▁other . ▁ ▁For ▁example , ▁each ▁encryption ▁key ▁can ▁be ▁generated ▁from ▁the ▁underlying ▁key ▁material ▁using ▁a ▁key ▁deriv ation ▁function . ▁ ▁For ▁example , ▁a ▁replacement ▁for ▁W EP , ▁Wi - Fi ▁Prote cted ▁Access ▁( W PA ), ▁uses ▁three ▁levels ▁of ▁keys : ▁master ▁key , ▁working ▁key ▁and ▁RC 4 ▁key . ▁The ▁master ▁W PA ▁key ▁is ▁shared ▁with ▁each ▁client ▁and ▁access ▁point ▁and ▁is ▁used ▁in ▁a ▁protocol ▁called ▁Tem por al ▁Key ▁Integr ity ▁Pro tocol ▁( T K IP ) ▁to ▁create ▁new ▁working ▁keys ▁frequently ▁enough ▁to ▁th wart ▁known ▁attack ▁methods . ▁The ▁working ▁keys ▁are ▁then ▁combined ▁with ▁a ▁longer , ▁ 4 8 - bit ▁IV ▁to ▁form ▁the ▁RC 4 ▁key ▁for ▁each ▁packet . ▁ ▁This ▁design ▁m im ics ▁the ▁W EP ▁approach ▁enough ▁to ▁allow ▁W PA ▁to ▁be ▁used ▁with ▁first - gener ation ▁Wi - Fi ▁network ▁cards , ▁some ▁of ▁which ▁implemented ▁port ions ▁of ▁W EP ▁in ▁hardware . ▁However , ▁not ▁all ▁first - gener ation ▁access ▁points ▁can ▁run ▁W PA . ▁ ▁Another , ▁more ▁conserv ative ▁approach ▁is ▁to ▁employ ▁a ▁ci pher ▁designed ▁to ▁prevent ▁related - key ▁attacks ▁altogether , ▁usually ▁by ▁incorpor ating ▁a ▁strong ▁key ▁schedule . ▁A ▁newer ▁version ▁of ▁Wi - Fi ▁Prote cted ▁Access , ▁W PA 2 , ▁uses ▁the ▁A ES ▁block ▁ci pher ▁instead ▁of ▁RC 4 , ▁in ▁part ▁for ▁this ▁reason .