Nick Szabo  🔑

Running a full node really only allows you to know if the chain is being 51% attacked. It doesn't actually make you any less vulnerable to such attacks (FNs are still vulnerable to double spend attacks/re-orgs). The security of both spv and full nodes relies on >50% being honest.

Knowing makes you less vulnerable if you have the capability to respond, e.g. by finding other correct nodes and maintaining your own un-attacked fork.

But there is nothing invalid about a chain that has been re-orged, miners will be economically incentivised to mine on the longest (re-orged) chain.

Right, knowing about a 51% attack doesn’t change anything. Miners are not required by consensus rules to build on the blocks of other miners.

I am not sure what you are trying to say here but miners are incentivised to mine on the longest (valid chain) to decrease the likelyhood of their blocks being orphaned

Assuming that incentives will make people do the right thing is still an assumption. Without full nodes to hold minors accountable that incentive goes away.

Agreed. I am talking about what security diffs a full node vs an SPV node has for an individual actor, not under the assumption that everyone runs SPV. The valid chain is the chain with the most difficulty that still complies with protocol rules.

And an SPV wallet cannot know the rules have been satisfied and therefore cannot know if it is following the chain at all.

How would one know how diverse are the nodes one is trusting? Are all of them accepting the new FedCoin inflation rule? Are they really just one big.... PayPal?

Much of this is common knowledge, knowable by credible opinion, but if one doubts the credible opinion one should indeed run their own full node. Casual users rely on such opinions much like they rely on brand names when they purchase other consumer products.

The fact that the Fed prints dollars is common knowledge. The relevant question is how to prevent it. It cannot be prevented if wallets trust some anonymous party to validate for them, and cannot be prevented if some non-anonymous party does so.

They don't have to trust"some anonymous party", they only have to trust the results of an extremely reliable network, 100s of jurisdictionally diverse nodes any one of which can yell on the internet if they catch any of the rest of them accepting invalid txs.

Especially for people just starting out with Bitcoin. You can have a good mobile wallet like @SamouraiWallet running on your phone in no time to get your feet wet with pocket change and test drive the technology. If that gets you interested you can set up your full node later.

These are true statements, but it remains true that this choice removes one from the consensus group.

I don't think so. It just removed my ability to *define* the consensus group. The node I trust to relay the blockchain status to me is still part of the consensus group.

You should be trusting much more than one node to do that relay.

How would you know how many nodes you are trusting?

How?

bitcoin-cli getpeerinfo