Quote from: person on May 13, 2015, 03:09:20 AM

Not sure where you got this from... but to effectively reverse a block, you need to create a longer chain, faster than the one with the block you want to reverse.
Last time I've checked the global hashrate, 51% of the network costs much more than $6000...

That is the price to rent, rather than buy the hash rate. The network pays out 25BTC per block, so that is market price ($6000).

If you paid more than that, you could rent it. At least in theory. In practice, miners aren't renting out their hashing power on a sufficiently liquid market. Mining pools "buy" hashing power, but 51% isn't available to rent. It would take so long to get people to re-target to your "pool" and many would leave once they saw what you are doing.

The point I was making is that it is an estimate of the lower bound on security. You shouldn't assume that a transaction worth $50 million is safe after 6 confirms.

3 months of blocks are worth $80. It would be an interesting experiment. A "pool" could announce that they are giving a special 10% reward for the next 3 months. You get paid (share difficulty) / (block difficulty) * 27.5 BTC. This gives 10% more than the expected value.

The pool can then forward those shares to another pool. This will cost around $8 million to fund the extra payout. It would be interesting what percentage of the hashing power that pool would end up with. Other pools could forward shares to them though, so they would have to add some kind of signature into their headers.