĂ© ovlivnÄnĂ mezi fĂĄzemi ĆĂzenĂ (mÄniÄe). SynchronnĂ stroje s pulznĂm tokem a permanentnĂmi magnety se jevĂ jako atraktivnĂ typ stroje, jejĂĆŸ pĆednostmi jsou vysokĂœ kroutĂcĂ moment, jednoduchĂĄ a robustnĂ konstrukce rotoru a skuteÄnost, ĆŸe permanentnĂ magnety i cĂvky jsou umĂstÄny spoleÄnÄ na statoru. FS-PMSM jsou pomÄrnÄ novĂ© typy stĆĂdavĂ©ho stroje stator-permanentnĂ magnet, kterĂ© pĆedstavujĂ vĂœznamnĂ© pĆednosti na rozdĂl od konvenÄnĂch rotorĆŻ - velkĂœ kroutĂcĂ moment, vysokĂœ toÄivĂœ moment, v podstatÄ sinusovĂ© zpÄtnĂ© EMF kĆivky, zĂĄroveĆ kompaktnĂ a robustnĂ konstrukce dĂky umĂstÄnĂ magnetĆŻ a vinutĂ kotvy na statoru. SrovnĂĄnĂ vĂœsledkĆŻ mezi FS-PMSM a klasickĂœmi motory na povrchu upevnÄnĂœmi PM (SPM) se stejnĂœmi parametry ukazuje, ĆŸe FS-PMSM vykazuje vÄtĆĄĂ vzduchovĂ© mezery hustoty toku, vyĆĄĆĄĂ toÄivĂœ moment na ztrĂĄty v mÄdi, ale takĂ© vyĆĄĆĄĂ pulzaci dĂky reluktanÄnĂmu momentu. Pro stroje buzenĂ© permanentnĂmi magnety se jednĂĄ o tradiÄnĂ rozpor mezi poĆŸadavkem na vysokĂœ kroutĂcĂ moment pod zĂĄkladnĂ rychlostĂ (oblast konstantnĂho momentu) a provozem nad zĂĄkladnĂ rychlostĂ (oblast konstantnĂho vĂœkonu), zejmĂ©na pro aplikace v hybridnĂch vozidlech. Je pĆedloĆŸena novĂĄ topologie synchronnĂho stroje s permanentnĂmi magnety a spĂnanĂœm tokem odolnĂ©ho proti poruchĂĄm, kterĂĄ je schopnĂĄ provozu bÄhem vinutĂ naprĂĄzdno a zkratovanĂ©ho vinutĂ i poruchĂĄch mÄniÄe. SchĂ©ma je zaloĆŸeno na dvojitÄ vinutĂ©m motoru napĂĄjenĂ©m ze dvou oddÄlenĂœch vektorovÄ ĆĂzenĂœch napÄĆ„ovĂœch zdrojĆŻ. VinutĂ jsou uspoĆĂĄdĂĄna takovĂœm zpĆŻsobem, aby tvoĆila dvÄ nezĂĄvislĂ© a oddÄlenĂ© sady. Simulace a experimentĂĄlnĂ vĂœzkum zpĆesnĂ vĂœkon bÄhem obou scĂ©nĂĄĆĆŻ jak za normĂĄlnĂho provozu, tak za poruch vÄetnÄ zkratovĂœch zĂĄvad a ukĂĄĆŸĂ robustnost pohonu za tÄchto podmĂnek. Tato prĂĄce byla publikovĂĄna v deseti konferenÄnĂch pĆĂspÄvcĂch, dvou Äasopisech a kniĆŸnĂ kapitole, kde byly pĆedstaveny jak topologie pohonu a aplikovanĂĄ ĆĂdĂcĂ schĂ©mata, tak analĂœzy jeho schopnosti odolĂĄvat poruchĂĄm.It has become clear that the most successful design approach involves a multiple phase drive in which each phase may be regarded as a single-module. The operation of any one module must have minimal impact upon the others, so that in the event of that module failing the others can continue to operate unaffected. The modular approach requires that there should be minimal electrical, magnetic and thermal interaction between phases of the drive. Flux-Switching permanent magnet synchronous machines (FS-PMSM) have recently emerged as an attractive machine type virtue of their high torque densities, simple and robust rotor structure and the fact that permanent magnets and coils are both located on the stator. Flux-switching permanent magnet (FS-PMSM) synchronous machines are a relatively new topology of stator PM brushless machine. They exhibit attractive merits including the large torque capability and high torque (power) density, essentially sinusoidal back-EMF waveforms, as well as having a compact and robust structure due to both the location of magnets and armature windings in the stator instead of the rotor as those in the conventional rotor-PM machines. The comparative results between a FS-PMSM and a traditional surface-mounted PM (SPM) motor having the same specifications reveal that FS-PMSM exhibits larger air-gap flux density, higher torque per copper loss, but also a higher torque ripple due to cogging -torque. However, for solely permanent magnets excited machines, it is a traditional contradiction between the requests of high torque capability under the base-speed (constant torque region) and wide speed operation above the base speed (constant power region) especially for hybrid vehicle applications. A novel fault-tolerant FS-PMSM drive topology is presented, which is able to operate during open- and short-circuit winding and converter faults. The scheme is based on a dual winding motor supplied from two separate vector-controlled voltage-sourced inverter drives. The windings are arranged in a way so as to form two independent and isolated sets. Simulation and experimental work will detail the driverâs performance during both healthy- and faulty- scenarios including short-circuit faults and will show the drive robustness to operate in these conditions. The work has been published in ten conference papers, two journal papers and a book chapter, presenting both the topology of the drive and the applied control schemes, as well as analysing the fault-tolerant capabilities of the drive.
