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# Mastering Bitcoin
Mastering Bitcoin is a book for developers, but the first two chapters cover bitcoin at a level that is approachable to non-programmers. Anyone with a basic understanding of technology can read the first two chapters and get a great understanding of bitcoin.
# Contributing
To contribute to this book, please fork and make changes to your forked copy, then submit a pull request. Or alternatively, if you cannot use the github.com pull request system, submit an Issue from the menu on the right. Major contributions will receive an acknowledgment in the preface of the book.
# Purchasing
"Mastering Bitcoin" will be available in print and e-book format in Fall 2014. To pre-order your copy, please visit:
http://bitcoinbook.info

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@ -17,7 +17,7 @@ Behind the scenes, bitcoin is also the name of the protocol, a network and a dis
In this chapter we'll get started by explaining some of the main concepts and terms, getting the necessary software and using bitcoin for simple transactions. In following chapters we'll start unwrapping the layers of technology that make bitcoin possible and examine the inner workings of the bitcoin network and protocol. In this chapter we'll get started by explaining some of the main concepts and terms, getting the necessary software and using bitcoin for simple transactions. In following chapters we'll start unwrapping the layers of technology that make bitcoin possible and examine the inner workings of the bitcoin network and protocol.
=== History of Bitcoin === Before Bitcoin
The emergence of viable digital money is closely linked to developments in cryptography. This is not surprising when one considers the fundamental challenges involved with using bits to represent value that can be exchanged for goods and services. Two fundamental questions for anyone accepting digital money are: The emergence of viable digital money is closely linked to developments in cryptography. This is not surprising when one considers the fundamental challenges involved with using bits to represent value that can be exchanged for goods and services. Two fundamental questions for anyone accepting digital money are:
@ -37,6 +37,8 @@ Bitcoin represents the culmination of decades of research in cryptography and di
* A de-centralized mathematical and deterministic currency issuance (distributed mining), and; * A de-centralized mathematical and deterministic currency issuance (distributed mining), and;
* A de-centralized transaction verification system (transaction script). * A de-centralized transaction verification system (transaction script).
=== History of Bitcoin
Bitcoin was invented in 2008 by Satoshi Nakamoto with the publication of a paper titled "Bitcoin: A Peer-to-Peer Electronic Cash System". Satoshi Nakamoto combined several prior inventions such as b-money and HashCash to create a completely de-centralized electronic cash system that does not rely on a central authority for currency issuance or settlement and validation of transactions. The key innovation was to use a Proof-Of-Work algorithm to conduct a global "election" every 10 minutes, allowing the de-centralized network to arrive at _consensus_ about the state of transactions. This elegantly solves the issue of double-spend where a single currency unit can be spent twice. Previously, the double-spend problem was a weakness of digital currency and was addressed by clearing all transactions through a central clearinghouse. Bitcoin was invented in 2008 by Satoshi Nakamoto with the publication of a paper titled "Bitcoin: A Peer-to-Peer Electronic Cash System". Satoshi Nakamoto combined several prior inventions such as b-money and HashCash to create a completely de-centralized electronic cash system that does not rely on a central authority for currency issuance or settlement and validation of transactions. The key innovation was to use a Proof-Of-Work algorithm to conduct a global "election" every 10 minutes, allowing the de-centralized network to arrive at _consensus_ about the state of transactions. This elegantly solves the issue of double-spend where a single currency unit can be spent twice. Previously, the double-spend problem was a weakness of digital currency and was addressed by clearing all transactions through a central clearinghouse.
The bitcoin network started in 2009, based on a reference implementation published by Nakamoto and since revised by many other programmers. During the first four years of operation, the network has grown to include an enormous amount of Proof-Of-Work computation, thereby increasing its security and resilience. In 2013, the total market value of bitcoin's primary monetary supply measure (M0) is estimated at more than 10 billion US dollars. The largest transaction processed by the network was $150 million US dollars, transmitted instantly and processed without any fees. The bitcoin network started in 2009, based on a reference implementation published by Nakamoto and since revised by many other programmers. During the first four years of operation, the network has grown to include an enormous amount of Proof-Of-Work computation, thereby increasing its security and resilience. In 2013, the total market value of bitcoin's primary monetary supply measure (M0) is estimated at more than 10 billion US dollars. The largest transaction processed by the network was $150 million US dollars, transmitted instantly and processed without any fees.
@ -132,10 +134,10 @@ Alice is now ready to start using her new bitcoin web-wallet.
[[getting_first_bitcoin]] [[getting_first_bitcoin]]
==== Getting your first bitcoins ==== Getting your first bitcoins
It is not possible to buy bitcoins at a bank or foreign exchange kiosks at this time. It is not possible to use a credit card to buy bitcoins, either. As of 2014, it is still quite difficult to acquire bitcoins in most countries. There are a number of specialized currency exchanges where you can buy and sell bitcoin in exchange for a local currency. These operate as web-based currency markets and include: It is not possible to buy bitcoins at a bank or foreign exchange kiosks at this time. As of 2014, it is still quite difficult to acquire bitcoins in most countries. There are a number of specialized currency exchanges where you can buy and sell bitcoin in exchange for a local currency. These operate as web-based currency markets and include:
* Bitstamp (bitstamp.net), a European currency market that supports several currencies including euros (EUR) and US dollars (USD) via wire transfer * Bitstamp (bitstamp.net), a European currency market that supports several currencies including euros (EUR) and US dollars (USD) via wire transfer
* Coinbase (coinbase.com), a US-based currency market in California that supports US dollar exchange to and from bitcoin. Coinbase can connect to US checking accounts via the ACH system. * Coinbase (coinbase.com), a US-based bitcoin wallet and platform where merchants and consumers can transact in bitcoin. Coinbase makes it easy to buy and sell bitcoin, allowing users to connect to US checking accounts via the ACH system.
Crypto-currency exchanges such as these operate at the intersection of national currencies and crypto-currencies. As such, they are subject to national and international regulations and are often specific to a single country or economic area and specialize in the national currencies of that area. Your choice of currency exchange will be specific to the national currency you use and limited to the exchanges that operate within the legal jurisdiction of your country. Similar to opening a bank account, it takes several days or weeks to set up the necessary accounts with the above services because they require various forms of identification to comply with KYC (Know Your Customer) and AML (Anti-Money Laundering) banking regulations. Once you have an account on a bitcoin exchange, you can then buy or sell bitcoins quickly just as you could with foreign currency with a brokerage account. Crypto-currency exchanges such as these operate at the intersection of national currencies and crypto-currencies. As such, they are subject to national and international regulations and are often specific to a single country or economic area and specialize in the national currencies of that area. Your choice of currency exchange will be specific to the national currency you use and limited to the exchanges that operate within the legal jurisdiction of your country. Similar to opening a bank account, it takes several days or weeks to set up the necessary accounts with the above services because they require various forms of identification to comply with KYC (Know Your Customer) and AML (Anti-Money Laundering) banking regulations. Once you have an account on a bitcoin exchange, you can then buy or sell bitcoins quickly just as you could with foreign currency with a brokerage account.
@ -146,6 +148,7 @@ There are three other methods for getting bitcoins as a new user:
* Find a friend who has bitcoins and buy some from them directly. Many bitcoin users started this way. * Find a friend who has bitcoins and buy some from them directly. Many bitcoin users started this way.
* Use a classified service like localbitcoins.com to find a seller in your area to buy bitcoins for cash in an in-person transaction. * Use a classified service like localbitcoins.com to find a seller in your area to buy bitcoins for cash in an in-person transaction.
* Sell a product or service for bitcoin. If you're a programmer, sell your programming skills. If you have an online store, see <<bitcoin-commerce>> to sell in bitcoin. * Sell a product or service for bitcoin. If you're a programmer, sell your programming skills. If you have an online store, see <<bitcoin-commerce>> to sell in bitcoin.
* Use a bitcoin ATM in your city. A map of bitcoin ATMs can be found at http://www.coindesk.com/bitcoin-atm-map/
Alice was introduced to bitcoin by a friend and so she has an easy way of getting her first bitcoin while she waits for her account on a California currency market to be verified and activated. Alice was introduced to bitcoin by a friend and so she has an easy way of getting her first bitcoin while she waits for her account on a California currency market to be verified and activated.
@ -160,6 +163,7 @@ First, Joe has to figure out the exchange rate so that he can give the correct a
* bitcoincharts.com, a market data listing service that shows the market rate of bitcoin across many exchanges around the globe, denominated in different local currencies * bitcoincharts.com, a market data listing service that shows the market rate of bitcoin across many exchanges around the globe, denominated in different local currencies
* bitcoinaverage.com, a site that provides a simple view of the volume-weighted-average for each currency * bitcoinaverage.com, a site that provides a simple view of the volume-weighted-average for each currency
* ZeroBlock, a free Android and iOS application that can display a bitcoin price from different exchanges * ZeroBlock, a free Android and iOS application that can display a bitcoin price from different exchanges
* bitcoinwisdom.com, another market data listing service
[[zeroblock-android]] [[zeroblock-android]]
.ZeroBlock - A bitcoin market-rate application for Android and iOS .ZeroBlock - A bitcoin market-rate application for Android and iOS
@ -184,7 +188,7 @@ If Alice has a smartphone or laptop with her, she will also be able to see the t
.Confirmations .Confirmations
**** ****
At first, Alice's address will show the transaction from Joe as "Unconfirmed". This means that the transaction has been propagated to the network but has not yet been included in the bitcoin transaction ledger, known as the blockchain. To be included, the transaction must be "picked up" by a miner and included in a block of transactions. Once a miner has discovered a solution to the Proof-of-Work algorithm for this block (in approximately 10 minutes), the transactions within the block will be accepted as "confirmed" by the network and can be spent. The transaction is seen by all instantly, but it is only "trusted" by all when it is included in a newly mined block. The more blocks mined after that block, the more trusted it is, as more and more computation is "piled" on top of it. At first, Alice's address will show the transaction from Joe as "Unconfirmed". This means that the transaction has been propagated to the network but has not yet been included in the bitcoin transaction ledger, known as the blockchain. To be included, the transaction must be "picked up" by a miner and included in a block of transactions. Once a miner has discovered a solution to the Proof-of-Work algorithm for this block (in approximately 10 minutes), the transactions within the block will be accepted as "confirmed" by the network and can be spent. The transaction is seen by all instantly, but it is only "trusted" by all when it is included in a newly mined block. As more blocks are mined after that block, the lower the risk that block can be removed or modified because the additional blocks must be removed first requiring additional computational power.
**** ****
Alice is now the proud owner of 0.10 bitcoin which she can spend. In the next chapter we will look at her first purchase with bitcoin and examine the underlying transaction and propagation technologies in more detail. Alice is now the proud owner of 0.10 bitcoin which she can spend. In the next chapter we will look at her first purchase with bitcoin and examine the underlying transaction and propagation technologies in more detail.

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[[ch02_bitcoin_overview]] [[ch02_bitcoin_overview]]
== How Bitcoin Works == How Bitcoin Works
=== Transactions, Blocks, Mining and the Blockchain === Transactions, Blocks, Mining, and the Blockchain
The bitcoin system, unlike traditional banking and payment systems, is based on de-centralized trust. Instead of a central trusted authority, in bitcoin, trust is achieved as an emergent property from the interactions of different participants in the bitcoin system. In this chapter we will examine bitcoin from a high-level by tracking a single transaction through the bitcoin system and watch as it becomes "trusted" and accepted by the bitcoin mechanism of distributed consensus and is finally recorded on the blockchain, the distributed ledger of all transactions. The bitcoin system, unlike traditional banking and payment systems, is based on de-centralized trust. Instead of a central trusted authority, in bitcoin, trust is achieved as an emergent property from the interactions of different participants in the bitcoin system. In this chapter we will examine bitcoin from a high-level by tracking a single transaction through the bitcoin system and watch as it becomes "trusted" and accepted by the bitcoin mechanism of distributed consensus and is finally recorded on the blockchain, the distributed ledger of all transactions.
@ -222,7 +222,7 @@ Jing started mining in 2010 using a very fast desktop computer to find a suitabl
=== Mining transactions in blocks === Mining transactions in blocks
A transaction transmitted across the network is not verified until it becomes part of the global distributed ledger, the blockchain. Every ten minutes, miners generate a new block that contains all the transactions since the last block. New transactions are constantly flowing into the network from user wallets and other applications. As these are seen by the bitcoin network nodes, they get added to a temporary "pool" of unverified transactions maintained by each node. As miners build a new block, they add unverified transactions from this pool to a new block and then attempt to solve a very hard problem (aka Proof-of-Work) to prove the validity of that new block. The process of mining is explained in detail in <<mining>>. A transaction transmitted across the network is not verified until it becomes part of the global distributed ledger, the blockchain. Every ten minutes on average, miners generate a new block that contains all the transactions since the last block. New transactions are constantly flowing into the network from user wallets and other applications. As these are seen by the bitcoin network nodes, they get added to a temporary "pool" of unverified transactions maintained by each node. As miners build a new block, they add unverified transactions from this pool to a new block and then attempt to solve a very hard problem (aka Proof-of-Work) to prove the validity of that new block. The process of mining is explained in detail in <<mining>>.
