When there is only 1 signer, stacks-signer crashes due to underflow in WSTS

[hstove]

I caught an issue when running the Nakamoto devnet locally. I only have 1 signer, and in that case threshold is set to 0, because 70% of 1 is 0 in integer terms. Same with dkg_threshold. This gets passed into WSTS, which generates a random number between 0 and threshold - 1, which is where the underflow happens.

I'll make an issue in WSTS, but adding here for visibility

• code for setting threshold in stacks-signer
• wsts underflow

Question: we can update WSTS to not underflow, but should threshold be 0 when there is 1 signer? Any other consequences we should think about?

[xoloki]

The threshold is a function of the number of reward slots/key_ids, not the number of signers. It's curious that a single signer would only have 1 reward slot.

What is the code that is doing the 70% calculation? It likely should be rounding up not down.

wsts should probably panic if given a threshold of 0, since it doesn't make any sense to continue at that point.

[hstove]

The threshold is a function of the number of reward slots/key_ids, not the number of signers. It's curious that a single signer would only have 1 reward slot.

Yeah, I can't say whether this is "correct" or not, but I see 1 slot taken by my 1 signer. For example, here is the result of me fetching /v2/stacker_set/$cycle (see weight = 1):

{"stacker_set":{"rewarded_addresses":[{"Standard":[{"version":26,"bytes":"ee9369fb719c0ba43ddf4d94638a970b84775f47"},"SerializeP2PKH"]}],"start_cycle_state":{"missed_reward_slots":[]},"signers":[{"signing_key":"03cd2cfdbd2ad9332828a7a13ef62cb999e063421c708e863a7ffed71fb61c88c9","stacked_amt":50160000000000,"weight":1}]}}

What is the code that is doing the 70% calculation? It likely should be rounding up not down.

In the top post I linked to a spot in stacks-signer, but the code is

let threshold = num_keys * 7 / 10;
let dkg_threshold = num_keys * 9 / 10;

Also I know that in our Clarity code, the same "round down" math is done to determine when an aggregate key has been approved via enough votes.

[xoloki]

We should definitely fix both the stacks-signer and clarity code to round up in those calculations.

[hstove]

Closing because #4455 merged