VRF tickets should be a chain

[nicola]

We are still working on this.

The current ticket does not use the ticket from the previous epoch as input.

This means that the ticket chain is not "specific" to a chain anymore. This has implications on the validity of SealRandomness.

[nicola]

We should not do this since this would make the ticket for leader election grindable. We can only do this if we have a separate ticket chain (hence a second VRF).

This has implications and we should discuss this in the next dev meeting.

We currently have two VRFs one is the electionProof one is the ticket. The ticket must have as input drand and the previous ticket, the electionProof only drand.

Currently the electionProof is correct, but the ticket is not

[nikkolasg]

Currently computing a ticket takes the previous ticket only if there are no new drand entry in the block !

• this code computes the ticket with a boolean haveNewEntries. Only if it is false, it adds the previous ticket to the drawing randomness logic
• That flag is given here and is true when there are new drand entry to include in the new block.

Basically, with drand frequency = filecoin frequency, it seems like the previous ticket is never used ?

[nicola]

Working on a PR: #3510

[arajasek]

Fixed by #3510