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chapter re-organization, mining first, then consensus

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*DRAFT - DO NOT SUBMIT ISSUES OR PULL REQUESTS YET PLEASE - CONSTANT CHANGES HAPPENING*
=== Introduction
((("blockchain")))
[[mining]]
=== Introduction - Mining and Consensus
Mining is the process by which new bitcoin is added to the money supply. Mining also serves to secure the bitcoin system against fraudulent transactions or transactions spending the same amount of bitcoin more than once, known as a double-spend. Miners act as a decentralized clearinghouse, validating new transactions and recording them on the global ledger. A new block, containing transactions which occurred since the last block, is "mined" every 10 minutes thereby adding those transactions to the blockchain. Transactions that become part of a block and added to the blockchain are considered "confirmed", which allows the new owners of bitcoin to spend the bitcoin they received in those transactions. Miners receive two types of reward for mining: new coins created with each new block and transaction fees from all the transactions included in the block. To earn this reward, the miners compete to solve a difficult mathematical problem based on a cryptographic hash algorithm. The solution to the problem, called the Proof-of-Work, is included in the new block and acts as proof that the miner expended significant computing effort. The competition to solve the Proof-of-Work algorithm to earn reward and the right to record transactions on the blockchain is the basis for bitcoin's security model.
=== Mining
Bitcoin's security is underpinned by computation. New blocks are added to the blockchain through a consensus mechanism called the _Proof-of-Work_ (PoW) that requires a predictable computational effort, one that takes approximately 10 minutes to solve on average. Specialized bitcoin nodes called _miners_ validate transactions and collect them into blocks, then attempt to find the solution that satisfies the Proof-of-Work algorithm. The first miner to find such a solution, propagates the newly created block across the network. All other nodes on the network verify that the new block contains valid transactions and satisfies the Proof-of-Work algorithm, then they add it to the blockchain, thereby extending it by one block. The miners add a special coin generation transaction into the blocks they build, which creates new bitcoin from nothing and is payable to the miner's own bitcoin address. Once the block is accepted as valid by the entire network, that transaction is also recorded on the blockchain, thereby rewarding the miner for the computational effort it took to satisfy the Proof-of-Work. This de-centralized consensus mechanism, based on a global competition and requiring computation to create new blocks, is the basis for the security of the bitcoin transaction ledger and also for the issuance of new bitcoin. {move the last sentence to the beginning of the paragraph - to explain more about security} The equilibrium between the incentive of bitcoin reward and the immense computing effort required to win it force the participants to behave honestly, without the need for a centralized clearinghouse or currency issuer. The bitcoin consensus mechanism is a dynamic, self-regulating and completely decentralized security model that operates at very large scale.
The process of new coin generation is called mining, because the reward is designed to simulate diminishing returns, just like mining for precious metals. Bitcoin's money supply is created through mining, just like a central bank issues new money by printing bank notes. The amount of newly created bitcoin a miner can add to a block decreases approximately every four years (or precisely every 210,000 blocks). It started at 50 bitcoin per block in January of 2009 and halved to 25 bitcoin per block in November of 2012. It will halve again to 12.5 bitcoin per block sometime in 2016. Based on this formula, bitcoin mining rewards decrease exponentially until approximately the year 2140 when all 21 million bitcoin have been issued.
Bitcoin miners also earn fees from transactions. Every transaction may include a transaction fee, in the form of a surplus of bitcoin between the transaction's inputs and outputs. The bitcoin miner gets to "keep the change" on the transactions.
Today the fees represent 1% or less of a bitcoin miner's income, the vast majority coming from the newly minted bitcoins. However, as the reward decreases over time and the number of transactions per block increases, a greater proportion of bitcoin mining earnings will come from fees. After 2140 all bitcoin miner earnings will be in the form of transaction fees.
=== Mining Nodes
Some of the nodes on the bitcoin network are specialized nodes called _miners_. In Chapter 1 we introduced Jing, a computer engineering student in Shanghai China, who is a bitcoin miner. Jing earns bitcoin by running a "mining rig" which is a specialized computer-hardware system designed to mine bitcoins. Jing's specialized mining hardware is connected to a server running a full bitcoin node. Unlike Jing, some miners mine without a full node as we will see in <<mining pools>>. Like every other full node, Jing's node receives and propagates unconfirmed transactions on the bitcoin network. Jing's node, however, also aggregates these transactions into new blocks.
