ps8 - Computer Science and Engineering, UCSD CSE 207:...

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Computer Science and Engineering, UCSD Spring 11 CSE 207: Modern Cryptography Instructor: Mihir Bellare Problem Set 8 May 25, 2011 Problem Set 8 Due: Wednesday June 1, 2011, in class. Problem 1. [60 points] In an identity-based, non-interactive key distribution system, there is a trusted authority (TA) who has a master secret key msk whose associated master public key mpk is assumed known to all parties in the system. A party with identity id ∈ { 0 , 1 } * is issued a secret key sk ( id ) computed by the TA as a function of id and msk . This is presumed delivered securely to id in a pre-processing phase. The system speciFes a key-agreement function KA with the property that KA ( mpk , id 1 , id 2 , sk ( id 1 )) = KA ( mpk , id 2 , id 1 , sk ( id 2 )) for all id 1 , id 2 ∈ { 0 , 1 } * . This common value, denoted Key ( { id 1 , id 2 } ), is a shared key between id 1 , id 2 that both parties can compute. They can now use it to symmetrically encrypt data they send each other. The intent, for security, is that nobody besides
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