Does It Matter Who Has the Longest Chain in Bitcoin? Not Really

Bitcoin exists on the blockchain. As bitcoin transactions occur, they’re batched into blocks, and the blocks get added to the chain. The chain gets progressively longer over time – but does the length of the chain really matter?

Jonald_Fyookball attempted to answer that question earlier today in a post on Yours.org. In that post, Fyookball described the situation leading up to the Bitcoin Cash network upgrade in November 2018.

There are two sides to the BCH network upgrade. The two sides both support BCH but differ in how the network should be upgraded. Without going into deep detail, the community is split – roughly 50/50 or 60/40 – over whether to increase blocksize to 128MB and re-implement OP_codes into bitcoin.

Some propose that hashpower should solve the issue. Bitcoin is designed so that miners can vote on their preferred upgrade using hashpower. The fork with the most hashpower support will win.

Jonald_Fyookball refutes that notion because it “shows a misunderstanding of the bitcoin system.”

“This attitude [of hashpower voting] stems from beliefs that:

a.) Bitcoin is defined by facts rather than opinions

b.) The longest chain necessarily defines Bitcoin

c.) The white paper states that the longest chain determines outcome of a consensus split

These are all false, as I will explain.”

Bitcoin Facts Versus Bitcoin Opinions

First, Jonald_Fyookball starts by mentioning that individuals are going to disagree about bitcoin. Inevitably, people have differing opinions about BCH and BTC. Some believe BCH is the true version of bitcoin, while others believe BCH is hijacking bitcoin’s identity.

Bitcoin was designed to facilitate splits. If there’s a split in the bitcoin ecosystem, then it indicates that people on either side have their own reasons for believing that their side is more legitimate than the other.

Jonald_Fyookball references Jameson Lopp, who said:

There Are Three Kinds of Chain Splits

Next, Jonald_Fyookball explains that there are three types of chain splits, including:

One Set of Network Consensus Rules

In the first type of chain split, there is only one set of network consensus rules. In this context, a chain split occurs when two miners find a block at roughly the same time. Each winning miner broadcasts the block to half the network. The fragmented part of the network continues to mine until finding a block. Eventually, one group outpaces the others, causing the shorter chain to be orphaned and the network to be reunited. The bitcoin whitepaper describes this system.

Two Sets of Competing Network Rules

In the second type of chain split, there are two sets of competing network rules. In this type of chain split, blocks on one network are invalid on the other. There’s a permanent, irreversible divergence of the bitcoin ledger. This can be called a consensus chain split. There are differing opinions about network rules. This is what happened when bitcoin split into BTC and BCH (or when BCH forked away from BTC, depending on how you view the issue).

Two Sets of Competing Network Rules with Capitulation and Chain Abandonment

Jonald_Fyookball mentions a third type of chain split – one that we haven’t seen occur in the bitcoin community. In this chain split, we have a consensus chain split, but the minority chain eventually capitulates and abandons the chain. We haven’t seen this in the bitcoin community.

What Does the Bitcoin Whitepaper Say About the “Longest Chain”?

The bitcoin whitepaper mentions chain splits, but people seem to forget what the whitepaper says about chain splits. As mentioned by Jonald_Fyookball:

“First, what does the whitepaper NOT say? It never says anything like: “if there is a disagreement in Bitcoin, then miners compete with Hashpower, and whoever builds the longest chain is entitled to call themselves the true Bitcoin.” (This is what certain redditors seem to believe).”

The whitepaper, despite what Reddit seems to believe, doesn’t mention anything along these lines. The “abstract” section of the whitepaper simply says this about the longest chain:

“The longest chain not only serves as proof of the sequence of events witnessed, but proof that it came from the largest pool of CPU power. As long as a majority of CPU power is controlled by nodes that are not cooperating to attack the network, they'll generate the longest chain and outpace attackers.”

The whitepaper, in this section, seems to be referring to the first type of chain split, where there’s a single set of consensus rules and one chain gets orphaned.

There’s another reference to the longest chain in the “proof of work” section of the whitepaper:

“The majority decision is represented by the longest chain, which has the greatest proof-of-work effort invested in it. If a majority of CPU power is controlled by honest nodes, the honest chain will grow the fastest and outpace any competing chains. To modify a past block, an attacker would have to redo the proof-of-work of the block and all blocks after it and then catch up with and surpass the work of the honest nodes.”

Again, this is a reference to transaction ordering and the security provided by a proof of work system. Some, however, assume this is a reference to a consensus chain split. However, even in this paragraph, the whitepaper claims the majority decision is represented by the longest chain.

“This does not necessarily imply any divine right to the Bitcoin name, the ticker symbol, the community, or anything else.”

There’s one final relevant section of the bitcoin whitepaper that deals with hashpower and long chains:

“They vote with their CPU power, expressing their acceptance of valid blocks by working on extending them and rejecting invalid blocks by refusing to work on them.”

As pointed out by Jonald_Fyookball, the whitepaper doesn’t say that the majority has dominion over what is valid. This is an important distinction missed by many in the bitcoin community.

These Arguments Are “Like Different Churches” Interpreting the Bible

Cornell Professor and blockchain expert Emin Gün Sirer tweeted a link to the post earlier today saying:

Sirer then got philosophical, referencing Nietzsche by sayin:

“Satoshi is dead. He is very likely physically dead, but even if not, he is metaphorically dead. We must decide what’s right on our own, from first principles. It is not written on any tablet or white paper.”

Sirer then added that miners cannot make unilateral changes to bitcoin, and the notion that miners are in complete control of the bitcoin network is mistaken:

“Miners cannot make unilateral changes — if they could, CoinGeek would give 1M coins to CSW. Funnier still is the fact that these arguments are coming out of the BCH camp — BCH's hash power is a fraction of BTC's. So the argument that hashpower decides social splits is laughable.”

Ultimately, debate continues to rage within the BCH community over what to do in the leadup to the November network upgrade.

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