Transactions are added to the new block, prioritized by the highest-fee transactions first and a few other criteria. Each miner starts the process of mining a new block of transactions as soon as they receive the previous block from the network, knowing they have lost that previous round of competition. They immediately create a new block, fill it with transactions and the fingerprint of the previous block and start calculating the Proof-of-Work for the new block. Each miner includes a special transaction in their block, one that pays their own bitcoin address a reward of newly created bitcoins (currently 25 BTC per block). If they find a solution that makes that block valid, they "win" this reward because their successful block is added to the global blockchain and the reward transaction they included becomes spendable. Jing, who participates in a mining pool, has set up his software to create new blocks that assign the reward to a pool address. From there, a share of the reward is distributed to Jing and other miners in proportion to the amount of work they contributed in the last round. Transactions are added to the new block, prioritized by the highest-fee transactions first and a few other criteria. Each miner starts the process of mining a new block of transactions as soon as they receive the previous block from the network, knowing they have lost that previous round of competition. They immediately create a new block, fill it with transactions and the fingerprint of the previous block and start calculating the Proof-of-Work for the new block. Each miner includes a special transaction in their block, one that pays their own bitcoin address a reward of newly created bitcoins (currently 25 BTC per block). If they find a solution that makes that block valid, they "win" this reward because their successful block is added to the global blockchain and the reward transaction they included becomes spendable. Jing, who participates in a mining pool, has set up his software to create new blocks that assign the reward to a pool address. From there, a share of the reward is distributed to Jing and other miners in proportion to the amount of work they contributed in the last round.
@ -241,7 +241,7 @@ image::images/Blockchain_height_and_depth.png["Alice's transaction included in a
=== Spending the transaction === Spending the transaction
Now that Alice's transaction has been embedded in the blockchain as part of a block, it is part of the distributed ledger of bitcoin and visible to all bitcoin applications. Each bitcoin client can independently verify the transaction as valid and spendable. Full-index clients can track the source of the funds from the moment the bitcoins were first generated in a block, incrementally from transaction to transaction, until they reach Bob's address. Lightweight clients can do a Simple Payment Verification (See SPV:<<spv>>) by confirming that the transaction is in the blockchain and has several blocks mined after it, thus providing assurance that the network accepts it as valid. Now that Alice's transaction has been embedded in the blockchain as part of a block, it is part of the distributed ledger of bitcoin and visible to all bitcoin applications. Each bitcoin client can independently verify the transaction as valid and spendable. Full-index clients can track the source of the funds from the moment the bitcoins were first generated in a block, incrementally from transaction to transaction, until they reach Bob's address. Lightweight clients can do a Simplified Payment Verification (See SPV:<<spv>>) by confirming that the transaction is in the blockchain and has several blocks mined after it, thus providing assurance that the network accepts it as valid.
Bob can now spend the output from this and other transactions, by creating his own transactions that reference these outputs as their inputs and assign them new ownership. For example, Bob can pay a contractor or supplier by transferring value from Alice's coffee cup payment to these new owners. Most likely, Bob's bitcoin software will aggregate many small payments into a larger payment, perhaps concentrating all the day's bitcoin revenue into a single transaction. This would move the various payments into a single address, utilized as the store's general "checking" account. For a diagram of an aggregating transaction, see <<transaction-aggregating>>. Bob can now spend the output from this and other transactions, by creating his own transactions that reference these outputs as their inputs and assign them new ownership. For example, Bob can pay a contractor or supplier by transferring value from Alice's coffee cup payment to these new owners. Most likely, Bob's bitcoin software will aggregate many small payments into a larger payment, perhaps concentrating all the day's bitcoin revenue into a single transaction. This would move the various payments into a single address, utilized as the store's general "checking" account. For a diagram of an aggregating transaction, see <<transaction-aggregating>>.

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Ownership of bitcoin is established through _digital keys_, _bitcoin addresses_ and _digital signatures_. The digital keys are not actually stored in the network, but are instead created and stored by end-users in a file, or simple database, called a _wallet_. The digital keys in a user's wallet are completely independent of the bitcoin protocol and can be generated and managed by the user's wallet software without reference to the blockchain or access to the Internet. Keys enable many of the interesting properties of bitcoin, including de-centralized trust and control, ownership attestation and the cryptographic-proof security model. Ownership of bitcoin is established through _digital keys_, _bitcoin addresses_ and _digital signatures_. The digital keys are not actually stored in the network, but are instead created and stored by end-users in a file, or simple database, called a _wallet_. The digital keys in a user's wallet are completely independent of the bitcoin protocol and can be generated and managed by the user's wallet software without reference to the blockchain or access to the Internet. Keys enable many of the interesting properties of bitcoin, including de-centralized trust and control, ownership attestation and the cryptographic-proof security model.
The digital keys within each user's wallet allow the user to sign transactions, thereby providing cryptographic proof of the ownership of the bitcoins sourced by the transaction. Keys come in pairs consisting of a private (secret) and public key. Think of the public key as similar to a bank account number and the private key as similar to the secret PIN number, or signature on a cheque that provides control over the account. These digital keys are very rarely seen by the users of bitcoin. For the most part, they are stored inside the wallet file and managed by the bitcoin wallet software. Every bitcoin transaction requires a valid signature to be included in the blockchain, which can only be generated with valid digital keys, therefore anyone with a copy of those keys has control of the bitcoin in that account. Keys come in pairs consisting of a private (secret) and public key. Think of the public key as similar to a bank account number and the private key as similar to the secret PIN number, or signature on a cheque that provides control over the account. These digital keys are very rarely seen by the users of bitcoin. For the most part, they are stored inside the wallet file and managed by the bitcoin wallet software.
In the payment portion of a bitcoin transaction, the recipient's public key is represented by its digital fingerprint, called a _bitcoin address_, which is used in the same way as the beneficiary name on a cheque (i.e. "Pay to the order of"). In most cases, a bitcoin address is generated from and corresponds to a public key. However, not all bitcoin addresses represent public keys; they can also represent other beneficiaries such as scripts, as we will see later in this chapter. This way, bitcoin addresses abstract the recipient of funds, making transaction destinations flexible, similar to paper cheques: a single payment instrument that can be used to pay into people's accounts, company accounts, pay for bills or pay to cash. The bitcoin address is the only representation of the keys that users will routinely see, as this is the part they need to share with the world. In the payment portion of a bitcoin transaction, the recipient's public key is represented by its digital fingerprint, called a _bitcoin address_, which is used in the same way as the beneficiary name on a cheque (i.e. "Pay to the order of"). In most cases, a bitcoin address is generated from and corresponds to a public key. However, not all bitcoin addresses represent public keys; they can also represent other beneficiaries such as scripts, as we will see later in this chapter. This way, bitcoin addresses abstract the recipient of funds, making transaction destinations flexible, similar to paper cheques: a single payment instrument that can be used to pay into people's accounts, company accounts, pay for bills or pay to cash. The bitcoin address is the only representation of the keys that users will routinely see, as this is the part they need to share with the world.
@ -20,13 +20,13 @@ Wikipedia has a good article that explains the details of how arithmetic operati
Glossing over details, here are the fundamental facts: Glossing over details, here are the fundamental facts:
An elliptic curve field is a set of points (x, y) each of which that satisfies the equation An elliptic curve field is a set of points (x, y) each of which satisfies the equation
y^2^ = x^3^ + ax + b (mod P) y^2^ = x^3^ + ax + b (mod P)
for some constants a, b and P (where P is prime). Bitcoin uses a standard curve known as secp256, where a=0, b=7, and P = 2^256^ - 2^32^ - 2^9^ - 2^8^ - 2^7^ - 2^6^ - 2^4^ - 1. for some constants a, b and P (where P is prime). Bitcoin uses a curve known as secp256k1, where a=0, b=7, and P = 2^256^ - 2^32^ - 2^9^ - 2^8^ - 2^7^ - 2^6^ - 2^4^ - 1.
So for example, (55066263022277343669578718895168534326250603453777594175500187360389116729240, 32670510020758816978083085130507043184471273380659243275938904335757337482424) is a point on the secp256 curve. You can check this yourself using Python. So for example, (55066263022277343669578718895168534326250603453777594175500187360389116729240, 32670510020758816978083085130507043184471273380659243275938904335757337482424) is a point on the secp256k1 curve. You can check this yourself using Python.
---- ----
Python 3.4.0 (default, Mar 30 2014, 19:23:13) Python 3.4.0 (default, Mar 30 2014, 19:23:13)

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[[ch5_intro]] [[ch5_intro]]
=== Introduction === Introduction
Transactions are the most important part of the bitcoin system. Everything else in bitcoin is designed to ensure that transactions can be created, propagated on the network, validated, and finally added to the global ledger of transactions, the blockchain. Transactions are data structures that encode the transfer of value between participants in the bitcoin system. Each transaction is an public entry in bitcoin's global double-entry bookkeeping ledger, the blockchain. Transactions are the most important part of the bitcoin system. Everything else in bitcoin is designed to ensure that transactions can be created, propagated on the network, validated, and finally added to the global ledger of transactions, the blockchain. Transactions are data structures that encode the transfer of value between participants in the bitcoin system. Each transaction is a public entry in bitcoin's global double-entry bookkeeping ledger, the blockchain.
In this chapter we will examine all the various forms of transactions, what do they contain, how to create them, how they are verified, and how they become part of the permanent record of all transactions. In this chapter we will examine all the various forms of transactions, what they contain, how to create them, how they are verified, and how they become part of the permanent record of all transactions.
[[tx_lifecycle]] [[tx_lifecycle]]
=== Transaction Lifecycle === Transaction Lifecycle
@ -70,7 +70,7 @@ The fundamental building block of a bitcoin transaction is an _unspent transacti
There are no accounts or balances in bitcoin, there are only _unspent transaction outputs_ (UTXO) scattered in the blockchain. There are no accounts or balances in bitcoin, there are only _unspent transaction outputs_ (UTXO) scattered in the blockchain.
==== ====
Unlike cash, which exists in specific denominations (one dollar, five dollars, ten dollars), a UTXO can have any arbitrary value denominated as a multiple of satoshis (the smallest bitcoin unit equal to 100 millionth of a bitcoin). While UTXO can be any arbitrary value, once created it is indivisible just like a coin that cannot be cut in half. If a UTXO is larger than the desired value of a transaction, it must still be consumed in its entirety and change must be generated in the transaction. In other words, if you have a 20 bitcoin UTXO and want to pay 1 bitcoin, your transaction must consume the entire 20 bitcoin UTXO and produce two outputs: one paying 1 bitcoin to your desired recipient and another paying 19 bitcoin in change back to your wallet. As a result, most bitcoin transactions will generate change. A UTXO can have an arbitrary value denominated as a multiple of satoshis. Just like dollars can be divided down to two decimal places as cents, bitcoins can be divided down to eight decimal places as satoshis. While UTXO can be any arbitrary value, once created it is indivisible just like a coin that cannot be cut in half. If a UTXO is larger than the desired value of a transaction, it must still be consumed in its entirety and change must be generated in the transaction. In other words, if you have a 20 bitcoin UTXO and want to pay 1 bitcoin, your transaction must consume the entire 20 bitcoin UTXO and produce two outputs: one paying 1 bitcoin to your desired recipient and another paying 19 bitcoin in change back to your wallet. As a result, most bitcoin transactions will generate change.
In simple terms, transactions consume the sender's available UTXO and create new UTXO locked to the recipient's bitcoin address. Imagine a shopper buying a $1.50 beverage, reaching into their wallet and trying to find a combination of coins and bank notes to cover the $1.50 cost. The shopper will choose exact change if available (a dollar bill and two quarters), or a combination of smaller denominations (six quarters), or if necessary, a larger unit such as a five dollar bank note. If they hand too much money, say $5, to the shop owner they will expect $3.50 change, which they will return to their wallet and have available for future transactions. Similarly, a bitcoin transaction must be created from a user's UTXO in whatever denominations that user has available. They cannot cut a UTXO in half any more than they can cut a dollar bill in half and use it as currency. The user's wallet application will typically select from the user's available UTXO various units to compose an amount greater than or equal to the desired transaction amount. As with real life, the bitcoin application can use several strategies to satisfy the purchase amount: combining several smaller units, finding exact change, or using a single unit larger than the transaction value and making change. In simple terms, transactions consume the sender's available UTXO and create new UTXO locked to the recipient's bitcoin address. Imagine a shopper buying a $1.50 beverage, reaching into their wallet and trying to find a combination of coins and bank notes to cover the $1.50 cost. The shopper will choose exact change if available (a dollar bill and two quarters), or a combination of smaller denominations (six quarters), or if necessary, a larger unit such as a five dollar bank note. If they hand too much money, say $5, to the shop owner they will expect $3.50 change, which they will return to their wallet and have available for future transactions. Similarly, a bitcoin transaction must be created from a user's UTXO in whatever denominations that user has available. They cannot cut a UTXO in half any more than they can cut a dollar bill in half and use it as currency. The user's wallet application will typically select from the user's available UTXO various units to compose an amount greater than or equal to the desired transaction amount. As with real life, the bitcoin application can use several strategies to satisfy the purchase amount: combining several smaller units, finding exact change, or using a single unit larger than the transaction value and making change.
