Contingency plans for a 51% attack

[bobitza]

Are there any contingency plans in case of a 51% attack?

I mean what do we do? Find out who's owning the IPs and hire al-Qaeda to suicide bomb them? lol

Now seriously, what do we do? Do we stop all transactions until the attack is over? Just lay down and let the Bitcoin idea die?

[Hawkix]

There is only risk for receivers of BTC during 51% attack. So, I would not accept BTC (and probably not send them, either). The question is, if we will know there is attack.

[schnell]

For it to be an 'attack' the blocks have to be blank, and not contain any tx. Therefore with every block the number of confirms goes down one on each transaction ever.

[Stephen Gornick]

Now seriously, what do we do? Do we stop all transactions until the attack is over? Just lay down and let the Bitcoin idea die?

There's not always going to be a way to know.  The total Thash/s might rise a bit or a lot, or not at all if the attacker had already have been mining with 51% just spread to various pools.

There would probably be an alert sent out:
 - http://en.bitcoin.it/wiki/Alerts

But there are no specific further actions, as the correct response with depend on what actually occurred:
 - http://en.bitcoin.it/wiki/Contingency_plans#Many_historical_blocks_replaced

[gmaxwell]

For it to be an 'attack' the blocks have to be blank, and not contain any tx. Therefore every block the number of confirms goes down one.

This is confused.

[bobitza]

@Stephen
Been in that wiki but didn't notice there is actually a Contingency plan section. I would like to quote a few lines for folks reading this thread

• Here is a message that could be used to spread the word: "A critical bug has been discovered in Bitcoin. Transactions must be considered REVERSIBLE for the time being. Do not send payments, and do not trust payments that you receive."
• If you run a Bitcoin-related site, shut down the site and replace it with this message.
  
• [Note: The following paragraph only applies to certain attacks and may need to be removed.]
  If you are solo mining or running a pool, you must stop mining until you upgrade to the latest version (which may not be released quite yet). If you are mining in a pool, shut down your miner until your pool upgrades. If you continue mining, any blocks you solve will end up being rejected eventually, and you will be working against the legitimate chain.
• Look to your favorite HTTPS-enabled Bitcoin sites for more news. Before running any software, check that a consensus exists among several sites. Do not trust information from Google, as it can be manipulated by the attacker. Other sites, such as bitcoin.org, can likewise be manipulated, though with more difficulty. The most trustworthy source of information is the text that appears at the bottom of the graphical Bitcoin client.

[schnell]

For it to be an 'attack' the blocks have to be blank, and not contain any tx. Therefore every block the number of confirms goes down one.

This is confused.

Fixed it a bit.

[gmaxwell]

For it to be an 'attack' the blocks have to be blank, and not contain any tx. Therefore every block the number of confirms goes down one.

This is confused.

Fixed it a bit.

It's just more clearly confused now.  The confirmation count is the number of blocks following when the transaction was initially confirmed. Every block implicitly confirms all prior in its chain because you couldn't have creates that block without processing all prior ones. Leaving transactions out has nothing to do with it... the effect of leaving transactions out is only that new transactions won't start getting confirmations.

[Come-from-Beyond]

If anyone attempts the attack we won't notice anything until it finishes. Then we'll just see that a lot of transactions disappeared. No pump in the hashrate, no confirmation numbers changed.

[bobitza]

Isn't the pools hashrate pie chart going to tell us if that happens?

[Come-from-Beyond]

Isn't the pools hashrate pie chart going to tell us if that happens?

No. It won't be shown even in Unknown part.

[Syke]

Are there any contingency plans in case of a 51% attack?

A "51% attack" could mean any number of different things. Each of those could require a different response. So what sort of attack are you concerned with?

[Come-from-Beyond]

Are there any contingency plans in case of a 51% attack?

A "51% attack" could mean any number of different things. Each of those could require a different response. So what sort of attack are you concerned with?

We should focus on the worst case scenario, when an attacker managed to create a fork with more than 120 blocks ahead.