This article is an excerpt from my book, A brief introduction to Bitcoin.

Bitcoin’s proof-of-work scheme prevents double-spending for slow payments where the payee waits for the transaction to be acknowledged in at least one block. Each new transaction goes through two stages of verification, once after creation and once after it has been included in a block, as described earlier. As a result, a double-spending of the same Bitcoins would require a very high computing effort for the generation of fake blocks. This type of double spending is discussed in the next chapter, as part of the larger issue…


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