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Author Topic: 0 confirmation - signed by miner?  (Read 3121 times)
DeathAndTaxes
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Gerald Davis


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February 03, 2012, 01:34:40 PM
 #21

How to give a miner an incentive...

Let's say I'm a merchant.  I make a sale, and see the customer's transaction broadcast.  I want to ensure it gets into a block as quickly as possible.

I could (if the client allowed it) broadcast a new transaction based on that not-yet-confirmed transaction, with a fee.  Miners would then want to include the customer's transaction since that's the only way that my fee-paying transaction to them would be claimable.

That would work however the attacker could do the same thing.  The double spend could contain a larger transaction fee and thus mining algorithm that is opportunistic would choose it for your transaction + transaction w/ fee sequence.

Given the "profit margin" for a double spend is potentially higher the attacker will always be able to "out-fee" a legit operator.
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February 03, 2012, 04:57:29 PM
 #22

The double spend could contain a larger transaction fee and thus mining algorithm that is opportunistic would choose it for your transaction + transaction w/ fee sequence.

Given the "profit margin" for a double spend is potentially higher the attacker will always be able to "out-fee" a legit operator.

No miners would voluntarily run a system that does this.  They may get higher fees, sure, but they make the system vulnerable to double spends by accepting later transactions to different destination addresses with higher fees.  By making the entire Bitcoin network vulnerable to double spends, they ensure that the higher fees they get are worth nothing.

A miner could use the fee in a "dependent transaction" to increase the speed at which the original transaction is included in a block, but would have to put constraints on rebroadcast transactions with higher fees.  Namely, the constraint would be that up to one output may have its value changed and up to one input may be added to increase transaction fee.  Otherwise, you open up double spends.

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Gerald Davis


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February 03, 2012, 05:07:27 PM
 #23

No miners would voluntarily run a system that does this.  They may get higher fees, sure, but they make the system vulnerable to double spends by accepting later transactions to different destination addresses with higher fees.  By making the entire Bitcoin network vulnerable to double spends, they ensure that the higher fees they get are worth nothing.

I think you forget that a double spend isn't "spend" wait ungodly amount of time then "double spend".
It is a near simultaneous release of two transactions. 

You are assuming the good transaction hits first.
What if the bad one does?
What if they hit at nearly the same time (most pools queue up transactions)?
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February 03, 2012, 05:09:27 PM
 #24

No miners would voluntarily run a system that does this.  They may get higher fees, sure, but they make the system vulnerable to double spends by accepting later transactions to different destination addresses with higher fees.  By making the entire Bitcoin network vulnerable to double spends, they ensure that the higher fees they get are worth nothing.

I think you forget that a double spend isn't "spend" wait ungodly amount of time then "double spend".
It is a near simultaneous release of two transactions. 

You are assuming the good transaction hits first.
What if the bad one does?
What if they hit at nearly the same time (most pools queue up transactions)?

Then the merchant should be able to see that they're being double-spent against and not give up the merchandise.

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Gerald Davis


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February 03, 2012, 05:12:12 PM
 #25

Then the merchant should be able to see that they're being double-spent against and not give up the merchandise.

Sweet you solved the 0-confirm double spend problem.  Strange nobody thought of that solution yet.


... or maybe it still isn't solved.  BTW a 0-confirm double spend is rather difficult to pull off but it isn't impossible.  You stating the difficulty of the attack isn't a solution.
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February 04, 2012, 07:39:42 PM
 #26

No miners would voluntarily run a system that does this.  They may get higher fees, sure, but they make the system vulnerable to double spends by accepting later transactions to different destination addresses with higher fees.  By making the entire Bitcoin network vulnerable to double spends, they ensure that the higher fees they get are worth nothing.
If you ask me, the reason - in part - that Bitcoin has been successful so far is that there are monetary incentives to keep the system running by the rules. If we start to depend on miners "doing the right thing" because we assume that they are concerned with the long-term survival of Bitcoin, I'm not sure things will continue to go well. Looking at the average human, it's hard for me to see that we are all that concerned with the long-term sustainability of important things that we depend on. I don't  think miners (being human beings) would be either.

This is an interesting discussion though. The 0-confirmation double spend problem would definitely be a valuable one to solve. I do think it would have to involve some form of centralization though. Not that this is necessarily a bad thing though, since no one would be forced to go this route.
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