11661855
Theoretical Analysis of XL over Small Fields
XL was first introduced to solve determined or overdetermined systems of equations over a finite field as an “algebraic attack” against multivariate cryptosystems. There has been a steady stream of announcements of cryptanalysis of primitives by such attacks, including stream ciphers (e.g. Toyocrypt), PKC’s, and more controversially block ciphers (AES/Rijndael and Serpent).
987186
Implementing Minimized Multivariate PKC on Low-Resource Embedded Systems
Multivariate (or $\mathcal{MQ}$) public-key cryptosystems (PKC) are alternatives to traditional PKCs based on large algebraic structures (e.g., RSA and ECC); they usually execute much faster than traditional PKCs on the same hardware. However, one major challenge in implementing multivariates in embedded systems is that the key size can be prohibitively large for applications with stringent resource constraints such as low-cost smart cards, sensor networks (e.g., Berkeley motes), and radio-frequency identification (RFID). In this paper, we investigate strategies for shortening the key of a multivariate PKC. We apply these strategies to the Tame Transformation Signatures (TTS) as an example and quantify the improvement in key size and running speed, both theoretically and via implementation. We also investigate ways to save die space and energy consumption in hardware, reporting on our ASIC implementation of TTS on a TSMC 0.25μm process. Even without any key shortening, the current consumption of TTS is only 21 μA for computing a signature, using 22,000 gate equivalents and 16,000 100-kHz cycles (160 ms). With circulant-matrix key shortening, the numbers go down to 17,000 gates and 4,400 cycles (44 ms). We therefore conclude: besides representing a future-proofing investment against the emerging quantum computers, multivariates can be immediately useful in niches.
2027380
A More Secure and Efficacious TTS Signature Scheme
In 2002 the authors introduced the new genre of digital signature scheme TTS (Tame Transformation Signatures) along with a sample scheme TTS/2. TTS is from the family of multivariate cryptographic schemes to which the NESSIE primitive SFLASH also belongs. It is a realization of T. Moh's theory ([31]) for digital signatures, based on Tame Transformations or Tame Maps. Properties of multivariate cryptosystems are determined mainly by their central maps. TTS uses Tame Maps as their central portion for even greater speed than C*-derived SFLASH family of schemes, which uses monomials in a large field for the central portion, previously usually acknowledged as fastest. We show a small flaw in TTS/2 and present an improved TTS implementation which we call TTS/4. We will examine in some detail how well TTS/4 performs, how it stands up to previously known attacks, and why it represents an advance over TTS/2. Based on this topical assessment, we consider TTS in general and TTS/4 in particular to be competitive or superior in several aspects to other schemes, partly because the theoretical roots of TTS induce many good traits. One specific area in which TTS/4 should excel is in low-cost smartcards. It seems that the genre has great potential for practical deployment and deserves further attention by the cryptological community.
9132194
Semi-normal Schedulings: Improvement on Goemans' Algorithm
Theoretical study of the multiprocessor job scheduling problem has made significant progress recently, which, however, seems not yet to imply practical algorithms. This paper offers new observations and introduces new techniques for the multiprocessor job scheduling problem P3|fix|C max. The concept of semi-normal schedulings is introduced and a very simple linear time algorithm for constructing semi-normal schedulings is developed. Thorough analysis is provided in the study of semi-normal schedulings, which enables us to conclude that the proposed algorithm is an approximation algorithm of ratio 9/8 for the P3|fix|C max problem. This improves the previous best (practical) ratio 7/6 by Goemans. Our techniques are also useful for multiprocessor job scheduling problems on systems with more than three processors.
1481165
Improved algorithms for path, matching, and packing problems
Improved randomized and deterministic algorithms are presented for PATH, MATCHING, and PACKING problems. Our randomized algorithms are based on the divide-and-conquer technique, and improve previous best algorithms for these problems. For example, for the <i>k</i>-PATH problem, our randomized algorithm runs in time <i>O</i>(4<sup><i>k</i></sup>k<sup>3.42</sup><i>m</i>) and space <i>O</i>(<i>nk</i>log<i>k</i> + <i>m</i>), improving the previous best randomized algorithm for the problem that runs in time <i>O</i>(5.44<sup><i>k</i></sup>km) and space <i>O</i>(2<sup><i>k</i></sup>kn + <i>m</i>). To achieve improved deterministic algorithms, we study a number of previously proposed de-randomization schemes, and also develop a new derandomization scheme. These studies result in a number of deterministic algorithms: one of time <i>O</i>(4<sup><i>k</i>+<i>o(k)</i></sup>m) for the <i>k</i>-PATH problem, one of time <i>O</i>(2.80<sup>3<i>k</i></sup>k nlog<sup>2</sup> <i>n</i>) for the 3-D MATCHING problem, and one of time <i>O</i>(4<sup>3<i>k</i>+<i>o(k)</i></sup>n) for the 3-SET PACKING problem. All these significantly improve previous best algorithms for the problems.
10702245
A wireless LAN-based indoor positioning technology
Context-aware computing is an emerging computing paradigm that can provide new or improved services by exploiting user context information. In this paper, we present a wireless-local-area-network-based (WLAN-based) indoor positioning technology. The wireless device deploys a position-determination model to gather location information from collected WLAN signals. A model-based signal distribution training scheme is proposed to trade off the accuracy of signal distribution and training workload. A tracking-assistant positioning algorithm is presented to employ knowledge of the area topology to assist the procedure of position determination. We have set up a positioning system at the IBM China Research Laboratory. Our experimental results indicate an accuracy of 2 m with a 90% probability for static devices and, for moving (walking) devices, an accuracy of 5 m with a 90% probability. Moreover, the complexity of the training procedure is greatly reduced compared with other positioning algorithms.
2698140
On fixed-parameter tractability and approximability of NP-hard optimization problems
Fixed-parameter tractability and approximability of NP-hard optimization problems are studied based on a model GC(s(n), Pi /sub k//sup L/). The main results are (1) a class of NP-hard optimization problems, including dominating-set and zero-one integer-programing, are fixed-parameter tractable if and only if GC(s(n), Pi /sub 2//sup L/) contained in P for some s(n) in omega (log n); (2) most approximable NP-hard optimization problems are fixed-parameter tractable. In particular, the class MAX NP is fixed-parameter tractable; (3) a class of optimization problems do not have fully polynomial time approximation scheme unless GC(s(n), Pi /sub k//sup L/) contained in P for some s(n) in omega (log n) and for some k>l; and (4) every fixed-parameter tractable optimization problem can be approximated in polynomial time to a non-trivial ratio.<<ETX>>
26308486
Model checking real-time value-passing systems
In this paper, to model check real-time value-passing systems, a formal languageTimed Symbolic Transition Graph and a logic system namedTimed Predicate μ-Calculus are proposed. An algorithm is presented which is local in that it generates and investigates the reachable state space in top-down fashion and maintains the partition for time evaluations as coarse as possible whileon-the-fly instantiating data variables. It can deal with not only data variables with finite value domain, but also the so calleddata independent variables with infinite value domain. To authors knowledge, this is the first algorithm for model checking timed systems containing value-passing features.