ME-02 Duplicated Method Calls Could Lead to Denial of Service

[xoloki]

Coordinator methods accepting signers shares and nonces, as well as signer methods
accepting shares and nonces do not check if said values have already been received
correctly. A malicious signer, for instance, could repeatedly send the same public shares
before the coordinator is able to process the public shares from other signers and in this
way put a high burden on the coordinator who could not possibly process all messages in
time and therefore stall without moving to the next stage. Moreover, older values are
overwritten and this could lead to signers losing track of what the valid values are.