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              The International Computer Science Institute
                     is pleased to present a talk:

                  Tuesday, August 25, 1992  2:00 p.m.

                              AMOS BEIMEL
                                Technion
                             Haifa, Israel

              ``Universally Ideal Secret Sharing Schemes''

           Given a set of parties {1,...,n}, an  access  structure
      is  a  monotone collection of subsets of the parties.  For a
      certain domain of secrets, a secret sharing  scheme  for  an
      access  structure  is  a  method  for a dealer to distribute
      shares to the parties, such that only subsets in the  access
      structure can reconstruct the secret.

           A secret sharing scheme is ideal if the domains of  the
      shares  are the same as the domain of the secrets. An access
      structure is universally ideal if there is an  ideal  secret
      sharing  scheme  for it over every finite domain of secrets.
      An obvious necessary condition for an access structure to be
      universally ideal is to be ideal over the binary and ternary
      domains of secrets.  In this work, we prove that this condi-
      tion  is  also  sufficient.   In  addition, we give an exact
      characterization for each of these two conditions, and  show
      that  each condition by itself is not sufficient for univer-
      sally ideal access structures.

        This talk will be held in the Main Lecture Hall at ICSI.
          1947 Center Street, Sixth Floor, Berkeley, CA 94704
       (On Center between Milvia and Martin Luther King Jr. Way)

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