@ -103,7 +103,7 @@ The transaction scripting language, used in the locking script mentioned above,
[options="header"] [options="header"]
|======= |=======
|Size| Field | Description |Size| Field | Description
| 8 bytes | Amount | Bitcoin Value in Satoshis (10^^-8 bitcoin) | 8 bytes | Amount | Bitcoin Value in Satoshis (10^-8^ bitcoin)
| 1-9 bytes (VarInt) | Locking-Script Size | Locking-Script length in bytes, to follow | 1-9 bytes (VarInt) | Locking-Script Size | Locking-Script length in bytes, to follow
| Variable | Locking-Script | A script defining the conditions needed to spend the output | Variable | Locking-Script | A script defining the conditions needed to spend the output
|======= |=======
@ -335,7 +335,7 @@ The combined script, which is validated by the transaction validation software i
The script above is a simple invocation of the CHECKSIG operator which validates the signature as belonging to the correct key and returns TRUE on the stack. The script above is a simple invocation of the CHECKSIG operator which validates the signature as belonging to the correct key and returns TRUE on the stack.
[[multisig]] [[multisig]]
==== Mutli-Signature ==== Multi-Signature
Multi-signature scripts set a condition where N public keys are recorded in the script and at least M of those must provide signatures to release the encumbrance. This is also known as an M-of-N scheme, where N is the total number of keys and M is the threshold of signatures required for validation. For example, a 2-of-3 multi-signature is one where 3 public keys are listed as potential signers and at least 2 of those must be used to create signatures for a valid transaction to spend the funds. At this time, standard multi-signature scripts are limited to at most 15 listed public keys, meaning you can do anything from a 1-of-1 to a 15-of-15 multi-signature or any combination within that range. The limitation to 15 listed keys may be lifted by the time of publication of this book, so check the +isStandard()+ function to see what is currently accepted by the network. Multi-signature scripts set a condition where N public keys are recorded in the script and at least M of those must provide signatures to release the encumbrance. This is also known as an M-of-N scheme, where N is the total number of keys and M is the threshold of signatures required for validation. For example, a 2-of-3 multi-signature is one where 3 public keys are listed as potential signers and at least 2 of those must be used to create signatures for a valid transaction to spend the funds. At this time, standard multi-signature scripts are limited to at most 15 listed public keys, meaning you can do anything from a 1-of-1 to a 15-of-15 multi-signature or any combination within that range. The limitation to 15 listed keys may be lifted by the time of publication of this book, so check the +isStandard()+ function to see what is currently accepted by the network.

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@ -21,7 +21,7 @@ image::images/FullNodeReferenceClient_Small.png["FullNodeReferenceClient_Small"]
All nodes include the routing function to participate in the network and may include other functionality. All nodes validate and propagate transactions and blocks, and discover and maintain connections to peers. In the full node example above, the routing function is indicated by an orange circle named "Network Routing Node". All nodes include the routing function to participate in the network and may include other functionality. All nodes validate and propagate transactions and blocks, and discover and maintain connections to peers. In the full node example above, the routing function is indicated by an orange circle named "Network Routing Node".
Some nodes, called full nodes, also maintain a complete and up-to-date copy of the blockchain. Full nodes can autonomously and authoritatively verify any transaction without external reference. Some nodes maintain only a subset of the blockchain and verify transactions using a method called _Simple Payment Verification_ or SPV. These nodes are known as SPV or Lightweight nodes. In the full node example above, the full node blockchain database function is indicated by a blue circle named "Full Blockchain". SPV nodes are drawn without the blue circle, showing that they do not have a full copy of the blockchain. Some nodes, called full nodes, also maintain a complete and up-to-date copy of the blockchain. Full nodes can autonomously and authoritatively verify any transaction without external reference. Some nodes maintain only a subset of the blockchain and verify transactions using a method called _Simplified Payment Verification_ or SPV. These nodes are known as SPV or Lightweight nodes. In the full node example above, the full node blockchain database function is indicated by a blue circle named "Full Blockchain". SPV nodes are drawn without the blue circle, showing that they do not have a full copy of the blockchain.
Mining nodes compete to create new blocks by running specialized hardware to solve the proof-of-work algorithm. Some mining nodes are also full nodes, maintaining a full copy of the blockchain while others are lightweight nodes participating in pool mining and depending on a pool server to maintain a full node. The mining function is shown in the full node above as a black circle named "Miner". Mining nodes compete to create new blocks by running specialized hardware to solve the proof-of-work algorithm. Some mining nodes are also full nodes, maintaining a full copy of the blockchain while others are lightweight nodes participating in pool mining and depending on a pool server to maintain a full node. The mining function is shown in the full node above as a black circle named "Miner".
@ -129,7 +129,7 @@ Full nodes are nodes that maintain a full blockchain with all transactions. More
Full blockchain nodes maintain a complete and up-to-date copy of the bitcoin blockchain with all the transactions, which they independently build and verify, starting with the very first block (genesis block) and building up to the latest known block in the network. A full blockchain node can independently and authoritatively verify any transaction without recourse or reliance on any other node or source of information. The full blockchain node relies on the network to receive updates about new blocks of transactions, which it then verifies and incorporates into its local copy of the blockchain. Full blockchain nodes maintain a complete and up-to-date copy of the bitcoin blockchain with all the transactions, which they independently build and verify, starting with the very first block (genesis block) and building up to the latest known block in the network. A full blockchain node can independently and authoritatively verify any transaction without recourse or reliance on any other node or source of information. The full blockchain node relies on the network to receive updates about new blocks of transactions, which it then verifies and incorporates into its local copy of the blockchain.
Running a full blockchain node gives you the pure bitcoin experience: independent verification of all transactions without the need to rely on, or trust, any other systems. It's easy to tell if you're running a full node because it requires several gigabytes of persistent storage (disk space) to store the full blockchain. If you need a lot of disk and it takes 2-3 days to "sync" to the network, you are running a full node. That is the price of complete independence and freedom from central authority. Running a full blockchain node gives you the pure bitcoin experience: independent verification of all transactions without the need to rely on, or trust, any other systems. It's easy to tell if you're running a full node because it requires 20 plus gigabytes of persistent storage (disk space) to store the full blockchain. If you need a lot of disk and it takes 2-3 days to "sync" to the network, you are running a full node. That is the price of complete independence and freedom from central authority.
There are a few alternative implementations of full-blockchain bitcoin clients, built using different programming languages and software architectures. However, the most common implementation is the reference client Bitcoin Core, also known as the Satoshi Client. More than 90% of the nodes on the bitcoin network run various versions of Bitcoin Core. It is identified as "Satoshi" in the sub-version string sent in the +version+ message and shown by the command +getpeerinfo+ as we saw above, for example +/Satoshi:0.8.6/+. There are a few alternative implementations of full-blockchain bitcoin clients, built using different programming languages and software architectures. However, the most common implementation is the reference client Bitcoin Core, also known as the Satoshi Client. More than 90% of the nodes on the bitcoin network run various versions of Bitcoin Core. It is identified as "Satoshi" in the sub-version string sent in the +version+ message and shown by the command +getpeerinfo+ as we saw above, for example +/Satoshi:0.8.6/+.
@ -149,15 +149,15 @@ This process of comparing the local blockchain with the peers and retrieving any
.Node synchronizing the blockchain by retrieving blocks from a peer .Node synchronizing the blockchain by retrieving blocks from a peer
image::images/InventorySynchronization.png["InventorySynchronization"] image::images/InventorySynchronization.png["InventorySynchronization"]
=== Simple Payment Verification (SPV) Nodes === Simplified Payment Verification (SPV) Nodes
Not all nodes have the ability to store the full blockchain. Many bitcoin clients are designed to run on space- and power-constrained devices, such as smartphones, tablets or embedded systems. For such devices, a _simple payment verification_ (SPV) method is used to allow them to operate without storing the full blockchain. These types of clients are called SPV clients or lightweight clients. As bitcoin adoption surges, the SPV node is becoming the most common form of bitcoin node, especially for bitcoin wallets. Not all nodes have the ability to store the full blockchain. Many bitcoin clients are designed to run on space- and power-constrained devices, such as smartphones, tablets or embedded systems. For such devices, a _simplified payment verification_ (SPV) method is used to allow them to operate without storing the full blockchain. These types of clients are called SPV clients or lightweight clients. As bitcoin adoption surges, the SPV node is becoming the most common form of bitcoin node, especially for bitcoin wallets.
SPV nodes download only the block headers and do not download the transactions included in each block. The resulting chain of blocks, without transactions, is 1,000 times smaller than the full blockchain. SPV nodes cannot construct a full picture of all the UTXOs that are available for spending, as they do not know about all the transactions on the network. SPV nodes verify transactions using a slightly different methodology that relies on peers to provide partial views of relevant parts of the blockchain on-demand. SPV nodes download only the block headers and do not download the transactions included in each block. The resulting chain of blocks, without transactions, is 1,000 times smaller than the full blockchain. SPV nodes cannot construct a full picture of all the UTXOs that are available for spending, as they do not know about all the transactions on the network. SPV nodes verify transactions using a slightly different methodology that relies on peers to provide partial views of relevant parts of the blockchain on-demand.
As an analogy, a full node is like a tourist in a strange city, equipped with a detailed map of every street and every address. By comparison, an SPV node is like a tourist in a strange city asking random strangers for turn-by-turn directions while knowing only one main avenue. While both tourists can verify the existence of a street by visiting it, the tourist without a map doesn't know what lies down any of the side streets and doesn't know what other streets exist. Positioned in front of 23 Church Street, the tourist without a map cannot know if there are a dozen other "23 Church Street" addresses in the city and whether this is the right one. The map-less tourist's best chance is to ask enough people and hope some of them are not trying to mug the tourist. As an analogy, a full node is like a tourist in a strange city, equipped with a detailed map of every street and every address. By comparison, an SPV node is like a tourist in a strange city asking random strangers for turn-by-turn directions while knowing only one main avenue. While both tourists can verify the existence of a street by visiting it, the tourist without a map doesn't know what lies down any of the side streets and doesn't know what other streets exist. Positioned in front of 23 Church Street, the tourist without a map cannot know if there are a dozen other "23 Church Street" addresses in the city and whether this is the right one. The map-less tourist's best chance is to ask enough people and hope some of them are not trying to mug the tourist.
Simple Payment Verification verifies transactions by reference to their _depth_ in the blockchain instead of their _height_. Whereas a full-blockchain node will construct a fully verified chain of thousands of blocks and transactions reaching down the blockchain (back in time) all the way to the genesis block, an SPV node will verify the chain of all blocks and link that chain to the transaction of interest. Simplified Payment Verification verifies transactions by reference to their _depth_ in the blockchain instead of their _height_. Whereas a full-blockchain node will construct a fully verified chain of thousands of blocks and transactions reaching down the blockchain (back in time) all the way to the genesis block, an SPV node will verify the chain of all blocks and link that chain to the transaction of interest.
For example, when examining a transaction in block 300,000, a full node links all 300,000 blocks down to the genesis block and builds a full database of UTXO, establishing the validity of the transaction by confirming that the UTXO remains unspent. An SPV node cannot validate whether the UTXO is unspent. Instead, the SPV node will establish a link between the transaction and the block that contains it, using a Merkle Path (see <<merkle_trees>>). Then, the SPV node waits until it sees the six blocks 300,001 through 300,006 piled on top of the block containing the transaction and verifies it by establishing its depth under blocks 300,006 to 300,001. The fact that other nodes on the network accepted block 300,000 and then did the necessary work to produce 6 more blocks on top of it is proof, by proxy, that the transaction was not a double-spend. For example, when examining a transaction in block 300,000, a full node links all 300,000 blocks down to the genesis block and builds a full database of UTXO, establishing the validity of the transaction by confirming that the UTXO remains unspent. An SPV node cannot validate whether the UTXO is unspent. Instead, the SPV node will establish a link between the transaction and the block that contains it, using a Merkle Path (see <<merkle_trees>>). Then, the SPV node waits until it sees the six blocks 300,001 through 300,006 piled on top of the block containing the transaction and verifies it by establishing its depth under blocks 300,006 to 300,001. The fact that other nodes on the network accepted block 300,000 and then did the necessary work to produce 6 more blocks on top of it is proof, by proxy, that the transaction was not a double-spend.

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@ -145,7 +145,7 @@ Each block in the bitcoin blockchain contains a summary of all the transactions
A _Merkle Tree_, also known as a _Binary Hash Tree_ is a data structure used for efficiently summarizing and verifying the integrity of large sets of data. Merkle Trees are binary trees containing cryptographic hashes. The term "tree" is used in computer science to describe a branching data structure, but these trees are usually displayed upside down with the "root" at the top and the "leaves" at the bottom of a diagram, as you will see in the examples that follow. A _Merkle Tree_, also known as a _Binary Hash Tree_ is a data structure used for efficiently summarizing and verifying the integrity of large sets of data. Merkle Trees are binary trees containing cryptographic hashes. The term "tree" is used in computer science to describe a branching data structure, but these trees are usually displayed upside down with the "root" at the top and the "leaves" at the bottom of a diagram, as you will see in the examples that follow.
