Secure key exchange mechanism in a wireless communication system

A method of secure key exchange between a master device and a plurality of devices in a wireless communications network, the method performed by the master comprising:

• generating a first salt for downlink communications;
• transmitting said first salt in plaintext to at least a first one of said plurality of devices over a first wireless communications link on a first frequency;
• transmitting said first salt in plaintext to at least a second one of said plurality of devices over a second wireless communications link on a second frequency different from said first frequency;
• generating a shared symmetric session key in accordance with said first salt and a master key, wherein the master key is shared with at least the first one of said plurality of devices over the first wireless communications link on the first frequency, and the master key further shared with at least the second one of said plurality of devices over the second wireless communications link on the second frequency;
• storing said shared symmetric session key for use in encrypting multicast communications that are to be transmitted from said master and to be received by at least the first one of said plurality of devices on said first frequency;
• storing said shared symmetric session key for use in encrypting the multicast communications that are to be transmitted from said master to be received by at least the second one of said plurality of devices on said second frequency in parallel with the multicast communications that are to be transmitted from said master to at least the first one of said plurality of devices on said first frequency;
• wherein the master conforms to an IO-link wireless standard;
• generating a plurality of second salts for uplink communications, one for each device of said plurality of devices;
• transmitting each one of said plurality of second salts in plaintext to each respective device of said plurality of devices, wherein parts of the plurality of the second salts are transmitted in parallel to parts of the plurality of devices over wireless communications links of different frequencies;
• generating a plurality of uplink symmetric session keys, each uplink symmetric session key is generated for each respective device of said plurality of devices in accordance with one of said second salts and a respective shared device key associated with said respective device;
• and
• storing said plurality of uplink symmetric session keys for use in decrypting unicast communications from each respective device to said master.