A Dynamically Reconfigurable Pattern Matcher for Regular Expressions on FPGA

An optically differential reconfigurable gate array (ODRGA) is a type of field programmable gate array (FPGA), but its gate array can be reconfigured optically in less than 6 ns. We have fabricated a 68 gate-count ODRGA. However, optical differential reconfiguration circuits, which are capable of optical detection of configuration contexts and which can support reconfiguration of an arbitrary part of its gate array bit-by-bit, occupy up to 47% of the implementation area of ODRGA-VLSI chip and prevent realization of a high gate-count ODRGA. Therefore, a dynamic optical differential reconfiguration circuit was developed to reduce the implementation area of optical reconfiguration circuits. It has been evaluated separately. This paper presents the first 476 gate count ODRGA-VLSI chip with a standard 0.35 /spl mu/m 3-metal CMOS process technology using an improved dynamic optical differential reconfiguration circuit. In addition, the dynamic reconfiguration frequency and performance of logic blocks are shown using HSPICE simulation results. Finally, this paper presents an estimation of the use of a standard 0.35 /spl mu/m 3-metal 14.2/spl times/74.2 mm chip.

In this paper, we propose a novel FPGA-based architecture for large-scale regular expression matching, called dynamic reconfigurable bit-parallel NFA architecture (Dynamic BP-NFA) that allows dynamic reconfiguration of the patterns using bit-parallel NFA-simulation. This is the first dynamic reconfigurable FPGA-based hardware with guaranteed performance for the class of extended patterns, where an extended pattern is a restricted regular expression in linear form consisting of letters, classes of letters, don't cares, optional letters, bounded and unbounded length gaps and repeatable letters. The key to our architecture is the use of bit-parallel pattern matching approach that has been developed in string matching communities for the decades. In this approach, the information of an input NFA is compactly encoded in bit-masks stored in a collection of registers and block RAMs. Then, the NFA is efficiently simulated by a fixed circuitry using a combination of bit- and arithmetic-operations on these bit-masks consuming one input letter per clock. As compared with the previous approaches of DFA-based dynamic reconfigurable architectures, experimental results show that the proposed architecture achieves higher throughput for the class of exact string patterns and comparable for the class of extended patterns.

Generation of Pattern-Matching Algorithms by Extended Regular Expressions

Many network security applications such as Intrusion Detection System (IDS), Firewall and Data Loss Prevention System (DLPS) are based on deep packet inspection, in this packets header as well as payload of the packets are checked with predefined attack signature to identify whether it contains malicious traffic or not. To perform this checking different pattern matching methods are used by NIDS. The most popular method to implement pattern matching is to use of Finite Automata (FA). Generally, regular expressions are used to represent most of the attack signatures defined by NIDS. They are implemented using finite automata, which takes the payload of packet as input string. However, existing approaches of Finite Automata (FA), both deterministic finite automata (DFA) and non-deterministic finite automata (NFA) for pattern matching are having their own advantages and some drawbacks. The DFA based pattern matching methods are fast enough but require more memory. However, NFA based pattern matching methods are comparatively takes less memory but the speed of matching is very slow, to overcome these drawbacks of finite automata there are many approaches have been proposed. This paper discuses comparative study of some Finite Automata (FA) based techniques for pattern matching in network intrusion detection system (NIDS).

We consider the problem of restoring regular expressions from good examples. We describe a natural learning algorithm for obtaining a “plausible” regular expression from one example. The algorithm is based on finding the longest substring which can be matched by some part of the so far obtained expression. We believe that the algorithm to a certain extent mimics humans guessing regular expressions from the same sort of examples. We show that for regular expressions of bounded length successful learning takes time linear in the length of the example, provided that the example is “good”. Under certain natural restrictions the run-time of the learning algorithm is polynomial also in unsuccessful cases. In the end we discuss the computer experiment of learning regular expressions via the described algorithm, showing that the proposed learning method is quite practical.

Application specific integrated circuits are used to provide real-time performance of handheld devices within the compact physical size and low energy dissipation. However, these circuits are inflexible for any modification like redesign and refabrication. Reconfigurable architectures are promising alternative for conventional computing devices such as application-specific integrated circuits. It provides high-level flexibility to adapt the applications through dynamic hardware customization even after fabrication. A reconfigurable computing system design considers the peculiarities of the targeted application domain along with architectural issues like dynamic reconfiguration, partial reconfiguration, hardware/software co-design and context management. A brief survey has been carried out to understand the concepts and applications of CGRA, FPGA, SoC, NoC, MPSoC, dynamic partial reconfiguration, hardware/software co-design, design-space exploration, multi-objective optimization, genetic algorithm and reconfigurable computing on wireless communications. This paper deals with the survey on modeling, design, implementation and evaluation of coarse-grained dynamically reconfigurable processor architectures targeting the real-time embedded computing domain.

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 Objectives: Effective data management has become an absolute necessity in today's world as a direct result of the widespread adoption of electronic medical records for patients. For medicine and healthcare domains, particularly effective web healthcare providers, computer-assisted categorization of such information into functional classifications such as medical issues or illnesses may save time and efforts. However, a substantial volume of data in the healthcare domain is still unstructured.
 Methods: The utilization of unstructured text datasets is a challenge in comparison with structured text datasets. Many researchers in various domains have proposed to convert unstructured text into structured text. The text needs to be built in a fixed and aligned pattern for easy comparison, matching, and classification. In the text classification process, accuracy is one of the challenges when text is unstructured. The text with a fixed pattern is easy to classify. The regular expressions are sequences of characters with fixed patterns of text. This strength of regular expression is used in the proposed text classification. Finding patterns in unstructured text is possible with the use of sequence alignment. Basically, sequence alignment is a concept of biomedical research, but the same concept is used to align text snippets that are not perfectly similar to each other.
 Results: The sequence alignment technique detects the similarity score assigned to each potential alignment in order to choose among the numerous local alignments of sequences. The proposed local pairwise alignment method is used to get sequence alignments, which are useful to generate regular expressions.
 Conclusions: A regular expression is a string of characters used to describe a text pattern. The regular expressions are typically created manually by the domain experts. The proposed work is the automatic generation of regular expressions from aligned sequences with a bottom up approach. The generated regular expressions are used as a dataset on which various machine learning algorithms are applied for text classification.

Deep packet inspection (DPI) is widely used in content-aware network applications such as network intrusion detection systems, traffic billing, load balancing, and government surveillance. Pattern matching is a core and critical step in DPI, which checks the payload of each packet for known signatures (patterns) in order to identify packets with certain characteristics (e.g., malicious packets that carry viruses or worms). Regular expression is the major tool for signature description due to its powerful and flexible expressive ability. However, this flexibility also brings great challenges for efficient implementation in practice. Despite of hundreds to thousands of empirical proposals, wire-speed matching for large scale regular expressions still remains a big challenge. The gap between the matching throughput and the link speed is widening with the ever-increasing network link speed and pattern scale. This survey begins with a full-scale application background of DPI and technical background of regular expression matching in order to provide a global view and essential knowledge for readers. We then analyze the challenges in regular expression matching originated from the state explosion of finite state automaton used for regular expression matching. The nature of state explosion is analyzed in details, and the state-of-the-art solutions are grouped into categories of methods to relieve state expansion and methods to avoid state explosion, suggestions are also provided for building compact and efficient automata in different scenarios. Furthermore, proposals employing parallel platforms, including field-programmable gate array, GPU, general multi-processors, and ternary content addressable memory, to accelerate the matching process are introduced and thoroughly discussed. We also provide guidelines for efficient deployment for each of these platforms.

This paper analyzes algorithmic characteristics of AES Encryption/Decryption, and proposes a design methodology for AES algorithm digital hardware circuit through integrating the technologies of pipeline and parallel connections with dynamic reconfiguration. And a dynamic reconfiguration circuit model was built to test out the design methodology. The results of simulation and verification experiments prove that this model highlights all the advantages of dynamic reconfiguration technology, considers the application of parallel connections, increases the throughput, and excels in processing speed. Thus it illustrates a good and prospect of application and extension.

Pattern matching is widely used in applications such as genomic data query analysis, network intrusion detection, and deep packet inspection (DPI). Performing pattern matching on plaintext data is straightforward, but the need to protect the security of analyzed data and analyzed patterns can significantly complicate the process. Due to the privacy security issues of data and patterns, researchers begin to explore pattern matching on encrypted data. However, existing solutions are typically built on static pattern matching methods, lacking dynamism, namely, the inability to perform addition or deletion operations on the analyzed data. This lack of flexibility might hinder the adaptability and effectiveness of pattern matching on encrypted data in the real‐world scenarios. In this paper, we design a dynamic pattern matching scheme on encrypted data with forward and backward security, which introduces much‐needed dynamism. Our scheme is able to implement the addition operation and the deletion operation on the encrypted data without affecting the security of the original pattern matching scheme. Specifically, we design secure addition and deletion algorithms based on fragmentation data structures, which are compatible with the static pattern matching scheme. Moreover, we make significant improvements to the key generation algorithm, the encryption algorithm, and the match algorithm of the static scheme to ensure forward and backward security. Theoretical analysis proves that our scheme satisfies forward and backward security while ensuring the nonfalsifiability of encrypted data. The experimental results show that our scheme has a slight increase in time cost compared to the static pattern matching scheme, demonstrating its practicality and effectiveness in dynamic scenarios.

