@Irene, August 2023
<aside> ➡️ TLDR: *Today (Aug 2023) controlling the 33% of consensus power (ie, NetworkQAP) requires controlling a number of sectors whose cumulative pledge is at least 34.2 M-FIL. If FILPrice = 4$, this means controlling ~$137M.
In the future, especially if baseline becomes larger than NetworkQAP, this value becomes at least 10x smaller. See [2023Q3] Cost of Consensus Security: Hardware.*
</aside>
During the PoRep Protocol, when adding new sectors, an SP needs to lock down the InitialPledge (IP). IP has two parts: InitialPledge = StoragePledge + ConsensusPledge.
By the original design, StoragePledge (SP) aims to cover for possible future storage fault fees (see ‣ ), it depends only on ExpectedDailyBlockReward for the sector (SP ≈ 20*BR) and does not provide sufficient guarantees for consensus security. On the other hand, ConsensusPledge(CP) was introduced to make consensus takeovers expensive attacks.
Since the goal of this doc is to review consensus security, for the rest of it we focus on ConsensusPledge. Moreover, currently SP is only 5% of IP and CP represents the large majority of IP. In other words, we consider “CP per 1GiB of QAP power” as the “price” of consensus power in Filecoin.
We have the following formula for CP for a sector: CP = 30% * SectorNormalizedCirculatingSupply https://github.com/filecoin-project/specs-actors/blob/master/actors/builtin/miner/monies.go#L167
That is:
$$ CP = 0.3 \cdot \frac{FILCirculatingSupply}{\max(baseline, NetworkQAP)}\cdot SectorQAP $$
Note that CP per QAP unity value changes over time since the fraction FILCirculatingSupply / max (baseline, NetworkQAP) is not constant. So CP depends on the time when a sector is added.
From March 2021 to now, $\max( baseline, NetworkQAP ) = NetworkQAP$
Source: https://dashboard.starboard.ventures/capacity-services#network-storage-capacity
So in the rest of this doc we consider the formula without the baseline value. That is
$$ CP = 0.3 \cdot \frac{FILCirculatingSupply}{NetworkQAP}\cdot SectorQAP $$
⚠️ Warning: Ignoring baseline in the formula for CP is fine for studying the consensus security in the present or close future (eg, 6 months from now). See next section for this. However during next year (2024) baseline may become larger than NetworkQAP. Soon (ie, few months) after this happens, the analysis in this doc will no longer hold and we might have much lower consensus security. See the CE doc:
https://docs.google.com/document/d/1V3Hm1uKemnuVBmdW3KJYqeecA5-A_qf2eQana-9NuUA/edit#heading=h.qa12l2lw9n0