((("Bitcoin Core", "compiling from source code", id="BCsource03")))((("Bitcoin Core", "compiling from source code", "downloading")))((("code examples, obtaining and using")))Bitcoin Core's source code can be downloaded as a archive or by cloning the authoritative source repository from GitHub. ((("Bitcoin Core downloads")))On the https://bitcoincore.org/bin/[Bitcoin Core download page], select the most recent version and download the compressed archive of the source code, e.g. +bitcoin-0.15.0.2.tar.gz+. ((("GitHub bitcoin page")))Alternatively, use the git command line to create a local copy of the source code from the https://github.com/bitcoin/bitcoin[GitHub bitcoin page].
((("Bitcoin Core", "compiling from source code", id="BCsource03")))((("Bitcoin Core", "compiling from source code", "downloading")))((("code examples, obtaining and using")))Bitcoin Core's source code can be downloaded as a archive or by cloning the authoritative source repository from GitHub. ((("Bitcoin Core downloads")))On the https://bitcoincore.org/bin/[Bitcoin Core download page], select the most recent version and download the compressed archive of the source code, e.g., +bitcoin-0.15.0.2.tar.gz+. ((("GitHub bitcoin page")))Alternatively, use the git command line to create a local copy of the source code from the https://github.com/bitcoin/bitcoin[GitHub bitcoin page].
[TIP]
====
@ -222,7 +222,7 @@ $ which bitcoin-cli
((("Bitcoin Core", "running core nodes", id="BCnode03")))((("bitcoin nodes", "running core nodes", id="BNcore03")))Bitcoin's peer-to-peer network is composed of network "nodes," run mostly by volunteers and some of the businesses that build bitcoin applications. Those running bitcoin nodes have a direct and authoritative view of the bitcoin blockchain, with a local copy of all the transactions, independently validated by their own system. By running a node, you don't have to rely on any third party to validate a transaction. Moreover, by running a bitcoin node you contribute to the bitcoin network by making it more robust.
Running a node, however, requires a permanently connected system with enough resources to process all bitcoin transactions. Depending on whether you choose to index all transactions and keep a full copy of the blockchain, you may also need a lot of disk space and RAM. As of early 2018, a full-index node needs 2 GB of RAM and a minimum of 160 GB of disk space (see https://blockchain.info/charts/blocks-size). Bitcoin nodes also transmit and receive bitcoin transactions and blocks, consuming internet bandwidth. If your internet connection is limited, has a low data cap, or is metered (charged by the gigabit), you should probably not run a bitcoin node on it, or run it in a way that constrains its bandwidth (see <<constrained_resources>>).
Running a node, however, requires a permanently connected system with enough resources to process all bitcoin transactions. Depending on whether you choose to index all transactions and keep a full copy of the blockchain, you may also need a lot of disk space and RAM. As of early 2018, a full-index node needs 2 GB of RAM and a minimum of 160 GB of disk space (see https://blockchain.info/charts/blocks-size[]). Bitcoin nodes also transmit and receive bitcoin transactions and blocks, consuming internet bandwidth. If your internet connection is limited, has a low data cap, or is metered (charged by the gigabit), you should probably not run a bitcoin node on it, or run it in a way that constrains its bandwidth (see <<constrained_resources>>).
[TIP]
====
@ -258,7 +258,7 @@ Using config file /home/ubuntu/.bitcoin/bitcoin.conf
...
----
You can hit Ctrl-C to shutdown the node once you determined the location of the config file. Usually the configuration file is inside the _.bitcoin_ data directory under your user's home directory. Open the configuration file in your preferred editor.
You can hit Ctrl-C to shutdown the node once you determine the location of the config file. Usually the configuration file is inside the _.bitcoin_ data directory under your user's home directory. Open the configuration file in your preferred editor.
