Bitcoin Developer Reference

The Developer Reference aims to provide technical details and API information to help you start building Bitcoin-based applications, but it is not a specification. To make the best use of this documentation, you may want to install the current version of Bitcoin Core, either from source or from a pre-compiled executable.

Questions about Bitcoin development are best asked on the Bitcoin StackExchange. Errors or suggestions related to documentation on this site can be submitted as an issue or posted to the bitcoin-documentation mailing list.

In the following documentation, some strings have been shortened or wrapped: “[…]” indicates extra data was removed, and lines ending in a single backslash “\” are continued below. If you hover your mouse over a paragraph, cross-reference links will be shown in blue. If you hover over a cross-reference link, a brief definition of the term will be displayed in a tooltip.

Not A Specification

This Developer Documentation describes how Bitcoin works to help educate new Bitcoin developers, but it is not a specification—and it never will be.

Bitcoin security depends on consensus. Should your program diverge from consensus, its security is weakened or destroyed. The cause of the divergence doesn’t matter: it could be a bug in your program, it could be an error in this documentation which you implemented as described, or it could be you do everything right but other software on the network behaves unexpectedly. The specific cause will not matter to the users of your software whose wealth is lost.

The only correct specification of consensus behavior is the actual behavior of programs on the network which maintain consensus. As that behavior is subject to arbitrary inputs in a large variety of unique environments, it cannot ever be fully documented here or anywhere else.

However, the Bitcoin Core developers are working on making their consensus code portable so other implementations can use it. Bitcoin Core 0.10.0 will provide libbitcoinconsensus, a first attempt at exporting some consensus code. Future versions of Bitcoin Core will likely provide consensus code that is more complete, more portable, and more consistent in diverse environments.

In addition, we also warn you that this documentation has not been extensively reviewed by Bitcoin experts and so likely contains numerous errors. At the bottom of the menu on the left, you will find links that allow you to report an issue or to edit the documentation on GitHub. Please use those links if you find any errors or important missing information.

Block Chain

The following subsections briefly document core block details.

Block Headers

Block headers are serialized in the 80-byte format described below and then hashed as part of Bitcoin’s proof-of-work algorithm, making the serialized header format part of the consensus rules.

The hashes are in internal byte order; the other values are all in little-endian order.

An example header in hex:

02000000 ........................... Block version: 2

b6ff0b1b1680a2862a30ca44d346d9e8
910d334beb48ca0c0000000000000000 ... Hash of previous block's header
9d10aa52ee949386ca9385695f04ede2
70dda20810decd12bc9b048aaab31471 ... Merkle root

24d95a54 ........................... Unix time: 1415239972
30c31b18 ........................... Target: 0x1bc330 * 256**(0x18-3)
fe9f0864 ........................... Nonce

Block Versions

• Version 1 was introduced in the genesis block (January 2009).

• Version 2 was introduced in Bitcoin Core 0.7.0 (September 2012) as a soft fork. As described in BIP34, valid version 2 blocks require a block height parameter in the coinbase. Also described in BIP34 are rules for rejecting certain blocks; based on those rules, Bitcoin Core 0.7.0 and later versions began to reject version 2 blocks without the block height in coinbase at block height 224,412 (March 2013) and began to reject new version 1 blocks three weeks later at block height 227,930.

• Version 3 blocks were introduced in Bitcoin Core 0.10.0 (February 2015) as a soft fork. When the fork reach full enforcement (July 2015), it required strict DER encoding of all ECDSA signatures in new blocks as described in BIP66. Transactions that do not use strict DER encoding had previously been non-standard since Bitcoin Core 0.8.0 (February 2012).

• Version 4 blocks specified in BIP65 and introduced in Bitcoin Core 0.11.2 (November 2015) as a soft fork became active in December 2015. These blocks now support the new OP_CHECKLOCKTIMEVERIFY opcode described in that BIP.

The mechanism used for the version 2, 3, and 4 upgrades is commonly called IsSuperMajority() after the function added to Bitcoin Core to manage those soft forking changes. See BIP34 for a full description of this method.

As of this writing, a newer method called version bits is being designed to manage future soft forking changes, although it’s not known whether version 4 will be the last soft fork to use the IsSuperMajority() function. Draft BIP9 describes the version bits design as of this writing, although it is still being actively edited and may substantially change while in the draft state.

Merkle Trees

The merkle root is constructed using all the TXIDs of transactions in this block, but first the TXIDs are placed in order as required by the consensus rules:

• The coinbase transaction’s TXID is always placed first.

• Any input within this block can spend an output which also appears in this block (assuming the spend is otherwise valid). However, the TXID corresponding to the output must be placed at some point before the TXID corresponding to the input. This ensures that any program parsing block chain transactions linearly will encounter each output before it is used as an input.

If a block only has a coinbase transaction, the coinbase TXID is used as the merkle root hash.

If a block only has a coinbase transaction and one other transaction, the TXIDs of those two transactions are placed in order, concatenated as 64 raw bytes, and then SHA256(SHA256()) hashed together to form the merkle root.

If a block has three or more transactions, intermediate merkle tree rows are formed. The TXIDs are placed in order and paired, starting with the coinbase transaction’s TXID. Each pair is concatenated together as 64 raw bytes and SHA256(SHA256()) hashed to form a second row of hashes. If there are an odd (non-even) number of TXIDs, the last TXID is concatenated with a copy of itself and hashed. If there are more than two hashes in the second row, the process is repeated to create a third row (and, if necessary, repeated further to create additional rows). Once a row is obtained with only two hashes, those hashes are concatenated and hashed to produce the merkle root.

TXIDs and intermediate hashes are always in internal byte order when they’re concatenated, and the resulting merkle root is also in internal byte order when it’s placed in the block header.

Target nBits

The target threshold is a 256-bit unsigned integer which a header hash must be equal to or below in order for that header to be a valid part of the block chain. However, the header field nBits provides only 32 bits of space, so the target number uses a less precise format called “compact” which works like a base-256 version of scientific notation:

As a base-256 number, nBits can be quickly parsed as bytes the same way you might parse a decimal number in base-10 scientific notation:

Although the target threshold should be an unsigned integer, the original nBits implementation inherits properties from a signed data class, allowing the target threshold to be negative if the high bit of the significand is set. This is useless—the header hash is treated as an unsigned number, so it can never be equal to or lower than a negative target threshold. Bitcoin Core deals with this in two ways:

• When parsing nBits, Bitcoin Core converts a negative target threshold into a target of zero, which the header hash can equal (in theory, at least).

• When creating a value for nBits, Bitcoin Core checks to see if it will produce an nBits which will be interpreted as negative; if so, it divides the significand by 256 and increases the exponent by 1 to produce the same number with a different encoding.

Some examples taken from the Bitcoin Core test cases:

Difficulty 1, the minimum allowed difficulty, is represented on mainnet and the current testnet by the nBits value 0x1d00ffff. Regtest mode uses a different difficulty 1 value—0x207fffff, the highest possible value below uint32_max which can be encoded; this allows near-instant building of blocks in regtest mode.

Serialized Blocks

Under current consensus rules, a block is not valid unless its serialized size is less than or equal to 1 MB. All fields described below are counted towards the serialized size.

The first transaction in a block must be a coinbase transaction which should collect and spend any transaction fees paid by transactions included in this block.

All blocks with a block height less than 6,930,000 are entitled to receive a block subsidy of newly created bitcoin value, which also should be spent in the coinbase transaction. (The block subsidy started at 50 bitcoins and is being halved every 210,000 blocks—approximately once every four years. As of November 2017, it’s 12.5 bitcoins.)

