  We explore the conversion of classical secret-sharing schemes to quantum
ones, and how this can be used to give efficient QSS schemes for general
adversary structures. Our first result is that quantum secret-sharing is
possible for any structure for which no two disjoint sets can reconstruct the
secret (this was also proved, somewhat differently, by D. Gottesman). To obtain
this we show that a large class of linear classical SS schemes can be converted
into quantum schemes of the same efficiency.
  We also give a necessary and sufficient condiion for the direct conversion of
classical schemes into quantum ones, and show that all group homomorphic
schemes satisfy it.
