@Lloyd

>  Proof-of-SquareSpace

I agree with your points about delegated proof of stake. I wrote my own critique about that as well. And your point, that other forms of PoS devolve to DPoS by virtue of people wanting to actively mint blocks without exposing their coins in hot wallets, is an interesting one. 

> how are the users meant to redelegate their stake to honest pools?

This could be mitigated partially if delegation didn't require any kind of blockchain transaction. For example, users could simply send a signed message saying "this other key can mint blocks with my coins", and then minting a block using those coins would require presenting the delegation signature. This only partially mitigates the problem since the dishonest pool would still be able to use those coins as well, so it would be a race at that point. Still better than nothing. And pools could simply require full custody of the coins.

From what you mentioned, it sounds like maybe Algorand does something similar to this. 

> I don't see a way to get around the conflicting requirement that the keys for large amounts of coins should be kept offline but those are exactly the coins we need online to make the scheme secure.

There are a couple solutions you didn't mention. One is your "traditional" locked-stake kind of systems, where participants are required to lock their stake for long periods of time. Since normal users aren't likely to want to do this, it will likely be left to more sophisticated stakers likely staking very large amounts. 

Both mechanisms you mentioned allow delegation, and it might seem like maybe there'd be a way to disallow delegation, however since users can always give custody of their coins to trusted pools, that would be a delgation mechanism of last resort that can't be removed. So you can do things that make it hard (for both users and pool operators) to delegate trustlessly, but you can't get rid of the ability to delgate entirely.

In general, the situations where I see people not pooling are:

A. They are entirely prevented by technical means. It seems reasonably clear that this is impossible.
B. The downsides are more than unsophisticated users are willing to incur (eg stake locking).
C. The rewards are so small that it isn't worth it for people to put in much effort to gain them.
D. The rewards are so frequent that pooling is unnecessary.

B excludes a lot of people from being able to help secure the chain, but this is not materially different from PoW mining in that regard. D is a bit border line. With 1 billion people attempting to participate and 10 minute blocks, 232 people would need to share the block reward in order to expect a payout on average once per month. With 8 billion people that would turn into more like 1700 people. This seems potentially doable (eg via cosigner requirements on minted blocks), but it is a lot of participants per block. 

I think options C and D combined would be an ideal approach here. Because minting uses very few real resources, minting could be pretty much have arbitrarily low ongoing costs. This means fees can be low and blocks can have low payouts. If the reward was low and people could expect to see it once every couple years, people could simply treat it like a lottery. Great if they win it now, but nothing that anyone needs to rely on (which would incentivize the pools to reduce variance that we want to avoid). If there is no locked stake or other major barriers in place to minting blocks, that would also help avoid the compultion to use a pool.

In any case, you bring up good points, and they certainly complicate the issue. By the way, if you were confused as to what VPoS was in the section from my above link, this might satisfy your curiosity.

Cheers




On Sat, May 22, 2021 at 5:41 PM Lloyd Fournier <lloyd.fourn@gmail.com> wrote:
Hi Billy,

I was going to write a post which started by dismissing many of the weak arguments that are made against PoS made in this thread and elsewhere.
Although I don't agree with all your points you have done a decent job here so I'll focus on the second part: why I think Proof-of-Stake is inappropriate for a Bitcoin-like system.

Proof of stake is not fit for purpose for a global settlement layer in a pure digital asset (i.e. "digital gold") which is what Bitcoin is trying to be.
PoS necessarily gives responsibilities to the holders of coins that they do not want and cannot handle.
In Bitcoin, large unsophisticated coin holders can put their coins in cold storage without a second thought given to the health of the underlying ledger.
As much as hardcore Bitcoiners try to convince them to run their own node, most don't, and that's perfectly acceptable.
At no point do their personal decisions affect the underlying consensus -- it only affects their personal security assurance (not that of the system itself).
In PoS systems this clean separation of responsibilities does not exist.

