| CPC H04W 12/0433 (2021.01) [H04B 1/713 (2013.01); H04L 9/0618 (2013.01); H04L 9/0643 (2013.01); H04L 9/08 (2013.01); H04L 9/085 (2013.01); H04L 9/0869 (2013.01); H04L 9/0894 (2013.01); H04L 9/14 (2013.01); H04L 9/3239 (2013.01); H04L 9/3242 (2013.01); H04L 12/189 (2013.01); H04L 63/0435 (2013.01); H04L 69/323 (2013.01); H04W 12/03 (2021.01); H04W 12/037 (2021.01); H04W 12/50 (2021.01); H04L 2209/80 (2013.01)] | 12 Claims |

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1. A method of secure communications between a master and a plurality of devices in a wireless communications network, the method comprising:
encrypting, on said master, downlink plaintext for multicast transmission to a plurality of devices over a wireless communications link utilizing a symmetric key encryption algorithm in accordance with a first counter value and a shared symmetric session key that exists independent of the first counter value; and
decrypting, on one of said devices, multicast downlink cyphertext received from said master over said wireless communications link utilizing a symmetric key decryption algorithm in accordance with a second counter value and said shared symmetric session key which exists independent of the second counter value;
wherein said wireless communications link is a short distance wireless link in that said master and said plurality of devices are located within a single industrial complex, and wherein said master and each of said devices have respective, independently counting jump counters and wherein the shared symmetric session key is changed from time to time, by using a random salt generated by said master and transmitted to said devices and by using multiple iterations of one-way functions, the time of each change of said shared symmetric session key being designated by the master setting an initial count value in said master's jump counter and the change of said shared symmetric session key occurring when said master's jump counter reaches a prescribed value known to the master and said devices, wherein the count of the jump counter of said master and the count of the jump counter of said devices change at a known rate and wherein the method further comprises transmitting from said master toward said devices a representation of each count value of the jump counter of said master as the master's jump counter counts.
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