We investigate unconditional security for message authentication protocols that are designed using two-channel cryptography. We look at both noninteractive message authentication protocols (NIMAPs) and interactive message authentication protocols (IMAPs). We provide a new proof of nonexistence of nontrivial unconditionally secure NIMAPs. This proof consists of a combinatorial counting argument and is much shorter than the previous proof by Wang et al., which was based on probability distribution arguments. Further, we propose a generalization of an unconditionally secure 3-round IMAP due to Naor, Segev and Smith. With a careful choice of parameters, our scheme improves that of Naor et al. Our scheme is very close to optimal for most parameter situations of practical interest.
Atefeh Mashatan, Douglas R. Stinson