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CH07-13: edits for arufino feedback (thanks!)
This commit is contained in:
David A. Harding
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@ -112,7 +112,8 @@ in the blockchain used by all full nodes, and miners only get paid for
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blocks that are widely accepted.
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Whichever block has a second block built on top of it first wins (unless
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there's another near-tie), which is called a _block-finding race_.
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there's another near-tie), which is called a _block-finding race_ and is
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illustrated in <<mining_race>>.
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Block-finding races give the advantage to the largest miners, so they
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act in opposition to Bitcoin's essential decentralization. To prevent
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block-finding races and allow miners of any size to participate equally
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@ -120,6 +121,7 @@ in the lottery that is Bitcoin mining, it's extremely useful to minimize
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the time between when one miner announces a new block and when other
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miners receive that block.
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[[mining_race]]
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.A blockchain fork requiring a mining race
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image::images/race1.dot.png["Mining race"]
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@ -141,8 +143,8 @@ found. For any transaction that isn't found in your local node's
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mempool, your node can send a request to the peer for a copy.
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Conversely, if the remote peer believes your node's mempool doesn't have
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some of transactions that appear in the block, it can include a copy of
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those transaction in the compact block.
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some of the transactions that appear in the block, it can include a copy of
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those transactions in the compact block.
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If the remote peer guesses correctly about what transactions your node
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has in its mempool, and which it does not, it will send a block nearly
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@ -159,7 +161,7 @@ each block.
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====
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There are two modes that Bitcoin Core currently implements for sending
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compact blocks:
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compact blocks, illustrated in <<bip152_illustration>>:
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Low-bandwidth mode::
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When your node requests that a peer use low-bandwidth mode (the default),
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@ -181,13 +183,14 @@ High-bandwidth mode::
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Skipping validation before relay allows new blocks to travel across
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the network with minimal delays at each hop.
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+
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The downside of high-bandwidth node is that your node is likely to
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The downside of high-bandwidth mode is that your node is likely to
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receive redundant information from each high-bandwidth peer it chooses.
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As of this writing, Bitcoin Core currently only asks three peers to use
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high-bandwidth mode (and it tries to choose peers that have a history of
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quickly announcing blocks).
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// released into the public domain by Nicolas Dorier
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[[bip152_illustration]]
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.BIP152 modes compared (from BIP152)
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image::images/bip152.png["BIP152"]
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@ -199,8 +202,9 @@ relay before compact blocks were implemented.
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=== Private Block Relay Networks
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Although compact blocks go a long way towards minimizing the latency
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of block propagation, it's possible to minimize latency further. Unlike
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Although compact blocks go a long way towards minimizing the time it
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takes for blocks to propagate across the network,
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it's possible to minimize latency further. Unlike
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compact blocks, though, the other solutions involve tradeoffs that
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make them unavailable or unsuitable for the public P2P relay network.
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For that reason, there has been experimentation with private relay
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@ -221,7 +225,7 @@ reconstructed if they are lost.
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FEC avoids the problem of a compact block (or some parts of it) not
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arriving due to problems with the underlying network connection.
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Those problems frequently occur but we mostly don't notice them
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Those problems frequently occur but we don't often notice them
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because we mostly use protocols that automatically re-request the
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missing data. However, requesting missing data triples the time to
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receive it. For example:
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@ -938,7 +942,7 @@ smaller of the numbers:
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|===
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If we count the frequency of each difference occurring, we see that the
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small differences are much more likely to occur that the large
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small differences are much more likely to occur than the large
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differences:
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[cols="1,1"]
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@ -1234,3 +1238,8 @@ the emergent consensus of the network and therefore will vary little
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between nodes. Furthermore, the mempool and orphan pools only
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contain unconfirmed transactions, while the UTXO database only contains
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confirmed outputs.
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Now that we have a understanding of many of the data types and
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structures used by nodes and clients to send data across the Bitcoin
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network, it's time to look at the software that's responsible for
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keeping the network secure and operational.
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@ -1,8 +1,15 @@
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[[blockchain]]
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== The Blockchain
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The blockchain is the history of every confirmed Bitcoin transaction.
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It's what allows every full node to indepdently determine what keys and
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scripts control which bitcoins. In this chapter, we'll look at the
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structure of the blockchain and see how it uses cryptographic
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commitments and other clever tricks to make every part of it easy for
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full nodes (and sometimes light clients) to validate.
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((("blockchain (the)", "overview of")))The blockchain data structure is
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an ordered, back-linked list of blocks of transactions. The blockchain
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an ordered, back-linked list of blocks of transactions.The blockchain
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can be stored as a flat file, or in a simple database.
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Blocks are linked "back," each referring to the previous block in the
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chain. ((("blocks", "block height")))The blockchain is often visualized
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@ -309,6 +316,11 @@ chain, making the blockchain longer with a new height of 277,315.
