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