Proving termination using dependent types: the case of XOR-terms

We study a normalization function in an algebra of terms quotiented by an associative, commutative and involutive operator (logical xor). This study is motivated by the formal verification of cryptographic systems, relying on a normalization function for xor-terms. Such a function is easy to define using general recursion. However, as it is to be used in a type theoretic proof assistant, we also need a proof of its termination. Instead of using a mixture of various rewriting orderings, we follow an approach involving the power of Type Theory with dependent types. The results are to be applied in the proof of the security API described in [14].