Combine decryption shares by using Lagrange Interpolation?
User received for all I ,
Share i = (tag/tagi’)si hzi = gQ(i) where Q is some
degree 2t polynomial s.t. Q(0) = (tag/tag’)s hz ,
Lagrange Interpolation: Gives li s.t Q(0) = S liQ(I) for
every 2t degree polynomial Q.
To combine shares, user computes
P ( Sharei ) li = P ( gQ(i) ) li = g S liQ(I) = gQ(0)