Topic: 51% attack (Read 735 times)

i'd take that over "the company has all the ripples and they could get shut down just like e-gold.com did"

I'm just speculating, I know it smells a bit like conspiracy theory.  More to say, such hack won't be possible with ASIC based hardware unless... the manufacturer delibarately puts some malicious code inside...

But, it's just another speculation.

biskup that is a very unpleasant scenario but as long as a large portion of miners are divers machines (different os, patched versions, etc.) then the attack surface is rather difficult to gain a large portion at one time before the miner operators notice (no more coin being delivered for work, etc.)

BTW, what do you think about Ripple? It seems that there is no this 51% chance to crash XRP.

Wow it's awesome

i still don't understand..

I'm worried of another theoretical possibility: what if mining rigs became infected with some type of worm/virus etc. which may turn the machine into remotely controlled "zombie"? This way the attacker (or group of attackers) could build their own mining botnet which would turn rogue at certain point and success with performing 51% attack. I know, it's all open source software, thousend times checked, verified etc. but as the current craze goes on, how could we be cetrain that all the miners are purchasing secure mining equipment?

so would someone explain this to me then?

is it possible/likely that one person purchased several Avalons or multiple folks are working together in a pool specifically to cheat the system?

how about the supposed BFL's? would they be detectable if they brought all their miners online to stage such an attack?

In the case you mention above, I maintain that you are playing with semantics.  The transaction has lost its confirmations but it isn't "reversed".  It still exists, and your client is welcome to continue to broadcast it.  Peers will still relay it.  When the 51% attack ends (if it ends), the transactions will begin receiving confirmations again.


In this second case, I'll admit I'm the one playing with semantics.  Those coins you thought you had cease to exist.  The attacker has different bitcoins (not yours) as evidenced by the fact that they require a signature from a different private key to spend. So the attacker isn't spending coins that don't belong to him, you just don't have as many coins as you thought you had.

Regardless, your two points are well taken.  I agree that it is possible for a 51% attack to be much more disruptive than many people realize. Not only does every bitcoin mined in an orphaned block cease to exist, but because of that every transaction that has occurred that can be traced back to those bitcoins is instantly cancelled.  It would be quite a mess if the number of blocks being orphaned was much more than 150.

Nah

Reverse other people's transactions: so, you made a transaction yesterday, got confirmed, has like 100 blocks or more of confirmation. With a 51% attack you can rebuild the blockchain from for example a week ago and of course, all the transactions of all these blocks, unless the attacker include them, will disappear or, at least, go back at 0 confirmations

Send coins that never belonged to him: so, yesterday you found a block and got 25btc right? Nice, the attacker start rebuilding the blockchain from, for example, a week ago, all the new blocks belong to him, so of course the reward. Your 25 btc will disappear because he found that block, not you

Not sure what you are referring to, but I suspect you are playing with semantics.

Errh... yes, he can

But now they don't have to. 

Hello,
Its nice to see that you want to help out newbies but if they have a question on 51% attacks they can check the wiki themselves.

I read an interesting thread on 51% attack.

https://bitcointalk.org/index.php?topic=156406.20

Since I'm a complete newbie I had to ask Mr. en.bitcoin.it/wiki. So for all other newbies that don't know what the 51% attack is and want to know, here's a snipp from en.bitcoin.it/wiki: ( https://en.bitcoin.it/wiki/Weaknesses )

An attacker that controls more than 50% of the network's computing power can, for the time that he is in control, exclude and modify the ordering of transactions. This allows him to:

    Reverse transactions that he sends while he's in control. This has the potential to double-spend transactions that previously had already been seen in the block chain.
    Prevent some or all transactions from gaining any confirmations
    Prevent some or all other miners from mining any valid blocks

The attacker can't:

    Reverse other people's transactions
    Prevent transactions from being sent at all (they'll show as 0/unconfirmed)
    Change the number of coins generated per block
    Create coins out of thin air
    Send coins that never belonged to him

With less than 50%, the same kind of attacks are possible, but with less than 100% rate of success. For example, someone with only 40% of the network computing power can overcome a 6-deep confirmed transaction with a 50% success rate.

It's much more difficult to change historical blocks, and it becomes exponentially more difficult the further back you go. As above, changing historical blocks only allows you to exclude and change the ordering of transactions. It's impossible to change blocks created before the last checkpoint.

Since this attack doesn't permit all that much power over the network, it is expected that no one will attempt it. A profit-seeking person will always gain more by just following the rules, and even someone trying to destroy the system will probably find other attacks more attractive. However, if this attack is successfully executed, it will be difficult or impossible to "untangle" the mess created -- any changes the attacker makes might become permanent.