Christine M. O'Keefe
Optimal Updating of Ideal Threshold Schemes
We consider the problem of changing the parameters of an established ideal $(k,n)$-threshold scheme without the use of secure channels. We identify the parameters $(k',n')$ to which such a scheme can be updated by means of a broadcast message and then prove a lower bound on the size of the relevant broadcast. The tightness of this bound is demonstrated by describing an optimal procedure for updating the parameters of an ideal scheme.