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<<chain_of_blocks>> shows the chain of three blocks, linked by
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references in the +previousblockhash+ field.
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[[chain_of_blocks]]
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[role="smallerfourtyfive"]
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.Blocks linked in a chain by reference to the previous block header hash
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image::images/mbc2_0901.png[]
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[[merkle_trees]]
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=== Merkle Trees
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@ -325,11 +337,6 @@ these trees are usually displayed upside down with the "root" at the top
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and the "leaves" at the bottom of a diagram, as you will see in the
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examples that follow.
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[[chain_of_blocks]]
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[role="smallerfourtyfive"]
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.Blocks linked in a chain by reference to the previous block header hash
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image::images/mbc2_0901.png[]
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Merkle trees are used in bitcoin to summarize all the transactions in a
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block, producing an overall commitment to the entire set of
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transactions and permitting a very efficient process to verify whether a
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@ -418,7 +425,7 @@ image::images/mbc2_0904.png["merkle_tree_large"]
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In <<merkle_tree_path>>, a node can prove that a transaction K is
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included in the block by producing a merkle path that is only four
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32-byte hashes long (128 bytes total). The path consists of the four
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hashes (shown with a shaded background in <<merkle_tree_path>>) H~L~,
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hashes (shown with a shaded background H~L~,
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H~IJ~, H~MNOP~, and H~ABCDEFGH~. With those four hashes provided as an
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authentication path, any node can prove that H~K~ (with a black
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background at the bottom of the diagram) is included in the merkle root
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@ -811,3 +818,9 @@ expected, switch to +mainnet+ to deploy it in production. As you make
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changes, improvements, bug fixes, etc., start the pipeline again,
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deploying each change first on +regtest+, then on +signet+ or +testnet+, and finally
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into production.((("", startref="BCTtest09")))
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Now that we know what data the blockchain contains and how cryptographic
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commitments securely tie the various parts together, we will look at the
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specical commitment that both provides computational security and
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ensures no block can be changed without invalidating all other blocks
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built on top of it: Bitcoin's mining function.
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@ -23,9 +23,9 @@ implementing the monetary supply.
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[TIP]
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====
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((("decentralized systems", "bitcoin mining and")))The purpose of mining
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is not the creation of new bitcoin. That's the incentive system. Mining
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is the mechanism by which Bitcoin's _consensus security_ is _decentralized_.
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((("decentralized systems", "bitcoin mining and")))
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Mining
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is one of the mechanisms by which Bitcoin's _consensus security_ is _decentralized_.
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====
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Miners record new transactions on the global ledger. A
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@ -79,7 +79,7 @@ In this chapter, we will first examine mining as a monetary supply
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mechanism and then look at the most important function of mining: the
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decentralized consensus mechanism that underpins Bitcoin's security.
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To understand mining and consensus, we will follow Alice's transaction
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To understand mining and consensus, we will track Alice's transaction
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as it is received and added to a block by Jing's mining equipment. Then
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we will follow the block as it is mined, added to the blockchain, and
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accepted by the Bitcoin network through the process of emergent
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@ -122,7 +122,7 @@ mined and more may be mined in the future, resulting in a lower total
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issuance of the currency.
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====
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In the example code in <<max_money>>, we calculate the total amount of
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In the code in <<max_money>>, we calculate the total amount of
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bitcoin that will be issued.
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[[max_money]]
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@ -591,7 +591,7 @@ as listed in <<block_header_structure_ch10>>.
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| 4 bytes | Nonce | A counter used for the Proof-of-Work algorithm
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|=======
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The version field was originally a integer field and was used in three
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The version field was originally an integer field and was used in three
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upgrades to the Bitcoin network, those defined in BIPs 34, 66, and 65.
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Each time, the version number was incremented. Later upgrades defined
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the version field as a bitfield, called _VersionBits_, allowing up to 29
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@ -717,9 +717,7 @@ Python 2.7.1
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----
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====
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<<sha256_example1>> shows the result of calculating the hash of +"I am
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Satoshi Nakamoto"+:
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+5d7c7ba21cbbcd75d14800b100252d5b428e5b1213d27c385bc141ca6b47989e+. This
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This
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256-bit number is the _hash_ or _digest_ of the phrase and depends on
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every part of the phrase. Adding a single letter, punctuation mark, or
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any other character will produce a different hash.
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@ -1463,6 +1461,11 @@ solutions. Let's say, for example, that the miners building on top of
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star-triangle-rhombus). They immediately propagate this new block and
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the entire network sees it as a valid solution as shown in <<fork4>>.
