Suppose A transfers 10 bitcoins to B, but he wants to delete this information from the blockchain, so that everyone does not know that this matter exists, and can go wrong.
First, let’s talk about the longest chain principle. Assuming that there are two miners digging at the same time behind a certain block, or there is a disagreement due to network delays, etc., at this time, each node first arbitrarily mines according to the block that it thinks is correct. Only when the next block is generated, there will be two chains at this time, but one is long. Bitcoin stipulates that the longest chain shall prevail. If a node is still stubborn to take the shorter chain as the criterion, he is fighting against most computing power. The result of this is that the blocks he digs are not recognized by everyone, which will waste time and computing power.
Going back to the above scenario, if A wants to renege on the account, he can only re-mining from the block before the block where the message of A->B10 bitcoins is recorded to create a branch chain, but the actual area is The block has advanced a lot, he can only keep chasing, and while chasing, the main chain is also advancing, he must advance faster than the main chain, if his computing power is large enough, theoretically pass longer The time can indeed catch up with success, and the tampering of transaction information has been realized. However, this is almost impossible, because no matter how large the computing power is, the average block generation speed is 10 minutes. From a non-technical point of view, if a person has more than half the computing power of the entire network, why is he not on the main chain? Continue mining? A person from a wealthy country would not be willing to be a thief.