Mithril Client fail to validate certificate chain if the previous certificate is more than one epoch older

[Alenar]

Issue

The Certificate Chain breaks when one Epoch does not have any associated Certificate.
⚠ We need to talk with the research team to find out if it is a bug or not

[jpraynaud]

Possible Recovery Solutions

• Using a higher Epoch Offset and embedding in the signed message multiple Next AVKs. This solution could work, but would be cumbersome (as the Signers would have to wait more epochs before being able to sign, for example 3 instead of 2)
• Use the Aggregator Beacon to orchestrate certificate creation for an epoch at a later epoch when the network is back up. This means that the Aggregator is in charge of broadcasting the epoch to be used by the Signers to individually sign, and is verifying if there is a gap. This solution is likely to be the most simple to deploy, but it might not cover all of the cases that would lead to an epoch gap in the chain (for example if the Signers were not able to gather Stake Distribution for previous Epochs on their end)
• In a multiple Aggregator network, if an Aggregator misses an epoch (due to networking or operations trouble), it should be able to recover the chain by retrieving from any other up to date aggregator
• A last option to recover from such an Epoch gap would be to re-genesis the chain (this will always work, but it will be hard to operate and should be reserved to emergency situations)

[jpraynaud]

Next Steps

We will review the recovery strategies with the research team to validate if we should implement one of them (and which one)