Jing's node is listening for new blocks, propagated on the bitcoin network, as do all nodes. However, the arrival of a new block has special significance for a mining node. The competition among miners effectively ends with the propagation of a new block which acts as an announcement of a winner. To a miner, receiving a new block means someone else won the competition and they lost. However, the end of one round of a competition is also the beginning of the next round. The new block is not just a checkered flag, marking the end of the race, it is also the starting pistol starting the race for the next block.
==== Bitcoin Economics and Currency Creation
Bitcoins are "minted" during the creation of each block at a fixed and diminishing rate. Each block, generated on average every 10 minutes, contains a _reward_ that consists of entirely new bitcoins. The reward was 50BTC for the first four years of operation of the network. Every four years the reward is decreased by 50%, resulting in a diminishing rate of issuance over time. In 2012, the reward was decreased to 25BTC and it will decrease again to 12.5BTC in 2016. By approximately 2140, the last fragments of a bitcoin will be mined, for a total of 21 million bitcoins. {Clarify coinbase transaction as first - includes the reward and transactions. Discuss how the coinbase transaction will change in 2140}
The finite and diminishing issuance creates a fixed monetary supply that resists inflation. Unlike a fiat currency which can be printed in infinite numbers by a central bank, bitcoin can never be inflated by printing.
===== Monetary supply
Bitcoin's monetary supply is defined as the number of coins in circulation (minted). Like any other currency, this measure of monetary supply is called M0, which represents the narrowest measure of the money supply. Just like any other currency, bitcoin can also have a _fractional reserve banking_ which means that an organization can trade bitcoins "off blockchain" which are not part of the M0 monetary measure, but of the broader monetary supply measures M1-M3. {have you explained M1-M3?}{also, i think you should explain fractional reserve banking a bit here}
While the total bitcoins in circulation will not exceed 21m, that monetary base can support a much broader economy through fractional reserve banking and expansion of the available credit.
===== Deflationary Money
The most important and debated consequence of a fixed and diminishing monetary issuance is that the currency will tend to be inherently _deflationary_. Deflation is the phenomenon of appreciation of value due to a mismatch in supply and demand that drives up the value (and exchange rate) of a currency. The opposite of inflation, price deflation means that your money has more purchasing power over time.
Many economists argue that a deflationary economy is a disaster that should be avoided at all costs. That is because in a period of rapid deflation, the incentives for regular people are to hoard the money and not spend it, hoping that prices will fall. Such a phenomenon unfolded during Japan's "Lost Decade", when a complete collapse of demand pushed the currency into a deflationary spiral.
Bitcoin experts argue that deflation is not bad *per se*. Rather, we associate deflation with a collapse in demand because that is the only example of deflation we have to study. In a fiat currency with the possibility of unlimited printing, it is very difficult to enter a deflationary spiral unless there is a complete collapse in demand and an unwillingness to print money. Deflation in bitcoin is not caused by a collapse in demand, but by predictably constrained supply.
In practice, it has become evident that the hoarding instinct caused by a deflationary currency can be overcome by discounting from vendors, until the discount overcomes the hoarding instinct of the buyer. Since the seller is also motivated to hoard, the discount becomes the equilibrium price at which the two hoarding instincts are matched. With discounts of 30% on the bitcoin price, most bitcoin retailers are not experiencing difficulty overcoming the hoarding instinct and generating revenue. It remains to be seen whether the deflationary aspect of the currency is really a problem when it is not driven by rapid economic retraction.
=== De-centralized Consensus
In the previous chapter we looked at the blockchain, the global public ledger (list) of all transactions, which everyone in the bitcoin network accepts as the authoritative record of ownership.
@ -12,7 +54,7 @@ But how can everyone in the network agree on a single universal "truth" about wh
Satoshi Nakamoto's main invention is the decentralized mechanism for _emergent consensus_. Emergent, because consensus is not achieved explicitly - there is no election or fixed moment when consensus occurs. Instead, consensus is an emergent artifact of the asynchronous interaction of thousands of independent nodes, all following simple rules. All the properties of bitcoin, including currency, transactions, payments and the security model that does not depend central authority or trust derive from this invention.
