Reliability of Soft Verification of Message Authentication Codes

It is known that Message Authentication Codes are extremely sensitive to any change of the message they are appended to. Even one or more bits of the changed message invert about 50% of bits of Message Authentication Codes, making in such a way the message useless. The hard condition for the successful verification of Message Authentication Codes is that all bits of the received Message Authentication Code and that one recalculated of the received message have to be equal. This condition for the successful verification of messages protected by Message Authentication Codes is not suitable in many applications. Therefore an introduction of a softer condition for the successful verification would enable the correction and improvement of the verification rate of messages corrupted by transmission over a noisy channel. The following paper is based on an algorithm for Soft Verification which introduces robustness into the verification of messages protected by Message Authentication Codes together with a correction of messages corrupted due to the noisy channel. A soft output of the algorithm gives information about the reduction of the security level of the successful authentication to the source decoder. This information can be compared to reliability values as soft output of SISO channel decoder.