Together, the transaction fees and block subsidy are called the block reward. A coinbase transaction is invalid if it tries to spend more value than is available from the block reward.

Transactions

The following subsections briefly document core transaction details.

OpCodes

The opcodes used in the pubkey scripts of standard transactions are:

• Various data pushing opcodes from 0x00 to 0x4e (1–78). These aren’t typically shown in examples, but they must be used to push signatures and public keys onto the stack. See the link below this list for a description.

• OP_TRUE/OP_1 (0x51) and OP_2 through OP_16 (0x52–0x60), which push the values 1 through 16 to the stack.

• OP_CHECKSIG consumes a signature and a full public key, and pushes true onto the stack if the transaction data specified by the SIGHASH flag was converted into the signature using the same ECDSA private key that generated the public key. Otherwise, it pushes false onto the stack.

• OP_DUP pushes a copy of the topmost stack item on to the stack.

• OP_HASH160 consumes the topmost item on the stack, computes the RIPEMD160(SHA256()) hash of that item, and pushes that hash onto the stack.

• OP_EQUAL consumes the top two items on the stack, compares them, and pushes true onto the stack if they are the same, false if not.

• OP_VERIFY consumes the topmost item on the stack. If that item is zero (false) it terminates the script in failure.

• OP_EQUALVERIFY runs OP_EQUAL and then OP_VERIFY in sequence.

• OP_CHECKMULTISIG consumes the value (n) at the top of the stack, consumes that many of the next stack levels (public keys), consumes the value (m) now at the top of the stack, and consumes that many of the next values (signatures) plus one extra value.

  The “one extra value” it consumes is the result of an off-by-one error in the Bitcoin Core implementation. This value is not used, so signature scripts prefix the list of secp256k1 signatures with a single OP_0 (0x00).

  OP_CHECKMULTISIG compares the first signature against each public key until it finds an ECDSA match. Starting with the subsequent public key, it compares the second signature against each remaining public key until it finds an ECDSA match. The process is repeated until all signatures have been checked or not enough public keys remain to produce a successful result.

  Because public keys are not checked again if they fail any signature comparison, signatures must be placed in the signature script using the same order as their corresponding public keys were placed in the pubkey script or redeem script. See the OP_CHECKMULTISIG warning below for more details.

• OP_RETURN terminates the script in failure when executed.

A complete list of opcodes can be found on the Bitcoin Wiki Script Page, with an authoritative list in the opcodetype enum of the Bitcoin Core script header file

Signature script modification warning: Signature scripts are not signed, so anyone can modify them. This means signature scripts should only contain data and data-pushing opcodes which can’t be modified without causing the pubkey script to fail. Placing non-data-pushing opcodes in the signature script currently makes a transaction non-standard, and future consensus rules may forbid such transactions altogether. (Non-data-pushing opcodes are already forbidden in signature scripts when spending a P2SH pubkey script.)

OP_CHECKMULTISIG warning: The multisig verification process described above requires that signatures in the signature script be provided in the same order as their corresponding public keys in the pubkey script or redeem script. For example, the following combined signature and pubkey script will produce the stack and comparisons shown:

OP_0 <A sig> <B sig> OP_2 <A pubkey> <B pubkey> <C pubkey> OP_3

Sig Stack       Pubkey Stack  (Actually a single stack)
---------       ------------
B sig           C pubkey
A sig           B pubkey
OP_0            A pubkey

1. B sig compared to C pubkey (no match)
2. B sig compared to B pubkey (match #1)
3. A sig compared to A pubkey (match #2)

Success: two matches found

But reversing the order of the signatures with everything else the same will fail, as shown below:

OP_0 <B sig> <A sig> OP_2 <A pubkey> <B pubkey> <C pubkey> OP_3

Sig Stack       Pubkey Stack  (Actually a single stack)
---------       ------------
A sig           C pubkey
B sig           B pubkey
OP_0            A pubkey

1. A sig compared to C pubkey (no match)
2. A sig compared to B pubkey (no match)

Failure, aborted: two signature matches required but none found so
                  far, and there's only one pubkey remaining

Address Conversion

The hashes used in P2PKH and P2SH outputs are commonly encoded as Bitcoin addresses. This is the procedure to encode those hashes and decode the addresses.

First, get your hash. For P2PKH, you RIPEMD-160(SHA256()) hash a ECDSA public key derived from your 256-bit ECDSA private key (random data). For P2SH, you RIPEMD-160(SHA256()) hash a redeem script serialized in the format used in raw transactions (described in a following sub-section). Taking the resulting hash:

1. Add an address version byte in front of the hash. The version bytes commonly used by Bitcoin are:

   • 0x00 for P2PKH addresses on the main Bitcoin network (mainnet)

   • 0x6f for P2PKH addresses on the Bitcoin testing network (testnet)

   • 0x05 for P2SH addresses on mainnet

   • 0xc4 for P2SH addresses on testnet

2. Create a copy of the version and hash; then hash that twice with SHA256: SHA256(SHA256(version . hash))

3. Extract the first four bytes from the double-hashed copy. These are used as a checksum to ensure the base hash gets transmitted correctly.

4. Append the checksum to the version and hash, and encode it as a base58 string: BASE58(version . hash . checksum)

Bitcoin’s base58 encoding, called Base58Check may not match other implementations. Tier Nolan provided the following example encoding algorithm to the Bitcoin Wiki Base58Check encoding page under the Creative Commons Attribution 3.0 license:

code_string = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
x = convert_bytes_to_big_integer(hash_result)

output_string = ""

while(x > 0) 
   {
       (x, remainder) = divide(x, 58)
       output_string.append(code_string[remainder])
   }

repeat(number_of_leading_zero_bytes_in_hash)
   {
   output_string.append(code_string[0]);
   }

output_string.reverse();

Bitcoin’s own code can be traced using the base58 header file.

To convert addresses back into hashes, reverse the base58 encoding, extract the checksum, repeat the steps to create the checksum and compare it against the extracted checksum, and then remove the version byte.

Raw Transaction Format

Bitcoin transactions are broadcast between peers in a serialized byte format, called raw format. It is this form of a transaction which is SHA256(SHA256()) hashed to create the TXID and, ultimately, the merkle root of a block containing the transaction—making the transaction format part of the consensus rules.

Bitcoin Core and many other tools print and accept raw transactions encoded as hex.

As of Bitcoin Core 0.9.3 (October 2014), all transactions use the version 1 format described below. (Note: transactions in the block chain are allowed to list a higher version number to permit soft forks, but they are treated as version 1 transactions by current software.)

A raw transaction has the following top-level format:

A transaction may have multiple inputs and outputs, so the txIn and txOut structures may recur within a transaction. CompactSize unsigned integers are a form of variable-length integers; they are described in the CompactSize section.

TxIn: A Transaction Input (Non-Coinbase)

Each non-coinbase input spends an outpoint from a previous transaction. (Coinbase inputs are described separately after the example section below.)

Outpoint: The Specific Part Of A Specific Output

Because a single transaction can include multiple outputs, the outpoint structure includes both a TXID and an output index number to refer to specific output.

TxOut: A Transaction Output

Each output spends a certain number of satoshis, placing them under control of anyone who can satisfy the provided pubkey script.

