In the present paper we describe the technology for translating algorithmic descriptions of discrete functions to SAT. The proposed technology is aimed at applications in algebraic cryptanalysis. We describe how cryptanalysis instances are reduced to SAT in such a way that it should be perceived as natural by the cryptographic community. Therefore, in the theoretical part of the paper we justify the main principles of general reduction to SAT for discrete functions from a class containing the majority of functions employed in cryptography. Based on these principles we describe the Transalg software system, developed with SAT-based cryptanalysis specifics in mind. We show the results of applications of Transalg to construction of a number of attacks on various cryptographic functions. Some of the corresponding attacks are state of the art. We also compare the functional capabilities of the proposed system with that of other software systems that can be used to reduce cryptanalysis instances to SAT, and also with the CBMC system widely employed in symbolic verification. In the paper we also present vast experimental data, obtained using the SAT-solvers that took first places at the SAT-competitions in the recent several years.
As we mentioned above, SAT-based cryptanalysis is still actively developing. The cryptographic attacks that employ SAT-solvers show very good results for a number of keystream generators: Geffe, Wolfram (present paper), Crypto-1, Hitag2 (see @cite_24 ). In @cite_61 there was described a successful SAT-based attack on the widely known A5 1 cryptographic keystream generator, which has been used in GSM networks to cipher traffic. Later several dozen cryptanalysis instances for this cipher were solved in the SAT@home volunteer computing project @cite_10 . This result together with other attacks on A5 1 (see @cite_66 @cite_124 @cite_12 ) provides an exhaustive argument towards not using A5 1 any more. The Bivium keystream cipher @cite_23 is a popular object of algebraic and SAT-based cryptanalysis @cite_29 @cite_89 @cite_24 @cite_96 . In @cite_92 there was constructed a SAT-based guess-and-determine attack on Bivium the estimated runtime of which is realistic for modern distributed computing systems. In @cite_14 there were described SAT-based guess-and-determine attacks on several variants of the alternating step generator.
@cite_61 @cite_14 @cite_92 @cite_29 @cite_96 @cite_89 @cite_24 @cite_23 @cite_124 @cite_10 @cite_66 @cite_12
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In logical cryptanalysis a problem of search of a secret key of a cryptographic system is formulated as a SAT problem, i.e. a problem of search of a satisfying assignment for some CNF. In this paper we consider some natural strategies for parallelization of these SAT problems. We apply coarse-grained approach which makes it possible to use distributed computing environments with slow interconnect. The main practical result of this paper is successful logical cryptanalysis of keystream generator A5 1 in BNB-Grid system. In this paper, we propose an algorithm for constructing guess-and-determine attacks on keystream generators and apply it to the cryptanalysis of the alternating step generator (ASG) and two its modifications (MASG and MASG0). In a guess-and-determine attack, we first guess some part of an initial state and then apply some procedure to determine, if the guess was correct and we can use the guessed information to solve the problem, thus performing an exhaustive search over all possible assignments of bits forming a chosen part of an initial state. We propose to use in the determine part the algorithms for solving Boolean satisfiability problem (SAT). It allows us to consider sets of bits with nontrivial structure. For each such set it is possible to estimate the runtime of a corresponding guess-and-determine attack via the Monte-Carlo method, so we can search for a set of bits yielding the best attack via a black-box optimization algorithm augmented with several SAT-specific features. We constructed and implemented such attacks on ASG, MASG, and MASG0 to prove that the constructed runtime estimations are reliable. We show, that the constructed attacks are better than the trivial ones, which imply exhaustive search over all possible states of the control register, and present the results of experiments on cryptanalysis of ASG and MASG MASG0 with total registers length of 72 and 96, which have not been previously published in the literature. In this paper we describe Grain of Salt, a tool developed to automatically test stream ciphers against standard SAT solver-based attacks. The tool takes as input a set of configuration options and the definition of each filter and feedback function of the stream cipher. It outputs a problem in the language of SAT solvers describing the cipher. The tool can automatically generate SAT problem instances for Crypto-1, HiTag2, Grain, Bivium-B and Trivium. In addition, through a simple text-based interface it can be extended to generate problems for any stream cipher that employs shift registers, feedback and filter functions to carry out its work. Bivium is a reduced version of the stream cipher Trivium. In this paper we investigate how fast a key recovery attack on Bivium using Grobner bases is. First we explain the attack scenario and the cryptographic background. Then we identify the factors that have impact on the computation time and show how to optimise them. As a side effect these experiments benchmark several Grobner basis implementations. The optimised version of the Grobner attack has an expected running time of 239.12 s, beating the attack time of our previous SAT solver attack by a factor of more than 330. Furthermore this approach is faster than an attack based on BDDs, an exhaustive key search, a generic time-memory trade-off attack and a guess-and-determine strategy. In this paper we present experimental results of an application of SAT solvers in current cryptography. Trivium is a very promising stream cipher candidate in the final phase of the eSTREAM project. We use the fastest industrial SAT solvers to attack a reduced version of Trivium - called Bivium. Our experimental attack time using the SAT solver is the best attack time that we are aware of, it is faster than the following attacks: exhaustive search, a BDD based attack, a graph theoretic approach and an attack based on Grobner bases. The attack recovers the internal state of the cipher by first setting up an equation system describing the internal state, then transforming it into CNF and then solving it. When one implements this attack, several questions have to be answered and several parameters have to be optimised. A citing sentence is one that appears in a scientific article and cites previous work. Citing sentences have been studied and used in many applications. For example, they have been used in