Bitcoin's consensus emerges from the interplay of four processes that occur independently on nodes across the network:
Bitcoin's de-centralized consensus emerges from the interplay of four processes that occur independently on nodes across the network:
* Independent verification of each transaction, by every full node, based on a comprehensive list of criteria
* Independent aggregation of those transactions into new blocks by mining nodes, coupled with demonstrated computation through a Proof-of-Work algorithm
@ -21,11 +63,11 @@ Bitcoin's consensus emerges from the interplay of four processes that occur inde
In the next few sections we will examine these processes and how they interact to create the emergent property of network-wide consensus that allows any bitcoin node to assemble its own copy of the authoritative, trusted, public, global ledger.
{check transition here - maybe move this above previous paragraph?} Each of these processes also aggregates smaller bitcoin units into larger data structures. First, unspent transaction outputs (UTXO) are aggregated into transactions. Next, many transactions are aggregated into a block. Finally, blocks are added to a chain of blocks, the blockchain. In the previous chapter we looked at transactions as a data structure. In this chapter we will also look at the larger data structures: blocks and the blockchain.
Before we explore the details of emergent consensus, we will first discuss mining and the central role it plays in this process.
=== Independent Verification of Transactions
In the previous chapter {check reference} we saw how wallet software creates transactions by collecting UTXO, providing the appropriate unlocking scripts and then constructing new outputs assigned to a new owner. The resulting transaction is then sent to the neighboring nodes in the bitcoin network so that it may be propagated across the entire bitcoin network.
In the previous chapter we saw how wallet software creates transactions by collecting UTXO, providing the appropriate unlocking scripts and then constructing new outputs assigned to a new owner. The resulting transaction is then sent to the neighboring nodes in the bitcoin network so that it may be propagated across the entire bitcoin network.
However, before forwarding transactions to its neighbors, every bitcoin node that receives a transaction will first verify the transaction. This ensures that only valid transactions are propagated across the network, while invalid transactions are discarded at the first node that encounters them.
@ -54,27 +96,6 @@ These conditions can be seen in detail in the functions +AcceptToMemoryPool+, +C
By independently verifying each transaction as it is received and before propagating it, every node builds a pool of valid new transactions (the transaction pool), roughly in the same order.
[[mining]]
=== Mining
Mining is the process by which new bitcoin is added to the money supply. Mining also serves to secure the bitcoin system against fraudulent transactions or transactions spending the same amount of bitcoin more than once, known as a double-spend. Miners act as a decentralized clearinghouse, validating new transactions and recording them on the global ledger. A new block, containing transactions which occurred since the last block, is "mined" every 10 minutes thereby adding those transactions to the blockchain. Transactions that become part of a block and added to the blockchain are considered "confirmed", which allows the new owners of bitcoin to spend the bitcoin they received in those transactions. Miners receive two types of reward for mining: new coins created with each new block and transaction fees from all the transactions included in the block. To earn this reward, the miners compete to solve a difficult mathematical problem based on a cryptographic hash algorithm. The solution to the problem, called the Proof-of-Work, is included in the new block and acts as proof that the miner expended significant computing effort. The competition to solve the Proof-of-Work algorithm to earn reward and the right to record transactions on the blockchain is the basis for bitcoin's security model.
Bitcoin's security is underpinned by computation. New blocks are added to the blockchain through a consensus mechanism called the _Proof-of-Work_ (PoW) that requires a predictable computational effort, one that takes approximately 10 minutes to solve on average. Specialized bitcoin nodes called _miners_ validate transactions and collect them into blocks, then attempt to find the solution that satisfies the Proof-of-Work algorithm. The first miner to find such a solution, propagates the newly created block across the network. All other nodes on the network verify that the new block contains valid transactions and satisfies the Proof-of-Work algorithm, then they add it to the blockchain, thereby extending it by one block. The miners add a special coin generation transaction into the blocks they build, which creates new bitcoin from nothing and is payable to the miner's own bitcoin address. Once the block is accepted as valid by the entire network, that transaction is also recorded on the blockchain, thereby rewarding the miner for the computational effort it took to satisfy the Proof-of-Work. This de-centralized consensus mechanism, based on a global competition and requiring computation to create new blocks, is the basis for the security of the bitcoin transaction ledger and also for the issuance of new bitcoin. {move the last sentence to the beginning of the paragraph - to explain more about security} The equilibrium between the incentive of bitcoin reward and the immense computing effort required to win it force the participants to behave honestly, without the need for a centralized clearinghouse or currency issuer. The bitcoin consensus mechanism is a dynamic, self-regulating and completely decentralized security model that operates at very large scale.
