In another embodiment the BCU 103 may associate two or more unique “active” key pairs—K1 pv/K1 pb, K2 pv/K2 pb, etc.—with an authorized user 101 of the PID 100, which key pairs—K1 pv/K1 pb, K2 pv/K2 pb, etc—may be updated by {HEAD ~ the BCU} 103 from {TAIL ~ time} to time, thereby replacing the previous key pairs 
In another embodiment the BCU 103 may associate two or more unique “ active ” key pairs — K1 pv / K1 pb , K2 pv / K2 pb , etc.—with an authorized user 101 of the PID 100 , which key pairs — K1 pv / K1 pb , K2 pv / K2 pb , etc — may be updated by { HEAD ~ the BCU } 103 from { TAIL ~ time } to time , thereby replacing the previous key pairs
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH