Topic: F.R.O.N.T. Attack Vector and What the Bitcoin Devs are doing to prevent it. (Read 4083 times)

On testnet it would probably not work as the monetary incentives are not what they are on a real chain. Those alt-chain-scams are not as competitive as bitcoin neither. I bet many mine their alts just to point to the high hash rate it still has.

are people still trying to act smart and say its a risk without actually trying to test it out.

go on testnet and try to freeze their blockchain. or try it on a near dead altcoin (theres loads of them that are clones of bitcoin)

I think definiting a maximum fee of say 1 BTC would make sense for a future Bitcoin version.

no, because elliptic curve cryptography won't likely be broken in my lifetime, and further more the strength of the checksum in bitcoin makes bruteforcing very difficult. On the otherhand, the block subsidy will decay to a point to where the scenario laid out in this discussion becomes a serious possibility and reason for concern, although it would take a "perfect storm" to exploit it. I would rather it not be possible at all then relying on the perfect storm never occurring.

To say that this is possible is like saying that the miners could go "on strike" in a way similar to how unions go on strike. It is not a real threat.

In theory someone could get really lucky and guess the private key of all of the addresses that contain bitcoin, however the chances of this happening are very small. Do you think we should patch the possibility of people being able to "guess" someone's private key?

Well, so what you're saying is. the attack is possible, but its like getting struck by lighting or the stars aligning? we all know those things have never happened, so therefore we should do nothing about this attack. Shall bitcoin endure stupidity, at the hands of incapable curators? If so, then whoa is bitcoin.

Again, that is not adequate justification for allowing the vulnerability to exist. you find a vulnerability, you patch it and you move on

State actors do not usually attack a currency that is not backed by an enemy of theirs. A country will generally only launch an attack against an economy or a currency as part of a war. Since bitcoin is not backed by any country no country will ever be at war with the country that backs bitcoin

it would be a State actor or a someone who stands to lose alot to a technology like bitcoin who would carry out an attack like this. The purpose of the post isn't fear it's education. i think the goal is clear. a currency not controlled or easily defeated by malicious actors.

Well, so what you're saying is. the attack is possible, but its like getting struck by lighting or the stars aligning? we all know those things have never happened, so therefore we should do nothing about this attack. Shall bitcoin endure stupidity, at the hands of incapable curators? If so, then whoa is bitcoin.

Bitcoin does not pose a serious threat to any major government that would have these kind of resources. Also for the amount of money that it would take to start an attack (to give a large TX fee to the miners) would be better spent on miners (either buying them outright or renting hashpower) to be used to attack the network via other means as a lot would need to take place at once in order for this attack to work

it would be a State actor or a someone who stands to lose alot to a technology like bitcoin who would carry out an attack like this. The purpose of the post isn't fear it's education. i think the goal is clear. a currency not controlled or easily defeated by malicious actors.

In additional to Danny's point above, you also have the issue that someone would need to incur the financial burden to pay these TX fees in the first place. There would be little economic benefit for someone to offer such a large TX fee, especially considering that the benefactor of such attack is unclear (therefore anyone attempting to profit off of an attack may or may not actually benefit in the event such attack is successful in slowing down the network).

IMO this attack vector would be something that is very easy to fix - simply fork the blockchain to institute a maximum TX fee on a per block and per TX basis, the max TX fee on a block basis could be a rolling average (plus some additional margin) of the last 'n' blocks and the max TX fee on a TX basis could be "x" times the min recommended TX fee, and if a TX would warrant larger then the max TX fee then the TX can be split up into smaller TXs.

Interesting attack indeed but h4xx0r who did you quote with the idea of giving to the next miner a share of your coinbase tx? It's trivial to give to the next miner outside the coinbase transaction by sending the reward as a transaction using one of the current inputs. Sure, then you have to scrape the bitcoins from elsewhere.

To recap the attack in laymen's terms:

If somebody paid 10,000BTC in transaction fees, miners would not care about block rewards for the next 10,000/25=400 blocks. Any miner that thinks it could outrun the biggest other miner would try to do so. If there is a draw between the top miners, such a battle could take a long time. If the top miners hold 10% of the mining power, they might try even when the other had a head start and was slowly building a chain that's growing faster than the own chain as they could still call their friends of other pools to team up catch that guy, essentially to the point where all miners took one side or the other and the weaker group gives up.

