Vitalik Buterin says Ethereum’s consensus is 'fragile' and should not be stretched

Vitalik Buterin warned in a blog post today that Ethereum’s consensus is fragile and should be used “sparingly” because of the high risk of forks in the chain.

Buterin wrote:

“There is a natural urge to try to extend the blockchain’s core with more and more functionality, because the blockchain’s core has the largest economic weight and the largest community watching it, but each such extention makes the core itself more fragile.”

Buterin added that we should be wary of projects that seek to increase the “scope” of blockchain consensus to anything other than verifying the core Ethereum protocol rules as this could lead to more “mandates” over time and an increased risk of forking the chain.

Ethereum (ETH) has over half a million validators securing the network that have collectively staked 18.5 million ETH, worth more than $34 billion. These validators finalize blocks every 6.4 minutes on the Ethereum network. The process is secured and sophisticated so that the chain recovers to the correct state even if a bug hits or a 51% attack occurs.

Stretching the consensus system for other purposes can introduce “high systemic risks to the ecosystem and should be discouraged and resisted,” Buterin wrote. He added:

“Dual-use of validator staked ETH, while it has some risks, is fundamentally fine, but attempting to “recruit” Ethereum social consensus for your application’s own purposes is not.”

Buterin further explained that so long as a protocol kept its losses contained to the validators and users in case of a complete collapse, it is “low-risk.” But, if the protocol is designed in a way that the original Ethereum chain has to fork or reorganize to solve its problems, then it is “high-risk, and I argue that we should strongly resist all attempts to create such expectations,” he wrote.

There could be a middle ground, Buterin suggested, if protocols in the low-risk category incentivize participants to slide into the higher-risk category. He also suggested using SchellingCoin-style techniques, a consensus mechanism where participants are asked to guess the average value of a certain parameter, like price, and those whose guesses are closest to the average are rewarded.

What are the risks of extending Ethereum’s consensus?

According to Buterin:

“As soon as a blockchain tries to “hook in” to the outside world, the outside world’s conflicts start to impact on the blockchain too.”

In other words, if Ethereum validators start voting on things like price oracles that include the currency of a country in the middle of a political crisis, it could lead to a split of the Ethereum chain.

Buterin added:

“…once a blockchain starts incorporating real-world price indices as a layer-1 protocol feature, it could easily succumb to interpreting more and more real-world information.”

Furthermore, introducing Layer 1 price indices could change blockchains from neutral technical platforms to explicitly financial tools. This, in turn, could attract legal trouble for blockchains, Buterin said.

Furthermore, it is not just price indices that pose a risk. Buterin wrote: