This paper discusses the main issues regarding the reliability and the efficacy of standard cryptographic techniques applied to pervasive computing. First of all, we describe a set of scenarios, where social interactions are supported by small-sized pervasive devices. These are expected to manage and exchange personal and sensible information with context-specific requirements. We present a general methodology that helps identifying the most suitable model for securing data storage, processing and communication. Three protocols and systems are formally described and compared in this framework, in respect of model’s complexity and safety warranties.