Understanding Bitcoin Confirmations: How Many Blocks and Minutes Are Needed for a Secure Transaction?

2023-09-21 05:33:37

The “rule of thumb” is 3-6 (about 30-60 minutes), but according to the developers, more confirmations are needed to avoid abuse. When someone sends bitcoins from one address to another, the transaction goes into a mempool, where it waits for miners to block it. When a transaction enters a block, it becomes part of the blockchain from then on – i.e. it has received the first confirmation. After several confirmations, the transaction can no longer be withdrawn or diverted, but how much is enough? According to Luke Dashjr, one of the earliest developers of Bitcoin, at least 12 blocks, or about 120 minutes, would be needed for a Bitcoin transaction, taking into account the state of mining. (The time required to create a new block is about 10 minutes.) Another well-known developer, Jameson Lopp, covered all the technical and mathematical aspects that could answer the question in his article “How many Bitcoin Confirmations is Enough”. According to Lopp, in order to be able to say almost 99.9% that the transaction is irreversible, the time and number of confirmations depends on what percentage of the hacker/attacker’s mining pool gives its total hashrate. Overall, Lopp’s data and findings agree with Luke Dashjr’s theory, according to which 12 confirmations are necessary, since two mining pools, for example, already account for more than 20% of the global hashrate. (Namely, Foundry USA gave 29.67% of its total hashrate, and Antpool gave 22.75% of its total hash rate in the last month.) The recommended waiting time therefore depends on the state of the network, but also on the risk tolerance of the receiving party. Some cryptocurrency exchanges have voted for three blocks, depending on the size of the deposit, while others require four, five or even six blocks.
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