What I mean by security:

  • you should be able to spend your Bitcoin whenever you want, and to whomever you want. (unconfiscatable and censorship resistant)
  • Bitcoin should not change. The finite supply – 21M – should not change. (sound money, non manipulable supply)

Does full nodes – nodes that receive, verify and broadcast txs – secure Bitcoin? Does Miners – who do proof of work and organise database of txs – secure Bitcoin? Does economics nodes – nodes weighted by its activity in Bitcoin network – secure Bitcoin?

Assuming that:
– bitcoin has been ossified. No soft forks. No hardforks.
– there is no imminent attack surface like weakening cryptography or emergence of powerful quantum computer.
– block subsidy has become negligible or zero.

Under this assumption, I think Bitcoin security depends on the transaction demand or in other words block space demand.

Higher the block space demand, higher the number of nodes with economic activity. For example, assume there is only two nodes. First is ‘bakt’ and second is ‘wechat’. First represent west side of earth and second represent east side. In this case this two node will keep an sql database for their user’s balance and will update on block-chain once a day or once a block. Thus, in this hypothetical scenario, there will be only be one tx per block. No demand for block space. bakt and wechat can collude and can change the Bitcoin. Here we can see that lesser the number of node, lesser the demand for block space.

Conversely, higher tx demand imply higher number of nodes demanding block space (given that they are trading with each other). If there are N nodes, then there are nearly ( N^2 ) / 2 connections between them.

If many users are represented by a single custodian node, those users can be subject to censorship and confiscation by that node.

Block space is limited, thus a limit on how many txs can take place on base layer everyday. Today it is around 3-5 lac. With future improvements it may go upto 10 lac and beyond.

Also layers on top of Bitcoin base layer – like lightning network(LN) – protects its user from confiscation and reduces tx fee. If LN node try to censor its user, user can move to other LN node. Thus LN protects from censorship and confiscation. LN can also increase block space demand.

Thus higher the number of economically active node, the better Bitcoin security. Past hyperbitcoinization, maybe there will be hundreds of thousands of Bitcoin citadels – each with their own values and beliefs – and each representing a node in Bitcoin, all connected with Bitcoin.

Visit the article by John Carvalho for more detained answer: https://medium.com/@BitcoinErrorLog/who-secures-bitcoin-95b19bbcda3c