Authenticating ad hoc networks by comparison of short digests

We show how to design secure authentication protocols for a non-standard class of scenarios. In these authentication is not bootstrapped from a PKI, shared secrets or trusted third parties, but rather using a minimum of work by human user(s) implementing the low-bandwidth unspoofable channels between them. We develop both pairwise and group protocols which are essentially optimal in human effort and, given that, computation. We compare our protocols with recent pairwise protocols proposed by, for example, Hoepman and Vaudenay. We introduce and analyse a new cryptographic primitive – a digest function – that is closely related to short-output universal hash functions.