On day one of the 2017 MIT Bitcoin Expo, Sia Co-Founder David Vorick, who has contributed to Bitcoin Core, gave a presentation on the important role played by full nodes in digital currency networks. In his view, economically relevant full nodes are the ones that have “voting” power (for lack of a better term) in attempted hard-forking changes to the rules of Bitcoin.



What Is the Role of the Full Node?

Early in his talk, Vorick focused on the general role played by full nodes on the network. “Full nodes validate transactions on the Bitcoin network,” he stated. “Bitcoin has this longest-chain rule where the chain with the most work in it is the one that everybody follows, except this chain also has to follow all of the rules that the network has. The full nodes are the ones [that] check that the chain follows the rules, and if a chain doesn’t follow the rules, it doesn’t matter how much hashrate is behind it, that chain is ignored.”

According to Vorick, of all the different types of Bitcoin users, full nodes are the only ones that check that the rules are followed. Those who run an SPV node or use some sort of web wallet are putting their trust in others to verify that certain rules are being followed correctly on the most-work chain.

“They’re faster,” Vorick said in terms of SPV nodes. “They download all the headers. They make sure that they are on the chain with the most work, but they don’t actually check that the chain with the most work is legal or is valid.”

Vorick went on to state that SPV nodes are essentially betting that the rest of the network will sufficiently handle the validation process for them.

“SPV nodes just blindly have faith in the broader network to do this process that makes sure that the longest chain is always valid,” Vorick continued. “They don’t actually know. They’re just assuming that the broader network is going to keep them safe.”

Without full nodes, Vorick says, miners are given the ability to do whatever they want. “If people can spend each other’s money [or] if miners can [produce] money out of nowhere, you have a useless system,” he added.

Upgrades in Bitcoin

Vorick also talked about how upgrades are made to the Bitcoin network. When talking about upgrades, he was referring to hard forks specifically. He also referred to soft forks as patches.

“Soft forks don’t actually change the rules; they just are more creative about how they use the rules,” Vorick explained.

In terms of attempted hard forks, Vorick claimed there are three potential outcomes. In one, the hard fork could fail and everyone may decide to ignore the failed chain. Vorick pointed to the recent block larger than 1 million bytes accidentally mined by Bitcoin.com as an example of a failed upgrade.

Another possible outcome from an attempted hard fork is that economic activity continues to take place on both chains. Vorick referred to this as a “partially successful upgrade,” and he used the split between Ethereum and Ethereum Classic as an example of this outcome.

The third possible outcome mentioned by Vorick is a successful hard fork with new rules where the new chain becomes the only chain people use and everyone ignores the old chain. Besides the hard fork that resulted in the split between Ethereum and Ethereum Classic, the Ethereum chain has also had multiple successful hard forks.

Economically Relevant Full Nodes Have the Power

When determining the level of success achieved by an attempted upgrade, Vorick claimed that it ultimately comes down to the desires of the full nodes. “If you’re not running a full node, sort of your opinion on whether or not you like a hard fork is less relevant because, ultimately, if you’re not validating the rules and someone gives you a transaction following a different rule set, you don’t have a way to detect that,” he explained. “So you can’t actually weigh in on an attempted hard fork, an attempted upgrade.”

Vorick then compared full nodes to representatives in a democracy; however, he also pointed out that some full nodes are much more economically relevant than others. BitPay, for example, has a bigger say in what happens than a full node sending and receiving one small payment per month.

According to Vorick, users can be dragged along with miners and large businesses if the cost of running a full node is too high. “If full nodes are expensive to run, only people who are capable of running nodes really have any say in what happens in a contentious upgrade,” he added.

As an example, Vorick pointed out that Ethereum Classic may not have ever existed if it cost too much for the original Ethereum chain’s early supporters to run full nodes.

“I would advocate that, right now, full [Bitcoin] nodes are too expensive,” Vorick concluded.