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[[fork4]]
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[role="smallereighty"]
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.Visualization of a blockchain fork event: a new block extends one fork, reorganizing the network
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image::images/mbc2_1005.png["Visualization of a blockchain fork event: a new block extends one fork"]
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All nodes that had chosen "triangle" as the winner in the previous round
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will simply extend the chain one more block. The nodes that chose
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"upside-down triangle" as the winner, however, will now see two chains:
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@ -1484,11 +1487,6 @@ star-triangle-rhombus, with "rhombus" as the last block in the chain.
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All miners immediately start working on candidate blocks that reference
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"rhombus" as their parent to extend the star-triangle-rhombus chain.
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[[fork4]]
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[role="smallereighty"]
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.Visualization of a blockchain fork event: a new block extends one fork, reorganizing the network
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image::images/mbc2_1005.png["Visualization of a blockchain fork event: a new block extends one fork"]
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[[fork5]]
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[role="smallereighty"]
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.Visualization of a blockchain fork event: the network reorganizes on a new longest chain
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@ -2506,3 +2504,7 @@ forces compromise.
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Some see this as a weakness of consensus systems. In time, you may come
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to see it as the system's greatest strength.
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At this point in the book, we've finished talking about the Bitcoin
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system itself. What's left are software, tools, and other protocols
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built on top of Bitcoin.
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@ -280,8 +280,6 @@ can be set up with multi-signature access and estate planning through a
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lawyer specialized as a "digital asset executor."((("",
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startref="Suser11")))((("", startref="UCsecurity11")))
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=== Conclusion
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Bitcoin is a completely new, unprecedented, and complex technology. Over
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time we will develop better security tools and practices that are easier
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to use by nonexperts. For now, Bitcoin users can use many of the tips
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@ -1253,8 +1253,6 @@ systems include Tumblebit and Teechan. At this time, however, the
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Lightning Network has already been deployed and has tens of thousands of
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users.
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=== Conclusion
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We have examined just a few of the emerging applications that can be
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built using the Bitcoin blockchain as a trust platform. These
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applications expand the scope of bitcoin beyond payments and beyond
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@ -85,7 +85,7 @@ minimum transaction relay fee must be a fairly small amount or it would
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create an incentive for users to begin sending transactions to miners
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directly, which would be bad for mining decentralization.
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When demand exceeds supply, then the only thing that prevents fee costs
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When demand exceeds supply, the only thing that prevents fee costs
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from rising to infinity is that higher prices curtail demand. Each time
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the price increases, the number of people who want to pay that price to
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include a transaction in a block decreases. Conversely, when prices
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@ -99,12 +99,12 @@ image::../images/fee-negative-feedback.png[Negative feedback loop]
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In particular, people who want to send a transaction during a period of
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high fees will try to find an alternative. There are many alternatives
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for most reasons people need to send a transaction, such as moving to an
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for most reasons why people need to send a transaction, such as moving to an
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offchain payment system like Lightning Network, using an alternative
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payment network, or taking care to construct the smallest transaction
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possible. But it's also possible to take advantage of the negative
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feedback loop to pay less fees. All you need to do is create a
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transaction now which pays a fee that's equal to or higher than what
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transaction which pays a fee that's equal to or higher than what
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miners will accept in the future--even if that price is below what they
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accept now. As the market of other people adapts to the higher price by
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lowering demand, and as miners confirm all transactions paying a higher
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@ -123,7 +123,7 @@ see this scenario illustrated in <<img_wait_times>>.
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[[img_wait_times]]
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.Wait times for different fee rates
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image::../images/fee-patience.png[Wait times for different feerates]
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image::../images/fee-patience.png[Wait times for different fee rates]
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In other words, you don't need to pay peak prices, or switch to another
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payment method, if you're willing to wait longer for your transaction to
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@ -206,28 +206,28 @@ different units:
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- weight/satoshi (also commonly used today)
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We recommend either the vByte/sat or weight/sat units for displaying
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feerates.
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fee rates.
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[WARNING]
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====
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Be careful accepting input for feerates. If a user copy and pastes a
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feerate printed in one enumerator into a field using a different
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Be careful accepting input for fee rates. If a user copy and pastes a
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fee rate printed in one enumerator into a field using a different
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enumerator, they could overpay fees by 1,000 times. If they instead
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switch the denominator, they could theoretically overpay by 100,000,000
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times. Wallets should make it hard for the user to pay an excessive
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feerate and may want to prompt the user to confirm any feerate that was
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fee rate and may want to prompt the user to confirm any fee rate that was
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not generated by the wallet itself using a trusted data source.
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An excessive fee, also called an _absurd fee_, is any feerate that's
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significantly higher than the amount that feerate estimators currently
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An excessive fee, also called an _absurd fee_, is any fee rate that's
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significantly higher than the amount that fee rate estimators currently
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expect is necessary to get a transaction confirmed in the next block.
