drand
Validate contents of group file on joining
When a node joins a DKG after the first epoch, they must provide the previous group file. Currently it is stored in the DBState object as the previous group file, but no validation of the current state vis-a-vis the provided group file is completed.
I propose we validate fields such as genesis seed, genesis time, beacon period, catchup period and scheme ID.
In case they don't match, we can simply error out the join command.
In reality, this should basically never happen, and there's no real recourse for a joining node if the leader provides them an invalid group file.
Alternatively, the leader could send the joiners the group file on proposal, but it could open up some weird attack vectors that I haven't thought deeply about
