> fork the chain at a snapshot before the attack, patch the protocol, and call that Bitcoin?

It won't work. The only way to authenticate who ones what coins is with signatures. If the signature algorithm is broken, you can't tell who the original owner is to move the coins to a safe signature algorithm.

You need to more to safer signature algorithm before the break, after the break it is game over.

> It’s worth remembering that Ethereum forked for much less

Ethereum could simply return the coins to the original owners. If the signature scheme is insecure, returning the coins just means the attacker can steal them again.

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realharo an hour ago | parent | next [-]

In practice, what you really need is consensus. As long as enough of the important participants agree, that's how it will be.

And since there are millions of identical copies of the entire pre-attack ledger out there, this should not be that difficult.

Potential future buyers might reevaluate whether this whole thing has any monetary value, but that's a separate concern. Bitcoin's market value was never about the technical details.

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rcbdev an hour ago | parent [-]

I'm not sure you fully grasped what was said in the parent comment. It literally does not matter anymore if we can all agree on the previous blocks, it would be impossible to identify who owns which wallet anymore. The seed phrase would be useless.

	▲	realharo an hour ago \| parent [-]
		Ah, then yeah, in that case, it'd be basically over. Maybe large exchanges would try to step in to make a fresh chain based on their combined account data, and just drop the people relying on self-custody. But I doubt the market would go for it - the uncertainty would crash it hard enough that it would never recover.

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glerk 9 hours ago | parent | prev [-]

> The only way to authenticate who owns what coins is with signatures

Maybe the only fully cryptographic absolutely zero-trust way? In practice there are very few bitcoin outputs that aren't linked to an offline identity and most users could easily produce a proof of ownership.

Of course, this is not ideal and everyone would prefer not to go down that route. But even if we prepare in time and Bitcoin provides a quantum-secure address scheme before "Q-day", what happens to all the wallets that didn't upgrade? Is it open season on them? Satoshi's wallet alone could crash Bitcoin's value as a currency if dumped on the open market. I think even with the upgrade plan in place, a hard-fork + recovery will be on the menu, with various degrees of community support.

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EthanHeilman 7 hours ago | parent [-]

> In practice there are very few bitcoin outputs that aren't linked to an offline identity and most users could easily produce a proof of ownership.

Any who is going to in charge of reading that proof of identity and moving the coins? A trusted centralized party? The point of Bitcoin is to avoid exactly that sort of trust relationship, otherwise use the banking system.

> Satoshi's wallet alone could crash Bitcoin's value as a currency if dumped on the open market.

No one knows, but the incentives are aligned with a softfork to burn Satoshi's coins.

	▲	realharo an hour ago \| parent \| next [-]
		>The point of Bitcoin is to avoid exactly that sort of trust relationship, otherwise use the banking system. Most participants don't care about this. For almost everyone, the point of Bitcoin is to go up. As long as they can find enough buyers that also believe it will go up, the rest is optional. Especially if it's temporary, for a one-time migration.
	▲	glerk 5 hours ago \| parent \| prev [-]
		> Any who is going to in charge of reading that proof of identity and moving the coins? A trusted centralized party? Basically you'd have to relax the trust/decentralization guarantees, but you don't have to relax them all the way. Most likely a consortium of trusted actors (Blockstream, major miners, major exchanges, bitcoin-adjacent companies,...). Or something like a consensus mechanism with aligned incentives a la Kleros. I think "we" could come up with "something", even if it is not perfect, because the value of Bitcoin is ultimately in the community of people who use Bitcoin, not just the protocol. "Hard-fork" might not be the right way to see this. It's more like starting a completely new protocol where people who held Bitcoin at a certain snapshot can redeem a one-time airdrop equivalent to the value they held, provided they can prove ownership. As that protocol's value overtakes the value of the original Bitcoin chain (which will eventually be completely dead), we can all agree to call it Bitcoin.