Bitcoin Core offers more than 100 configuration options that modify the behavior of the network node, the storage of the blockchain, and many other aspects of its operation. To see a listing of these options, run +bitcoind --help+:
@ -510,7 +510,7 @@ It will take some time, perhaps more than a day, for the +bitcoind+ client to "c
In <<cup_of_coffee>>, ((("use cases", "buying coffee", id="alicethree")))Alice bought a cup of coffee from Bob's Cafe. Her transaction was recorded on the blockchain with transaction ID (txid) +0627052b6f28912f2703066a912ea577f2ce4da4caa5a5fbd8a57286c345c2f2+. Let's use the API to retrieve and examine that transaction by passing the transaction ID as a parameter:
In <<cup_of_coffee>>, ((("use cases", "buying coffee", id="alicethree")))Alice bought a cup of coffee from Bob's Cafe. Her transaction was recorded on the blockchain with transaction ID (+txid+) +0627052b6f28912f2703066a912ea577f2ce4da4caa5a5fbd8a57286c345c2f2+. Let's use the API to retrieve and examine that transaction by passing the transaction ID as a parameter:
((("transaction IDs (txd)")))((("malleability")))A transaction ID is not authoritative until a transaction has been confirmed. Absence of a transaction hash in the blockchain does not mean the transaction was not processed. This is known as "transaction malleability," because transaction hashes can be modified prior to confirmation in a block. After confirmation, the txid is immutable and authoritative.
((("transaction IDs (txd)")))((("malleability")))A transaction ID is not authoritative until a transaction has been confirmed. Absence of a transaction hash in the blockchain does not mean the transaction was not processed. This is known as "transaction malleability," because transaction hashes can be modified prior to confirmation in a block. After confirmation, the +txid+ is immutable and authoritative.
====
The command +getrawtransaction+ returns a serialized transaction in hexadecimal notation. To decode that, we use the +decoderawtransaction+ command, passing the hex data as a parameter. You can copy the hex returned by +getrawtransaction+ and paste it as a parameter to +decoderawtransaction+:
The transaction decode shows all the components of this transaction, including the transaction inputs and outputs. In this case we see that the transaction that credited our new address with 15 millibits used one input and generated two outputs. The input to this transaction was the output from a previously confirmed transaction (shown as the vin txid starting with +7957a35fe+). The two outputs correspond to the 15 millibit credit and an output with change back to the sender.
The transaction decode shows all the components of this transaction, including the transaction inputs and outputs. In this case we see that the transaction that credited our new address with 15 millibits used one input and generated two outputs. The input to this transaction was the output from a previously confirmed transaction (shown as the vin +txid+ starting with +7957a35fe+). The two outputs correspond to the 15 millibit credit and an output with change back to the sender.
We can further explore the blockchain by examining the previous transaction referenced by its txid in this transaction using the same commands (e.g., +getrawtransaction+). Jumping from transaction to transaction we can follow a chain of transactions back as the coins are transmitted from owner address to owner address.
We can further explore the blockchain by examining the previous transaction referenced by its +txid+ in this transaction using the same commands (e.g., +getrawtransaction+). Jumping from transaction to transaction we can follow a chain of transactions back as the coins are transmitted from owner address to owner address.
@ -443,7 +443,6 @@ K = 04F028892BAD7ED57D2FB57BF33081D5CFCF6F9ED3D3D7F159C2E2FFF579DC341A↵
++++
[[comp_pub]]
[role="pagebreak-before"]
===== Compressed public keys
((("public and private keys", "compressed public keys")))Compressed public keys were introduced to bitcoin to reduce the size of transactions and conserve disk space on nodes that store the bitcoin blockchain database. Most transactions include the public key, which is required to validate the owner's credentials and spend the bitcoin. Each public key requires 520 bits (prefix + x + y), which when multiplied by several hundred transactions per block, or tens of thousands of transactions per day, adds a significant amount of data to the blockchain.
The example in <<addr_example_run>>, produces a bitcoin address (+1PRTT...+) from a _compressed_ public key (see <<comp_pub>>). If you used the uncompressed public key instead, it would produce a different bitcoin address (+14K1y...+).
The code in <<addr_example_run>> produces a bitcoin address (+1PRTT...+) from a _compressed_ public key (see <<comp_pub>>). If you used the uncompressed public key instead, it would produce a different bitcoin address (+14K1y...+).