Merkle trees are used in bitcoin to summarize all the transactions in a block, producing an overall digital fingerprint of the entire set of transactions, which can be used to prove that a transaction is included in the set. A merkle tree is constructed by recursively hashing pairs of nodes until there is only one hash, called the _root_, or _merkle root_. The cryptographic hash algorithm used in bitcoin's merkle trees is SHA256 applied twice, also known as double-SHA256. Merkle trees are used in bitcoin to summarize all the transactions in a block, producing an overall digital fingerprint of the entire set of transactions, providing a very efficient process to verify if a transaction is included in a block. A merkle tree is constructed by recursively hashing pairs of nodes until there is only one hash, called the _root_, or _merkle root_. The cryptographic hash algorithm used in bitcoin's merkle trees is SHA256 applied twice, also known as double-SHA256.
When N data elements are hashed and summarized in a Merkle Tree, you can check to see if any one data element is included in the tree with at most +2*log~2~(N)+ calculations, making this a very efficient data structure. When N data elements are hashed and summarized in a Merkle Tree, you can check to see if any one data element is included in the tree with at most +2*log~2~(N)+ calculations, making this a very efficient data structure.
@ -194,11 +194,11 @@ The efficiency of merkle trees becomes obvious as the scale increases. For examp
| 65,535 transactions | 16 megabytes | 16 hashes | 512 bytes | 65,535 transactions | 16 megabytes | 16 hashes | 512 bytes
|======= |=======
As you can see from the table above, while the block size increases rapidly, from 4KB with 16 transactions to a block size of 16 MB to fit 65,535 transactions, the merkle path required to prove the inclusion of a transaction increases much more slowly, from 128 bytes to only 512 bytes. With merkle trees, a node can download just the block headers (80 bytes per block) and still be able to identify a transaction's inclusion in a block by retrieving a small merkle path from a full node, without storing or transmitting the vast majority of the blockchain which may be several gigabytes in size. Nodes which do not maintain a full blockchain, called Simple Payment Verification or SPV nodes use merkle paths to verify transactions without downloading full blocks. As you can see from the table above, while the block size increases rapidly, from 4KB with 16 transactions to a block size of 16 MB to fit 65,535 transactions, the merkle path required to prove the inclusion of a transaction increases much more slowly, from 128 bytes to only 512 bytes. With merkle trees, a node can download just the block headers (80 bytes per block) and still be able to identify a transaction's inclusion in a block by retrieving a small merkle path from a full node, without storing or transmitting the vast majority of the blockchain which may be several gigabytes in size. Nodes which do not maintain a full blockchain, called Simplified Payment Verification or SPV nodes use merkle paths to verify transactions without downloading full blocks.
=== Merkle Trees and Simple Payment Verification (SPV) === Merkle Trees and Simplified Payment Verification (SPV)
Merkle trees are used extensively by Simple Payment Verification nodes. SPV nodes don't have all transactions and do not download full blocks, just block headers. In order to verify that a transaction is included in a block, without having to download all the transactions in the block, they use an _authentication path_, or merkle path. Merkle trees are used extensively by Simplified Payment Verification nodes. SPV nodes don't have all transactions and do not download full blocks, just block headers. In order to verify that a transaction is included in a block, without having to download all the transactions in the block, they use an _authentication path_, or merkle path.
Consider for example an SPV node that is interested in incoming payments to an address contained in its wallet. The SPV node will establish a bloom filter on its connections to peers to limit the transactions received to only those containing addresses of interest. When a peer sees a transaction that matches the bloom filter, it will send that block using a +merkleblock+ message. The +merkleblock+ message contains the block header as well as a merkle path that links the transaction of interest to the merkle root in the block. The SPV node can use this merkle path to connect the transaction to the block and verify that the transaction is included in the block. The SPV node also uses the block header to link the block to the rest of the blockchain. The combination of these two links, between the transaction and block, and between the block and blockchain, proves that the transaction is recorded in the blockchain. All in all, the SPV node will have received less than a kilobyte of data for the block header and merkle path, an amount of data that is more than a thousand times less than a full block (about 1 megabyte currently). Consider for example an SPV node that is interested in incoming payments to an address contained in its wallet. The SPV node will establish a bloom filter on its connections to peers to limit the transactions received to only those containing addresses of interest. When a peer sees a transaction that matches the bloom filter, it will send that block using a +merkleblock+ message. The +merkleblock+ message contains the block header as well as a merkle path that links the transaction of interest to the merkle root in the block. The SPV node can use this merkle path to connect the transaction to the block and verify that the transaction is included in the block. The SPV node also uses the block header to link the block to the rest of the blockchain. The combination of these two links, between the transaction and block, and between the block and blockchain, proves that the transaction is recorded in the blockchain. All in all, the SPV node will have received less than a kilobyte of data for the block header and merkle path, an amount of data that is more than a thousand times less than a full block (about 1 megabyte currently).

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@ -4,7 +4,7 @@
[[mining]] [[mining]]
=== Introduction - Mining and Consensus === 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 that 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 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 provide processing power to the bitcoin network in exchange for the opportunity to be rewarded bitcoin. Miners validate new transactions and recording them on the global ledger. A new block, containing transactions that 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.
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, similar to how 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 bitcoin (20.99999998 million) will have been issued. After 2140, no new bitcoins are issued. 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, similar to how 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 bitcoin (20.99999998 million) will have been issued. After 2140, no new bitcoins are issued.
@ -16,7 +16,7 @@ In this chapter, we will first examine mining as a monetary supply mechanism and
==== Bitcoin Economics and Currency Creation ==== 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 entirely new bitcoins, created ex nihilo (from nothing). Every 210,000 blocks or approximately every four years the currency issuance rate is decreased by 50%. For the first four years of operation of the network, each block contained 50 new bitcoin. In November of 2012, the new bitcoin issuance rate was decreased to 25 bitcoin per block and it will decrease again to 12.5 bitcoin at block 420,000, which will be mined sometime in 2016. The rate of new coins decreases like this exponentially over 64 "halvings", until block 13,230,000 (mined approximately in year 2137) when it reaches the minimum currency unit of 1 satoshi. Finally, after 13.44 million blocks, in approximately 2140, all 2,099,999,997,690,000 satoshis, or almost 21 million bitcoin will be issued. Thereafter, blocks will contain no new bitcoin, and miners will be rewarded solely through the transaction fees. Bitcoins are "minted" during the creation of each block at a fixed and diminishing rate. Each block, generated on average every 10 minutes, contains entirely new bitcoins, created from nothing. Every 210,000 blocks or approximately every four years the currency issuance rate is decreased by 50%. For the first four years of operation of the network, each block contained 50 new bitcoin. In November of 2012, the new bitcoin issuance rate was decreased to 25 bitcoin per block and it will decrease again to 12.5 bitcoin at block 420,000, which will be mined sometime in 2016. The rate of new coins decreases like this exponentially over 64 "halvings", until block 13,230,000 (mined approximately in year 2137) when it reaches the minimum currency unit of 1 satoshi. Finally, after 13.44 million blocks, in approximately 2140, all 2,099,999,997,690,000 satoshis, or almost 21 million bitcoin will be issued. Thereafter, blocks will contain no new bitcoin, and miners will be rewarded solely through the transaction fees.
[[bitcoin_money_supply]] [[bitcoin_money_supply]]
.Supply of bitcoin currency over time based on a geometrically decreasing issuance rate .Supply of bitcoin currency over time based on a geometrically decreasing issuance rate
@ -60,24 +60,24 @@ However, before forwarding transactions to its neighbors, every bitcoin node tha
Each node verifies every transaction against a long checklist of criteria: Each node verifies every transaction against a long checklist of criteria:
* Check the syntactic correctness of the transaction's data structure * The transaction's syntax and data structure must be correct
* Make sure neither lists of inputs or outputs are empty * Neither lists of inputs or outputs are empty
* The transaction size in bytes is less than MAX_BLOCK_SIZE * The transaction size in bytes is less than MAX_BLOCK_SIZE
* Each output value, as well as the total, must be within the allowed range of values (less than 21m coins, more than 0) * Each output value, as well as the total, must be within the allowed range of values (less than 21m coins, more than 0)
* Check that none of the inputs have hash=0, N=-1 (coinbase transactions should not be relayed) * None of the inputs have hash=0, N=-1 (coinbase transactions should not be relayed)
* Check that nLockTime is less than or equal to INT_MAX * nLockTime is less than or equal to INT_MAX
* Check that the transaction size in bytes is greater than or equal to 100 * The transaction size in bytes is greater than or equal to 100
* Check that the number of signature operations contained in the transaction is less than the signature operation limit * The number of signature operations contained in the transaction is less than the signature operation limit
* Reject "nonstandard" transactions: unlocking script (scriptSig) doing anything other than pushing numbers on the stack, or the locking script (scriptPubkey) not matching isStandard forms * Unlocking script (scriptSig) only push numbers on the stack, and the locking script (scriptPubkey) must match isStandard forms (this rejects "nonstandard" transactions)
* Check for a matching transaction in the pool, or in a block in the main branch, if so reject this transaction * A matching transaction in the pool, or in a block in the main branch, must exist
* For each input, if the referenced output exists in any other transaction in the pool, reject this transaction * For each input, if the referenced output exists in any other transaction in the pool, reject this transaction
* For each input, look in the main branch and the transaction pool to find the referenced output transaction. If the output transaction is missing for any input, this will be an orphan transaction. Add to the orphan transactions, if a matching transaction is not already in the pool * For each input, look in the main branch and the transaction pool to find the referenced output transaction. If the output transaction is missing for any input, this will be an orphan transaction. Add to the orphan transactions, if a matching transaction is not already in the pool
* For each input, if the referenced output transaction is a coinbase output, it must have at least COINBASE_MATURITY (100) confirmations; else reject this transaction * For each input, if the referenced output transaction is a coinbase output, it must have at least COINBASE_MATURITY (100) confirmations
* For each input, if the referenced output does not exist (e.g. never existed or has already been spent), reject this transaction * For each input, the referenced output must exist and cannot already be spent
* Using the referenced output transactions to get input values, check that each input value, as well as the sum, are in the allowed range of values (less than 21m coins, more than 0) * Using the referenced output transactions to get input values, check that each input value, as well as the sum, are in the allowed range of values (less than 21m coins, more than 0)
* Reject if the sum of input values < sum of output values * Reject if the sum of input values < sum of output values
* Reject if transaction fee would be too low to get into an empty block * Reject if transaction fee would be too low to get into an empty block
* Verify the unlocking scripts for each input against the corresponding output locking scripts * The unlocking scripts for each input must validate against the corresponding output locking scripts
These conditions can be seen in detail in the functions +AcceptToMemoryPool+, +CheckTransaction+, and +CheckInputs+ in the bitcoin reference client. Note that the conditions change over time, to address new types of Denial-of-Service attacks or sometimes to relax the rules so as to include more types of transactions. These conditions can be seen in detail in the functions +AcceptToMemoryPool+, +CheckTransaction+, and +CheckInputs+ in the bitcoin reference client. Note that the conditions change over time, to address new types of Denial-of-Service attacks or sometimes to relax the rules so as to include more types of transactions.
@ -95,7 +95,7 @@ After validating transactions, a bitcoin node will add them to the _memory pool_
Let's follow the blocks that were created during the time Alice bought a cup of coffee from Bob's Cafe (see <<cup_of_coffee>>). Alice's transaction was included in block 277,316. For the purpose of demonstrating the concepts in this chapter let's assume that block was mined by Jing's mining system and follow Alice's transaction as it becomes part of this new block. Let's follow the blocks that were created during the time Alice bought a cup of coffee from Bob's Cafe (see <<cup_of_coffee>>). Alice's transaction was included in block 277,316. For the purpose of demonstrating the concepts in this chapter let's assume that block was mined by Jing's mining system and follow Alice's transaction as it becomes part of this new block.
Jing's mining node maintains a local copy of the blockchain, the list of all blocks created since the beginning of the bitcoin system in 2009. By the time Alice buys the cup of coffee, Jing's node has assembled a chain of 277,314 blocks. Jing's node is listening for transactions, trying to mine a new block and also listening for blocks discovered by other nodes. As Jing's node is mining, it receives block 277,315 through the bitcoin network. The arrival of this block signifies the end of the competition for block 277,315 and the beginning of the competition to create block 277,316. Jing's mining node maintains a local copy of the blockchain, the list of all blocks created since the beginning of the bitcoin system in 2009. By the time Alice buys the cup of coffee, Jing's node has assembled a chain up to block 277,314. Jing's node is listening for transactions, trying to mine a new block and also listening for blocks discovered by other nodes. As Jing's node is mining, it receives block 277,315 through the bitcoin network. The arrival of this block signifies the end of the competition for block 277,315 and the beginning of the competition to create block 277,316.
During the previous 10 minutes, while Jing's node was searching for a solution to block 277,315, it was also collecting transactions in preparation for the next block. By now it has collected a few hundred transactions in the memory pool. Upon receiving block 277,315 and validating it, Jing's node will also check all the transactions in the memory pool and remove any that were included in block 277,315. Whatever transaction remain in the memory pool are unconfirmed and are waiting to be recorded in a new block. During the previous 10 minutes, while Jing's node was searching for a solution to block 277,315, it was also collecting transactions in preparation for the next block. By now it has collected a few hundred transactions in the memory pool. Upon receiving block 277,315 and validating it, Jing's node will also check all the transactions in the memory pool and remove any that were included in block 277,315. Whatever transaction remain in the memory pool are unconfirmed and are waiting to be recorded in a new block.