Example

The sample raw transaction itemized below is the one created in the Simple Raw Transaction section of the Developer Examples. It spends a previous pay-to-pubkey output by paying to a new pay-to-pubkey-hash (P2PKH) output.

01000000 ................................... Version

01 ......................................... Number of inputs
|
| 7b1eabe0209b1fe794124575ef807057
| c77ada2138ae4fa8d6c4de0398a14f3f ......... Outpoint TXID
| 00000000 ................................. Outpoint index number
|
| 49 ....................................... Bytes in sig. script: 73
| | 48 ..................................... Push 72 bytes as data
| | | 30450221008949f0cb400094ad2b5eb3
| | | 99d59d01c14d73d8fe6e96df1a7150de
| | | b388ab8935022079656090d7f6bac4c9
| | | a94e0aad311a4268e082a725f8aeae05
| | | 73fb12ff866a5f01 ..................... Secp256k1 signature
|
| ffffffff ................................. Sequence number: UINT32_MAX

01 ......................................... Number of outputs
| f0ca052a01000000 ......................... Satoshis (49.99990000 BTC)
|
| 19 ....................................... Bytes in pubkey script: 25
| | 76 ..................................... OP_DUP
| | a9 ..................................... OP_HASH160
| | 14 ..................................... Push 20 bytes as data
| | | cbc20a7664f2f69e5355aa427045bc15
| | | e7c6c772 ............................. PubKey hash
| | 88 ..................................... OP_EQUALVERIFY
| | ac ..................................... OP_CHECKSIG

00000000 ................................... locktime: 0 (a block height)

Coinbase Input: The Input Of The First Transaction In A Block

The first transaction in a block, called the coinbase transaction, must have exactly one input, called a coinbase. The coinbase input currently has the following format.

Most (but not all) blocks prior to block height 227,836 used block version 1 which did not require the height parameter to be prefixed to the coinbase script. The block height parameter is now required.

Although the coinbase script is arbitrary data, if it includes the bytes used by any signature-checking operations such as OP_CHECKSIG, those signature checks will be counted as signature operations (sigops) towards the block’s sigop limit. To avoid this, you can prefix all data with the appropriate push operation.

An itemized coinbase transaction:

01000000 .............................. Version

01 .................................... Number of inputs
| 00000000000000000000000000000000
| 00000000000000000000000000000000 ...  Previous outpoint TXID
| ffffffff ............................ Previous outpoint index
|
| 29 .................................. Bytes in coinbase
| |
| | 03 ................................ Bytes in height
| | | 4e0105 .......................... Height: 328014
| |
| | 062f503253482f0472d35454085fffed
| | f2400000f90f54696d65202620486561
| | 6c74682021 ........................ Arbitrary data
| 00000000 ............................ Sequence

01 .................................... Output count
| 2c37449500000000 .................... Satoshis (25.04275756 BTC)
| 1976a914a09be8040cbf399926aeb1f4
| 70c37d1341f3b46588ac ................ P2PKH script
| 00000000 ............................ Locktime

CompactSize Unsigned Integers

The raw transaction format and several peer-to-peer network messages use a type of variable-length integer to indicate the number of bytes in a following piece of data.

Bitcoin Core code and this document refers to these variable length integers as compactSize. Many other documents refer to them as var_int or varInt, but this risks conflation with other variable-length integer encodings—such as the CVarInt class used in Bitcoin Core for serializing data to disk. Because it’s used in the transaction format, the format of compactSize unsigned integers is part of the consensus rules.

For numbers from 0 to 252, compactSize unsigned integers look like regular unsigned integers. For other numbers up to 0xffffffffffffffff, a byte is prefixed to the number to indicate its length—but otherwise the numbers look like regular unsigned integers in little-endian order.

For example, the number 515 is encoded as 0xfd0302.

Wallets

Deterministic Wallet Formats

Type 1: Single Chain Wallets

Type 1 deterministic wallets are the simpler of the two, which can create a single series of keys from a single seed. A primary weakness is that if the seed is leaked, all funds are compromised, and wallet sharing is extremely limited.

Type 2: Hierarchical Deterministic (HD) Wallets

For an overview of HD wallets, please see the developer guide section. For details, please see BIP32.

P2P Network

This section describes the Bitcoin P2P network protocol (but it is not a specification). It does not describe the discontinued direct IP-to-IP payment protocol, the BIP70 payment protocol, the GetBlockTemplate mining protocol, or any network protocol never implemented in an official version of Bitcoin Core.

All peer-to-peer communication occurs entirely over TCP.

Note: unless their description says otherwise, all multi-byte integers mentioned in this section are transmitted in little-endian order.

Constants And Defaults

The following constants and defaults are taken from Bitcoin Core’s chainparams.cpp source code file.

Note: the testnet start string and nBits above are for testnet3; the original testnet used a different string and higher (less difficult) nBits.

Command line parameters can change what port a node listens on (see -help). Start strings are hardcoded constants that appear at the start of all messages sent on the Bitcoin network; they may also appear in data files such as Bitcoin Core’s block database. The nBits displayed above are in big-endian order; they’re sent over the network in little-endian order.

Bitcoin Core’s chainparams.cpp also includes other constants useful to programs, such as the hash of the genesis blocks for the different networks.

Protocol Versions

The table below lists some notable versions of the P2P network protocol, with the most recent versions listed first. (If you know of a protocol version that implemented a major change but which is not listed here, please open an issue.)

As of Bitcoin Core 0.14.2, the most recent protocol version is 70015.

Message Headers

All messages in the network protocol use the same container format, which provides a required multi-field message header and an optional payload. The message header format is:

The following example is an annotated hex dump of a mainnet message header from a verack message which has no payload.

f9beb4d9 ................... Start string: Mainnet
76657261636b000000000000 ... Command name: verack + null padding
00000000 ................... Byte count: 0
5df6e0e2 ................... Checksum: SHA256(SHA256(<empty>))

Data Messages

The following network messages all request or provide data related to transactions and blocks.

Many of the data messages use inventories as unique identifiers for transactions and blocks. Inventories have a simple 36-byte structure:

The currently-available type identifiers are:

Type identifier zero and type identifiers greater than three are reserved for future implementations. Bitcoin Core ignores all inventories with one of these unknown types.

Block

The block message transmits a single serialized block in the format described in the serialized blocks section. See that section for an example hexdump. It can be sent for two different reasons:

1. GetData Response: Nodes will always send it in response to a getdata message that requests the block with an inventory type of MSG_BLOCK (provided the node has that block available for relay).

2. Unsolicited: Some miners will send unsolicited block messages broadcasting their newly-mined blocks to all of their peers. Many mining pools do the same thing, although some may be misconfigured to send the block from multiple nodes, possibly sending the same block to some peers more than once.

GetBlocks

The getblocks message requests an inv message that provides block header hashes starting from a particular point in the block chain. It allows a peer which has been disconnected or started for the first time to get the data it needs to request the blocks it hasn’t seen.

Peers which have been disconnected may have stale blocks in their locally-stored block chain, so the getblocks message allows the requesting peer to provide the receiving peer with multiple header hashes at various heights on their local chain. This allows the receiving peer to find, within that list, the last header hash they had in common and reply with all subsequent header hashes.

Note: the receiving peer itself may respond with an inv message containing header hashes of stale blocks. It is up to the requesting peer to poll all of its peers to find the best block chain.

If the receiving peer does not find a common header hash within the list, it will assume the last common block was the genesis block (block zero), so it will reply with in inv message containing header hashes starting with block one (the first block after the genesis block).

