This article was written by Minlu Kuo
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Hello everyone, I'm Minlu.
Today I'm going to talk about "double spend", aka "double pay".
As the name implies. A double spend means that the same bitcoin was paid twice at the same time, a fraudulent practice that takes advantage of the time difference in block confirmation.
To start with an example.
A buys goods worth 1 bitcoin each from B and C, but A is short of the amount of only 1.5 bitcoins. Thus, A. used the "double spend" method for the purpose of fraudulent procurement. The two specific methods are as follows.
Keywords: 0 confirmation
A broadcasts the private-key-signed bitcoins to two different directions of the network simultaneously, with one broadcasting the transaction to B and the other broadcasting the transaction to C. According to the Bitcoin network broadcast rules, only the first of two transactions to be packed out of a block can be finalized. Transactions that are not packed out of the block are simply voided. Then if B and C ship the transaction without waiting for it to be packed into a block, only one of them will receive the bitcoin, and A will have completed a "double spend".
Keywords: arithmetic attack
A launches an arithmetic attack at the same time as the bitcoin 1 confirmation received by B. When the new block chain exceeds the length of the old block, it nullifies the block data for which B received 1 bitcoin, thus completing the "double spend" by transferring 1 bitcoin to C.
In everyday life, a blank check is also a form of "double spend".
A man who is married in the country uses the excuse of being single to cheat on his marriage in the country, and the clueless beauty gets married to him because he didn't go to the Civil Affairs Bureau to confirm it. Then the act of the beautiful girl is 0 confirmation and the act of the man is "double flower".
The same man who was married in this country used the excuse of being single to go abroad (USA, Japan, Russia) to cheat on his marriage, and the clueless foreign beauty queen married him after confirming that the man was unmarried in this country. Then the act of a foreign girl who confirms whether a man is married or not only in her own country is a confirmation, and the act of a man is a "double flower".
Many people selectively filter out this important information because they have never heard of the terms "0 confirmation" and "1 confirmation". A "0 confirmation" in the blockchain means that the data is not yet packed in blocks; a "1 confirmation" means that the data is already packed in 1 block; and a "5 confirmation" means that the data is already packed in 5 blocks.
And so on, the higher the number of confirmed blocks, the greater the reliability. It's like in example 3, if the foreign beauty queen had begged for confirmation of the cheating man's marital status in multiple countries around the world - "N confirmation" - she naturally wouldn't have been cheated.
That's all for today's post, feel free to leave your questions in the comments section and I'll take the time to answer them all.
Review of previous articles.
4 [Easy to understand blockchain] 51% arithmetic attack (51% Attack)
3 [Easy to understand blockchain] Distributed ledger (Distributed ledger)
2 [Easy to understand blockchain] PoS (Proof of Stake) Proof of Interest
1 [Easy To Understand Blockchain] PoW (Proof Of Work) Proof Of Work
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