Two Decades of Maude

This paper is a tribute to José Meseguer, from the rest of us in the Maude team, reviewing the past, the present, and the future of the language and system with which we have been working for around two decades under his leadership. After reviewing the origins and the language's main features, we present the latest additions to the language and some features currently under development. This paper is not an introduction to Maude, and some familiarity with it and with rewriting logic are indeed assumed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Asymmetric Unification: A New Unification Paradigm for Cryptographic Protocol Analysis

The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-38574-2_16We present a new paradigm for unification arising out of a technique commonly used in cryptographic protocol analysis tools that employ unification modulo equational theories. This paradigm relies on: (i) a decomposition of an equational theory into (R,E) where R is confluent, terminating, and coherent modulo E, and (ii) on reducing unification problems to a set of problems s=?ts=?t under the constraint that t remains R/E-irreducible. We call this method asymmetric unification. We first present a general-purpose generic asymmetric unification algorithm. and then outline an approach for converting special-purpose conventional unification algorithms to asymmetric ones, demonstrating it for exclusive-or with uninterpreted function symbols. We demonstrate how asymmetric unification can improve performanceby running the algorithm on a set of benchmark problems. We also give results on the complexity and decidability of asymmetric unification.S. Escobar and S. Santiago were partially supported by EU (FEDER) and the Spanish MEC/MICINN under grant TIN 2010-21062-C02-02, and by Generalitat Valenciana PROMETEO2011/052. The following authors were partially supported by NSF: S. Escobar, J. Meseguer, and R. Sasse under CNS 09-04749 and CCF 09- 05584; D. Kapur under CNS 09-05222; C. Lynch, Z. Liu, and C. Meadows under CNS 09-05378, and P. Narendran and S. Erbatur under CNS 09-05286. Part of the S. Erbatur’s work was supported while with the Department of Computer Science, University at Albany, and part of R. Sasse’s work was supported while with the Department of Computer Science, University of Illinois at Urbana-Champaign.Erbatur, S.; Escobar Román, S.; Kapur, D.; Liu, Z.; Lynch, CA.; Meadows, C.; Meseguer, J.... (2013). Asymmetric Unification: A New Unification Paradigm for Cryptographic Protocol Analysis. En Automated Deduction – CADE-24. Springer. 231-248. https://doi.org/10.1007/978-3-642-38574-2_16S231248IEEE 802.11 Local and Metropolitan Area Networks: Wireless LAN Medium Access Control (MAC) and Physical (PHY) Specifications (1999)Basin, D., Mödersheim, S., Viganò, L.: An on-the-fly model-checker for security protocol analysis. In: Snekkenes, E., Gollmann, D. (eds.) ESORICS 2003. LNCS, vol. 2808, pp. 253–270. Springer, Heidelberg (2003)Blanchet, B.: An efficient cryptographic protocol verifier based on Prolog rules. In: CSFW, pp. 82–96. IEEE Computer Society (2001)Bürckert, H.-J., Herold, A., Schmidt-Schauß, M.: On equational theories, unification, and (un)decidability. Journal of Symbolic Computation 8(1/2), 3–49 (1989)Comon-Lundh, H., Delaune, S.: The finite variant property: How to get rid of some algebraic properties. In: Giesl, J. (ed.) RTA 2005. LNCS, vol. 3467, pp. 294–307. Springer, Heidelberg (2005)Durán, F., Meseguer, J.: A Maude coherence checker tool for conditional order-sorted rewrite theories. In: Ölveczky, P.C. (ed.) WRLA 2010. LNCS, vol. 6381, pp. 86–103. Springer, Heidelberg (2010)Erbatur, S., Escobar, S., Kapur, D., Liu, Z., Lynch, C., Meadows, C., Meseguer, J., Narendran, P., Santiago, S., Sasse, R.: Effective symbolic protocol analysis via equational irreducibility conditions. In: Foresti, S., Yung, M., Martinelli, F. (eds.) ESORICS 2012. LNCS, vol. 7459, pp. 73–90. Springer, Heidelberg (2012)Erbatur, S., Escobar, S., Kapur, D., Liu, Z., Lynch, C., Meadows, C., Meseguer, J., Narendran, P., Sasse, R.: Asymmetric unification: A new unification paradigm for cryptographic protocol analysis. In: UNIF 2011 (2011), https://sites.google.com/a/cs.uni.wroc.pl/unif-2011/programEscobar, S., Sasse, R., Meseguer, J.: Folding variant narrowing and optimal variant termination. J. Log. Algebr. Program. 81(7-8), 898–928 (2012)Harju, T., Karhumäki, J., Krob, D.: Remarks on generalized post correspondence problem. In: Puech, C., Reischuk, R. (eds.) STACS 1996. LNCS, vol. 1046, pp. 39–48. Springer, Heidelberg (1996)Hopcroft, J.E., Motwani, R., Ullman, J.D.: Introduction to automata theory, languages, and computation - international edition, 2nd edn. Addison-Wesley (2003)Jouannaud, J.-P., Kirchner, H.: Completion of a set of rules modulo a set of equations. SIAM J. Comput. 15(4), 1155–1194 (1986)Liu, Z., Lynch, C.: Efficient general unification for XOR with homomorphism. In: Bjørner, N., Sofronie-Stokkermans, V. (eds.) CADE 2011. LNCS, vol. 6803, pp. 407–421. Springer, Heidelberg (2011)Liu, Z.: Dealing Efficiently with Exclusive OR, Abelian Groups and Homomorphism in Cryptographic Protocol Analysis. PhD thesis, Clarkson University (2012), http://people.clarkson.edu/~clynch/papers/Dissertation_of_Zhiqiang_Liu.pdfLowe, G., Roscoe, A.W.R.: Using CSP to detect errors in the TMN protocol. IEEE Transactions on Software Engineering 23, 659–669 (1997)Meseguer, J.: Conditional rewriting logic as a united model of concurrency. Theor. Comput. Sci. 96(1), 73–155 (1992)Schmidt, B., Meier, S., Cremers, C.J.F., Basin, D.A.: Automated analysis of Diffie-Hellman protocols and advanced security properties. In: Proc. CSF 2012, pp. 78–94. IEEE (2012)Tatebayashi, M., Matsuzaki, N., Newman Jr., D.B.: Key distribution protocol for digital mobile communication systems. In: Brassard, G. (ed.) CRYPTO 1989. LNCS, vol. 435, pp. 324–334. Springer, Heidelberg (1990)TeReSe, editor. Term Rewriting Systems. Cambridge University Press (2003)Viry, P.: Equational rules for rewriting logic. Theor. Comp. Sci. 285(2), 487–517 (2002

