The Weizmann Institute of Science Faculty of Mathematics and Computer Science Theory of Computation Research Seminar Dani Halevy will speak on The LSD Broadcast Encryption Scheme Seminar Room, Room 261, Ziskind Building on Tuesday, June 25, 2002 at 11:00 (NOTE CHANGE IN TIME.) Abstract: The SD (Subset Difference) scheme of Naor Naor and Lotspiech makes it possible to revoke any $r$ out of the $n$ users in a memoryless broadcast encryption scheme by predistributing $O(log^2(n))$ keys per user and sending $O(r)$ messages. In this talk we describe an improved broadcast encryption scheme called LSD (Layered Subset Difference) which reduces the number of keys by almost a square root while increasing the number of messages only by a small constant. In addition, we show how to generalize the construction to any privileged set defined by $r$ inclusion and exclusion conditions on the vertices of the user tree. The new scheme is completely practical, and makes it possible to address arbitrary privileged subsets of 256,000,000 possible customers by predistributing to each one of them just 146 keys, which require less than one kilobyte of memory in the user's smart card. Joint work with Adi Shamir. --------------------------------------------------------- TechnionMathNet2 TECHMATH2 Editor:Michael Cwikel Announcement from: Miriam Abraham