Messaging protocols for resource limited systems such as distributed IoT systems are often vulnerable to attacks due to security choices made to conserve resources such as time, memory, or bandwidth. Protocol dialects are a light weight, modular mechanism to provide security guarantees such as authentication or integrity. In this paper we propose a generic dialect for the Constrained Application Protocol (CoAP) messaging protocol. The CoAP protocol, dialect, and an attack models are formalized in the rewriting logic system Maude. A number of properties relating CoAP and its dialected form are given, including a stuttering bisimulation, thus ensuring that dialecting preserves important properties of a CoAP application. The ideas are illustrated with some simple scenarios.