Protocol Speci cation and Analysis in Maude

This paper proposes rewriting logic as an executable speciication formalism for security protocols that ooers some novel advantages. A message-passing object-oriented approach seems particularly natural for communication protocols and can be naturally formalized in rewriting logic. This is illustrated by using the Needham-Schroeder Public-Key protocol as a running example. The rewriting logic-based Maude interpreter CELM96] offers also some useful advantages. EEcient executability allows prototyping and debugging of protocol speciications. But since a concurrent system can have many diierent behaviors, to properly analyze the system it becomes important to explore not just the single execution provided by some default strategy, but many other executions. Maude supports user-deened execution strategies, including strategies such as breadth-rst-search that can exhaustively explore all the executions of a system. This is very helpful in uncovering security aws under unforeseen attack scenarios such as those found for NSPK. We also discuss future developments along of this work, including (1) narrowing using symbolic execution techniques, (2) modularity and compositionality issues in formal reasoning, and (3) combination of rewriting logic and temporal logic.