@ -356,7 +356,7 @@ In the simplest terms, mining is the process of hashing the block header repeate
==== Proof-of-Work Algorithm ==== Proof-of-Work Algorithm
A hash algorithm takes an arbitrary-length data input and produces a fixed-length deterministic result, a digital fingerprint of the input. For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm. The key characteristic of a cryptographic hash algorithm is that it is impossible to find two different inputs that produce the same fingerprint. As a corollary, it is also impossible to select an input in such a way as to produce a desired fingerprint, other than trying random inputs. A hash algorithm takes an arbitrary-length data input and produces a fixed-length deterministic result, a digital fingerprint of the input. For any specific input, the resulting hash will always be the same and can be easily calculated and verified by anyone implementing the same hash algorithm. The key characteristic of a cryptographic hash algorithm is that it is virtually impossible to find two different inputs that produce the same fingerprint. As a corollary, it is also virtually impossible to select an input in such a way as to produce a desired fingerprint, other than trying random inputs.
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". 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".
@ -432,7 +432,7 @@ To make a challenge out of this algorithm, let's set an arbitrary target: find a
To give a simple analogy, imagine a game where players throw a pair of dice repeatedly, trying to throw less than a specified target. In the first round, the target is 12. Unless you throw double-six, you win. In the next round the target is 11. Players must throw 10 or less to win, again an easy task. Let's say a few rounds later the target is down to 5. Now, more than half the dice throws will add up to more than 5 and therefore be invalid. It takes exponentially more dice throws to win, the lower the target gets. Eventually, when the target is 2 (the minimum possible), only one throw out of every 36, or 2% of them will produce a winning result. To give a simple analogy, imagine a game where players throw a pair of dice repeatedly, trying to throw less than a specified target. In the first round, the target is 12. Unless you throw double-six, you win. In the next round the target is 11. Players must throw 10 or less to win, again an easy task. Let's say a few rounds later the target is down to 5. Now, more than half the dice throws will add up to more than 5 and therefore be invalid. It takes exponentially more dice throws to win, the lower the target gets. Eventually, when the target is 2 (the minimum possible), only one throw out of every 36, or 2% of them will produce a winning result.
In the example above, the winning "nonce" is 13 and this result can be confirmed by anyone independently. Anyone can add the number 13 as a suffix to the phrase "I am Satoshi Nakamoto" and compute the hash, verifying that it is less than the target. The successful result is also proof-of-work, as it proves we did the work to find that nonce. While it only takes one hash computation to verify, it took us 13 hash computations to find a nonce that worked. If we had a lower target (higher difficulty) it would take many more hash computations to find a suitable nonce, but only one hash computation for anyone to verify. Furthermore, by knowing the target, anyone can estimate the difficulty using statistics and therefore know how much work was needed to find such a nonce. In the hashing example above, the winning "nonce" is 13 and this result can be confirmed by anyone independently. Anyone can add the number 13 as a suffix to the phrase "I am Satoshi Nakamoto" and compute the hash, verifying that it is less than the target. The successful result is also proof-of-work, as it proves we did the work to find that nonce. While it only takes one hash computation to verify, it took us 13 hash computations to find a nonce that worked. If we had a lower target (higher difficulty) it would take many more hash computations to find a suitable nonce, but only one hash computation for anyone to verify. Furthermore, by knowing the target, anyone can estimate the difficulty using statistics and therefore know how much work was needed to find such a nonce.
Bitcoin's Proof-of-Work is very similar to the problem above. The miner constructs a candidate block filled with transactions. Next, the miner calculates the hash of this block's header and see if it is smaller than the current _target_. If the hash is not less than the target, the miner will modify the nonce (usually just incrementing it by one) and try again. At the current difficulty in the bitcoin network, miners have to try quadrillions of times before finding a nonce that results in a low enough block header hash. Bitcoin's Proof-of-Work is very similar to the problem above. The miner constructs a candidate block filled with transactions. Next, the miner calculates the hash of this block's header and see if it is smaller than the current _target_. If the hash is not less than the target, the miner will modify the nonce (usually just incrementing it by one) and try again. At the current difficulty in the bitcoin network, miners have to try quadrillions of times before finding a nonce that results in a low enough block header hash.
@ -620,14 +620,14 @@ In the next section we'll look at the process each node uses to validate a block
The third step in bitcoin's consensus mechanism is independent validation of each new block by every node on the network. As the newly solved block moves across the network, each node performs a series of tests to validate it before propagating it to its peers. This ensures that only valid blocks are propagated on the network. The independent validation also ensures that miners who act honestly get their blocks incorporated in the blockchain, thus earning the reward. Those miners who act dishonestly have their blocks rejected and not only lose the reward but also waste the effort expended to find a Proof-of-Work solution, thus incurring the cost of electricity without compensation. The third step in bitcoin's consensus mechanism is independent validation of each new block by every node on the network. As the newly solved block moves across the network, each node performs a series of tests to validate it before propagating it to its peers. This ensures that only valid blocks are propagated on the network. The independent validation also ensures that miners who act honestly get their blocks incorporated in the blockchain, thus earning the reward. Those miners who act dishonestly have their blocks rejected and not only lose the reward but also waste the effort expended to find a Proof-of-Work solution, thus incurring the cost of electricity without compensation.
When a node receives a new block, it will validate the block by checking it against a long list of criteria. These criteria can be seen in the Bitcoin Core client in the functions +CheckBlock+ and +CheckBlockHeader+. These criteria include: When a node receives a new block, it will validate the block by checking it against a long list of criteria that must all be met; otherwise the block is rejected. These criteria can be seen in the Bitcoin Core client in the functions +CheckBlock+ and +CheckBlockHeader+ and include:
* Check the syntactic validity of the block data structure * The block data structure is syntactically valid
* Check the Proof-of-Work, by checking the block header hash is less than the target difficulty * The block header hash is less than the target difficulty (enforces the Proof-of-Work)
* Check the block timestamp is less than two hours in the future (allowing for time errors) * The block timestamp is less than two hours in the future (allowing for time errors)
* Check the block size is within acceptable limits * The block size is within acceptable limits
* Check the first transaction (and only the first) is a coinbase generation transaction * The first transaction (and only the first) is a coinbase generation transaction
* Validate all transactions within the block, using the transaction checklist discussed in <<tx_verification>> * All transactions within the block are valid using the transaction checklist discussed in <<tx_verification>>
The independent validation of each new block by every node on the network ensures that the miners can't cheat. In previous sections we saw how the miners get to write a transaction that awards them the new bitcoins created within the block and claim the transaction fees. Why doesn't the miner write themselves a transaction for a thousand bitcoin instead of the correct reward? Because every node validates blocks according to the same rules. An invalid coinbase transaction would make the entire block invalid, which would result in the block being rejected and therefore that transaction would never become part of the ledger. The miner has to construct a perfect block, based on the shared rules that all nodes follow and mine it with a correct solution to the Proof-of-Work. To do so they expend a lot of electricity in mining and if they cheat all the electricity and effort is wasted. This is why independent validation is a key component of decentralized consensus. The independent validation of each new block by every node on the network ensures that the miners can't cheat. In previous sections we saw how the miners get to write a transaction that awards them the new bitcoins created within the block and claim the transaction fees. Why doesn't the miner write themselves a transaction for a thousand bitcoin instead of the correct reward? Because every node validates blocks according to the same rules. An invalid coinbase transaction would make the entire block invalid, which would result in the block being rejected and therefore that transaction would never become part of the ledger. The miner has to construct a perfect block, based on the shared rules that all nodes follow and mine it with a correct solution to the Proof-of-Work. To do so they expend a lot of electricity in mining and if they cheat all the electricity and effort is wasted. This is why independent validation is a key component of decentralized consensus.
@ -781,5 +781,5 @@ The massive increase of total hashing power has arguably made bitcoin impervious
Not all attackers will be motivated by profit, however. One potential attack scenario is where an attacker intends to disrupt the bitcoin network without the possibility of profiting from such disruption. A malicious attack aimed at crippling bitcoin would require enormous investment and covert planning, but could conceivably be launched by a well funded, most likely state-sponsored attacker. Alternatively, a well-funded attacker could attack bitcoin's consensus by simultaneously amassing mining hardware, compromising pool operators and attacking other pools with denial-of-service. All of these scenarios are theoretically possible, but increasingly impractical as the bitcoin network's overall hashing power continues to grow exponentially. Recent advancements in bitcoin, such as P2Pool mining, aim to further de-centralize mining control, making bitcoin consensus even harder to attack. Not all attackers will be motivated by profit, however. One potential attack scenario is where an attacker intends to disrupt the bitcoin network without the possibility of profiting from such disruption. A malicious attack aimed at crippling bitcoin would require enormous investment and covert planning, but could conceivably be launched by a well funded, most likely state-sponsored attacker. Alternatively, a well-funded attacker could attack bitcoin's consensus by simultaneously amassing mining hardware, compromising pool operators and attacking other pools with denial-of-service. All of these scenarios are theoretically possible, but increasingly impractical as the bitcoin network's overall hashing power continues to grow exponentially. Recent advancements in bitcoin, such as P2Pool mining, aim to further de-centralize mining control, making bitcoin consensus even harder to attack.
Undoubtedly, a serious consensus attack would erode confidence in bitcoin in the short term, possibly causing a significant price decline. However, the bitcoin network and software is constantly evolving, so consensus attacks would be met with immediate counter-measures by the bitcoin community, making bitcoin hardier, stealthier and more robust. Undoubtedly, a serious consensus attack would erode confidence in bitcoin in the short term, possibly causing a significant price decline. However, the bitcoin network and software is constantly evolving, so consensus attacks would be met with immediate counter-measures by the bitcoin community, making bitcoin hardier, stealthier, and more robust.

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@ -1,9 +1,9 @@
[[ch9]] [[ch9]]
== Alternative chains, currencies and applications == Alternative chains, currencies, and applications
Bitcoin was neither the beginning nor the end of the digital currency evolution. It came from twenty years of research in distributed systems and currencies and brought a revolutionary new technology into the space: the de-centralized consensus mechanism based on Proof-of-Work. The invention at the heart of bitcoin has ushered a wave of innovation in currencies, financial services, economics, distributed systems, voting systems, corporate governance and contracts. Bitcoin was neither the beginning nor the end of the digital currency evolution. It came from twenty years of research in distributed systems and currencies and brought a revolutionary new technology into the space: the de-centralized consensus mechanism based on Proof-of-Work. The invention at the heart of bitcoin has ushered a wave of innovation in currencies, financial services, economics, distributed systems, voting systems, corporate governance, and contracts.
In this chapter we'll examine the many offshoots of the bitcoin and blockchain inventions, the alternative chains, currencies and applications built since the introduction of this technology in 2009. In this chapter we'll examine the many offshoots of the bitcoin and blockchain inventions, the alternative chains, currencies, and applications built since the introduction of this technology in 2009.
For every alt-coin mentioned in this chapter, 50 or more will go unmentioned, eliciting howls of anger from their creators and fans. The purpose of this chapter is not to evaluate or qualify alt-coins, or to mention the most "significant" ones based on some subjective assessment. Instead, we will highlight a few examples that show the breadth and variety of the ecosystem, noting the first-of-a-kind for each innovation or significant differentiation. Some of the most interesting examples of alt-coins are in fact complete failures from a monetary perspective. That perhaps makes them even more interesting for study and highlights the fact that this chapter is not to be used as an investment guide. For every alt-coin mentioned in this chapter, 50 or more will go unmentioned, eliciting howls of anger from their creators and fans. The purpose of this chapter is not to evaluate or qualify alt-coins, or to mention the most "significant" ones based on some subjective assessment. Instead, we will highlight a few examples that show the breadth and variety of the ecosystem, noting the first-of-a-kind for each innovation or significant differentiation. Some of the most interesting examples of alt-coins are in fact complete failures from a monetary perspective. That perhaps makes them even more interesting for study and highlights the fact that this chapter is not to be used as an investment guide.
@ -13,11 +13,11 @@ With new coins introduced every day, it would be impossible not to miss some imp
Bitcoin is an open source project and its code has been used as the basis for many other software projects. The most common form of software spawned from bitcoin's source code are alternative de-centralized currencies, or _alt-coins_, which use the same basic building blocks to implement digital currencies. Bitcoin is an open source project and its code has been used as the basis for many other software projects. The most common form of software spawned from bitcoin's source code are alternative de-centralized currencies, or _alt-coins_, which use the same basic building blocks to implement digital currencies.
There are a number of protocol layers implemented on top of bitcoin's blockchain. These _meta-coins_, _meta-chains_, or _blockchain apps_ use the blockchain as an application platform or extend the bitcoin protocol by adding protocol layers. Examples include Colored Coins, Mastercoin and Counterparty. There are a number of protocol layers implemented on top of bitcoin's blockchain. These _meta-coins_, _meta-chains_, or _blockchain apps_ use the blockchain as an application platform or extend the bitcoin protocol by adding protocol layers. Examples include Colored Coins, Mastercoin, and Counterparty.
In the next section we will examine a few notable alt-coins, such as Litecoin, Dogecoin, Freicoin, Primecoin, Peercoin, Darkcoin and Zerocoin. These alt-coins are notable for historical reasons or because they are good examples a specific type of alt-coin innovation, not because they are the most valuable or "best" alt-coins. In the next section we will examine a few notable alt-coins, such as Litecoin, Dogecoin, Freicoin, Primecoin, Peercoin, Darkcoin, and Zerocoin. These alt-coins are notable for historical reasons or because they are good examples for a specific type of alt-coin innovation, not because they are the most valuable or "best" alt-coins.
