improve robustness of dynamic committee model

[omershlo]

Our dynamic model relies on the fact the DKR is non-interactive therefore we have clear separation between the secret distribution and old committee and secret receiving by new committee : We say that at any point in time the total number of adversary controlled parties is t.

we can improve our model. inspiration : https://eprint.iacr.org/2019/017.pdf https://eprint.iacr.org/2020/464.pdf