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For starters, the incentives are just not there to destroy Bitcoin. Most governments are either positive or neutral toward Bitcoin. The ones that are hostile toward it would rather make it illegal to fight it with the law instead of with technical attacks. Financial corporations? The smart ones would realize they would benefit more from embracing Bitcoin than fighting it. And the non-smart ones don't even realize how much of a threat Bitcoin may be to their business models. But let's just go with your assumption that some entity with big pockets decide to run a majority attack against Bitcoin miners. How much effort and money would it require? 1 year and 20 billion dollars; here is why: The best 20-28nm mining ASICs require about 1 watt per Ghash/sec. The network is currently at 170,000,000 Ghash/sec so it would require at least 170 megawatt of ASICs, or a ~200 megawatt datacenter (with PUE = 1.15). The fastest TOP500 supercomputer facilities barely reach 20 megawatt. The biggest datacenters in the world are just about 100 megawatt. So the attacker would require two of the world's most powerful datacenters (in terms of electricity and cooling) to attack Bitcoin. But it would take at least 1 year to plan, design, build, and deploy the hardware in two such facilities. And the Bitcoin network will continue to grow during this time. It has grown by 400x in the last year (400,000 to 170,000,000 Ghash/sec). By the lowest estimate, the network will grow at least by 10x in the next year (170,000,000 Ghash/sec to 1,700,000,000 Ghash/sec). So you need to plan to build not 2, but 20 world-class 100 megawatt datacenters by August 2015 to be ready to have a chance to majority-attack Bitcoin. Knowing that a 100 megawatt datacenter costs $1 billion [1], you need pockets with $20 billion in them. And if you under-estimate the growth of the Bitcoin network in the next 12 months, you will have failed and wasted $20 billion for nothing. [1] http://www.greendatacenternews.org/articles/share/416983/ |