The following annotated hexdump shows a getblocks message. (The message header has been omitted.)

71110100 ........................... Protocol version: 70001
02 ................................. Hash count: 2

d39f608a7775b537729884d4e6633bb2
105e55a16a14d31b0000000000000000 ... Hash #1

5c3e6403d40837110a2e8afb602b1c01
714bda7ce23bea0a0000000000000000 ... Hash #2

00000000000000000000000000000000
00000000000000000000000000000000 ... Stop hash

GetData

The getdata message requests one or more data objects from another node. The objects are requested by an inventory, which the requesting node typically received previously by way of an inv message.

The response to a getdata message can be a tx message, block message, merkleblock message, cmpctblock message, or notfound message.

This message cannot be used to request arbitrary data, such as historic transactions no longer in the memory pool or relay set. Full nodes may not even be able to provide older blocks if they’ve pruned old transactions from their block database. For this reason, the getdata message should usually only be used to request data from a node which previously advertised it had that data by sending an inv message.

The format and maximum size limitations of the getdata message are identical to the inv message; only the message header differs.

GetHeaders

Added in protocol version 31800.

The getheaders message requests a headers message that provides block headers starting from a particular point in the block chain. It allows a peer which has been disconnected or started for the first time to get the headers it hasn’t seen yet.

The getheaders message is nearly identical to the getblocks message, with one minor difference: the inv reply to the getblocks message will include no more than 500 block header hashes; the headers reply to the getheaders message will include as many as 2,000 block headers.

Headers

Added in protocol version 31800.

The headers message sends block headers to a node which previously requested certain headers with a getheaders message. A headers message can be empty.

The following annotated hexdump shows a headers message. (The message header has been omitted.)

01 ................................. Header count: 1

02000000 ........................... Block version: 2
b6ff0b1b1680a2862a30ca44d346d9e8
910d334beb48ca0c0000000000000000 ... Hash of previous block's header
9d10aa52ee949386ca9385695f04ede2
70dda20810decd12bc9b048aaab31471 ... Merkle root
24d95a54 ........................... Unix time: 1415239972
30c31b18 ........................... Target (bits)
fe9f0864 ........................... Nonce

00 ................................. Transaction count (0x00)

Inv

The inv message (inventory message) transmits one or more inventories of objects known to the transmitting peer. It can be sent unsolicited to announce new transactions or blocks, or it can be sent in reply to a getblocks message or mempool message.

The receiving peer can compare the inventories from an inv message against the inventories it has already seen, and then use a follow-up message to request unseen objects.

The following annotated hexdump shows an inv message with two inventory entries. (The message header has been omitted.)

02 ................................. Count: 2

01000000 ........................... Type: MSG_TX
de55ffd709ac1f5dc509a0925d0b1fc4
42ca034f224732e429081da1b621f55a ... Hash (TXID)

01000000 ........................... Type: MSG_TX
91d36d997037e08018262978766f24b8
a055aaf1d872e94ae85e9817b2c68dc7 ... Hash (TXID)

MemPool

Added in protocol version 60002.

The mempool message requests the TXIDs of transactions that the receiving node has verified as valid but which have not yet appeared in a block. That is, transactions which are in the receiving node’s memory pool. The response to the mempool message is one or more inv messages containing the TXIDs in the usual inventory format.

Sending the mempool message is mostly useful when a program first connects to the network. Full nodes can use it to quickly gather most or all of the unconfirmed transactions available on the network; this is especially useful for miners trying to gather transactions for their transaction fees. SPV clients can set a filter before sending a mempool to only receive transactions that match that filter; this allows a recently-started client to get most or all unconfirmed transactions related to its wallet.

The inv response to the mempool message is, at best, one node’s view of the network—not a complete list of unconfirmed transactions on the network. Here are some additional reasons the list might not be complete:

• Before Bitcoin Core 0.9.0, the response to the mempool message was only one inv message. An inv message is limited to 50,000 inventories, so a node with a memory pool larger than 50,000 entries would not send everything. Later versions of Bitcoin Core send as many inv messages as needed to reference its complete memory pool.

• The mempool message is not currently fully compatible with the filterload message’s BLOOM_UPDATE_ALL and BLOOM_UPDATE_P2PUBKEY_ONLY flags. Mempool transactions are not sorted like in-block transactions, so a transaction (tx2) spending an output can appear before the transaction (tx1) containing that output, which means the automatic filter update mechanism won’t operate until the second-appearing transaction (tx1) is seen—missing the first-appearing transaction (tx2). It has been proposed in Bitcoin Core issue #2381 that the transactions should be sorted before being processed by the filter.

There is no payload in a mempool message. See the message header section for an example of a message without a payload.

MerkleBlock

Added in protocol version 70001 as described by BIP37.

The merkleblock message is a reply to a getdata message which requested a block using the inventory type MSG_MERKLEBLOCK. It is only part of the reply: if any matching transactions are found, they will be sent separately as tx messages.

If a filter has been previously set with the filterload message, the merkleblock message will contain the TXIDs of any transactions in the requested block that matched the filter, as well as any parts of the block’s merkle tree necessary to connect those transactions to the block header’s merkle root. The message also contains a complete copy of the block header to allow the client to hash it and confirm its proof of work.

The annotated hexdump below shows a merkleblock message which corresponds to the examples below. (The message header has been omitted.)

01000000 ........................... Block version: 1
82bb869cf3a793432a66e826e05a6fc3
7469f8efb7421dc88067010000000000 ... Hash of previous block's header
7f16c5962e8bd963659c793ce370d95f
093bc7e367117b3c30c1f8fdd0d97287 ... Merkle root
76381b4d ........................... Time: 1293629558
4c86041b ........................... nBits: 0x04864c * 256**(0x1b-3)
554b8529 ........................... Nonce

07000000 ........................... Transaction count: 7
04 ................................. Hash count: 4

3612262624047ee87660be1a707519a4
43b1c1ce3d248cbfc6c15870f6c5daa2 ... Hash #1
019f5b01d4195ecbc9398fbf3c3b1fa9
bb3183301d7a1fb3bd174fcfa40a2b65 ... Hash #2
41ed70551dd7e841883ab8f0b16bf041
76b7d1480e4f0af9f3d4c3595768d068 ... Hash #3
20d2a7bc994987302e5b1ac80fc425fe
25f8b63169ea78e68fbaaefa59379bbf ... Hash #4

01 ................................. Flag bytes: 1
1d ................................. Flags: 1 0 1 1 1 0 0 0

Note: when fully decoded, the above merkleblock message provided the TXID for a single transaction that matched the filter. In the network traffic dump this output was taken from, the full transaction belonging to that TXID was sent immediately after the merkleblock message as a tx message.

Parsing A MerkleBlock Message

As seen in the annotated hexdump above, the merkleblock message provides three special data types: a transaction count, a list of hashes, and a list of one-bit flags.

You can use the transaction count to construct an empty merkle tree. We’ll call each entry in the tree a node; on the bottom are TXID nodes—the hashes for these nodes are TXIDs; the remaining nodes (including the merkle root) are non-TXID nodes—they may actually have the same hash as a TXID, but we treat them differently.

Keep the hashes and flags in the order they appear in the merkleblock message. When we say “next flag” or “next hash”, we mean the next flag or hash on the list, even if it’s the first one we’ve used so far.

Start with the merkle root node and the first flag. The table below describes how to evaluate a flag based on whether the node being processed is a TXID node or a non-TXID node. Once you apply a flag to a node, never apply another flag to that same node or reuse that same flag again.

