diff --git a/ch02.asciidoc b/ch02.asciidoc index 3341558d..b59bc890 100644 --- a/ch02.asciidoc +++ b/ch02.asciidoc @@ -642,10 +642,28 @@ block and announced it to the network. After other miners validated the winning block, they started a new lottery to generate the next block. -Jing's winning block became part of the blockchain as block #277316, -containing 419 transactions, including Alice's transaction. The block -containing Alice's transaction is counted as one "confirmation" of that -transaction. +Jing's winning block containing Alice's transaction became part of the +blockchain. The block containing Alice's transaction is counted as one +"confirmation" of that transaction. After the block containing Alice's +transaction has propagated through the network, creating an alternative +block with a different version of Alice's transaction (such as a +transaction that doesn't pay Bob) would require performing the same +amount of work as it will take all Bitcoin miners to create an entirely +new block. For the entire network to accept an alternative block, an +additional new block would need to be mined on top of the alternative. + +That means miners have a choice. They can work with Alice on an +alternative version of the transaction where she pays Bob, perhaps with +Alice paying miners a share of the money she previously paid Bob. This +dishonest behavior will require they expend the effort required to +create two new blocks. Instead, miners who behave honestly can create a +single new block and and receive all of the fees from the tranactions +they include in it, plus the block reward. Normally, the high cost of +dishonestly creating two blocks for a small additional payment is much +less profitable than honestly creating a new block, making it unlikely +that a confirmed tranaction will be deliberately changed. For Bob, this +means that he can begin to believe that the payment from Alice can be +relied upon. [TIP] ==== @@ -654,28 +672,28 @@ https://blockstream.info/block/000000000000000000027d39da52dd790d98f85895b02e764 ==== ((("confirmations", "role in transactions")))Approximately 19 minutes -later, a new block, #277317, is mined by another miner. Because this new -block is built on top of block #277316 that contained Alice's -transaction, it added even more computation to the blockchain, thereby -strengthening the trust in those transactions. Each block mined on top -of the one containing the transaction counts as an additional -confirmation for Alice's transaction. As the blocks pile on top of each -other, it becomes exponentially harder to reverse the transaction, -thereby making it more and more trusted by the network. +after Jing's block, a new block is mined by another miner. Because this +new block is built on top of the block that contained Alice's +transaction (giving Alice's transaction two confirmations) Alice's +transaction can now only be changed if two alternative blocks are +mined--plus a new block built on top of them--for a total of three +blocks that would need to be mined for Alice to take back the money she +sent Bob. Each block mined on top of the one containing Alice's +transaction counts as an additional confirmation. As the blocks pile on +top of each other, it becomes harder to reverse the transaction, thereby +giving Bob more and more confidence that Alice's payment is secure. ((("genesis block")))((("blocks", "genesis block")))((("blockchain (the)", "genesis block")))In the diagram in <>, we can see block the block which contains Alice's transaction. Below it are hundreds of thousands of blocks, linked to each other in a chain of blocks (blockchain) all the way back to block #0, known as the _genesis -block_. Over time, as the "height" in blocks increases, so does the -computation difficulty for each block and the chain as a whole. The -blocks mined after the one that contains Alice's transaction act as -further assurance, as they pile on more computation in a longer and -longer chain. By convention, any block with more than six confirmations -is considered irrevocable, because it would require an immense amount of -computation to invalidate and recalculate six blocks. We will examine -the process of mining and the way it builds trust in more detail in +block_. Over time, as the "height" of new blocks increases, so does the +computation difficulty for the chain as a whole. +By convention, any block with more than six confirmations +is considered very hard to change, because it would require an immense amount of +computation to recalculate six blocks (plus one new block). We will examine +the process of mining and the way it builds confidence in more detail in <>.((("", startref="BToverview02")))((("", startref="MACover02")))