The process of new coin generation is called mining, because the reward is designed to simulate diminishing returns, just like mining for precious metals. Bitcoin's money supply is created through mining, just like a central bank issues new money by printing bank notes. The amount of newly created bitcoin a miner can add to a block decreases approximately every four years (or precisely every 210,000 blocks). It started at 50 bitcoin per block in January of 2009 and halved to 25 bitcoin per block in November of 2012. It will halve again to 12.5 bitcoin per block sometime in 2016. Based on this formula, bitcoin mining rewards decrease exponentially until approximately the year 2140 when all 21 million bitcoin have been issued.
Bitcoin miners also earn fees from transactions. Every transaction may include a transaction fee, in the form of a surplus of bitcoin between the transaction's inputs and outputs. The bitcoin miner gets to "keep the change" on the transactions.
Today the fees represent 1% or less of a bitcoin miner's income, the vast majority coming from the newly minted bitcoins. However, as the reward decreases over time and the number of transactions per block increases, a greater proportion of bitcoin mining earnings will come from fees. After 2140 all bitcoin miner earnings will be in the form of transaction fees.
=== Mining Nodes
Some of the nodes on the bitcoin network are specialized nodes called _miners_. In Chapter 1 we introduced Jing, a computer engineering student in Shanghai China, who is a bitcoin miner. Jing earns bitcoin by running a "mining rig" which is a specialized computer-hardware system designed to mine bitcoins. Jing's specialized mining hardware is connected to a server running a full bitcoin node. Unlike Jing, some miners mine without a full node as we will see in <<mining pools>>. Like every other full node, Jing's node receives and propagates unconfirmed transactions on the bitcoin network. Jing's node, however, also aggregates these transactions into new blocks.
Jing's node is listening for new blocks, propagated on the bitcoin network, as do all nodes. However, the arrival of a new block has special significance for a mining node. The competition among miners effectively ends with the propagation of a new block which acts as an announcement of a winner. To a miner, receiving a new block means someone else won the competition and they lost. However, the end of one round of a competition is also the beginning of the next round. The new block is not just a checkered flag, marking the end of the race, it is also the starting pistol starting the race for the next block.
The role of a mining node is to act as a gatekeeper to the public ledger. Mining nodes secure the network by validating transactions and controlling access to the blockchain. This places enormous power in mining nodes. To ensure that they follow the rules and behave honestly the bitcoin consensus mechanism imposes incentives by imposing a heavy burden and offering a lavish reward. The burden is the computational effort expended in mining which consumes electricity and therefore has a real-world cost. For those who carry that burden honestly, there is a possibility of reward. Each new block adds new bitcoin to the monetary supply; transactions within a block include transaction fees. The miner that successfully creates a new block collects both the new bitcoin and the transaction fees as a reward. Rewards are not all profit, in fact the miner will spend most of its winnings on electricity. Even successful miners are in a precarious position of marginal profitability, constantly competing under the scrutiny of the entire network. This fragile equilibrium and fierce competition ensures that honesty is the only winning strategy.
=== Aggregating Transactions into Blocks
After validating transactions, a bitcoin node will add them to the _memory pool_, or _transaction pool_, where transactions await until they can be included (mined) into a block. Jing's node collects, validates and relays new transactions just like any other node. Unlike other nodes, however, Jing's node will then aggregate these transactions into a _candidate block_.
@ -87,7 +108,7 @@ During the previous 10 minutes, while Jing's node was searching for a solution t
Jing's node immediately constructs a new empty block, a candidate for block 277,316. This block is called a candidate block because it is not yet a valid block, as it does not contain a valid proof-of-work. The block becomes valid only if the miner succeeds in finding a solution to the proof-of-work algorithm.
