Miscellaneous Bitcoin Disputes FAQ

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Are current "SPV" nodes not actually the kind of SPV nodes that Satoshi talked about in the whitepaper?

It's often claimed that when Satoshi said that he was OK with regular users using SPV wallets, he was actually referring to a type of SPV that doesn't exist today, which included "fraud proofs", or an ability for full nodes to prove to an SPV client that a transaction was fraudulent. Those making this claim cite the SPV section of the whitepaper as evidence.

Toward the end of the two paragraphs in the SPV section, Satoshi writes:

While network nodes can verify transactions for themselves, the simplified method can be fooled by an attacker's fabricated transactions for as long as the attacker can continue to overpower the network. One strategy to protect against this would be to accept alerts from network nodes when they detect an invalid block, prompting the user's software to download the full block and alerted transactions to confirm the inconsistency

Those saying that current SPV nodes are not the kind Satoshi described in the whitepaper are making two claims:

  • When Satoshi says "One strategy to protect against this..." he is describing a necessary feature of an SPV implementation, without which it can't be considered SPV. He is not just offering an optional idea.
  • When Satoshi talks about alerts, he is specifically talking about cryptographic proofs of fraud, not any other kind of alert.

Both of these claims seem implausible. The second claim is not only implausible because Satoshi never mentions cryptographic proofs, but also because it is unknown whether such a proof of technically possible.