Any time you begin processing a node for the first time, evaluate the next flag. Never use a flag at any other time.

When processing a child node, you may need to process its children (the grandchildren of the original node) or further-descended nodes before returning to the parent node. This is expected—keep processing depth first until you reach a TXID node or a non-TXID node with a flag of 0.

After you process a TXID node or a non-TXID node with a flag of 0, stop processing flags and begin to ascend the tree. As you ascend, compute the hash of any nodes for which you now have both child hashes or for which you now have the sole child hash. See the merkle tree section for hashing instructions. If you reach a node where only the left hash is known, descend into its right child (if present) and further descendants as necessary.

However, if you find a node whose left and right children both have the same hash, fail. This is related to CVE-2012-2459.

Continue descending and ascending until you have enough information to obtain the hash of the merkle root node. If you run out of flags or hashes before that condition is reached, fail. Then perform the following checks (order doesn’t matter):

• Fail if there are unused hashes in the hashes list.

• Fail if there are unused flag bits—except for the minimum number of bits necessary to pad up to the next full byte.

• Fail if the hash of the merkle root node is not identical to the merkle root in the block header.

• Fail if the block header is invalid. Remember to ensure that the hash of the header is less than or equal to the target threshold encoded by the nBits header field. Your program should also, of course, attempt to ensure the header belongs to the best block chain and that the user knows how many confirmations this block has.

For a detailed example of parsing a merkleblock message, please see the corresponding merkle block examples section.

Creating A MerkleBlock Message

It’s easier to understand how to create a merkleblock message after you understand how to parse an already-created message, so we recommend you read the parsing section above first.

Create a complete merkle tree with TXIDs on the bottom row and all the other hashes calculated up to the merkle root on the top row. For each transaction that matches the filter, track its TXID node and all of its ancestor nodes.

Start processing the tree with the merkle root node. The table below describes how to process both TXID nodes and non-TXID nodes based on whether the node is a match, a match ancestor, or neither a match nor a match ancestor.

Any time you begin processing a node for the first time, a flag should be appended to the flag list. Never put a flag on the list at any other time, except when processing is complete to pad out the flag list to a byte boundary.

When processing a child node, you may need to process its children (the grandchildren of the original node) or further-descended nodes before returning to the parent node. This is expected—keep processing depth first until you reach a TXID node or a node which is neither a TXID nor a match ancestor.

After you process a TXID node or a node which is neither a TXID nor a match ancestor, stop processing and begin to ascend the tree until you find a node with a right child you haven’t processed yet. Descend into that right child and process it.

After you fully process the merkle root node according to the instructions in the table above, processing is complete. Pad your flag list to a byte boundary and construct the merkleblock message using the template near the beginning of this subsection.

CmpctBlock

Added in protocol version 70014 as described by BIP152.

Version 1 compact blocks are pre-segwit (txids) Version 2 compact blocks are post-segwit (wtxids)

The cmpctblock message is a reply to a getdata message which requested a block using the inventory type MSG_CMPCT_BLOCK. If the requested block was recently announced and is close to the tip of the best chain of the receiver and after having sent the requesting peer a sendcmpct message, nodes respond with a cmpctblock message containing data for the block.

If the requested block is too old, the node responds with a full non-compact block

Upon receipt of a cmpctblock message, after sending a sendcmpct message, nodes should calculate the short transaction ID for each unconfirmed transaction they have available (ie in their mempool) and compare each to each short transaction ID in the cmpctblock message. After finding already-available transactions, nodes which do not have all transactions available to reconstruct the full block should request the missing transactions using a getblocktxn message.

A node must not send a cmpctblock message unless they are able to respond to a getblocktxn message which requests every transaction in the block. A node must not send a cmpctblock message without having validated that the header properly commits to each transaction in the block, and properly builds on top of the existing, fully-validated chain with a valid proof-of-work either as a part of the current most-work valid chain, or building directly on top of it. A node may send a cmpctblock message before validating that each transaction in the block validly spends existing UTXO set entries.

The cmpctblock message contains a vector of PrefilledTransaction whose structure is defined below.

The cmpctblock message is compromised of a serialized HeaderAndShortIDs structure which is defined below. A HeaderAndShortIDs structure is used to relay a block header, the short transactions IDs used for matching already-available transactions, and a select few transactions which we expect a peer may be missing.

Important protocol version 70015 notes regarding Compact Blocks

New banning behavior was added to the compact block logic in protocol version 70015 to prevent node abuse, the new changes are outlined below as defined in BIP152.

Any undefined behavior in this spec may cause failure to transfer block to, peer disconnection by, or self-destruction by the receiving node. A node receiving non-minimally-encoded CompactSize encodings should make a best-effort to eat the sender’s cat.

As high-bandwidth mode permits relaying of cmpctblock messages prior to full validation (requiring only that the block header is valid before relay), nodes SHOULD NOT ban a peer for announcing a new block with a cmpctblock message that is invalid, but has a valid header.

For avoidance of doubt, nodes SHOULD bump their peer-to-peer protocol version to 70015 or higher to signal that they will not ban or punish a peer for announcing compact blocks prior to full validation, and nodes SHOULD NOT announce a cmpctblock message to a peer with a version number below 70015 before fully validating the block.

Version 2 compact blocks notes

Transactions inside cmpctblock messages (both those used as direct announcement and those in response to getdata) and in blocktxn messages should include witness data, using the same format as responses to getdata MSG_WITNESS_TX, specified in BIP144.

Upon receipt of a getdata message containing a request for a MSG_CMPCT_BLOCK object for which a cmpctblock message is not sent in response, the block message containing the requested block in non-compact form MUST be encoded with witnesses (as is sent in reply to a MSG_WITNESS_BLOCK) if the protocol version used to encode the cmpctblock message would have been 2, and encoded without witnesses (as is sent in response to a MSG_BLOCK) if the protocol version used to encode the cmpctblock message would have been 1.

Short Transaction ID calculation

Short transaction IDs are used to represent a transaction without sending a full 256-bit hash. They are calculated as follows,

• A single-SHA256 hashing the block header with the nonce appended (in little-endian)
• Running SipHash-2-4 with the input being the transaction ID (wtxid in version 2 of compact blocks) and the keys (k0/k1) set to the first two little-endian 64-bit integers from the above hash, respectively.
• Dropping the 2 most significant bytes from the SipHash output to make it 6 bytes.
• Two null-bytes appended so it can be read as an 8-byte integer.

SendCmpct

Added in protocol version 70014 as described by BIP152.

The sendcmpct message is defined as a message containing a 1-byte integer followed by a 8-byte integer. The first integer is interpreted as a boolean and should have a value of either 1 or 0. The second integer is be interpreted as a little-endian version number.

Upon receipt of a sendcmpct message with the first and second integers set to 1, the node should announce new blocks by sending a cmpctblock message.

Upon receipt of a sendcmpct message with the first integer set to 0, the node shouldn’t announce new blocks by sending a cmpctblock message, but instead announce new blocks by sending invs or headers, as defined by BIP130.

Upon receipt of a sendcmpct message with the second integer set to something other than 1, nodes should treat the peer as if they had not received the message (as it indicates the peer will provide an unexpected encoding in cmpctblock messages, and/or other, messages). This allows future versions to send duplicate sendcmpct messages with different versions as a part of a version handshake for future versions.

