Abstract: A method and system are provided for securing messages within a communication network of an industrial process control system, such as a substation automation system. A multi-block message to be transmitted via a communication network is secured by a block-based authentication, encryption and/or integrity information. Only residue of the previous block in the form of block-based information is needed to generate the block based information of the next block. Therefore, the previous block can already be transmitted while block-based information of the next block is generated. The method and system of the present disclosure enable on-the-fly authentication of the multi-block message and authentication at an increased rate.