[Feature]: Use the bitcoin block height as the DKG ID

[djordon]

Feature - Use the bitcoin block height as the DKG ID

1. Description

The DKG ID (the distributed key generation "identifier") is a number used in WSTS to prevent replay attacks during each DKG round. The signers already used signed messages that include the bitcoin chain tip as part of the signed message, but we should take the additional step of using the bitcoin block height as the DKG ID to make replay attacks even harder.

1.1 Context & Purpose

We currently do not support running DKG more than once, but when we do, the most straightforward thing to do is fix the DKG ID to zero for each DKG round. Doing so is probably not problematic, since we use signed messages and we include the bitcoin block hash as part of the message that is signed. The issue is that we do not always reject messages where the block hash is not the canonical one. will help by making it more difficult to do any replay type attacks. We already require that DkgBegin messages originate from the current coordinator, we just need to make sure that the chain tip is canonical and grab the block height of the current chain tip.

2. Technical Details:

We should return the chain tip height as part of the MsgChainTipReport and use that height when creating a new SignerStateMachine whenever the signers receive a DkgBegin message from the coordinator.

2.1 Acceptance Criteria:

• Ensure that the DKG ID is set to the current bitcoin block height.
• Use the block hash of the bitcoin chain tip for storing the signer state machine in memory.
• Remove signer state machines at the end of DKG.

3. Related Issues and Pull Requests (optional):

• Relates to [Feature]: Reject many WSTS messages with incorrect bitcoin chain tips #1176. When both of these are done, the end effect is that signing rounds are tightly coupled with the coordinator's tenure of a bitcoin block for both DKG and signing rounds.
• Relates to [Feature]: Load the correct signer state machine when signing inputs #1152 for signing rounds.