Personal Networks and PN federations are new networking paradigms that merge concepts from ad hoc, P2P and wireless networks, built around user?s needs. Even though they are a promise of a practical achievement of ubiquitous computing, managing security associations in these frameworks proves to be a challenge. We present in this paper a security architecture, including a uniform personal namespace using crypto-based identifiers and a key management scheme based on identity-based cryptography. We also provide an evaluation of our scheme, in terms of computation complexity, communication cost and security.