Broadcast Encryption Scheme Realizing Information Granularity byTree StructureSource:Cryptology and Information Security Conference 2009

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(digital content)/

(1/5)(Information Granularity)

(2/5)(Tree-based Information Granularity)

(3/5)(Broadcast Encryption)session key(Encryption)(Decryption)informationinformation(Encryption)(Decryption)cipher blockenabling blockdksession keyski

(4/5)CP: Ui:IDi:UiE:G:(base point)GOEOEEscp:CPX:CPl:CPM:mtMt=1,...,2l-1

(5/5)Not:Emt(t=1,,f)Lj:E(j=1,,l)lidj:jLpkj:jLskj:jut: mtski: UiH: vEEk():kDk():k

(1/3)CP step 1. a, bGF (p)p EE y2 = x3 + ax + b mod p a, b4a3 + 27b2 0 (mod p)step 2. E G G G = OEOE E step 3. scpscpZpX = scpGstep 4. E RCP scp RpGX

(2/3)step 1. Ml 2 l-1step 2. 1 2root M2l-1 mt (t =1,, 2l-1) step 3. E mt Not E (t = 1,, f)mtm2tm2t+1

(2/3)step 4. E Lj E (j= 1,, l)step 5. Lskj Lpkj 1.lidjZpj=1,, l2. j LskjE QjLskj = lidjQj3. j LpkjPjPj + Qj = RLpkj=lidjPj+XLpkj+ Lskj = lidjR + XCP lidjQ j LskjNot (t= 1,, 2l-1)Lj (j = 1,, l)Lpkj

Covert channeljskij*mtSuccess ?