Pattern matching combined with regular expressions has many applications including semistructured data matching and lexical analysis in compilers. Variables in patterns allow one to refer to parts of the matching input. But some regular patterns suffer from inherent ambiguity, yielding more than one valid result. A match policy like shortest or longest match can disambiguate such patterns.In this paper, we show that regular pattern matching corresponds to sequential transduction. We derive straightforward ways to optimally compile regular patterns to sequential machines and to decide when regular patterns are unambiguous. Unambiguous patterns can be matched in a single traversal of the input. Ambiguities in patterns correspond to nondeterminism in sequential machines. Applying the match policy optimally yields two deterministic sequential machines, which produce the shortest match in two consecutive runs.

A noticeable fraction of Algorithms papers in the last few decades improve the running time of well-known algorithms for fundamental problems by logarithmic factors. For example, the {O}(n^2) dynamic programming solution to the Longest Common Subsequence problem (LCS) was improved to O(n^2/log^{2}n) in several ways and using a variety of ingenious tricks. This line of research, also known as the art of shaving log factors, lacks a tool for proving negative results. Specifically, how can we show that it is unlikely that LCS can be solved in time O(n^2/log^3n)?\nPerhaps the only approach for such results was suggested in a recent paper of Abboud, Hansen, Vassilevska W. and Williams (STOC'16). The authors blame the hardness of shaving logs on the hardness of solving satisfiability on boolean formulas (Formula-SAT) faster than exhaustive search. They show that an O(n^2/log^{1000} n) algorithm for LCS would imply a major advance in circuit lower bounds. Whether this approach can lead to tighter barriers was unclear.\nIn this paper, we push this approach to its limit and, in particular, prove that a well-known barrier from complexity theory stands in the way for shaving five additional log factors for fundamental combinatorial problems. For LCS, regular expression pattern matching, as well as the Fréchet distance problem from Computational Geometry, we show that an O(n^2/log^{7+epsilon}{n}) runtime would imply new Formula-SAT algorithms.\nOur main result is a reduction from SAT on formulas of size s over n variables to LCS on sequences of length N=2^{n/2} * s^{1+o(1)}. Our reduction is essentially as efficient as possible, and it greatly improves the previously known reduction for LCS with N=2^{n/2} * s^c, for some c >= 100.

Many applications require searching for multiple patterns in large data streams for which there is no preprocessed index to rely on for efficient lookups. An multiple instruction stream-single data stream (MISD) VLSI architecture that is based on a recursive divide and conquer approach to pattern matching is proposed. This architecture allows searching for multiple patterns simultaneously. The patterns can be constructed much like regular expressions, and add features such as requiring subpatterns to match in a specific order with some fuzzy distance between them, and the ability to allow errors according to prescribed thresholds, or ranges of such. The current implementation permits up to 127 simultaneous patterns at a clock frequency of 100 MHz, and does 1.024/spl times/10/sup 11/ character comparisons per second.

Regular expressions, or regexes, have been used traditionally as a pattern matching tool to search for structures in a set of objects, like flies, text documents or folders. Pattern matching can be used to look for flies whose name contains a given string, to search flies that contain a specific pattern within them, or simply to extract text in a set of documents. It is very popular to apply regexes to detect and extract patterns that represent phone numbers, URLs, email addresses, etc. These kind of information can be characterized because it has a well defined structure. Nevertheless, regexes are not very frequently used because its high complexity in both, syntax and grammatical rules, makes regexes difficult to understand. For this reason, the development of programs able to automatically generate, and evaluate, regexes has become a valuable task. This work analyzes the performance of different grammatical evolutionary approaches in the generation of regexes able to extract URL patterns. Four different types of grammars have been evaluated: a context-free grammar, a context-free grammar with a penalized fitness function, an extensible context-free grammar, and a Christiansen grammar. For the considered problem, the experimental results show that the best performance of the system, measured as cumulative success rate, is achieved using Christiansen grammars.

The regular language-constrained orienteering problem with time windows