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Author Topic: Shouldn't 51% attack really be >50% attack?  (Read 909 times)
statix
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July 02, 2012, 07:33:57 AM
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Why is it commonly known as 51% attack when, as far as I know, you'll only need to have >50% of hashing power to successfully pull out the attack.

The term has bothered me quite a bit for awhile.
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Gareth Nelson
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July 02, 2012, 07:36:43 AM
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Why is it commonly known as 51% attack when, as far as I know, you'll only need to have >50% of hashing power to successfully pull out the attack.

The term has bothered me quite a bit for awhile.

Because the 50.000001% attack isn't as catchy
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July 02, 2012, 07:38:37 AM
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Why is it commonly known as 51% attack when, as far as I know, you'll only need to have >50% of hashing power to successfully pull out the attack.

The term has bothered me quite a bit for awhile.

Because the 50.000001% attack isn't as catchy

Yeah, it's kinda like how "we are the 47%" isn't as catchy as "we are the 99%"

But I admit, I have thought the same thing.

Meni Rosenfeld
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July 02, 2012, 07:49:00 AM
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I usually call it the >50% attack.

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ribuck
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July 02, 2012, 08:02:24 AM
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There's not really a hard limit for the percentage.

If an attacker has 47%, they might get lucky and maintain the longest chain for 6 blocks, which is enough for a devastating attack. On the other hand, they might have 53% for a while, and not manage a 6-block attack during that time.

Satoshi did a mathematical analysis of this in section 11 of his paper.

So I think "51% attack" is a good name for this attack, even though it's not a complete explanation.
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July 02, 2012, 08:43:29 AM
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There's not really a hard limit for the percentage.

If an attacker has 47%, they might get lucky and maintain the longest chain for 6 blocks, which is enough for a devastating attack. On the other hand, they might have 53% for a while, and not manage a 6-block attack during that time.

Satoshi did a mathematical analysis of this in section 11 of his paper.

So I think "51% attack" is a good name for this attack, even though it's not a complete explanation.
With 47% the attacker has a chance to succeed, but no certainty. With >50% he is guaranteed to win eventually, no matter how many blocks are waited (though "eventually" can be a very long time, on average inversely proportional to the excess).

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July 02, 2012, 08:58:32 AM
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The right term is majority attack.
Gareth Nelson
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July 02, 2012, 09:11:14 AM
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Why is it commonly known as 51% attack when, as far as I know, you'll only need to have >50% of hashing power to successfully pull out the attack.

The term has bothered me quite a bit for awhile.

Because the 50.000001% attack isn't as catchy

Yeah, it's kinda like how "we are the 47%" isn't as catchy as "we are the 99%"

But I admit, I have thought the same thing.

Nice quote!

53% of the US population pay taxes
DannyHamilton
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July 02, 2012, 03:44:43 PM
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Nice quote!

53% of the US population pay taxes

Actually, I'm pretty sure 100% of the U.S. population pays taxes, but we will avoid getting into a political discussion in this thread.

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