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 already noted, @cite_25 was the first paper to demonstrate the applicability of SAT-based cryptanalysis to relevant cryptographic algorithms. In that paper using the solver @cite_95 it was possible to quite effectively find single-block collisions for MD4. Using new propositional encoding methods (in particular, the system) and state-of-the-art SAT solvers it is possible to find preimages for MD4 and MD5 several hundred times faster than it was done in @cite_25 . Nevertheless, on the current stage SAT-based cryptanalysis is less effective than specialized methods (see, for example @cite_58 @cite_99 @cite_82 ) on problems of finding collisions of cryptographic hash functions. However, as far as we know, it is the SAT-based approach that yields best known preimage attacks on truncated variants of hash functions @cite_32 @cite_78 @cite_54 . In application to MD4-39 for a long time the SAT-based preimage attack from @cite_32 was considered to be the best. In @cite_15 we significantly improved the results from @cite_32 . It was possible for the large part thanks to functional capabilities of the system.
@cite_99 @cite_78 @cite_54 @cite_32 @cite_95 @cite_15 @cite_58 @cite_25 @cite_82
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In this paper we construct preimage attack on the truncated variant of the MD4 hash function. Specifically, we study the MD4-39 function defined by the first 39 steps of the MD4 algorithm. We suggest a new attack on MD4-39, which develops the ideas proposed by H. Dobbertin in 1998. Namely, the special relaxation constraints are introduced in order to simplify the equations corresponding to the problem of finding a preimage for an arbitrary MD4-39 hash value. The equations supplemented with the relaxation constraints are then reduced to the Boolean Satisfiability Problem (SAT) and solved using the state-of-the-art SAT solvers. We show that the effectiveness of a set of relaxation constraints can be evaluated using the black-box function of a special kind. Thus, we suggest automatic method of relaxation constraints generation by applying the black-box optimization to this function. The proposed method made it possible to find new relaxation constraints that contribute to a SAT-based preimage attack on MD4-39 which significantly outperforms the competition. 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. Hash functions are important cryptographic primitives which map arbitrarily long messages to fixed-length message digests in such a way that: (1) it is easy to compute the message digest given a message, while (2) inverting the hashing process (e.g. finding a message that maps to a specific message digest) is hard. One attack against a hash function is an algorithm that nevertheless manages to invert the hashing process. Hash functions are used in e.g. authentication, digital signatures, and key exchange. A popular hash function used in many practical application scenarios is the Secure Hash Algorithm (SHA-1). In this thesis we investigate the current state of the art in carrying out preimage attacks against SHA-1 using SAT solvers, and we attempt to find out if there is any room for improvement in either the encoding or the solving processes. We run a series of experiments using SAT solvers on encodings of reduceddifficulty versions of SHA-1. Each experiment tests one aspect of the encoding or solving process, such as e.g. determining whether there exists an optimal restart interval or determining which branching heuristic leads to the best average solving time. An important part of our work is to use statistically sound methods, i.e. hypothesis tests which take sample size and variation into account. Our most important result is a new encoding of 32-bit modular addition which significantly reduces the time it takes the SAT solver to find a solution compared to previously known encodings. Other results include the fact that reducing the absolute size of the search space by fixing bits of the message up to a certain point actually results in an instance that is harder for the SAT solve 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. Inverting a function f at a given point y in its range involves finding any x in the domain such that f(x) = y. This is a general problem. We wish to find a heuristic for inverting those functions which satisfy certain statistical properties similar to those of random functions. As an example, we choose popular secure hash functions which are expected to be hard to invert and any successful strategy to do so will be quite useful. This provides an excellent challenge for SAT solvers. We first find the limits of inverting via direct encoding of these functions as SAT: for MD4 this is one round and twelve steps and for MD5 it is one round and ten steps. Then, we show that by adding customized constraints obtained by modifying an earlier attack by Dobbertin, we can invert MD4 up to 2 rounds and 7 steps in < 8 hours. 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 ... 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 . Scholars are increasingly citing electronic web references which are not preserved in libraries or full text archives. WebCite is a new standard for citing web references. To webcite a document involves archiving the cited Web page through www.webcitation.org and citing the WebCite permalink instead of (or in addition to) the unstable live Web page. This journal has amended its instructions for authors accordingly, asking authors to archive cited Web pages before submitting a manuscript. Almost 200 other journals are already using the system. We discuss the rationale for WebCite, its technology, and how scholars, editors, and publishers can benefit from the service. Citing scholars initiate an archiving process of all cited Web references, ideally before they submit a manuscript. Authors of online documents and websites which are expected to be cited by others can ensure that their work is permanently available by creating an archived copy using WebCite and providing the citation information including the WebCite link on their Web document(s). Editors should ask their authors to cache all cited Web addresses (Uniform Resource Locators, or URLs) prospectively before submitting their manuscripts to their journal. Editors and publishers should also instruct their copyeditors to cache cited Web material if the author has not done so already. Finally, WebCite can process publisher submitted citing articles (submitted for example as eXtensible Markup Language [XML] documents) to automatically archive all cited Web pages shortly before or on publication. Finally, WebCite can act as a focussed crawler, caching retrospectively references of already published articles. Copyright issues In recent years scholars have built maps of science by connecting the academic fields that cite each other, are cited together, or that cite a similar literature. But since scholars cannot always publish in the fields they cite, or that cite them, these science maps are only rough proxies for the potential of a scholar, organization, or country, to enter a new academic field. Here we use a large dataset of scholarly publications disambiguated at the individual level to create a map of science-or research space-where links connect pairs of fields based on the probability that an individual has published in both of them. We find that the research space is a significantly more accurate predictor of the fields that individuals and organizations will enter in the future than citation based science maps. At the country level, however, the research space and citations based science maps are equally accurate. These findings show that data on career trajectories-the set of fields that individuals have previously published in-provide more accurate predictors of future research output for more focalized units-such as individuals or organizations-than citation based science maps.