Nodes should check for a protocol version of >= 70014 before sending sendcmpct messages. Nodes shouldn’t send a request for a MSG_CMPCT_BLOCK object to a peer before having received a sendcmpct message from that peer. Nodes shouldn’t request a MSG_CMPCT_BLOCK object before having sent all sendcmpct messages to that peer which they intend to send, as the peer cannot know what version protocol to use in the response.

The structure of a sendcmpct message is defined below.

GetBlockTxn

Added in protocol version 70014 as described by BIP152.

The getblocktxn message is defined as a message containing a serialized BlockTransactionsRequest message. Upon receipt of a properly-formatted getblocktxn message, nodes which recently provided the sender of such a message a cmpctblock message for the block hash identified in this message must respond with either an appropriate blocktxn message, or a full block message.

A blocktxn message response must contain exactly and only each transaction which is present in the appropriate block at the index specified in the getblocktxn message indexes list, in the order requested.

The structure of BlockTransactionsRequest is defined below.

BlockTxn

Added in protocol version 70014 as described by BIP152.

The blocktxn message is defined as a message containing a serialized BlockTransactions message. Upon receipt of a properly-formatted requested blocktxn message, nodes should attempt to reconstruct the full block by taking the prefilledtxn transactions from the original cmpctblock message and placing them in the marked positions, then for each short transaction ID from the original cmpctblock message, in order, find the corresponding transaction either from the blocktxn message or from other sources and place it in the first available position in the block then once the block has been reconstructed, it shall be processed as normal, keeping in mind that short transaction IDs are expected to occasionally collide, and that nodes must not be penalized for such collisions, wherever they appear.

The structure of BlockTransactions is defined below.

NotFound

Added in protocol version 70001.

The notfound message is a reply to a getdata message which requested an object the receiving node does not have available for relay. (Nodes are not expected to relay historic transactions which are no longer in the memory pool or relay set. Nodes may also have pruned spent transactions from older blocks, making them unable to send those blocks.)

The format and maximum size limitations of the notfound message are identical to the inv message; only the message header differs.

Tx

The tx message transmits a single transaction in the raw transaction format. It can be sent in a variety of situations;

• Transaction Response: Bitcoin Core and BitcoinJ will send it in response to a getdata message that requests the transaction with an inventory type of MSG_TX.

• MerkleBlock Response: Bitcoin Core will send it in response to a getdata message that requests a merkle block with an inventory type of MSG_MERKLEBLOCK. (This is in addition to sending a merkleblock message.) Each tx message in this case provides a matched transaction from that block.

• Unsolicited: BitcoinJ will send a tx message unsolicited for transactions it originates.

For an example hexdump of the raw transaction format, see the raw transaction section.

Control Messages

The following network messages all help control the connection between two peers or allow them to advise each other about the rest of the network.

Note that almost none of the control messages are authenticated in any way, meaning they can contain incorrect or intentionally harmful information. In addition, this section does not yet cover P2P protocol operation over the Tor network; if you would like to contribute information about Tor, please open an issue.

Addr

The addr (IP address) message relays connection information for peers on the network. Each peer which wants to accept incoming connections creates an addr message providing its connection information and then sends that message to its peers unsolicited. Some of its peers send that information to their peers (also unsolicited), some of which further distribute it, allowing decentralized peer discovery for any program already on the network.

An addr message may also be sent in response to a getaddr message.

Each encapsulated network IP address currently uses the following structure:

The following annotated hexdump shows part of an addr message. (The message header has been omitted and the actual IP address has been replaced with a RFC5737 reserved IP address.)

fde803 ............................. Address count: 1000

d91f4854 ........................... Epoch time: 1414012889
0100000000000000 ................... Service bits: 01 (network node)
00000000000000000000ffffc0000233 ... IP Address: ::ffff:192.0.2.51
208d ............................... Port: 8333

[...] .............................. (999 more addresses omitted)

Alert

Added in protocol version 311. Removed in protocol version 70013 and released in Bitcoin Core 0.13.0

The legacy p2p network alert messaging system has been retired; however, internal alerts, partition detection warnings and the -alertnotify option features remain. See Alert System Retirement for details.

FeeFilter

Added in protocol version 70013 as described by BIP133.

The feefilter message is a request to the receiving peer to not relay any transaction inv messages to the sending peer where the fee rate for the transaction is below the fee rate specified in the feefilter message.

feefilter was introduced in Bitcoin Core 0.13.0 following the introduction of mempool limiting in Bitcoin Core 0.12.0. Mempool limiting provides protection against attacks and spam transactions that have low fee rates and are unlikely to be included in mined blocks. The feefilter messages allows a node to inform its peers that it will not accept transactions below a specified fee rate into its mempool, and therefore that the peers can skip relaying inv messages for transactions below that fee rate to that node.

The receiving peer may choose to ignore the message and not filter transaction inv messages.

The fee filter is additive with bloom filters. If an SPV client loads a bloom filter and sends a feefilter message, transactions should only be relayed if they pass both filters.

Note however that feefilter has no effect on block propagation or responses to getdata messages. For example, if a node requests a merkleblock from its peer by sending a getdata message with inv type MSG_FILTERED_BLOCK and it has previously sent a feefilter to that peer, the peer should respond with a merkleblock containing all the transactions matching the bloom filter, even if they are below the feefilter fee rate.

inv messages generated from a mempool message are subject to a fee filter if it exists.

The annotated hexdump below shows a feefilter message. (The message header has been omitted.)

7cbd000000000000 ... satoshis per kilobyte: 48,508

FilterAdd

Added in protocol version 70001 as described by BIP37.

The filteradd message tells the receiving peer to add a single element to a previously-set bloom filter, such as a new public key. The element is sent directly to the receiving peer; the peer then uses the parameters set in the filterload message to add the element to the bloom filter.

Because the element is sent directly to the receiving peer, there is no obfuscation of the element and none of the plausible-deniability privacy provided by the bloom filter. Clients that want to maintain greater privacy should recalculate the bloom filter themselves and send a new filterload message with the recalculated bloom filter.

Note: a filteradd message will not be accepted unless a filter was previously set with the filterload message.

The annotated hexdump below shows a filteradd message adding a TXID. (The message header has been omitted.) This TXID appears in the same block used for the example hexdump in the merkleblock message; if that merkleblock message is re-sent after sending this filteradd message, six hashes are returned instead of four.

20 ................................. Element bytes: 32
fdacf9b3eb077412e7a968d2e4f11b9a
9dee312d666187ed77ee7d26af16cb0b ... Element (A TXID)

FilterClear

Added in protocol version 70001 as described by BIP37.

The filterclear message tells the receiving peer to remove a previously-set bloom filter. This also undoes the effect of setting the relay field in the version message to 0, allowing unfiltered access to inv messages announcing new transactions.

Bitcoin Core does not require a filterclear message before a replacement filter is loaded with filterload. It also doesn’t require a filterload message before a filterclear message.

There is no payload in a filterclear message. See the message header section for an example of a message without a payload.

FilterLoad

Added in protocol version 70001 as described by BIP37.

The filterload message tells the receiving peer to filter all relayed transactions and requested merkle blocks through the provided filter. This allows clients to receive transactions relevant to their wallet plus a configurable rate of false positive transactions which can provide plausible-deniability privacy.

The annotated hexdump below shows a filterload message. (The message header has been omitted.) For an example of how this payload was created, see the filterload example.

