n Security properties: the goals that a protocol is meant to satisfy, relatively to specific kinds and levels of threat ñ the intruders and their capabilities n We will consider the following security properties: n Secrecy n messages, keys, etc. have not become known n Authentication n Guarantees about the parties involved in the protocol n Non-repudiation n Evidence of the involvement of the other party n Anonymity n Protecting the identity of agents wrt particular events