Quote from: QuestionAuthority on June 16, 2014, 02:56:20 PM

Quote from: tbearhere on June 16, 2014, 02:47:44 PM

Quote from: Mikerogers on June 08, 2014, 04:13:59 AM

This is fucking serious people get off GHash the consequences for 51% are huge. It could be detrimental for bitcoin going forward. Once people realize that the Achilles heel in bitcoin is real, they'll permanently mark it with a negative stigma.

seriously i dont understand why 51% or more makes a difference. can someone explain please. ty

Quote

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.

thank you, now i understand why