Integrating Scale Out and Fault Tolerance in Stream Processing using Operator State Management
As users of big data applications expect fresh results, we witness a new breed of stream processing systems (SPS) that are designed to scale to large numbers of cloud-hosted machines. Such systems face new challenges: (i) to benefit from the pay-as-you-go model of cloud computing, they must scale out on demand, acquiring additional virtual machines (VMs) and parallelising operators when the workload increases; (ii) failures are common with deployments on hundreds of VMs - systems must be fault-tolerant with fast recovery times, yet low per-machine overheads. An open question is how to achieve these two goals when stream queries include stateful operators, which must be scaled out and recovered without affecting query results. Our key idea is to expose internal operator state explicitly to the SPS through a set of state management primitives. Based on them, we describe an integrated approach for dynamic scale out and recovery of stateful operators. Externalised operator state is checkpointed periodically by the SPS and backed up to upstream VMs. The SPS identifies individual operator bottlenecks and automatically scales them out by allocating new VMs and partitioning the check-pointed state. At any point, failed operators are recovered by restoring checkpointed state on a new VM and replaying unprocessed tuples. We evaluate this approach with the Linear Road Benchmark on the Amazon EC2 cloud platform and show that it can scale automatically to a load factor of L=350 with 50 VMs, while recovering quickly from failures. Copyright © 2013 ACM
Magic-State Functional Units: Mapping and Scheduling Multi-Level Distillation Circuits for Fault-Tolerant Quantum Architectures
Quantum computers have recently made great strides and are on a long-term
path towards useful fault-tolerant computation. A dominant overhead in
fault-tolerant quantum computation is the production of high-fidelity encoded
qubits, called magic states, which enable reliable error-corrected computation.
We present the first detailed designs of hardware functional units that
implement space-time optimized magic-state factories for surface code
error-corrected machines. Interactions among distant qubits require surface
code braids (physical pathways on chip) which must be routed. Magic-state
factories are circuits comprised of a complex set of braids that is more
difficult to route than quantum circuits considered in previous work [1]. This
paper explores the impact of scheduling techniques, such as gate reordering and
qubit renaming, and we propose two novel mapping techniques: braid repulsion
and dipole moment braid rotation. We combine these techniques with graph
partitioning and community detection algorithms, and further introduce a
stitching algorithm for mapping subgraphs onto a physical machine. Our results
show a factor of 5.64 reduction in space-time volume compared to the best-known
previous designs for magic-state factories.Comment: 13 pages, 10 figure
Multiphase induction motor drives - a technology status review
The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio
Algorithmic Based Fault Tolerance Applied to High Performance Computing
We present a new approach to fault tolerance for High Performance Computing
system. Our approach is based on a careful adaptation of the Algorithmic Based
Fault Tolerance technique (Huang and Abraham, 1984) to the need of parallel
distributed computation. We obtain a strongly scalable mechanism for fault
tolerance. We can also detect and correct errors (bit-flip) on the fly of a
computation. To assess the viability of our approach, we have developed a fault
tolerant matrix-matrix multiplication subroutine and we propose some models to
predict its running time. Our parallel fault-tolerant matrix-matrix
multiplication scores 1.4 TFLOPS on 484 processors (cluster jacquard.nersc.gov)
and returns a correct result while one process failure has happened. This
represents 65% of the machine peak efficiency and less than 12% overhead with
respect to the fastest failure-free implementation. We predict (and have
observed) that, as we increase the processor count, the overhead of the fault
tolerance drops significantly
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