Taking Down The Bitcoin Network

Re:Taking Down The Bitcoin Network by gst on Tuesday June 14, 2011 @10:38AM (#2653130)

"Even in a worst case scenario, if a government or some other anti-Bitcoin faction gets a hold of greater than 50% of the processing power (an extremely expensive feat, and hardly worth it unless you're really determined to destroy the network), the rest of the network can be reconfigured to reject that block chain."

At this point the author shows that he does not have much technical background in regard to the Bitcoin network. Once an adversary gains >50% of the processing power you have basically lost. Yes - you can manually blacklist a single "fork" of the blockchain, but the adversary can fork as often as he wants and you cannot immediately tell if a new block has been generated by the adversary.

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Re:Taking Down The Bitcoin Network by gasull on Tuesday June 14, 2011 @10:48AM (#2653179)

> Once an adversary gains >50% of the processing power you have basically lost.

Wrong. An attacker having more than 50% of the network would just stop payments until the rest of the network rejects the attacker nodes.

https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_...

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Re:Taking Down The Bitcoin Network by gst on Tuesday June 14, 2011 @11:47AM (#2653481)

You can't "reject attacker nodes". There is nothing in the blockchain that identifies a given miner.

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Re:Taking Down The Bitcoin Network by gasull on Tuesday June 14, 2011 @11:55AM (#2653526)

I've seen pie charts with the computing power of several mining pools and the total. I believe you can find the IP of a miner that has a lot of computing power.

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Re:Taking Down The Bitcoin Network by gst on Tuesday June 14, 2011 @12:19PM (#2653608)

If there's a public mining pool it's easy to estimate it's computing power. Just take part in the mining pool and compare your own computing power with the percentage of the 50 BTC that you get for each block. Or, alternatively, you can track the BTC that you get from the mining pool back to the block where they were generated, and so you know that this block must have been generated by the mining pool (again, allowing you to use the amount of blocks generated by the mining pool to estimate it's overall computing power).

However, if the attacker does not use a public mining pool, but private infrastructure, things get more complicated: The only way how Bitcoin clients can agree on a common view of the block chain is to treat the highest block number as the authoritative one. A malicious miner can now just generate new blocks and inject them over Tor to some of the Bitcoin nodes. As Bitcoin nodes distribute the blockchain amongst each others, those "malicious" blocks will quickly spread throughout the Bitcoin network.

The only way how you could prevent this problem is some kind of whitelisting approach, where miners need to be manually approved before their blocks are accepted. However, this would totally change the current Bitcoin infrastructure and turn a completely decentralized network into a more centralized one.

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Re:Taking Down The Bitcoin Network by gasull on Tuesday June 14, 2011 @12:26PM (#2653635)

This is very interesting. Thank you for the info.

I think a solution to this attack would be a web of trust, like PGP/GnuPG works for verifying signatures.

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Re:Taking Down The Bitcoin Network by weavejester on Tuesday June 14, 2011 @10:41AM (#2653149)

Right. In fact, it's hard to imagine any network working if over 50% of the power rests with users who are trying to subvert or destroy the system.

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