In addition to the alt-coins, there are also a number of alternative blockchain implementations that are not really "coins", which I call _alt-chains_. These alt-chains implement a consensus algorithm and distributed ledger as a platform for contracts, name registration or other applications. Alt-chains use the same basic building blocks and sometimes also use a currency or token as a payment mechanism, but their primary purpose is not currency. We will look at Namecoin, Ethereum and NXT as examples of alt-chains. In addition to the alt-coins, there are also a number of alternative blockchain implementations that are not really "coins", which I call _alt-chains_. These alt-chains implement a consensus algorithm and distributed ledger as a platform for contracts, name registration, or other applications. Alt-chains use the same basic building blocks and sometimes also use a currency or token as a payment mechanism, but their primary purpose is not currency. We will look at Namecoin, Ethereum, and NXT as examples of alt-chains.
In addition to the Proof-of-Work consensus mechanism used in bitcoin, alternatives include experimental protocols based on Proof-of-Resource and Proof-of-Publishing. We will examine Maidsafe and Twister as examples of these consensus mechanisms. In addition to the Proof-of-Work consensus mechanism used in bitcoin, alternatives include experimental protocols based on Proof-of-Resource and Proof-of-Publishing. We will examine Maidsafe and Twister as examples of these consensus mechanisms.
@ -25,15 +25,15 @@ Finally, there are a number of bitcoin contenders that offer digital currency or
=== Meta-Coin Platforms === Meta-Coin Platforms
Meta-coins and meta-chains are software layers implemented on top of bitcoin, either implementing a currency-inside-a-currency, or a platform/protocol overlay inside the bitcoin system. These function layers extend the core bitcoin protocol and add features and capabilities by encoding additional data inside bitcoin transactions and bitcoin addresses. The first implementations of meta-coins used various "hacks" to add meta-data to the bitcoin blockchain, such as using bitcoin addresses to encode data or using unused transaction fields (eg. the transaction sequence field) to encode meta-data about the added protocol layer. Since the introduction of the OP_RETURN transaction scripting opcode, the meta-coins have been able to record meta-data more directly in the blockchain and most are migrating to using that instead. Meta-coins and meta-chains are software layers implemented on top of bitcoin, either implementing a currency-inside-a-currency, or a platform/protocol overlay inside the bitcoin system. These function layers extend the core bitcoin protocol and add features and capabilities by encoding additional data inside bitcoin transactions and bitcoin addresses. The first implementations of meta-coins used various "hacks" to add meta-data to the bitcoin blockchain, such as using bitcoin addresses to encode data or using unused transaction fields (e.g. the transaction sequence field) to encode meta-data about the added protocol layer. Since the introduction of the OP_RETURN transaction scripting opcode, the meta-coins have been able to record meta-data more directly in the blockchain and most are migrating to using that instead.
==== Colored Coins ==== Colored Coins
Colored Coins is a meta-protocol that overlays information on small amounts of bitcoin. A "colored" coin is an amount of bitcoin repurposed to express another asset. Imagine for example taking a $1 USD note and putting a stamp on it that said "This is a 1 share certificate of Acme Inc.". Now the $1 serves two purposes: it is a currency note and also a share certificate. Because it is more valuable as a share, you would not want to use it to buy candy, so effectively it is no longer useful as currency. Colored coins work in a same way by converting a specific, very small, amount of bitcoin into a traded certificate that represents another asset. The term "color" refers to the idea of giving special meaning through the addition of an attribute such as a color - it is a metaphor not an actual color association. There are no colors in colored coins. Colored Coins is a meta-protocol that overlays information on small amounts of bitcoin. A "colored" coin is an amount of bitcoin repurposed to express another asset. Imagine for example taking a $1 USD note and putting a stamp on it that said "This is a 1 share certificate of Acme Inc.". Now the $1 serves two purposes: it is a currency note and also a share certificate. Because it is more valuable as a share, you would not want to use it to buy candy, so effectively it is no longer useful as currency. Colored coins work in the same way by converting a specific, very small, amount of bitcoin into a traded certificate that represents another asset. The term "color" refers to the idea of giving special meaning through the addition of an attribute such as a color - it is a metaphor not an actual color association. There are no colors in colored coins.
Colored coins are managed by specialized "wallets" that record and interpret the metadata attached to the "colored" bitcoins. Using such a wallet, the user will convert an amount of bitcoins from uncolored currency, into colored coins, by adding a label that has a special meaning. For example, a label could represent stock certificates, coupons, real property, commodities, collectible tokens etc. It is entirely up to the users of colored coins to assign and interpret the meaning of the "color" associated with specific coins. To color the coins, the user defines the associated metadata, such as the type of issuance, whether it can be subdivided into smaller units, a symbol and description and other related information. Once colored, these coins can be bought and sold, subdivided, aggregated and receive dividend payments. The colored coins can also be "uncolored" to remove the special association and redeem them for their face-value in bitcoin. Colored coins are managed by specialized "wallets" that record and interpret the metadata attached to the "colored" bitcoins. Using such a wallet, the user will convert an amount of bitcoins from uncolored currency, into colored coins, by adding a label that has a special meaning. For example, a label could represent stock certificates, coupons, real property, commodities, collectible tokens, etc. It is entirely up to the users of colored coins to assign and interpret the meaning of the "color" associated with specific coins. To color the coins, the user defines the associated metadata, such as the type of issuance, whether it can be subdivided into smaller units, a symbol and description, and other related information. Once colored, these coins can be bought and sold, subdivided, aggregated and receive dividend payments. The colored coins can also be "uncolored" by removing the special association and redeem them for their face-value in bitcoin.
To demonstrate the use of colored coins, we have created a set of 20 colored coins with symbol "MasterBTC" that represent coupons for a free copy of this book. Each unit of MasterBTC is represented by these colored coins can now be sold or given to any bitcoin user with a colored-coin-capable wallet, who can then transfer them to others or redeem them with the issuer for a free copy of the book. This example of colored coins can be seen here: https://cpr.sm/FoykwrH6UY To demonstrate the use of colored coins, we have created a set of 20 colored coins with symbol "MasterBTC" that represent coupons for a free copy of this book. Each unit of MasterBTC, represented by these colored coins, can now be sold or given to any bitcoin user with a colored-coin-capable wallet, who can then transfer them to others or redeem them with the issuer for a free copy of the book. This example of colored coins can be seen here: https://cpr.sm/FoykwrH6UY
.The metadata profile of the colored coins recorded as a coupon for a free copy of the book .The metadata profile of the colored coins recorded as a coupon for a free copy of the book
==== ====
@ -61,17 +61,17 @@ To demonstrate the use of colored coins, we have created a set of 20 colored coi
==== Mastercoin ==== Mastercoin
Mastercoin is a protocol layer on top of bitcoin that supports a platform for various applications extending the bitcoin system. Mastercoin uses the currency MST as a token for conducting Mastercoin transactions but it not primarily a currency. Rather it is a platform for building other things, such as user currencies, smart property tokens, de-centralized asset exchanges, contracts etc. Think of Mastercoin as an application-layer protocol on top of bitcoin's financial transaction transport-layer, just like HTTP runs on top of TCP. Mastercoin is a protocol layer on top of bitcoin that supports a platform for various applications extending the bitcoin system. Mastercoin uses the currency MST as a token for conducting Mastercoin transactions but it is not primarily a currency. Rather it is a platform for building other things, such as user currencies, smart property tokens, de-centralized asset exchanges, contracts, etc. Think of Mastercoin as an application-layer protocol on top of bitcoin's financial transaction transport-layer, just like HTTP runs on top of TCP.
Mastercoin operates primarily through transactions sent to and from a special bitcoin address called the "exodus" address (+1EXoDusjGwvnjZUyKkxZ4UHEf77z6A5S4P+), just like HTTP uses a specific TCP port (port 80) to differentiate its traffic from the rest of the TCP traffic. The Mastercoin protocol is gradually transitioning from using the specialized exodus address and multi-signatures to using the OP_RETURN bitcoin operator to encode transaction metadata. Mastercoin operates primarily through transactions sent to and from a special bitcoin address called the "exodus" address (+1EXoDusjGwvnjZUyKkxZ4UHEf77z6A5S4P+), just like HTTP uses a specific TCP port (port 80) to differentiate its traffic from the rest of the TCP traffic. The Mastercoin protocol is gradually transitioning from using the specialized exodus address and multi-signatures to using the OP_RETURN bitcoin operator to encode transaction metadata.
==== Counterparty ==== Counterparty
Counterparty is another protocol layer implemented on top of bitcoin. Counterparty enables user currencies, tradable tokens, financial instruments, de-centralized asset exchanges and other features. Counterparty is implemented primarily using the OP_RETURN operator in bitcoin's scripting language to record metadata enhancing bitcoin transactions with additional meaning. Counterparty uses the currency XCP as a token for conducting Counterparty transactions. Counterparty is another protocol layer implemented on top of bitcoin. Counterparty enables user currencies, tradable tokens, financial instruments, de-centralized asset exchanges, and other features. Counterparty is implemented primarily using the OP_RETURN operator in bitcoin's scripting language to record metadata enhancing bitcoin transactions with additional meaning. Counterparty uses the currency XCP as a token for conducting Counterparty transactions.
=== Alt-coins === Alt-coins
Alt-coins are digital currencies implemented using the same design pattern as bitcoin, with a completely separate blockchain and network. The vast majority of alt-coins are derived from bitcoin's source code, also known as "forks". Some are implemented "from scratch" based on the blockchain model but without using any of bitcoin's source code. Alt-coins and alt-chains (in the next section) are both separate implementations of blockchain technology and both forms use their own blockchain. The difference in the terms is to indicate that alt-coins are primarily used as currency, whereas alt-chains are used for other purposes, not primarily currency. Alt-coins are digital currencies implemented using the same design pattern as bitcoin, but with a completely separate blockchain and network. The vast majority of alt-coins are derived from bitcoin's source code, also known as "forks". Some are implemented "from scratch" based on the blockchain model but without using any of bitcoin's source code. Alt-coins and alt-chains (in the next section) are both separate implementations of blockchain technology and both forms use their own blockchain. The difference in the terms is to indicate that alt-coins are primarily used as currency, whereas alt-chains are used for other purposes, not primarily currency.
The first alt-coins appeared in August of 2011 as forks of the bitcoin source code. Strictly speaking, the first major fork of bitcoin's code was not an alt-coin but the alt-chain _Namecoin_, which will be discussed in the next section. The first alt-coins appeared in August of 2011 as forks of the bitcoin source code. Strictly speaking, the first major fork of bitcoin's code was not an alt-coin but the alt-chain _Namecoin_, which will be discussed in the next section.
@ -79,9 +79,9 @@ Based on the date of announcement, the first alt-coin appears to be _IXCoin_, la
In September of 2011, _Tenebrix_ was launched. Tenebrix was the first crypto-currency to implement an alternative Proof-of-Work algorithm, namely _scrypt_, an algorithm originally designed for password stretching (brute-force resistance). The stated goal of Tenebrix was to make a coin that was resistant to mining with GPUs and ASICs, by using a memory-intensive algorithm. Tenebrix did not succeed as a currency, but it was the basis for Litecoin, which has enjoyed great success and has spawned hundreds of clones. In September of 2011, _Tenebrix_ was launched. Tenebrix was the first crypto-currency to implement an alternative Proof-of-Work algorithm, namely _scrypt_, an algorithm originally designed for password stretching (brute-force resistance). The stated goal of Tenebrix was to make a coin that was resistant to mining with GPUs and ASICs, by using a memory-intensive algorithm. Tenebrix did not succeed as a currency, but it was the basis for Litecoin, which has enjoyed great success and has spawned hundreds of clones.
_Litecoin_, in addition to using scrypt as the Proof-of-Work algorithm, also implemented a faster block generation time, targeted at 2.5 minutes instead of bitcoin's 10 minutes. The resulting currency is touted as "silver to bitcoin's gold" and intended as a light-weight alternative currency. Due to the faster confirmation time and 84 million total currency limit, many adherents of Litecoin believe it is better suited for retail transactions than bitcoin. _Litecoin_, in addition to using scrypt as the Proof-of-Work algorithm, also implemented a faster block generation time, targeted at 2.5 minutes instead of bitcoin's 10 minutes. The resulting currency is touted as "silver to bitcoin's gold" and is intended as a light-weight alternative currency. Due to the faster confirmation time and the 84 million total currency limit, many adherents of Litecoin believe it is better suited for retail transactions than bitcoin.
Alt-coins continued to proliferate in 2011 and 2012, either based on bitcoin, or on Litecoin. In the beginning of 2013 there were 20 alt-coins vying for position in the market. By the end of 2013 however, this number had exploded to 200, with 2013 quickly becoming the "year of the alt-coins". The growth of alt-coins continued in 2014 with more than 500 alt-coins now in existence. More than half the alt-coins today are clones of Litecoin. Alt-coins continued to proliferate in 2011 and 2012, either based on bitcoin or on Litecoin. In the beginning of 2013 there were 20 alt-coins vying for position in the market. By the end of 2013 however, this number had exploded to 200, with 2013 quickly becoming the "year of the alt-coins". The growth of alt-coins continued in 2014 with more than 500 alt-coins now in existence. More than half the alt-coins today are clones of Litecoin.