scientific paper summarization, automatic survey generation, paraphrase identification, and citation function classification. Citing sentences that cite multiple papers are common in scientific writing. This observation should be taken into consideration when using citing sentences in applications. For instance, when a citing sentence is used in a summary of a scientific paper, only the fragments of the sentence that are relevant to the summarized paper should be included in the summary. In this paper, we present and compare three different approaches for identifying the fragments of a citing sentence that are related to a given target reference. Our methods are: word classification, sequence labeling, and segment classification. Our experiments show that segment classification achieves the best results. In a document network such as a citation network of scientific documents, web-logs, etc., the content produced by authors exhibits their interest in certain topics. In addition some authors influence other authors' interests. In this work, we propose to model the influence of cited authors along with the interests of citing authors. Moreover, we hypothesize that apart from the citations present in documents, the context surrounding the citation mention provides extra topical information about the cited authors. However, associating terms in the context to the cited authors remains an open problem. We propose novel document generation schemes that incorporate the context while simultaneously modeling the interests of citing authors and influence of the cited authors. Our experiments show significant improvements over baseline models for various evaluation criteria such as link prediction between document and cited author, and quantitatively explaining unseen text. Abstract Documents in computer-readable form can be used to provide information about other documents, i.e. those they cite. To do this efficiently requires procedures for computer recognition of citing statements. This is not easy, especially for multi-sentence citing statements. Computer recognition procedures have been developed which are accurate to the following extent: 73 of the words in statements selected by computer procedures as being citing statements are words which are correctly attributable to the corresponding documents. The retrieval effectiveness of computer-recognized citing statements was tested in the following way. First, for eight retrieval requests in inorganiic chemistry, average recall by search of Chemical Abstracts Service indexing and Chemical Abstracts abstract text words was found to be 50 . Words from citing statements referring to the papers to be retrieved were then added to the index terms and abstract words as additional access points, and searching was repeated. Average recall increased to 70 . Only words from citing statements published within a year of the cited papers were used. The retrieval effect of citing statement words alone (published within a year) without index or abstract terms was the following: average recall was 40 . When just the words of the titles of the cited papers were added to those citing statement words, average recall increased to 50 . Purpose  The purpose of this paper is to suggest an alternative to the widely used Times Cited criterion for analysing citation networks. The approach involves taking account of the natures of the papers that cite a given paper, so as to differentiate between papers that attract the same number of citations.Design methodology approach  ArticleRank is an algorithm that has been derived from Google's PageRank algorithm to measure the influence of journal articles. ArticleRank is applied to two datasets  a citation network based on an early paper on webometrics, and a selfcitation network based on the 19 most cited papers in the Journal of Documentation  using citation data taken from the Web of Knowledge database.Findings  ArticleRank values provide a different ranking of a set of papers from that provided by the corresponding Times Cited values, and overcomes the inability of the latter to differentiate between papers with the same numbers of citations. The difference in rankings between Times Cited ... Several standard cryptographic hash functions were broken in 2005. Some essential building blocks of these attacks lend themselves well to automation by encoding them as CNF formulas, which are within reach of modern SAT solvers. In this paper we demonstrate effectiveness of this approach. In particular, we are able to generate full collisions for MD4 and MD5 given only the differential path and applying a (minimally modified) off-the-shelf SAT solver. To the best of our knowledge, this is the first example of a SAT-solver-aided cryptanalysis of a non-trivial cryptographic primitive. We expect SAT solvers to find new applications as a validation and testing tool of practicing cryptanalysts. Citation relationship between scientific publications has been successfully used for scholarly bibliometrics, information retrieval and data mining tasks, and citation-based recommendation algorithms are well documented. While previous studies investigated citation relations from various viewpoints, most of them share the same assumption that, if paper1 cites paper2 (or author1 cites author2), they are connected, regardless of citation importance, sentiment, reason, topic, or motivation. However, this assumption is oversimplified. In this study, we employ an innovative "context-rich heterogeneous network" approach, which paves a new way for citation recommendation task. In the network, we characterize 1) the importance of citation relationships between citing and cited papers, and 2) the topical citation motivation. Unlike earlier studies, the citation information, in this paper, is characterized by citation textual contexts extracted from the full-text citing paper. We also propose algorithm to cope with the situation when large portion of full-text missing information exists in the bibliographic repository. Evaluation results show that, context-rich heterogeneous network can significantly enhance the citation recommendation performance. A new form of document coupling called co-citation is defined as the frequency with which two documents are cited together. The co-citation frequency of two scientific papers can be determined by comparing lists of citing documents in the Science Citation Index and counting identical entries. Networks of co-cited papers can be generated for specific scientific specialties, and an example is drawn from the literature of particle physics. Co-citation patterns are found to differ significantly from bibliographic coupling patterns, but to agree generally with patterns of direct citation. Clusters of co-cited papers provide a new way to study the specialty structure of science. They may provide a new approach to indexing and to the creation of SDI profiles.