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Note that wallets should not entirely prevent users from choosing an
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excessive feerate--they should only make using such a feerate hard to do
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excessive fee rate--they should only make using such a fee rate hard to do
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by accident. There are legitimate reasons for users to overpay fees on
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rare occasions.
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====
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=== Estimating appropriate feerates
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=== Estimating appropriate fee rates
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We've established that you can pay a lower fee rate if you're willing to
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wait longer for your transaction to be confirmed, with the exception
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@ -266,7 +266,7 @@ current list, see https://www.lopp.net/bitcoin-information/fee-estimates.html
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As mentioned, fee rate estimation can never be perfect. One common
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problem is that the fundamental demand might change, adjusting the
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equilibrium and either increasing prices (fees) to new heights or
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decreasing them towards the minimum, as show in
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decreasing them towards the minimum, as shown in
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<<img_equilibrium_change>>. If fee rates go down, then a transaction
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that previously paid a normal fee rate might now be paying a high fee
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rate and it will be confirmed earlier than expected. There's no way to
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@ -491,7 +491,7 @@ separate transaction. Using extra block space requires paying extra
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fees beyond the the cost of the fee bump.
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There are several challenges with CPFP, some of which we'll explore in
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the <<transaction_pinning>> section. One other problem which we
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<<transaction_pinning>>. One other problem which we
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specifically need to mention is the minimum relay fee rate problem,
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which is addressed by package relay.
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@ -502,7 +502,7 @@ each node's mempool. Of course, computers have physical limits, whether
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it's the memory (RAM) or disk space--it's not possible for a full node
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to store an unlimited number of unconfirmed transactions. Later
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versions of Bitcoin Core limited the size of the mempool to hold about
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one day worth of transactions, storing only the transactions or packages
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one day's worth of transactions, storing only the transactions or packages
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with the highest fee rate.
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That works extremely well for most things, but it creates a dependency
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@ -536,7 +536,7 @@ problem.
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=== Transaction Pinning
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Although both RBF and CPFP fee bumping work in the basic cases we
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described in the sections about them, there are rules related to both
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described, there are rules related to both
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methods that are designed to prevent denial of service attacks on miners
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and relaying full nodes. An unfortunate side effect of those rules
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is that they can sometimes prevent someone from being able to use fee
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@ -566,7 +566,7 @@ large child transaction. If Alice then wants to replace her original
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transaction, she needs to pay a fee that's larger than what both she and
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Bob originally paid. For example, if Alice's original transaction was
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about 100 vbytes and Bob's transaction was about 100,000 vbytes, and
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they both used the same feerate, Alice now needs to pay more than 1,000
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they both used the same fee rate, Alice now needs to pay more than 1,000
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times as much as she originally paid in order to RBF fee bump her
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transaction.
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@ -593,7 +593,7 @@ Additionally, a transaction and all of its descendants is not
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+
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To prevent these problems, and other related
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problems, Bitcoin Core limits a parent transaction to having a maximum
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of 25 ancestors or descendants in its mempool pool and limits the
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of 25 ancestors or descendants in its mempool and limits the
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total size of all those transactions to 100,000 vbytes. The downside
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of this approach is that users are prevented from creating CPFP fee
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bumps if a transaction already has too many descendants (or if it and
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@ -631,7 +631,7 @@ allow fee bumping with either RBF (using special sighash flags) or CPFP,
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but both of those protocols are vulnerable to transaction pinning.
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Given that the involved transactions are time sensitive, allowing a
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counterparty to use transaction pinning to delay confirmation of a
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transaction can easily lead to an repeatable exploit that malicious
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transaction can easily lead to a repeatable exploit that malicious
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parties could use to steal money from honest parties.
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LN developer Matt Corallo proposed a solution: give the rules for CPFP
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@ -735,7 +735,7 @@ transaction it created. Under normal circumstances, this +nLocktime+ has
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no effect—the transactions could only be included in block
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#100,001 anyway; it's the next block.
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But under a blockchain fork attack, the miners would not be able to pull
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But under a reorganization attack, the miners would not be able to pull
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high-fee transactions from the mempool, because all those transactions
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would be timelocked to block #100,001. They can only remine #100,000
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with whatever transactions were valid at that time, essentially gaining
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@ -746,3 +746,9 @@ profitable in some cases and so can help preserve the stability of the
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Bitcoin network as the block subsidy declines. We recommend all wallets
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||||
implement anti fee sniping when it doesn't interfere with the wallet's
|
||||
other uses of the nLockTime field.
|
||||
|
||||
As Bitcoin continues to mature, and as the subsidy continues to decline,
|
||||
fees become more and more important to Bitcoin users, both in their
|
||||
day-to-day use for getting transactions confirmed quickly and in
|
||||
providing an incentive for miners to continue securing Bitcoin
|
||||
transactions with new proof-of-work.
|
||||
|
||||
Loading…
Reference in New Issue
Block a user