Creating an alt-coin is easy, which is why there are now more than 500 of them. Most of the alt-coins differ very slightly from bitcoin and do not offer anything worth studying. Many are in fact just attempts to enrich their creators. Among the copycats and pump-and-dump schemes, there are however some notable exceptions and very important innovations. These alt-coins take radically different approaches or add significant innovation to bitcoin's design pattern. There are three primary areas where alt-coins differentiate from bitcoin: Creating an alt-coin is easy, which is why there are now more than 500 of them. Most of the alt-coins differ very slightly from bitcoin and do not offer anything worth studying. Many are in fact just attempts to enrich their creators. Among the copycats and pump-and-dump schemes, there are however some notable exceptions and very important innovations. These alt-coins take radically different approaches or add significant innovation to bitcoin's design pattern. There are three primary areas where alt-coins differentiate from bitcoin:
@ -89,7 +89,7 @@ Creating an alt-coin is easy, which is why there are now more than 500 of them.
* Different Proof-of-Work or consensus mechanism * Different Proof-of-Work or consensus mechanism
* Specific features, such as strong anonymity * Specific features, such as strong anonymity
A graphical timeline of alt-coins and alt-chains can be found at http://mapofcoins.com A graphical timeline of alt-coins and alt-chains can be found at http://mapofcoins.com.
==== Evaluating an alt-coin ==== Evaluating an alt-coin
@ -101,7 +101,7 @@ Here are some questions to ask about how well an alt-coin differentiates from bi
* Does the alt-coin differentiate sufficiently from bitcoin? * Does the alt-coin differentiate sufficiently from bitcoin?
* Is the difference compelling enough to attract users away from bitcoin? * Is the difference compelling enough to attract users away from bitcoin?
* Does the alt-coin address an interesting niche market or application? * Does the alt-coin address an interesting niche market or application?
* Can the alt-coin attract enough miners to be secure against consensus attacks? * Can the alt-coin attract enough miners to be secured against consensus attacks?
Here are some of the key financial and market metrics to examine: Here are some of the key financial and market metrics to examine:
@ -119,34 +119,34 @@ Bitcoin has a few monetary parameters that give it distinctive characteristics o
*Litecoin* *Litecoin*
One of the first alt-coins, released in 2011, Litecoin is the second most successful digital currency after bitcoin. It's primary innovations were the use of _scrypt_ as the Proof-of-Work algorithm (inherited from Tenebrix) and the faster/lighter currency parameters. One of the first alt-coins, released in 2011, Litecoin is the second most successful digital currency after bitcoin. Its primary innovations were the use of _scrypt_ as the Proof-of-Work algorithm (inherited from Tenebrix) and the faster/lighter currency parameters.
* Block generation time: 2.5 minutes * Block generation time: 2.5 minutes
* Total currency: 84 million coins by 2140 * Total currency: 84 million coins by 2140
* Consensus Algorithm: scrypt Proof-of-Work * Consensus Algorithm: scrypt Proof-of-Work
* Market capitalization: $160 million USD in Summer 2014 * Market capitalization: $160 million USD in mid-2014
*Dogecoin* *Dogecoin*
Dogecoin was released in December of 2013, based on a fork of Litecoin. Dogecoin is notable because it has a monetary policy of rapid issuance and a very high currency cap, to encourage spending and tipping. Dogecoin is also notable because it was started as a joke but became quite popular, with a large and active community, before declining rapidly in 2014. Dogecoin was released in December of 2013, based on a fork of Litecoin. Dogecoin is notable because it has a monetary policy of rapid issuance and a very high currency cap, to encourage spending and tipping. Dogecoin is also notable because it was started as a joke but became quite popular, with a large and active community, before declining rapidly in 2014.
* Block generation time: 60 seconds * Block generation time: 60 seconds
* Total currency: 100,000,000,000 (100 trillion) Doge by 2015 * Total currency: 100,000,000,000 (100 billion) Doge by 2015
* Consensus algorithm: scrypt Proof-of-Work * Consensus algorithm: scrypt Proof-of-Work
* Market capitalization: $12 million USD in Summer 2014 * Market capitalization: $12 million USD in mid-2014
*Freicoin* *Freicoin*
Freicoin was introduced in July 2012. It is a _demurrage currency_, meaning that is has a negative interest rate for stored value. Value stored in Freicoin is assessed a 4.5% APR fee, to encourage consumption and discourage hoarding of money. Freicoin is notable in that it implements a monetary policy that is the exact opposite of Bitcoin's deflationary policy. Freicoin has not seen success as a currency, but is an interesting example of the variety of monetary policies that can be expressed by alt-coins. Freicoin was introduced in July 2012. It is a _demurrage currency_, meaning that it has a negative interest rate for stored value. Value stored in Freicoin is assessed a 4.5% APR fee, to encourage consumption and discourage hoarding of money. Freicoin is notable in that it implements a monetary policy that is the exact opposite of Bitcoin's deflationary policy. Freicoin has not seen success as a currency, but is an interesting example of the variety of monetary policies that can be expressed by alt-coins.
* Block generation: 10 minutes * Block generation: 10 minutes
* Total currency: 100 million coins by 2140 * Total currency: 100 million coins by 2140
* Consensus algorithm: SHA256 Proof-of-Work * Consensus algorithm: SHA256 Proof-of-Work
* Market capitalization: $130,000 USD in Summer 2014 * Market capitalization: $130,000 USD in mid-2014
==== Consensus Innovation: Peercoin, Myriad, Blackcoin, Vericoin, NXT ==== Consensus Innovation: Peercoin, Myriad, Blackcoin, Vericoin, NXT
Bitcoin's consensus mechanism is based on Proof-of-Work using the SHA256 algorithm. The first alt-coins introduced scrypt as an alternative Proof-of-Work algorithms, as a way to make mining more CPU-friendly and less susceptible to centralization with ASICs. Since then, innovation in the consensus mechanism has continued at a frenetic pace. Several alt-coins adopted a variety of algorithms such as scrypt, scrypt-N, Skein, Groestl, SHA3, X11, Blake and others. Some alt-coins combined multiple algorithms for Proof-of-Work. In 2013 we saw the invention of an alternative to Proof-of-Work, called _Proof-of-Stake_, which forms the basis of many modern alt-coins. Bitcoin's consensus mechanism is based on Proof-of-Work using the SHA256 algorithm. The first alt-coins introduced scrypt as an alternative Proof-of-Work algorithms, as a way to make mining more CPU-friendly and less susceptible to centralization with ASICs. Since then, innovation in the consensus mechanism has continued at a frenetic pace. Several alt-coins adopted a variety of algorithms such as scrypt, scrypt-N, Skein, Groestl, SHA3, X11, Blake, and others. Some alt-coins combined multiple algorithms for Proof-of-Work. In 2013 we saw the invention of an alternative to Proof-of-Work, called _Proof-of-Stake_, which forms the basis of many modern alt-coins.
Proof-of-Stake is a system by which existing owners of a currency can "stake" currency as interest-bearing collateral. Somewhat like a Certificate of Deposit (CD), participants can reserve a portion of their currency holdings, while earning an investment return in the form of new currency (issued as interest payments) and transaction fees. Proof-of-Stake is a system by which existing owners of a currency can "stake" currency as interest-bearing collateral. Somewhat like a Certificate of Deposit (CD), participants can reserve a portion of their currency holdings, while earning an investment return in the form of new currency (issued as interest payments) and transaction fees.
@ -157,7 +157,7 @@ Peercoin was introduced in August of 2012 and is the first alt-coin to use a hyb
* Block generation: 10 minutes * Block generation: 10 minutes
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: (Hybrid) Proof-of-Stake with initial Proof-of-Work * Consensus algorithm: (Hybrid) Proof-of-Stake with initial Proof-of-Work
* Market capitalization: $14 million USD in Summer 2014 * Market capitalization: $14 million USD in mid-2014
*Myriad* *Myriad*
@ -166,7 +166,7 @@ Myriad was introduced in February 2014 and is notable because it uses five diffe
* Block generation: 30 second average (2.5 minutes target per mining algorithm) * Block generation: 30 second average (2.5 minutes target per mining algorithm)
* Total currency: 2 billion by 2024 * Total currency: 2 billion by 2024
* Consensus algorithm: Multi-Algorithm Proof-of-Work * Consensus algorithm: Multi-Algorithm Proof-of-Work
* Market capitalization: $120,000 USD in Summer 2014 * Market capitalization: $120,000 USD in mid-2014
*Blackcoin* *Blackcoin*
@ -175,16 +175,16 @@ Blackcoin was introduced in February 2014 and uses a Proof-of-Stake consensus al
* Block generation: 1 minute * Block generation: 1 minute
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: Proof-of-Stake * Consensus algorithm: Proof-of-Stake
* Market capitalization: $3.7 million USD in Summer 2014 * Market capitalization: $3.7 million USD in mid-2014
*Vericoin* *VeriCoin*
Vericoin was launched in May 2014. It uses a Proof-of-Stake consensus algorithm with a variable interest rate that dynamically adjusts based on market forces of supply and demand. VeriCoin was launched in May 2014. It uses a Proof-of-Stake consensus algorithm with a variable interest rate that dynamically adjusts based on market forces of supply and demand. It also is the first alt-coin featuring auto-exchange to Bitcoin for payment in Bitcoin from the wallet.
* Block generation: 1 minute * Block generation: 1 minute
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: Proof-of-Stake * Consensus algorithm: Proof-of-Stake
* Market capitalization: $1.1 million USD in Summer 2014 * Market capitalization: $1.1 million USD in mid-2014
*NXT* *NXT*
@ -193,21 +193,21 @@ NXT (pronounced "Next") is a "pure" Proof-of-Stake alt-coin, in that it does not
* Block generation: 1 minute * Block generation: 1 minute
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: Proof-of-Stake * Consensus algorithm: Proof-of-Stake
* Market capitalization: $30 million USD in Summer 2014 * Market capitalization: $30 million USD in mid-2014
==== Dual-Purpose Mining Innovation: Primecoin, Curecoin, Gridcoin ==== Dual-Purpose Mining Innovation: Primecoin, Curecoin, Gridcoin
Bitcoin's Proof-of-Work algorithm has only one purpose: securing the bitcoin network. Compared to traditional payment system security, the cost of mining is not very high. However, it has been criticized by many as "wasteful". The next set of alt-coins attempt to address this concern. Dual-purpose Proof-of-Work algorithms solve a specific "useful" problem, while producing Proof-of-Work to secure the network. The risk of adding an external use to the currency's security is that it also adds external influence to the supply/demand curve. Bitcoin's Proof-of-Work algorithm has only one purpose: securing the bitcoin network. Compared to traditional payment system security, the cost of mining is not very high. However, it has been criticized by many as being “wasteful". The next set of alt-coins attempt to address this concern. Dual-purpose Proof-of-Work algorithms solve a specific "useful" problem, while producing Proof-of-Work to secure the network. The risk of adding an external use to the currency's security is that it also adds external influence to the supply/demand curve.
*Primecoin* *Primecoin*
Primecoin was announced in July 2013. It's Proof-of-Work algorithm searches for prime numbers, computing Cunningham and bi-twin prime chains. Prime numbers are useful in a variety of scientific disciplines. The Primecoin blockchain contains the discovered prime numbers, thereby producing a public record of scientific discovery in parallel to the public ledger of transactions. Primecoin was announced in July 2013. Its Proof-of-Work algorithm searches for prime numbers, computing Cunningham and bi-twin prime chains. Prime numbers are useful in a variety of scientific disciplines. The Primecoin blockchain contains the discovered prime numbers, thereby producing a public record of scientific discovery in parallel to the public ledger of transactions.
* Block generation: 1 minute * Block generation: 1 minute
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: Proof-of-Work with prime number chain discovery * Consensus algorithm: Proof-of-Work with prime number chain discovery
* Market capitalization: $1.3 million USD in Summer 2014 * Market capitalization: $1.3 million USD in mid-2014
*Curecoin* *Curecoin*
@ -216,7 +216,7 @@ Curecoin was announced in May 2013. It combines a SHA256 Proof-of-Work algorithm
* Block generation: 10 minutes * Block generation: 10 minutes
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: Proof-of-Work with protein folding research * Consensus algorithm: Proof-of-Work with protein folding research
* Market capitalization: $58,000 USD in Summer 2014 * Market capitalization: $58,000 USD in mid-2014
*Gridcoin* *Gridcoin*
@ -225,7 +225,7 @@ Gridcoin was introduced in October 2013. It supplements scrypt-based Proof-of-Wo
* Block generation: 150 seconds * Block generation: 150 seconds
* Total currency: No limit * Total currency: No limit
* Consensus algorithm: Proof-of-Work with BOINC grid-computing subsidy * Consensus algorithm: Proof-of-Work with BOINC grid-computing subsidy
* Market capitalization: $122,000 USD in Summer 2014 * Market capitalization: $122,000 USD in mid-2014
==== Anonymity-Focused Alt-Coins: CryptoNote, Bytecoin, Monero, Zerocash/Zerocoin, Darkcoin ==== Anonymity-Focused Alt-Coins: CryptoNote, Bytecoin, Monero, Zerocash/Zerocoin, Darkcoin
@ -233,7 +233,7 @@ Bitcoin is often mistakenly characterized as "anonymous" currency. In fact, it i
*Zerocoin/Zerocash* *Zerocoin/Zerocash*
Zerocoin is a theoretical approach to digital currency anonymity introduced in 2013 by researchers at Johns Hopkins. Zerocash is an alt-coin implementation of Zercoin that is in development and not yet released. Zerocoin is a theoretical approach to digital currency anonymity introduced in 2013 by researchers at Johns Hopkins. Zerocash is an alt-coin implementation of Zerocoin that is in development and not yet released.
