Subject: [bitcoindev] Removing checkpoints in Bitcoin Core v30

From: Sjors Provoost <[email-masked]>
Date: Mon, 28 Apr 2025 13:34:23 +0200

Dear list,

I thought this was already communicated, but I can't find a thread.

A recent pull request was merged into Bitcoin Core that removes existing checkpoints and all related support code.[0] The current plan is for this change to be part of v30 which should be released this fall.

Checkpoints are no longer needed in order to protect against low proof-of-work header spam attacks, thanks to the headers pre-sync functionality included since v24. [1]

The existing checkpoints no longer provide enough security against those attacks. Adding new checkpoints is not desirable.

However, if someone is aware of another attack, please disclose it (ideally responsibly) so the change can be reverted. [2]

Since older versions of Bitcoin Core, as well as other Bitcoin implementations, still enforce the checkpoints, an extremely large reorg (attack by aliens, NSA, etc) would split the network. This may already be the case due to the way some older soft forks have been grandfathered / buried in Bitcoin Core.[3]

I think many would consider Bitcoin a total loss in such a scenario and not worth salvaging - especially if the attacker didn't airdrop you any coins in the reorg. But it could be useful for someone to write a BIP that describes what happens in such a scenario. It could recommend ways to at least regain consistency, and perhaps permanently apply some soft fork rules from genesis (e.g. activate them if the last checkpoint header is absent).

Kind regards,

Sjors Provoost

[0] https://github.com/bitcoin/bitcoin/pull/31649
[1] https://bitcoin.stackexchange.com/a/121235/4948
[2] https://github.com/bitcoin/bitcoin/blob/master/SECURITY.md
[3] https://github.com/bitcoin/bips/blob/master/bip-0090.mediawiki

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