02 ......... Filter bytes: 2
b50f ....... Filter: 1010 1101 1111 0000
0b000000 ... nHashFuncs: 11
00000000 ... nTweak: 0/none
00 ......... nFlags: BLOOM_UPDATE_NONE

Initializing A Bloom Filter

Filters have two core parameters: the size of the bit field and the number of hash functions to run against each data element. The following formulas from BIP37 will allow you to automatically select appropriate values based on the number of elements you plan to insert into the filter (n) and the false positive rate (p) you desire to maintain plausible deniability.

• Size of the bit field in bytes (nFilterBytes), up to a maximum of 36,000: (-1 / log(2)**2 * n * log(p)) / 8

• Hash functions to use (nHashFuncs), up to a maximum of 50: nFilterBytes * 8 / n * log(2)

Note that the filter matches parts of transactions (transaction elements), so the false positive rate is relative to the number of elements checked—not the number of transactions checked. Each normal transaction has a minimum of four matchable elements (described in the comparison subsection below), so a filter with a false-positive rate of 1 percent will match about 4 percent of all transactions at a minimum.

According to BIP37, the formulas and limits described above provide support for bloom filters containing 20,000 items with a false positive rate of less than 0.1 percent or 10,000 items with a false positive rate of less than 0.0001 percent.

Once the size of the bit field is known, the bit field should be initialized as all zeroes.

Populating A Bloom Filter

The bloom filter is populated using between 1 and 50 unique hash functions (the number specified per filter by the nHashFuncs field). Instead of using up to 50 different hash function implementations, a single implementation is used with a unique seed value for each function.

The seed is nHashNum * 0xfba4c795 + nTweak as a uint32_t, where the values are:

• nHashNum is the sequence number for this hash function, starting at 0 for the first hash iteration and increasing up to the value of the nHashFuncs field (minus one) for the last hash iteration.

• 0xfba4c795 is a constant optimized to create large differences in the seed for different values of nHashNum.

• nTweak is a per-filter constant set by the client to require the use of an arbitrary set of hash functions.

If the seed resulting from the formula above is larger than four bytes, it must be truncated to its four most significant bytes (for example, 0x8967452301 & 0xffffffff → 0x67452301).

The actual hash function implementation used is the 32-bit Murmur3 hash function.

Warning: the Murmur3 hash function has separate 32-bit and 64-bit versions that produce different results for the same input. Only the 32-bit Murmur3 version is used with Bitcoin bloom filters.

The data to be hashed can be any transaction element which the bloom filter can match. See the next subsection for the list of transaction elements checked against the filter. The largest element which can be matched is a script data push of 520 bytes, so the data should never exceed 520 bytes.

The example below from Bitcoin Core bloom.cpp combines all the steps above to create the hash function template. The seed is the first parameter; the data to be hashed is the second parameter. The result is a uint32_t modulo the size of the bit field in bits.

MurmurHash3(nHashNum * 0xFBA4C795 + nTweak, vDataToHash) % (vData.size() * 8)

Each data element to be added to the filter is hashed by nHashFuncs number of hash functions. Each time a hash function is run, the result will be the index number (nIndex) of a bit in the bit field. That bit must be set to 1. For example if the filter bit field was 00000000 and the result is 5, the revised filter bit field is 00000100 (the first bit is bit 0).

It is expected that sometimes the same index number will be returned more than once when populating the bit field; this does not affect the algorithm—after a bit is set to 1, it is never changed back to 0.

After all data elements have been added to the filter, each set of eight bits is converted into a little-endian byte. These bytes are the value of the filter field.

Comparing Transaction Elements To A Bloom Filter

To compare an arbitrary data element against the bloom filter, it is hashed using the same parameters used to create the bloom filter. Specifically, it is hashed nHashFuncs times, each time using the same nTweak provided in the filter, and the resulting output is modulo the size of the bit field provided in the filter field. After each hash is performed, the filter is checked to see if the bit at that indexed location is set. For example if the result of a hash is 5 and the filter is 01001110, the bit is considered set.

If the result of every hash points to a set bit, the filter matches. If any of the results points to an unset bit, the filter does not match.

The following transaction elements are compared against bloom filters. All elements will be hashed in the byte order used in blocks (for example, TXIDs will be in internal byte order).

• TXIDs: the transaction’s SHA256(SHA256()) hash.

• Outpoints: each 36-byte outpoint used this transaction’s input section is individually compared to the filter.

• Signature Script Data: each element pushed onto the stack by a data-pushing opcode in a signature script from this transaction is individually compared to the filter. This includes data elements present in P2SH redeem scripts when they are being spent.

• PubKey Script Data: each element pushed onto the the stack by a data-pushing opcode in any pubkey script from this transaction is individually compared to the filter. (If a pubkey script element matches the filter, the filter will be immediately updated if the BLOOM_UPDATE_ALL flag was set; if the pubkey script is in the P2PKH format and matches the filter, the filter will be immediately updated if the BLOOM_UPDATE_P2PUBKEY_ONLY flag was set. See the subsection below for details.)

The following annotated hexdump of a transaction is from the raw transaction format section; the elements which would be checked by the filter are emphasized in bold. Note that this transaction’s TXID (01000000017b1eab[...]) would also be checked, and that the outpoint TXID and index number below would be checked as a single 36-byte element.

01000000 ................................... Version

01 ......................................... Number of inputs
|
| 7b1eabe0209b1fe794124575ef807057
| c77ada2138ae4fa8d6c4de0398a14f3f ......... Outpoint TXID
| 00000000 ................................. Outpoint index number
|
| 49 ....................................... Bytes in sig. script: 73
| | 48 ..................................... Push 72 bytes as data
| | | 30450221008949f0cb400094ad2b5eb3
| | | 99d59d01c14d73d8fe6e96df1a7150de
| | | b388ab8935022079656090d7f6bac4c9
| | | a94e0aad311a4268e082a725f8aeae05
| | | 73fb12ff866a5f01 ..................... Secp256k1 signature
|
| ffffffff ................................. Sequence number: UINT32_MAX

01 ......................................... Number of outputs
| f0ca052a01000000 ......................... Satoshis (49.99990000 BTC)
|
| 19 ....................................... Bytes in pubkey script: 25
| | 76 ..................................... OP_DUP
| | a9 ..................................... OP_HASH160
| | 14 ..................................... Push 20 bytes as data
| | | cbc20a7664f2f69e5355aa427045bc15
| | | e7c6c772 ............................. PubKey hash
| | 88 ..................................... OP_EQUALVERIFY
| | ac ..................................... OP_CHECKSIG

00000000 ................................... locktime: 0 (a block height)

Updating A Bloom Filter

Clients will often want to track inputs that spend outputs (outpoints) relevant to their wallet, so the filterload field nFlags can be set to allow the filtering node to update the filter when a match is found. When the filtering node sees a pubkey script that pays a pubkey, address, or other data element matching the filter, the filtering node immediately updates the filter with the outpoint corresponding to that pubkey script.

If an input later spends that outpoint, the filter will match it, allowing the filtering node to tell the client that one of its transaction outputs has been spent.

The nFlags field has three allowed values:

In addition, because the filter size stays the same even though additional elements are being added to it, the false positive rate increases. Each false positive can result in another element being added to the filter, creating a feedback loop that can (after a certain point) make the filter useless. For this reason, clients using automatic filter updates need to monitor the actual false positive rate and send a new filter when the rate gets too high.

GetAddr

The getaddr message requests an addr message from the receiving node, preferably one with lots of IP addresses of other receiving nodes. The transmitting node can use those IP addresses to quickly update its database of available nodes rather than waiting for unsolicited addr messages to arrive over time.