@ -64,15 +64,15 @@ You may also notice a lot of strange and indecipherable fields and hexadecimal s
((("transactions", "outputs and inputs", id="Tout06")))((("outputs and inputs", "outputs defined")))((("unspent transaction outputs (UTXO)")))((("UTXO sets")))((("transactions", "outputs and inputs", "output characteristics")))((("outputs and inputs", "output characteristics")))The fundamental building block of a bitcoin transaction is a _transaction output_. Transaction outputs are indivisible chunks of bitcoin currency, recorded on the blockchain, and recognized as valid by the entire network. Bitcoin full nodes track all available and spendable outputs, known as _unspent transaction outputs_, or _UTXO_. The collection of all UTXO is known as the _UTXO set_ and currently numbers in the millions of UTXO. The UTXO set grows as new UTXO is created and shrinks when UTXO is consumed. Every transaction represents a change (state transition) in the UTXO set.
((("balances")))When we say that a user's wallet has "received" bitcoin, what we mean is that the wallet has detected a UTXO that can be spent with one of the keys controlled by that wallet. Thus, a user's bitcoin "balance" is the sum of all UTXO that user's wallet can spend and which may be scattered among hundreds of transactions and hundreds of blocks. The concept of a balance is created by the wallet application. The wallet calculates the user's balance by scanning the blockchain and aggregating the value of any UTXO the wallet can spend with the keys it controls. Most wallets maintain a database or use a database service to store a quick reference set of all the UTXO they can spend with the keys they control.
((("balances")))When we say that a user's wallet has "received" bitcoin, what we mean is that the wallet has detected an UTXO that can be spent with one of the keys controlled by that wallet. Thus, a user's bitcoin "balance" is the sum of all UTXO that user's wallet can spend and which may be scattered among hundreds of transactions and hundreds of blocks. The concept of a balance is created by the wallet application. The wallet calculates the user's balance by scanning the blockchain and aggregating the value of any UTXO the wallet can spend with the keys it controls. Most wallets maintain a database or use a database service to store a quick reference set of all the UTXO they can spend with the keys they control.
((("satoshis")))A transaction output can have an arbitrary (integer) value denominated as a multiple of satoshis. Just as dollars can be divided down to two decimal places as cents, bitcoin can be divided down to eight decimal places as satoshis. Although an output can have any arbitrary value, once created it is indivisible. This is an important characteristic of outputs that needs to be emphasized: outputs are _discrete_ and _indivisible_ units of value, denominated in integer satoshis. An unspent output can only be consumed in its entirety by a transaction.
((("change, making")))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 UTXO worth 20 bitcoin and want to pay only 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 of the indivisible nature of transaction outputs, most bitcoin transactions will have to generate change.
((("change, making")))If an 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 an UTXO worth 20 bitcoin and want to pay only 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 of the indivisible nature of transaction outputs, most bitcoin transactions will have to generate change.
Imagine a shopper buying a $1.50 beverage, reaching into her 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 e.g. a dollar bill and two quarters (a quarter is $0.25), or a combination of smaller denominations (six quarters), or if necessary, a larger unit such as a $5 note. If she hands too much money, say $5, to the shop owner, she will expect $3.50 change, which she will return to her 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. Users 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 to compose an amount greater than or equal to the desired transaction amount.
Similarly, a bitcoin transaction must be created from a user's UTXO in whatever denominations that user has available. Users cannot cut an 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 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. All of this complex assembly of spendable UTXO is done by the user's wallet automatically and is invisible to users. It is only relevant if you are programmatically constructing raw transactions from UTXO.
@ -171,7 +171,7 @@ Here are some hints:
To build a transaction, a wallet selects from the UTXO it controls, UTXO with enough value to make the requested payment. Sometimes one UTXO is enough, other times more than one is needed. For each UTXO that will be consumed to make this payment, the wallet creates one input pointing to the UTXO and unlocks it with an unlocking script.
Let's look at the components of an input in greater detail. The first part of an input is a pointer to a UTXO by reference to the transaction hash and an output index, which identifies the specific UTXO in that transaction. The second part is an unlocking script, which the wallet constructs in order to satisfy the spending conditions set in the UTXO. Most often, the unlocking script is a digital signature and public key proving ownership of the bitcoin. However, not all unlocking scripts contain signatures. The third part is a sequence number, which will be discussed later.