=== Transaction Age, Fees and Priority
==== Transaction Age, Fees and Priority
To construct the candidate block Jing's bitcoin node selects transactions from the memory pool, by applying a priority metric to each transaction and adding the highest priority transactions first. Transactions are prioritized based on the "age" of the UTXO that is being spent in their inputs, allowing for old and high-value inputs to be prioritized over newer and smaller inputs. Prioritized transactions can be sent without any fees, if there is enough space in the block.
@ -154,7 +175,7 @@ $ bitcoin-cli getblock 0000000000000001b6b9a13b095e96db41c4a928b97ef2d944a9b31b2
----
====
=== The Generation Transaction
==== The Generation Transaction
The first transaction added to the block is a special transaction, called a _generation transaction_ or _coinbase transaction_. This transaction is constructed by Jing's node and is his reward for the mining effort. Jing's node creates the generation transaction as a payment to his own wallet: "Pay Jing's address 25.09094928 bitcoin". The total amount of reward that Jing collects for mining a block is the sum of the coinbase reward (25 new bitcoins) and the transaction fees (0.09094928) from all the transactions included in the block.
@ -207,7 +228,7 @@ $ bitcoin-cli getrawtransaction d5ada064c6417ca25c4308bd158c34b77e1c0eca2a73cda1
Unlike regular transactions, the generation transaction does not consume (spend) UTXO as inputs. Instead, it has only one input, called the _coinbase_, which creates bitcoin from nothing. The generation transaction has one output, payable to the miner's own bitcoin address. The output of the generation transaction sends the value of 25.09094928 bitcoins to the miner's bitcoin address, in this case +1MxTkeEP2PmHSMze5tUZ1hAV3YTKu2Gh1N+.
=== Coinbase Reward and Fees
==== Coinbase Reward and Fees
To construct the generation transaction, Jing's node first calculates the total amount of transaction fees, by adding all the inputs and outputs of the 418 transactions that were added to the block. The fees are calculated as:
@ -253,7 +274,7 @@ Next, the function uses the binary-right-shift operator to divide the reward (+n
Finally, the coinbase reward (+nSubsidy+) is added to the transaction fees (+nFees+), and the sum is returned.
=== Structure of the Generation Transaction
==== Structure of the Generation Transaction
With these calculations, Jing's node then constructs the generation transaction to pay himself 25.09094928 bitcoin. The generation transaction is the first transaction in the block, so we can see it in more detail using the Bitcoin Core command-line interface:
@ -334,7 +355,9 @@ The final field is the nonce, which is initialized to zero.
With all the other fields filled, the block header is now complete and the process of mining can begin. The goal is now to find a value for the nonce that results in a block header hash that is less than the difficulty target. The mining node will need to test billions or trillions of nonce values before a nonce is found that satisfies the requirement.
=== Proof-of-Work
=== Mining the Block
==== Proof-of-Work Algorithm
With SHA-256, the output is always 256 bits long, regardless of the size of the input. In the example below, we will use the Python interpreter to calculate the SHA256 hash of the phrase "I am Satoshi Nakamoto".
@ -393,8 +416,6 @@ Each phrase produces a completely different hash result. They seem completely ra
To make a challenge out of this algorithm, let's set an arbitrary target: find a phrase starting with "I am Satoshi Nakamoto" which produces a hash that starts with a zero. In numerical terms, that means finding a hash value that is less than +0x1000000000000000000000000000000000000000000000000000000000000000+. Fortunately, this isn't so difficult! If you notice above, we can see that the phrase "I am Satoshi Nakamoto13" produces the hash 0ebc56d59a34f5082aaef3d66b37a661696c2b618e62432727216ba9531041a5, which fits our criteria. It only took 13 attempts to find it.
==== Proof-of-Work Algorithm
Bitcoin's proof-of-work is very similar to the problem above. First, a miner will generate a new block, containing:
((("block")))
* Transactions waiting to be included in a block
@ -517,27 +538,7 @@ Note that the target difficulty is independent of the number of transactions or
The target difficulty is closely related to the cost of electricity and the exchange rate of bitcoin vis-a-vis the currency used to pay for electricity. High performance mining systems are about as efficient as possible with the current generation of silicon fabrication, converting electricity into hashing computation at the highest rate possible. The primary influence on the mining market is the price of one kilowatt-hour in bitcoin, as that determines the profitability of mining and therefore the incentives to enter or exit the mining market.