I think that the more rigorously studied PoS protocols will work fine within the security claims made in their papers.
People who believe that these protocols are destined for catastrophic consensus failure are certainly in for a surprise.
But the devil is in the detail.
Let's look at what the implications of using the leading proof of stake protocols would have on Bitcoin:

### Proof of SquareSpace (Cardano, Polkdadot)

Cardano is a UTXO based PoS coin based on Ouroboros Praos[3] with an inbuilt on-chain delegation system[5].
In these protocols, coin holders who do not want to run their node with their hot keys in it delegate it to a "Stake Pool".
I call the resulting system Proof-of-SquareSpace since most will choose a pool by looking around for one with a nice website and offering the largest share of the block reward.
On the surface this might sound no different than someone with an mining rig shopping around for a good mining pool but there are crucial differences:

1. The person making the decision is forced into it just because they own the currency -- someone with a mining rig has purchased it with the intent to make profit by participating in consensus.

2. When you join a mining pool your systems are very much still online. You are just partaking in a pool to reduce your profit variance. You still see every block that you help create and *you never help create a block without seeing it first*.

3. If by SquareSpace sybil attack you gain a dishonest majority and start censoring transactions how are the users meant to redelegate their stake to honest pools?
I guess they can just send a transaction delegating to another pool...oh wait I guess that might be censored too! This seems really really bad.
In Bitcoin, miners can just join a different pool at a whim. There is nothing the attacker can do to stop them. A temporary dishonest majority heals relatively well.

There is another severe disadvantage to this on-chain delegation system: every UTXO must indicate which staking account this UTXO belongs to so the appropriate share of block rewards can be transferred there.
Being able to associate every UTXO to an account ruins one of the main privacy advantages of the UTXO model.
It also grows the size of the blockchain significantly.

### "Pure" proof of stake (Algorand)

Algorand's[4] approach is to only allow online stake to participate in the protocol.
Theoretically, This means that keys holding funds have to be online in order for them to author blocks when they are chosen.
Of course in reality no one wants to keep their coin holding keys online so in Alogorand you can authorize a set of "participation keys"[1] that will be used to create blocks on your coin holding key's behalf.
Hopefully you've spotted the problem.
You can send your participation keys to any malicious party with a nice website (see random example [2]) offering you a good return.
Damn it's still Proof-of-SquareSpace!
The minor advantage is that at least the participation keys expire after a certain amount of time so eventually the SquareSpace attacker will lose their hold on consensus.
Importantly there is also less junk on the blockchain because the participation keys are delegated off-chain and so are not making as much of a mess.

### Conclusion

I don't see a way to get around the conflicting requirement that the keys for large amounts of coins should be kept offline but those are exactly the coins we need online to make the scheme secure.
If we allow delegation then we open up a new social attack surface and it degenerates to Proof-of-SquareSpace.

For a "digital gold" like system like Bitcoin we optimize for simplicity and desperately want to avoid extraneous responsibilities for the holder of the coin.
After all, gold is an inert element on the periodic table that doesn't confer responsibilities on the holder to maintain the quality of all the other bars of gold out there.
Bitcoin feels like this too and in many ways is more inert and beautifully boring than gold.
For Bitcoin to succeed I think we need to keep it that way and Proof-of-Stake makes everything a bit too exciting.

I suppose in the end the market will decide what is real digital gold and whether these bad technical trade offs are worth being able to say it uses less electricity. It goes without saying that making bad technical decisions to appease the current political climate is an anathema to Bitcoin.

Would be interested to know if you or others think differently on these points.