Let's look at the components of an input in greater detail. The first part of an input is a pointer to an UTXO by reference to the transaction hash and an output index, which identifies the specific UTXO in that transaction. The second part is an unlocking script, which the wallet constructs in order to satisfy the spending conditions set in the UTXO. Most often, the unlocking script is a digital signature and public key proving ownership of the bitcoin. However, not all unlocking scripts contain signatures. The third part is a sequence number, which will be discussed later.
Consider our example in <<transactions_behind_the_scenes>>. The transaction inputs are an array (list) called +vin+:
@ -359,7 +359,7 @@ Eugenia's wallet application will calculate the appropriate fee by measuring the
[role="pagebreak-before less_space_h1"]
=== Transaction Scripts and Script Language
((("transactions", "scripts and Script language", id="Tsript06")))((("scripting", "transactions and", id="Stransact06")))The bitcoin transaction script language, called _Script_, is a Forth-like reverse-polish notation stack-based execution language. If that sounds like gibberish, you probably haven't studied 1960s programming languages, but that's ok—we will explain it all in this chapter. Both the locking script placed on a UTXO and the unlocking script are written in this scripting language. When a transaction is validated, the unlocking script in each input is executed alongside the corresponding locking script to see if it satisfies the spending condition.
((("transactions", "scripts and Script language", id="Tsript06")))((("scripting", "transactions and", id="Stransact06")))The bitcoin transaction script language, called _Script_, is a Forth-like reverse-polish notation stack-based execution language. If that sounds like gibberish, you probably haven't studied 1960s programming languages, but that's ok—we will explain it all in this chapter. Both the locking script placed on an UTXO and the unlocking script are written in this scripting language. When a transaction is validated, the unlocking script in each input is executed alongside the corresponding locking script to see if it satisfies the spending condition.
Script is a very simple language that was designed to be limited in scope and executable on a range of hardware, perhaps as simple as an embedded device. It requires minimal processing and cannot do many of the fancy things modern programming languages can do. For its use in validating programmable money, this is a deliberate security feature.
@ -124,7 +124,6 @@ First, the multisignature script that Mohammed's company uses for all incoming p
If the placeholders are replaced by actual public keys (shown here as 520-bit numbers starting with 04) you can see that this script becomes very long:
Almost all the scripts described in this chapter can only be implemented as P2SH scripts. They cannot be used directly in the locking script of a UTXO.((("", startref="mohamseven")))
Almost all the scripts described in this chapter can only be implemented as P2SH scripts. They cannot be used directly in the locking script of an UTXO.((("", startref="mohamseven")))
==== P2SH Addresses
@ -356,7 +355,7 @@ BIP-68 and BIP-112 were activated in May 2016 as a soft fork upgrade to the cons
The +nSequence+ field was originally intended (but never properly implemented) to allow modification of transactions in the mempool. In that use, a transaction containing inputs with +nSequence+ value below 2^32^ - 1 (0xFFFFFFFF) indicated a transaction that was not yet "finalized." Such a transaction would be held in the mempool until it was replaced by another transaction spending the same inputs with a higher +nSequence+ value. Once a transaction was received whose inputs had an +nSequence+ value of 0xFFFFFFFF it would be considered "finalized" and mined.
The original meaning of +nSequence+ was never properly implemented and the value of +nSequence+ is customarily set to 0xFFFFFFFF in transactions that do not utilize timelocks. For transactions with nLocktime or +CHECKLOCKTIMEVERIFY+, the +nSequence+ value must be set to less than 2^31^ for the timelock guards to have effect, as explained below.
The original meaning of +nSequence+ was never properly implemented and the value of +nSequence+ is customarily set to 0xFFFFFFFF in transactions that do not utilize timelocks. For transactions with nLocktime or +CHECKLOCKTIMEVERIFY+, the +nSequence+ value must be set to less than 2^31^ for the timelock guards to have an effect, as explained below.
===== nSequence as a consensus-enforced relative timelock
@ -383,7 +382,7 @@ The standard is defined in https://github.com/bitcoin/bips/blob/master/bip-0068.