*CryptoNote* *CryptoNote*
@ -246,25 +246,25 @@ Bytecoin was the first implementation spawned from CryptoNote, offering a viable
* Block generation: 2 minutes * Block generation: 2 minutes
* Total currency: 184 billion BCN * Total currency: 184 billion BCN
* Consensus algorithm: Cryptonight Proof-of-Work * Consensus algorithm: Cryptonight Proof-of-Work
* Market capitalization: $3 million USD in Summer 2014 * Market capitalization: $3 million USD in mid-2014
*Monero* *Monero*
Monero is another implementation of CryptoNote. It has a slightly flatter issuance curve than Bytecoin, issuing 80% of the currency in the first 4 years. It offers the same anonymity features inherited from CryptoNote. Monero is another implementation of CryptoNote. It has a slightly flatter issuance curve than Bytecoin, issuing 80% of the currency in the first 4 years. It offers the same anonymity features inherited from CryptoNote.
* Block generation: 1 minute * Block generation: 1 minute
* Total currency: 184 billion XMR * Total currency: 18.4 million XMR
* Consensus algorithm: Cryptonight Proof-of-Work * Consensus algorithm: Cryptonight Proof-of-Work
* Market capitalization: $5 million USD in Summer 2014 * Market capitalization: $5 million USD in mid-2014
*Darkcoin* *Darkcoin*
Darkcoin was launched in March of 2014. Darkcoin implements anonymous currency using a re-mixing protocol for all transactions called DarkSend. Darkcoin is also notable for using 11 rounds of different hash functions (blake, bmw, groestl, jh, keccak, skein, luffa, cubehash, shavite, simd, echo) for the Proof-of-Work algorithm. Darkcoin was launched in January of 2014. Darkcoin implements anonymous currency using a re-mixing protocol for all transactions called DarkSend. Darkcoin is also notable for using 11 rounds of different hash functions (blake, bmw, groestl, jh, keccak, skein, luffa, cubehash, shavite, simd, echo) for the Proof-of-Work algorithm.
* Block generation: 2.5 minutes * Block generation: 2.5 minutes
* Total currency: 22 million DRK * Total currency: maximum 22 million DRK
* Consensus algorithm: Multi-algorithm Multi-round Proof-of-Work * Consensus algorithm: Multi-algorithm Multi-round Proof-of-Work
* Market capitalization: $19 million USD in Summer 2014 * Market capitalization: $19 million USD in mid-2014
=== Non-currency alt-chains === Non-currency alt-chains
@ -272,7 +272,7 @@ Alt-chains are alternative implementations of the blockchain design pattern, whi
==== Namecoin ==== Namecoin
Namecoin was the first "fork" of the bitcoin code. Namecoin is a de-centralized key-value registration and transfer platform using a blockchain. It supports a global domain name registry similar to the domain-name registration system on the Internet. Namecoin is currently used as an alternative Domain Name Service (DNS) for the root-level domain +.bit+. Namecoin can also be used to register names and key-value pairs in other namespaces, for storing things like email addresses, encryption keys, SSL certificates, file signatures, voting systems, stock certificates and a myriad other applications. Namecoin was the first "fork" of the bitcoin code. Namecoin is a de-centralized key-value registration and transfer platform using a blockchain. It supports a global domain name registry similar to the domain-name registration system on the Internet. Namecoin is currently used as an alternative Domain Name Service (DNS) for the root-level domain +.bit+. Namecoin can also be used to register names and key-value pairs in other namespaces, for storing things like email addresses, encryption keys, SSL certificates, file signatures, voting systems, stock certificates and a myriad of other applications.
The Namecoin system includes the namecoin currency (symbol NMC), which is used to pay transaction fees for registration and transfer of names. At current prices, the fee to register a name is 0.01 NMC or approximately 1 US cent. As in bitcoin, the fees are collected by Namecoin miners. The Namecoin system includes the namecoin currency (symbol NMC), which is used to pay transaction fees for registration and transfer of names. At current prices, the fee to register a name is 0.01 NMC or approximately 1 US cent. As in bitcoin, the fees are collected by Namecoin miners.
@ -281,12 +281,13 @@ Namecoin's basic parameters are the same as bitcoin's:
* Block generation: 10 minutes * Block generation: 10 minutes
* Total currency: 21 million NMC by 2140 * Total currency: 21 million NMC by 2140
* Consensus algorithm: SHA256 Proof-of-Work * Consensus algorithm: SHA256 Proof-of-Work
* Market capitalization: $10 million USD in Summer 2014 * Market capitalization: $10 million USD in mid-2014
Namecoin currently has two namespaces: Namecoin's namespaces are not restricted, and anyone can use any namespace in any way. However, certain namespaces have an agreed upon specification so that when it is read from the blockchain, software knows how to read and proceed from there. If it is malformed, then whatever software you used to read from the specific namespace will throw an error. Some of the popular namespaces are:
* +d/+ is the domain-name namespace for +.bit+ domains * +d/+ is the domain-name namespace for +.bit+ domains
* +id/+ is the namespace for storing person identifiers such as email addresses, PGP keys etc. * +id/+ is the namespace for storing person identifiers such as email addresses, PGP keys etc.
* +u/+ is an additional, more structured specification to store identities (based on openspecs).
The Namecoin client is very similar to Bitcoin Core, as it is derived from the same source code. Upon installation, the client will download a full copy of the namecoin blockchain and then will be ready to query and register names. There are three main commands: The Namecoin client is very similar to Bitcoin Core, as it is derived from the same source code. Upon installation, the client will download a full copy of the namecoin blockchain and then will be ready to query and register names. There are three main commands:
@ -334,7 +335,7 @@ Namecoin registrations need to be updated every 36,000 blocks (approximately 200
==== Bitmessage ==== Bitmessage
Bitmessage is a bitcoin alt-chain that implements a de-centralized secure messaging service, essentially a server-less encrypted email system. Bitmessage allows users to compose and send message to each other, using a bitmessage address. The messages operate in much the same way as a bitcoin transaction, but they are transient - they do not persist beyond 2 days and if not delivered to the destination node in that time, they are lost. Senders and recipients are pseudonymous, they have no identifiers other than a bitmessage address, but are strongly authenticated, meaning that messages cannot be "spoofed". Bitmessages are encrypted to the recipient and therefore the bitmessage network is resistant to holistic surveillance - an eavesdropper has to compromise the recipient's device in order to intercept messages. Bitmessage is a bitcoin alt-chain that implements a de-centralized secure messaging service, essentially a server-less encrypted email system. Bitmessage allows users to compose and send messages to each other, using a bitmessage address. The messages operate in much the same way as a bitcoin transaction, but they are transient - they do not persist beyond 2 days and if not delivered to the destination node in that time, they are lost. Senders and recipients are pseudonymous, they have no identifiers other than a bitmessage address, but are strongly authenticated, meaning that messages cannot be "spoofed". Bitmessages are encrypted to the recipient and therefore the bitmessage network is resistant to holistic surveillance - an eavesdropper has to compromise the recipient's device in order to intercept messages.
==== Ethereum ==== Ethereum
@ -354,7 +355,7 @@ else:
=== Future of Currencies === Future of Currencies
The future of cryptographic currencies overall is even brighter than the future of bitcoin. Bitcoin introduced a completely new form of de-centralized organization and consensus that has spawned hundreds of incredible innovations. These inventions will likely affect broad sectors of the economy, from distributed systems science, to finance, economics, currencies, central banking and corporate governance. Many human activities that previously required centralized institutions or organizations to function as authoritative or trusted points of control can now be de-centralized. The invention of the blockchain and consensus system will significantly reduce the cost of organization and coordination on large scale systems, while removing opportunities for concentration of power, corruption and regulatory capture. The future of cryptographic currencies overall is even brighter than the future of bitcoin. Bitcoin introduced a completely new form of de-centralized organization and consensus that has spawned hundreds of incredible innovations. These inventions will likely affect broad sectors of the economy, from distributed systems science, to finance, economics, currencies, central banking, and corporate governance. Many human activities that previously required centralized institutions or organizations to function as authoritative or trusted points of control can now be de-centralized. The invention of the blockchain and consensus system will significantly reduce the cost of organization and coordination on large scale systems, while removing opportunities for concentration of power, corruption and regulatory capture.

31
preface.asciidoc
View File

@ -115,7 +115,11 @@ address (aka public key)::
((("bitcoin address"))) ((("bitcoin address")))
((("address", see="bitcoin address"))) ((("address", see="bitcoin address")))
((("public key", see="bitcoin address"))) ((("public key", see="bitcoin address")))
A bitcoin address looks like +1DSrfJdB2AnWaFNgSbv3MZC2m74996JafV+, they always start with a one. You can have as many as you like, share them so people can send you coins. A bitcoin address looks like +1DSrfJdB2AnWaFNgSbv3MZC2m74996JafV+, they always start with a one. Just like you ask others to send an email to your email address, you would ask others to send you bitcoin to your bitcoin address.
bip::
((("bip")))
Bitcoin Improvement Proposals. A set of proposals that members of the bitcoin community have submitted to improve bitcoin. For example BIP0021 is a proposal to improve the bitcoin URI scheme.
bitcoin:: bitcoin::
((("bitcoin"))) ((("bitcoin")))
@ -131,7 +135,7 @@ blockchain::
confirmations:: confirmations::
((("confirmations"))) ((("confirmations")))
Once a transaction is included in a block, it has "one confirmation". As soon as _another_ block is mined on the same blockchain, the transaction has two confirmations etc. Six or more confirmations is considered final. Once a transaction is included in a block, it has "one confirmation". As soon as _another_ block is mined on the same blockchain, the transaction has two confirmations etc. Six or more confirmations is considered sufficient proof that a transaction cannot be reversed.
difficulty:: difficulty::
((("difficulty"))) ((("difficulty")))
@ -147,7 +151,7 @@ difficulty re-targeting::
fees:: fees::
((("fees"))) ((("fees")))
An excess amount included in each transaction as a network fee or additional reward to the miner who finds the proof-of-work for the new block. Currently 0.5 mBTC minimum. The sender of a transaction often includes a fee to the network for processing their requested transaction. Most transactions require a minimum fee of 0.5mBTC.
hash:: hash::
((("hash"))) ((("hash")))
@ -176,7 +180,7 @@ reward::
secret key (aka private key):: secret key (aka private key)::
((("secret key"))) ((("secret key")))
((("private key", see="secret key"))) ((("private key", see="secret key")))
The secret number that unlocks bitcoins sent to the corresponding address. The secret number that unlocks bitcoins sent to the corresponding address. A secret key looks like +5J76sF8L5jTtzE96r66Sf8cka9y44wdpJjMwCxR3tzLh3ibVPxh+
transaction:: transaction::
((("transaction"))) ((("transaction")))
@ -184,7 +188,7 @@ transaction::
wallet:: wallet::
((("wallet"))) ((("wallet")))
Software that holds all your addresses. Use it to send bitcoin and manage your keys. Software that holds all your bitcoin addresses and secret keys. Use it to send, receive and store your bitcoin.
++++ ++++
<?hard-pagebreak?> <?hard-pagebreak?>
@ -199,15 +203,24 @@ Many contributors offered comments, corrections and additions to the early-relea
===== (Name - Github ID) ===== (Name - Github ID)
* *Minh T. Nguyen - enderminh: Github contribution editor* * *Minh T. Nguyen - enderminh: Github contribution editor*
* Ed Eykholt - edeykholt
* Michalis Kargakis - kargakis
* Erik Wahlström - erikwam * Erik Wahlström - erikwam
* Eric Winchell - winchell
* Richard Kiss - richardkiss * Richard Kiss - richardkiss
* Eric Winchell - winchell
* Sergej Kotliar - ziggamon * Sergej Kotliar - ziggamon
* Nagaraj Hubli - nagarajhubli * Nagaraj Hubli - nagarajhubli
* Michalis Kargakis - kargakis * ethers
* Ish Ot Jr. - ishotjr
* Alex Waters - alexwaters * Alex Waters - alexwaters
* Mihail Russu - MihailRussu * Mihail Russu - MihailRussu
* Ish Ot Jr. - ishotjr
* James Addison - jayaddison * James Addison - jayaddison
* Joe Bauers - joebauers * Nekomata - nekomata-3
* Simon de la Rouviere - simondlr
* Chapman Shoop - belovachap
* Holger Schinzel - schinzelh
* effectsToCause - vericoin
* Stephan Oeste - Emzy * Stephan Oeste - Emzy
* Joe Bauers - joebauers
* Jason Bisterfeldt - jbisterfeldt
* Ed Leafe - EdLeafe