Also the attack does only work if the biggest selfish miner is bigger than the total of his run-up competitor with all non-selfish miners, so it assumes a pretty corrupt mining landscape.

The attack's effects:

During such an episode, massive re-orgs would happen, clients would act strangely, Finney attacks would be slightly easier etc. and we would have a slightly higher level of drama. And we will never know who sponsored that drama but it would not be a cheap endeavor.

On 06/10/2014 08:43 p.m., Tom Harding wrote:
> On 10/5/2014 4:00 PM, Sergio Lerner wrote:
>> If everyone acts rationally in his own interest, then the best choice
>> for the remaining miners is to try to mine a competing block at the
>> same height n including the high-fee transaction, to collect the fee
>> for themselves.
>
> Sergio --
>
> Just some thoughts on your interesting problem.
>
>
> Since everybody but M10 is on equal footing, I would expect M10 to
> have some fixed advantage depending on assumptions, and the bigger the
> advantage, the shorter the "freeze time".
>

Yes, that's how simulation works. The problem is that the existence of
high-fee delays the decision to switch to M10. Since the network is
moving slower (because of fragmentation) the effect of the high-fee is
twofold: it delays the convergence because it promotes selfishness and
it delays convergence because it promotes fragmentation.

During that time window where the network is frozen, any other high-fee
transaction only makes things worse. This is a very rare example where
a well distributed network (100 miners having 1% each) is much much
worse than 3 miners having 33% each.

Using the my previous terminology, automatic fee-sharing ("ORBS") is a
solution to the freeze problem ("FRONT") but opens the windows to
"CHAKIDO" double-spending. and CHAKIDO double-spending is a much worse
problem than FRONT.
But as Tamas pointed out, sooner or later someone will implement
something like ORBS, get over the critical mass of miner adoption, and
then the CHAKIDO problem will be inevitable.

The only clean solution to this problem is the DECOR+ protocol, which
shares block-rewards by including "uncles" (as GHOST does) and splitting
the reward between all miners at the same height until coinbase maturity
is over. This way the best choice is always cooperative.

PS: Using so many acronyms makes arguments much more concise, but
suggest we should have all the attack terminology described in a single
"Bitcoin Security Wiki"...

It's an interesting math problem.

If you have 51% of the global hash power, then it is generally in your favor financially to mine only on top of your own blocks, ignoring all other blocks.

As your hash power drops below 51% it begins to become beneficial to build on to of the most recent block, due to the cost associated with the orphan risk.  However, with 49% of the hash power, it would probably be beneficial ignore any block that has a larger than average block reward.

The lower your percentage of the hash power, the higher value a block reward must be to overcome the cost associated with the orphan risk.

Assuming for the sake of calculation that all solved blocks are instantaneously known by all miners, and that there are never any splits caused by two or more miners simultaneously solving the current block...

Is there a formula that can indicate for every percentage of global hash power how much higher than the average block reward would be necessary to result in a positive expectation for ignoring the most recently solved block and continuing to attempt to mine it one's self?

Anything over 50% requires a no increase above average reward to result in positive expectation.
As you approach 0% the required increase above average reward approaches infinity.

What does the curve look like between those two extremes?

Interesting attack indeed but h4xx0r who did you quote with the idea of giving to the next miner a share of your coinbase tx? It's trivial to give to the next miner outside the coinbase transaction by sending the reward as a transaction using one of the current inputs. Sure, then you have to scrape the bitcoins from elsewhere.

To recap the attack in laymen's terms:

If somebody paid 10,000BTC in transaction fees, miners would not care about block rewards for the next 10,000/25=400 blocks. Any miner that thinks it could outrun the biggest other miner would try to do so. If there is a draw between the top miners, such a battle could take a long time. If the top miners hold 10% of the mining power, they might try even when the other had a head start and was slowly building a chain that's growing faster than the own chain as they could still call their friends of other pools to team up catch that guy, essentially to the point where all miners took one side or the other and weaker group gives up.

During such an episode, massive re-orgs would happen, clients would act strangely, Finney attacks would be slightly easier etc. and we would have a slightly higher level of drama. And we will never know who sponsored that drama but it would not be a cheap endeavor.