==== Mining New Bitcoins
Bitcoins are "minted" during the creation of each block at a fixed and diminishing rate. Each block, generated on average every 10 minutes, contains a _reward_ that consists of entirely new bitcoins. The reward was 50BTC for the first four years of operation of the network. Every four years the reward is decreased by 50%, resulting in a diminishing rate of issuance over time. In 2012, the reward was decreased to 25BTC and it will decrease again to 12.5BTC in 2016. By approximately 2140, the last fragments of a bitcoin will be mined, for a total of 21 million bitcoins. {Clarify coinbase transaction as first - includes the reward and transactions. Discuss how the coinbase transaction will change in 2140}
The finite and diminishing issuance creates a fixed monetary supply that resists inflation. Unlike a fiat currency which can be printed in infinite numbers by a central bank, bitcoin can never be inflated by printing.
===== Monetary supply
Bitcoin's monetary supply is defined as the number of coins in circulation (minted). Like any other currency, this measure of monetary supply is called M0, which represents the narrowest measure of the money supply. Just like any other currency, bitcoin can also have a _fractional reserve banking_ which means that an organization can trade bitcoins "off blockchain" which are not part of the M0 monetary measure, but of the broader monetary supply measures M1-M3. {have you explained M1-M3?}{also, i think you should explain fractional reserve banking a bit here}
While the total bitcoins in circulation will not exceed 21m, that monetary base can support a much broader economy through fractional reserve banking and expansion of the available credit.
===== Deflationary Money
The most important and debated consequence of a fixed and diminishing monetary issuance is that the currency will tend to be inherently _deflationary_. Deflation is the phenomenon of appreciation of value due to a mismatch in supply and demand that drives up the value (and exchange rate) of a currency. The opposite of inflation, price deflation means that your money has more purchasing power over time.
Many economists argue that a deflationary economy is a disaster that should be avoided at all costs. That is because in a period of rapid deflation, the incentives for regular people are to hoard the money and not spend it, hoping that prices will fall. Such a phenomenon unfolded during Japan's "Lost Decade", when a complete collapse of demand pushed the currency into a deflationary spiral.
Bitcoin experts argue that deflation is not bad *per se*. Rather, we associate deflation with a collapse in demand because that is the only example of deflation we have to study. In a fiat currency with the possibility of unlimited printing, it is very difficult to enter a deflationary spiral unless there is a complete collapse in demand and an unwillingness to print money. Deflation in bitcoin is not caused by a collapse in demand, but by predictably constrained supply.
In practice, it has become evident that the hoarding instinct caused by a deflationary currency can be overcome by discounting from vendors, until the discount overcomes the hoarding instinct of the buyer. Since the seller is also motivated to hoard, the discount becomes the equilibrium price at which the two hoarding instincts are matched. With discounts of 30% on the bitcoin price, most bitcoin retailers are not experiencing difficulty overcoming the hoarding instinct and generating revenue. It remains to be seen whether the deflationary aspect of the currency is really a problem when it is not driven by rapid economic retraction.
=== Selecting the Highest-Difficulty Chain
[[forks]]
==== Blockchain Forks
@ -600,17 +601,9 @@ As of version 0.9, Bitcoin Core's +alertnotify+ option will send alerts whenever
image::images/BlockChainWithForks.png["chainforks"]
==== Competition and Coinbase
==== Mining Pools
Jing started mining for bitcoin in 2010, when mining was not as competitive as it is today. At that time, Jing could mine bitcoin using a desktop computer. Today, he uses a much more powerful mining system based on Application Specific Integrated Circuits (ASICs), which are specialized silicon chips designed exclusively for one application - bitcoin mining. Over time, the way Jing participates in the mining process has changed slightly, but the fundamentals remain the same. We will start by looking at how Jing mined in 2010, when things were simpler and then look at how he mines today, as bitcoin mining has become a more complex and competitive activity.
In 2010, Jing mined on a desktop computer. At the time, he would run a full bitcoin node, connected to the bitcoin network.
===== Managed Pools
===== P2Pool
==== Mining Economics
==== Consensus Attacks
===== 51% Attack
===== Selfish Mining Attack
=== Mining Pools
==== Managed Pools
==== P2Pool
=== Consensus Attacks
==== 51% Attack
==== Selfish Mining Attack