Quote from: Gavin Andresen on February 15, 2011, 09:56:17 PM

One more thought: the "finney attack" can only be profitable if the reward from cheating is greater than (reward of mining times the probability your block will be rejected because you delay announcing it while you "run down to the store").

Reward for block is currently $50, that will (hopefully!) continue to rise for the next decade or two.

Say it takes you 5 minutes to complete a transaction at the corner store (half the average block gen time)... today you'd have to make a $25-or-greater purchase just to break even.

Seems likely this attack will be completely impractical for transactions under $200 when the block reward is worth more than $400. 0-confirmations (just wait N seconds to look for a quick double-spend) for any transaction under $200 seems "good enough" to me.

Read through all of this and here is the solution to fast transactions without the fear of loss due to double spends. Simply accept any transaction with the value below REWARD * Gold value/2. (NOTE: I hate valuing items with no intrinsic value with another item with no intrinsic value - Gold is the real constant here not dollars.)

So long as minners are getting paid fairly for the job they do it's not a problem.