Helmut Seidl and Kumar Neeraj Verma. Cryptographic Protocol Verification Using Tractable Classes of Horn Clauses. In Thomas W. Reps, Mooly Sagiv and Jörg Bauer, editors, Program Analysis and Compilation, Theory and Practice, volume 4444 of Lecture Notes in Computer Science, pages 97-119, 2007. Springer.

We consider secrecy problems for cryptographic protocols modeled using Horn clauses and present general classes of Horn clauses which can be efficiently decided. Besides simplifying the methods for the class of flat and one-variable clauses introduced for modeling of protocols with single blind copying [7,25], we also generalize this class by considering k-variable clauses instead of one-variable clauses with suitable restrictions similar to those for the class $\mathcal{S^{+}}$ . This class allows to conveniently model protocols with joint blind copying. We show that for a fixed k, our new class can be decided in DEXPTIME, as in the case of one variable.

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