Guided Unfoldings for Finding Loops in Standard Term Rewriting

In this paper, we reconsider the unfolding-based technique that we have introduced previously for detecting loops in standard term rewriting. We improve it by guiding the unfolding process, using distinguished positions in the rewrite rules. This results in a depth-first computation of the unfoldings, whereas the original technique was breadth-first. We have implemented this new approach in our tool NTI and compared it to the previous one on a bunch of rewrite systems. The results we get are promising (better times, more successful proofs).Comment: Pre-proceedings paper presented at the 28th International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2018), Frankfurt am Main, Germany, 4-6 September 2018 (arXiv:1808.03326

Constrained narrowing for conditional equational theories modulo axioms

For an unconditional equational theory (Sigma, E) whose oriented equations (E) over arrow are confluent and terminating, narrowing provides an E-unification algorithm. This has been generalized by various authors in two directions: (i) by considering unconditional equational theories (Sigma, E boolean OR B) where the (E) over arrow are confluent, terminating and coherent modulo axioms B, and (ii) by considering conditional equational theories. Narrowing for a conditional theory (Sigma, E boolean OR B) has also been studied, but much less and with various restrictions. In this paper we extend these prior results by allowing conditional equations with extra variables in their conditions, provided the corresponding rewrite rules (E) over arrow are confluent, strictly coherent, operationally terminating modulo B and satisfy a natural determinism condition allowing incremental computation of matching substitutions for their extra variables. We also generalize the type structure of the types and operations in Sigma to be order-sorted. The narrowing method we propose, called constrained narrowing, treats conditions as constraints whose solution is postponed. This can greatly reduce the search space of narrowing and allows notions such as constrained variant and constrained unifier that can cover symbolically possibly infinite sets of actual variants and unifiers. It also supports a hierarchical method of solving constraints. We give an inference system for hierarchical constrained narrowing modulo B and prove its soundness and completeness. (C) 2015 Elsevier B.V. All rights reserved.We thank the anonymous referees for their constructive criticism and their very detailed and helpful suggestions for improving an earlier version of this work. We also thank Luis Aguirre for kindly giving us additional suggestions to improve the text. This work has been partially supported by NSF Grant CNS 13-19109 and by the EU (FEDER) and the Spanish MINECO under grant TIN 2013-45732-C4-1-P, and by Generalitat Valenciana PROMETEOII/2015/013.Cholewa, A.; Escobar Román, S.; Meseguer, J. (2015). Constrained narrowing for conditional equational theories modulo axioms. Science of Computer Programming. 112:24-57. https://doi.org/10.1016/j.scico.2015.06.001S245711

Complete Sets of Reductions Modulo A Class of Equational Theories which Generate Infinite Congruence Classes

In this paper we present a generalization of the Knuth-Bendix procedure for generating a complete set of reductions modulo an equational theory. Previous such completion procedures have been restricted to equational theories which generate finite congruence classes. The distinguishing feature of this work is that we are able to generate complete sets of reductions for some equational theories which generate infinite congruence classes. In particular, we are able to handle the class of equational theories which contain the associative, commutative, and identity laws for one or more operators. We first generalize the notion of rewriting modulo an equational theory to include a special form of conditional reduction. We are able to show that this conditional rewriting relation restores the finite termination property which is often lost when rewriting in the presence of infinite congruence classes. We then develop Church-Rosser tests based on the conditional rewriting relation and set forth a completion procedure incorporating these tests. Finally, we describe a computer program which implements the theory and give the results of several experiments using the program

An interactive semantics of logic programming

We apply to logic programming some recently emerging ideas from the field of reduction-based communicating systems, with the aim of giving evidence of the hidden interactions and the coordination mechanisms that rule the operational machinery of such a programming paradigm. The semantic framework we have chosen for presenting our results is tile logic, which has the advantage of allowing a uniform treatment of goals and observations and of applying abstract categorical tools for proving the results. As main contributions, we mention the finitary presentation of abstract unification, and a concurrent and coordinated abstract semantics consistent with the most common semantics of logic programming. Moreover, the compositionality of the tile semantics is guaranteed by standard results, as it reduces to check that the tile systems associated to logic programs enjoy the tile decomposition property. An extension of the approach for handling constraint systems is also discussed.Comment: 42 pages, 24 figure, 3 tables, to appear in the CUP journal of Theory and Practice of Logic Programmin