((("scripting", "timelocks", "relative timelocks with CHECKSEQUENCEVERIFY")))((("CHECKSEQUENCEVERIFY (CSV)")))Just like CLTV and +nLocktime+, there is a script opcode for relative timelocks that leverages the +nSequence+ value in scripts. That opcode is +CHECKSEQUENCEVERIFY+, commonly referred to as +CSV+ for short.
The +CSV+ opcode when evaluated in a UTXO's redeem script allows spending only in a transaction whose input +nSequence+ value is greater than or equal to the +CSV+ parameter. Essentially, this restricts spending the UTXO until a certain number of blocks or seconds have elapsed relative to the time the UTXO was mined.
The +CSV+ opcode when evaluated in an UTXO's redeem script allows spending only in a transaction whose input +nSequence+ value is greater than or equal to the +CSV+ parameter. Essentially, this restricts spending the UTXO until a certain number of blocks or seconds have elapsed relative to the time the UTXO was mined.
As with CLTV, the value in +CSV+ must match the format in the corresponding +nSequence+ value. If +CSV+ is specified in terms of blocks, then so must +nSequence+. If +CSV+ is specified in terms of seconds, then so must +nSequence+.
@ -648,7 +647,6 @@ Segregated Witness therefore is an architectural change to bitcoin that aims to
In this section we will look at some of the benefits of Segregated Witness, describe the mechanism used to deploy and implement this architecture change, and demonstrate the use of Segregated Witness in transactions and addresses.
[role="pagebreak-before"]
Segregated Witness is defined by the following BIPs:
https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki[BIP-141] :: The main definition of Segregated Witness.
:: Base32 address format for native v0-16 witness outputs
https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki[BIP-173]:: Base32 address format for native v0-16 witness outputs
BIP-173 only encodes witness (P2WPKH and P2WSH) scripts. It is not compatible with non-segwit P2PKH or P2SH scripts. BIP-173 is a checksummed Base32 encoding, as compared to the Base58 encoding of a "traditional" bitcoin address. BIP-173 addesses are also called _bech32_ addresses, pronounced "beh-ch thirty two", alluding to the use of a "BCH" error detection algorithm and 32-character encoding set.
@ -333,6 +333,6 @@ When a transaction is added to the transaction pool, the orphan pool is checked
Both the transaction pool and orphan pool (where implemented) are stored in local memory and are not saved on persistent storage; rather, they are dynamically populated from incoming network messages. When a node starts, both pools are empty and are gradually populated with new transactions received on the network.
Some implementations of the bitcoin client also maintain a UTXO database or pool, which is the set of all unspent outputs on the blockchain. Although the name "UTXO pool" sounds similar to the transaction pool, it represents a different set of data. Unlike the transaction and orphan pools, the UTXO pool is not initialized empty but instead contains millions of entries of unspent transaction outputs, everything that is unspent from all the way back to the genesis block. The UTXO pool may be housed in local memory or as an indexed database table on persistent storage.
Some implementations of the bitcoin client also maintain an UTXO database or pool, which is the set of all unspent outputs on the blockchain. Although the name "UTXO pool" sounds similar to the transaction pool, it represents a different set of data. Unlike the transaction and orphan pools, the UTXO pool is not initialized empty but instead contains millions of entries of unspent transaction outputs, everything that is unspent from all the way back to the genesis block. The UTXO pool may be housed in local memory or as an indexed database table on persistent storage.
Whereas the transaction and orphan pools represent a single node's local perspective and might vary significantly from node to node depending upon when the node was started or restarted, the UTXO pool represents the emergent consensus of the network and therefore will vary little between nodes. Furthermore, the transaction and orphan pools only contain unconfirmed transactions, while the UTXO pool only contains confirmed outputs.
@ -455,7 +455,6 @@ Prototype implementations of the Lightning Network have been released by several
The Lightning Network is one possible way of implementing routed payment channels. There are several other designs that aim to achieve similar goals, such as Teechan and Tumblebit.
[role="pagebreak-before less_space_heading"]
==== Basic Lightning Network Example
((("Lightning Network", "basic example")))Let's see how this works.
Andreas M. Antonopoulos
6 years ago