The article proposes a solution to the problem of protecting communication channels between field devices and the PLC level. The authors determine the model of the intruder for such channels in non-critical ACS TP. The article also provides a list of the most likely attacks. The protection of data transmitted through a physically insecure communication channel can be ensured by various cryptographic means. Standardized cryptographic primitives provide a high level of security, however, their implementation may require significant computing resources. Field devices often do not provide these resources. Otherwise, field data has a short lifetime and size. In view of this, it would be interesting to consider the applicability of low-resource cryptographic tools to solve this problem. Algorithms of this class provide low-resource implementation and are able to grant protection in a certain period of time. Using such algorithms to ensure data protection during their lifetime from an attacker with a certain potential can solve this problem. As a solution, it is proposed to use the lightweight «Mora» hash function with a block size of 64 bits. This function is «Streebog»-like, which allows to provide good cryptographic qualities. The small block size allows to obtain good performance with a sufficient level of resistance in the formed model of the intruder. The article provides a full description of the hash function, as well as the results of the cryptanalysis. The experiment showed the 30 times superiority of the «Mora» in the speed of work against the «Streebog».