[1]: https://developer.algorand.org/docs/run-a-node/participate/generate_keys/
[2]: https://staking.staked.us/algorand-staking
[3]: https://eprint.iacr.org/2017/573.pdf
[4]: https://algorandcom.cdn.prismic.io/algorandcom%2Fece77f38-75b3-44de-bc7f-805f0e53a8d9_theoretical.pdf
[5]: https://hydra.iohk.io/build/790053/download/1/delegation_design_spec.pdf

Cheers,

LL

On Fri, 21 May 2021 at 19:21, Billy Tetrud via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
I think there is a lot of misinformation and bias against Proof of Stake. Yes there have been lots of shady coins that use insecure PoS mechanisms. Yes there have been massive issues with distribution of PoS coins (of course there have also been massive issues with PoW coins as well). However, I want to remind everyone that there is a difference between "proved to be impossible" and "have not achieved recognized success yet". Most of the arguments levied against PoS are out of date or rely on unproven assumptions or extrapolation from the analysis of a particular PoS system. I certainly don't think we should experiment with bitcoin by switching to PoS, but from my research, it seems very likely that there is a proof of stake consensus protocol we could build that has substantially higher security (cost / capital required to execute an attack) while at the same time costing far less resources (which do translate to fees on the network) *without* compromising any of the critical security properties bitcoin relies on. I think the critical piece of this is the disagreements around hardcoded checkpoints, which is a critical piece solving attacks that could be levied on a PoS chain, and how that does (or doesn't) affect the security model. 

@Eric Your proof of stake fallacy seems to be saying that PoS is worse when a 51% attack happens. While I agree, I think that line of thinking omits important facts:
* The capital required to 51% attack a PoS chain can be made substantially greater than on a PoS chain. 
* The capital the attacker stands to lose can be substantially greater as well if the attack is successful.
* The effectiveness of paying miners to raise the honest fraction of miners above 50% may be quite bad.
* Allowing a 51% attack is already unacceptable. It should be considered whether what happens in the case of a 51% may not be significantly different. The currency would likely be critically damaged in a 51% attack regardless of consensus mechanism.

> Proof-of-stake tends towards oligopolistic control

People repeat this often, but the facts support this. There is no centralization pressure in any proof of stake mechanism that I'm aware of. IE if you have 10 times as much coin that you use to mint blocks, you should expect to earn 10x as much minting revenue - not more than 10x. By contrast, proof of work does in fact have clear centralization pressure - this is not disputed. Our goal in relation to that is to ensure that the centralization pressure remains insignifiant. Proof of work also clearly has a lot more barriers to entry than any proof of stake system does. Both of these mean the tendency towards oligopolistic control is worse for PoW.

> Energy usage, in-and-of-itself, is nothing to be ashamed of!!

I certainly agree. Bitcoin's energy usage at the moment is I think quite warranted. However, the question is: can we do substantially better. I think if we can, we probably should... eventually.

> Proof of Stake is only resilient to ⅓ of the network demonstrating a Byzantine Fault, whilst Proof of Work is resilient up to the ½ threshold

I see no mention of this in the pos.pdf you linked to. I'm not aware of any proof that all PoS systems have a failure threshold of 1/3. I know that staking systems like Casper do in fact have that 1/3 requirement. However there are PoS designs that should exceed that up to nearly 50% as far as I'm aware. Proof of work is not in fact resilient up to the 1/2 threshold in the way you would think. IE, if 100% of miners are currently honest and have a collective 100 exahashes/s hashpower, an attacker does not need to obtain 100 exahashes/s, but actually only needs to accumulate 50 exahashes/s. This is because as the attacker accumulates hashpower, it drives honest miners out of the market as the difficulty increases to beyond what is economically sustainable. Also, its been shown that the best proof of work can do is require an attacker to obtain 33% of the hashpower because of the selfish mining attack discussed in depth in this paper: https://arxiv.org/abs/1311.0243. Together, both of these things reduce PoW's security by a factor of about 83% (1 - 50%*33%).

 > Proof of Stake requires other trade-offs which are incompatible with Bitcoin's objective (to be a trustless digital cash) — specifically the famous "security vs. liveness" guarantee

Do you have a good source that talks about why you think proof of stake cannot be used for a trustless digital cash? 

> You cannot gain tokens without someone choosing to give up those coins - a form of permission.

