Quote from: r0ach on July 28, 2014, 06:42:05 PM

Quote from: raid_n on July 28, 2014, 05:58:52 PM

There is very little real incentive to perform a > 50% attack because you'd shake confidence, no matter what method is used for block creation.

People keep using the phrase 51% attack to try and downplay the issue, like it's just some theoretical thing that won't happen because self motivated greed will prevent it, aka the rational miner factor. Since when are rational miners considered even the top 10 security risks? Did you also forget Bitcoin is advertised as having "no trusted third parties"? Those pools that you can count with less than 5 fingers are your trusted third parties, which is why the system as is, has failed completely.

[snip]

Unless all current Bitcoin development is redirected towards getting rid of the mining pools, there's really no reason to support it.

Here is what happens when you have a real attack:
1) The attacker can attempt a double spend
2) The attacker withholds a transaction to cause economic harm

Double spending is something that is quite time critical for the attacker. The further down a block is in the chain the more unlikely it becomes that the attacker can successfully replace the above chain with a new one.
Large double spends will be noticed and as an effect people will lose trust and move to something else. So realistically the attacker would try to pull off a one shot double spend for a very large amount of coins.
I do not know what policies are in place for big exchanges but you would expect them to wait quite a few blocks for very large sums.
The attacker would have to put in immense financial efforts to reach the >50% hash power and would probably gain little from the attack.
It only really makes sense if you are out to destroy bitcoin as a whole.

Equal argumentations can be made for Transaction withholding.

"Those pools that you can count with less than 5 fingers are your trusted third parties, which is why the system as is, has failed completely"

Those pools can't sign transactions for your coins. They can't double spend your transactions unless you WANT them to by broadcasting two different transactions for the same input.
If you send me coins I can require you to wait 1000 blocks before I send you goods or no blocks. This gives me the freedom to choose.
I can happily trust that in the current system it is very very very unlikely that a new chain with 1000 blocks will appear out of thin air to double spend that transaction.