Thread by @el33th4xor

I cannot believe that Crypto Twitter is still hopelessly confused about "weak subjectivity."

Every now and then, a community convinces itself of a wrong thing, or worse, it adopts a mental framework that is hopelessly confused and leads to brain fog. This is one of those instances.

Remember how CT thought, for the longest time, that PoW and PoS were two consensus protocols, and that they were the two kinds of consensus protocols that existed?

threadreaderapp.com/thread/1006931…

It took a lot of effort to eradicate that idea (though there are vestiges of it remaining in Wikipedia even today). Everyone now knows that consensus protocols are Classical (e.g. PBFT, HotStuff), Nakamoto (e.g. Bitcoin), and Avalanche. PoW and PoS are Sybil control mechanisms.

Remember when "nothing-at-stake" was touted as an insurmountable problem that would make PoS inherently insecure and unachievable? Remember serious-sounding-people talk about "stake grinding" attacks?

This April Fools piece hilariously was the last nail in the coffin of that stupidity.

blog.ethereum.org/2017/04/01/eth…

"Weak subjectivity" is a similarly hollow concern, around which serious-sounding-people with brain fog will write long pieces, but at the heart of it all, there's nothing there.

The core question to ask of any protocol is: what assumptions does it make?

Any given system will make multiple assumptions (e.g. "x should always be greater than 10"). Any given subcomponent of a large system will have its own assumptions.

While discussions can focus on subcomponents, such as the decision protocol versus the bootstrap protocol, at the end of the day, the only thing that matters are the strongest set of assumptions a system makes.

For example, if phase 1 assumes that x should be in the range [0..99], and phase 2 assumes that x should be in the range [0..49], then this system works only when x is in the range [0..49]. The weaker assumption in phase 1 is immaterial.

Systems with weaker assumptions (your heart rate is >0) are better than systems with stronger assumptions (your heart rate is >190), because stronger assumptions are less likely to be correct.

Cryptotwitter never figured out how to properly characterize assumptions related to bootstrapping PoS chains, or to put them in context next to assumptions related to decision protocols.

I have treated the phrase "weak subjectivity" by itself is a marker for a confused mental framework, and have tried not to engage with it. It is not a phrase that you see in any academic literature. It's just Twitter.

Weak subjectivity refers to a set of assumptions regarding bootstrapping a PoS system, and these assumptions are different from that for, say, PoW-based coins.

PoW-based coins typically require a majority of their nodes to be honest. They need 51% to be honest to thwart reorgs and double-spends, and they need 67% honest to thwart selfish mining attacks. But to bootstrap, they need just 1 correct node.

PoS-based coins are a mess, because they have typically been designed by people suffering from this brain fog. I cannot even begin to characterize many of them, and the folks who write those crap papers don't know how to enunciate their assumptions. But...

I can talk about Avalanche. Avalanche has a parameterizable decision protocol that can withstand huge attackers, even 80%, with safety, but not liveness. It requires 51% honest nodes for liveness and safety together. And its bootstrap requires 51%.

The strongest assumption made by Avalanche is thus
51% honest. This is equal to or weaker than the strongest assumption made by PoW coins, which assume 67% honesty. Remember, weaker is good in this game.

So, if someone is still going on and on about "weak subjectivity," and how it's a problem for any coin, then all they are doing is marking themselves as someone who is clueless, regurgitating drek from social media instead of anything scientific.