This is not a practical constraint. Just like in mining, some nodes may reject you, but there will likely be more that will accept you, some sellers may reject you, but most would accept your money as payment for bitcoins. I don't think requiring the "permission" of one of millions of people in the market can be reasonably considered a "permissioned currency".  

> 2. Proof of stake must have a trusted means of timestamping to regulate overproduction of blocks

Both PoW and PoS could mine/mint blocks twice as fast if everyone agreed to double their clock speeds. Both systems rely on an honest majority sticking to standard time.  


On Wed, May 19, 2021 at 5:32 AM Michael Dubrovsky via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
Ah sorry, I didn't realize this was, in fact, a different thread! :)

On Wed, May 19, 2021 at 10:07 AM Michael Dubrovsky <mike@powx.org> wrote:
Folks, I suggest we keep the discussion to PoW, oPoW, and the BIP itself. PoS, VDFs, and so on are interesting but I guess there are other threads going on these topics already where they would be relevant. 

Also, it's important to distinguish between oPoW and these other "alternatives" to Hashcash. oPoW is a true Proof of Work that doesn't alter the core game theory or security assumptions of Hashcash and actually contains SHA (can be SHA3, SHA256, etc hash is interchangeable).

Cheers,
Mike 

On Tue, May 18, 2021 at 4:55 PM Erik Aronesty via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
1. i never suggested vdf's to replace pow.

2. my suggestion was specifically *in the context of* a working
proof-of-burn protocol

- vdfs used only for timing (not block height)
- blind-burned coins of a specific age used to replace proof of work
- the required "work" per block would simply be a competition to
acquire rewards, and so miners would have to burn coins, well in
advance, and hope that their burned coins got rewarded in some far
future
- the point of burned coins is to mimic, in every meaningful way, the
value gained from proof of work... without some of the security
drawbacks
- the miner risks losing all of his burned coins (like all miners risk
losing their work in each block)
- new burns can't be used
- old burns age out (like ASICs do)
- other requirements on burns might be needed to properly mirror the
properties of PoW and the incentives Bitcoin uses to mine honestly.

3. i do believe it is *possible* that a "burned coin + vdf system"
might be more secure in the long run, and that if the entire space
agreed that such an endeavor was worthwhile, a test net could be spun
up, and a hard-fork could be initiated.

4. i would never suggest such a thing unless i believed it was
possible that consensus was possible.  so no, this is not an "alt
coin"

On Tue, May 18, 2021 at 10:02 AM Zac Greenwood <zachgrw@gmail.com> wrote:
>
> Hi ZmnSCPxj,
>
> Please note that I am not suggesting VDFs as a means to save energy, but solely as a means to make the time between blocks more constant.
>
> Zac
>
>
> On Tue, 18 May 2021 at 12:42, ZmnSCPxj <ZmnSCPxj@protonmail.com> wrote:
>>
>> Good morning Zac,
>>
>> > VDFs might enable more constant block times, for instance by having a two-step PoW:
>> >
>> > 1. Use a VDF that takes say 9 minutes to resolve (VDF being subject to difficulty adjustments similar to the as-is). As per the property of VDFs, miners are able show proof of work.
>> >
>> > 2. Use current PoW mechanism with lower difficulty so finding a block takes 1 minute on average, again subject to as-is difficulty adjustments.
>> >
>> > As a result, variation in block times will be greatly reduced.
>>
>> As I understand it, another weakness of VDFs is that they are not inherently progress-free (their sequential nature prevents that; they are inherently progress-requiring).
>>
>> Thus, a miner which focuses on improving the amount of energy that it can pump into the VDF circuitry (by overclocking and freezing the circuitry), could potentially get into a winner-takes-all situation, possibly leading to even *worse* competition and even *more* energy consumption.
>> After all, if you can start mining 0.1s faster than the competition, that is a 0.1s advantage where *only you* can mine *in the entire world*.
>>
>> Regards,
>> ZmnSCPxj
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--
Michael Dubrovsky
Founder; PoWx


--
Michael Dubrovsky
Founder; PoWx
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