On Joint Cryptographic Verification and Channel Decoding via the Maximum Likelihood Criterion

The scenario is considered where a message, together with its message authentication code (MAC), is transmitted over a noisy channel. It is assumed that a forward error correcting channel code is used to reduce the error rate, but no repeat mechanism (ARQ) is used to correct the remaining errors. In such systems, uncorrected errors usually cause rejection of messages with an incorrect MAC. This paper introduces a technique for joint verification and decoding of the received message, based on targeting the maximum likelihood (message, MAC) pair. This allows the acceptance of corrected messages and their MACs, even if a few bits of the MAC are incorrect. This is comparable to the situation where handwritten signatures are accepted provided they are not too different from a reference. The algorithm also outputs a reliability measure on the verified message in the form of a log-likelihood ratio (LLR). A simulation-based comparison shows that the proposed scheme gives a large improvement of the acceptance rate of MACs, with respect to an equally secure conventional system.