Paper 2008/039

New Results on Unconditionally Secure Multireceiver Manual Authentication

Shuhong Wang and Reihaneh Safavi-Naini

Abstract

Manual authentication is a recently proposed model of communication motivated by the settings where the only trusted infrastructure is a low bandwidth authenticated channel, possibly realized by the aid of a human, that connects the sender and the receiver who are otherwise connected through an insecure channel and do not have any shared key or public key infrastructure. A good example of such scenarios is pairing of devices in Bluetooth. Manual authentication systems are studied in computational and information theoretic security model and protocols with provable security have been proposed. In this paper we extend the results in information theoretic model in two directions. Firstly, we extend a single receiver scenario to multireceiver case where the sender wants to authenticate the same message to a group of receivers. We show new attacks (compared to single receiver case) that can launched in this model and demonstrate that the single receiver lower bound $2\log(1/\epsilon)+O(1)$ on the bandwidth of manual channel stays valid in the multireceiver scenario. We further propose a protocol that achieves this bound and provides security, in the sense that we define, if up to $c$ receivers are corrupted. The second direction is the study of non-interactive protocols in unconditionally secure model. We prove that unlike computational security framework, without interaction a secure authentication protocol requires the bandwidth of the manual channel to be at least the same as the message size, hence non-trivial protocols do not exist.