In fact, double spending on zero-confirmation transactions is much more likely to succeed than people think, so in large transactions, at least wait until the transaction is confirmed before paying. According to nakamoto satoshi’s creation paper, at least six confirmations can be considered irreversible. Currency trading platform development + V: RuIEC1688
Two forms of double payment
First, a quick explanation of what double payments are. So the so-called double payment situation, let’s say A pays B A sum of money, and then she pays C the same sum of money again, and A basically tries to make two payments, one of which she knows will be rejected. Of course, when we think about payments, some of A’s accounts got overdrawn by writing these two payments. That’s close to how bitcoin works, but not exactly.
Bitcoin is not based on an account model, but on unspent transaction output (UTXO). The output of a transaction basically contains an address and a quantity. Once the output is used, it cannot be spent again. Consider a UTXO (as a sum sent to you), which can be any number, such as 0.413 BTC.
Bitcoin’s double payments mean that a single coin (UTXO) is spent twice. Typically, this means that A sends her 0.413BTC to B, and she then sends the same amount of Bitcoin to C.
Bitcoin’s solution is that one of the transactions is incorporated into a block that determines who actually gets paid. If two transactions are somehow passed to multiple blocks, the subsequent blocks will be rejected by the software. If both transactions are in the same block, that block will also be rejected by the software.
Basically, bitcoin software detects double payments and should reject the block if they occur. However, sending the same UTXO in two different transactions is not the only two-flower method.
In fact, there is a morbid situation of double payment for the same UTXO in the same transaction. In this case, A sends the same coin to B twice. So, A actually paid 0.413 BTC, but B received 0.826 BTC. This is obviously not a valid transaction as only one UTXO worth 0.413 BTC was sent. This is equivalent to A sending B twice for the same $10, and B receiving $20.
So does the double spending problem go against the trading of currency trading platform?
So, to summarize the two types of double payment attempts we have defined:
1. Use two or more transactions to spend the same UTXO;
2. Using a transaction costs the same UTXO more than once;
It turns out that The Bitcoin Core software handles the first problem correctly, and the second problem is the one we care about. Anyone can construct a two-flower transaction like this, but getting nodes to accept it is another matter.
There are currently two ways to incorporate transactions into a block:
A. Pay enough to broadcast the transaction to the network, and the mining union is responsible for incorporating the transaction into the block;
B. As a miner, put transactions into a block;
(A) You don’t need to do much more than create transactions and broadcast them to nodes on the network.
(B) You need to find sufficient proof of work. This is also the key to the bug.
(A) is not A possible attack vector because these transactions are immediately marked as invalid and nodes on the network reject them. Without miners’ cooperation, such deals cannot enter miners’ memory banks because they do not circulate.
(B) is the only case in which a vulnerability is revealed. In other words, to exploit this loophole, you need proof of work, or enough mining equipment and electricity.
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