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CH02::mining: explain how confirmations add security

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Previous text didn't explain how including a transaction in a block
gave it security.  We add a short explanation here, knowing that we'll
go into more detail in the mining chapter.
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David A. Harding 2023-02-04 20:57:41 -10:00
parent cb3420c572
commit e472d344af
1 changed files with 38 additions and 20 deletions
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@ -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 <<block-alice1>>, 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
<<mining>>.((("", startref="BToverview02")))((("",
startref="MACover02")))