user114595: Since the 51% attack happens if there are more than 50% of nodes that fake the data on the blockchain, can it be actually 81% or 91% that is needed to fake the data, because it would be much harder if more than 80% of the nodes are "bad guys".
So what I mean is, can it be the case that even 79% cannot be an attack, but need to be a higher number, such as 81% or 91%.
It may appear if the verification of data can reach a 50% level, reaching out to 1 more node of those 50% can make it become 80% to 100% easily, so one extra step is all it takes?

user109555: This question is based on false assumptions. The node network does not vote. It exists as a social consensus. The consensus relies on node operators to choose to follow the same rules. In some discussions this is referred to as "supermajority", which is accurate. It is completely inaccurate to believe nodes can vote, or that nodes can be reliably counted. All Bitcoin nodes are independent
The so-called 51% attack scenario is derived from the Satoshi white paper, under the heading "Calculations". This warns that a miner with more than 50% of the hash power can overtake all the other miners and mine blocks containing his own fraudulent transactions. The scenario is a consequence of the "longest chain" principle in the design. When there is a tied mining race, the node network will have a temporary chain tip fork, which is usually resolve din the next block, in favor of the longest chain. Nodes with the shorter chain will perform a chain tip reorg, to resynchronize. A 51% miner can simulate a tied mining race with hash power
Satoshi's scenario describes an attack which replaces one block at a time. The white paper includes some mathematical projections which display that it becomes exponentially more difficult to force chain tip forks more than one block long
It is now known that 51% hash power is not necessary, and that an attacker who shadow-mines a chain tip of multiple blocks secretly, in parallel with the regular mining network can create a chain tip fork of arbitrary length, just by winning one block more quickly than the regular mining network
Shadow mining scenario: acquire at least 15% of the hash rate. Mine in secret, in parallel, for an hour or a few hours. Eventually, the 15% hash power means a 15% chance of winning a block. Do not broadcast the winning block. Keep mining for 10 more blocks, and then broadcast the 11-block tip. The "longest chain" logic in the node software will recognize the attacker's 11 blocks as longer than the regular mining network, and will automatically reorg the chain tip
Attacks like this have been seen several times on Bitcoin Gold and Bitcoin Cash SV

114595: <p>Since the 51% attack happens if there are more than 50% of nodes that fake the data on the blockchain, can it be actually 81% or 91% that is needed to fake the data, because it would be much harder if more than 80% of the nodes are &quot;bad guys&quot;.</p>
<p>So what I mean is, can it be the case that even 79% cannot be an attack, but need to be a higher number, such as 81% or 91%.</p>
<p>It may appear if the verification of data can reach a 50% level, reaching out to 1 more node of those 50% can make it become 80% to 100% easily, so one extra step is all it takes?</p>
 109555: <p>This question is based on false assumptions. The node network does not vote. It exists as a social consensus. The consensus relies on node operators to choose to follow the same rules. In some discussions this is referred to as &quot;supermajority&quot;, which is accurate. It is completely inaccurate to believe nodes can vote, or that nodes can be reliably counted. All Bitcoin nodes are independent</p>
<p>The so-called 51% attack scenario is derived from the Satoshi white paper, under the heading &quot;Calculations&quot;. This warns that a miner with more than 50% of the hash power can overtake all the other miners and mine blocks containing his own fraudulent transactions. The scenario is a consequence of the &quot;longest chain&quot; principle in the design. When there is a tied mining race, the node network will have a temporary chain tip fork, which is usually resolve din the next block, in favor of the longest chain. Nodes with the shorter chain will perform a chain tip reorg, to resynchronize. A 51% miner can simulate a tied mining race with hash power</p>
<p>Satoshi's scenario describes an attack which replaces one block at a time. The white paper includes some mathematical projections which display that it becomes exponentially more difficult to force chain tip forks more than one block long</p>
<p>It is now known that 51% hash power is not necessary, and that an attacker who shadow-mines a chain tip of multiple blocks secretly, in parallel with the regular mining network can create a chain tip fork of arbitrary length, just by winning one block more quickly than the regular mining network</p>
<p>Shadow mining scenario: acquire at least 15% of the hash rate. Mine in secret, in parallel, for an hour or a few hours. Eventually, the 15% hash power means a 15% chance of winning a block. Do not broadcast the winning block. Keep mining for 10 more blocks, and then broadcast the 11-block tip. The &quot;longest chain&quot; logic in the node software will recognize the attacker's 11 blocks as longer than the regular mining network, and will <strong>automatically</strong> reorg the chain tip</p>
<p>Attacks like this have been seen several times on Bitcoin Gold and Bitcoin Cash SV</p>