There is no payload in a getaddr message. See the message header section for an example of a message without a payload.

Ping

The ping message helps confirm that the receiving peer is still connected. If a TCP/IP error is encountered when sending the ping message (such as a connection timeout), the transmitting node can assume that the receiving node is disconnected. The response to a ping message is the pong message.

Before protocol version 60000, the ping message had no payload. As of protocol version 60001 and all later versions, the message includes a single field, the nonce.

The annotated hexdump below shows a ping message. (The message header has been omitted.)

0094102111e2af4d ... Nonce

Pong

Added in protocol version 60001 as described by BIP31.

The pong message replies to a ping message, proving to the pinging node that the ponging node is still alive. Bitcoin Core will, by default, disconnect from any clients which have not responded to a ping message within 20 minutes.

To allow nodes to keep track of latency, the pong message sends back the same nonce received in the ping message it is replying to.

The format of the pong message is identical to the ping message; only the message header differs.

Reject

Added in protocol version 70002 as described by BIP61.

The reject message informs the receiving node that one of its previous messages has been rejected.

The following table lists message reject codes. Codes are tied to the type of message they reply to; for example there is a 0x10 reject code for transactions and a 0x10 reject code for blocks.

The annotated hexdump below shows a reject message. (The message header has been omitted.)

02 ................................. Number of bytes in message: 2
7478 ............................... Type of message rejected: tx
12 ................................. Reject code: 0x12 (duplicate)
15 ................................. Number of bytes in reason: 21
6261642d74786e732d696e707574732d
7370656e74 ......................... Reason: bad-txns-inputs-spent
394715fcab51093be7bfca5a31005972
947baf86a31017939575fb2354222821 ... TXID

SendHeaders

The sendheaders message tells the receiving peer to send new block announcements using a headers message rather than an inv message.

There is no payload in a sendheaders message. See the message header section for an example of a message without a payload.

VerAck

Added in protocol version 209.

The verack message acknowledges a previously-received version message, informing the connecting node that it can begin to send other messages. The verack message has no payload; for an example of a message with no payload, see the message headers section.

Version

The version message provides information about the transmitting node to the receiving node at the beginning of a connection. Until both peers have exchanged version messages, no other messages will be accepted.

If a version message is accepted, the receiving node should send a verack message—but no node should send a verack message before initializing its half of the connection by first sending a version message.

The following service identifiers have been assigned.

The following annotated hexdump shows a version message. (The message header has been omitted and the actual IP addresses have been replaced with RFC5737 reserved IP addresses.)

72110100 ........................... Protocol version: 70002
0100000000000000 ................... Services: NODE_NETWORK
bc8f5e5400000000 ................... Epoch time: 1415483324

0100000000000000 ................... Receiving node's services
00000000000000000000ffffc61b6409 ... Receiving node's IPv6 address
208d ............................... Receiving node's port number

0100000000000000 ................... Transmitting node's services
00000000000000000000ffffcb0071c0 ... Transmitting node's IPv6 address
208d ............................... Transmitting node's port number

128035cbc97953f8 ................... Nonce

0f ................................. Bytes in user agent string: 15
2f5361746f7368693a302e392e332f ..... User agent: /Satoshi:0.9.3/

cf050500 ........................... Start height: 329167
01 ................................. Relay flag: true

Bitcoin Core APIs

Hash Byte Order

Bitcoin Core RPCs accept and return the byte-wise reverse of computed SHA-256 hash values. For example, the Unix sha256sum command displays the SHA256(SHA256()) hash of mainnet block 300,000’s header as:

> /bin/echo -n '020000007ef055e1674d2e6551dba41cd214debbee34aeb544c7ec670000000000000000d3998963f80c5bab43fe8c26228e98d030edf4dcbe48a666f5c39e2d7a885c9102c86d536c890019593a470d' | xxd -r -p | sha256sum -b | xxd -r -p | sha256sum -b
5472ac8b1187bfcf91d6d218bbda1eb2405d7c55f1f8cc820000000000000000

The result above is also how the hash appears in the previous-header-hash part of block 300,001’s header:

020000005472ac8b1187bfcf91d6d218bbda1eb2405d7c55f1f8cc82000\
0000000000000ab0aaa377ca3f49b1545e2ae6b0667a08f42e72d8c24ae\
237140e28f14f3bb7c6bcc6d536c890019edd83ccf

However, Bitcoin Core’s RPCs use the byte-wise reverse for hashes, so if you want to get information about block 300,000 using the getblock RPC, you need to reverse the requested hash:

> bitcoin-cli getblock \
  000000000000000082ccf8f1557c5d40b21edabb18d2d691cfbf87118bac7254

(Note: hex representation uses two characters to display each byte of data, which is why the reversed string looks somewhat mangled.)

The rationale for the reversal is unknown, but it likely stems from Bitcoin Core’s use of hashes (which are byte arrays in C++) as integers for the purpose of determining whether the hash is below the network target. Whatever the reason for reversing header hashes, the reversal also extends to other hashes used in RPCs, such as TXIDs and merkle roots.

As header hashes and TXIDs are widely used as global identifiers in other Bitcoin software, this reversal of hashes has become the standard way to refer to certain objects. The table below should make clear where each byte order is used.

Note: RPCs which return raw results, such as getrawtransaction or the raw mode of getblock, always display hashes as they appear in blocks (internal byte order).

The code below may help you check byte order by generating hashes from raw hex.

#!/usr/bin/env python

from sys import byteorder
from hashlib import sha256

## You can put in $data an 80-byte block header to get its header hash,
## or a raw transaction to get its txid
data = "00".decode("hex")
hash = sha256(sha256(data).digest()).digest()

print "Warning: this code only tested on a little-endian x86_64 arch"
print
print "System byte order:", byteorder
print "Internal-Byte-Order Hash: ", hash.encode('hex_codec')
print "RPC-Byte-Order Hash:      ", hash[::-1].encode('hex_codec')

Remote Procedure Calls (RPCs)

Bitcoin Core provides a remote procedure call (RPC) interface for various administrative tasks, wallet operations, and queries about network and block chain data.

If you start Bitcoin Core using bitcoin-qt, the RPC interface is disabled by default. To enable it, set server=1 in bitcoin.conf or supply the -server argument when invoking the program. If you start Bitcoin Core using bitcoind, the RPC interface is enabled by default.

The interface requires the user to provide a password for authenticating RPC requests. This password can be set either using the rpcpassword property in bitcoin.conf or by supplying the -rpcpassword program argument. Optionally a username can be set using the rpcuser configuration value. See the Examples Page for more information about setting Bitcoin Core configuration values.

Open-source client libraries for the RPC interface are readily available in most modern programming languages, so you probably don’t need to write your own from scratch. Bitcoin Core also ships with its own compiled C++ RPC client, bitcoin-cli, located in the bin directory alongside bitcoind and bitcoin-qt. The bitcoin-cli program can be used as a command-line interface (CLI) to Bitcoin Core or for making RPC calls from applications written in languages lacking a suitable native client. The remainder of this section describes the Bitcoin Core RPC protocol in detail.

The Bitcoin Core RPC service listens for HTTP POST requests on port 8332 in mainnet mode or 18332 in testnet or regtest mode. The port number can be changed by setting rpcport in bitcoin.conf. By default the RPC service binds to your server’s localhost loopback network interface so it’s not accessible from other servers. Authentication is implemented using HTTP basic authentication. RPC HTTP requests must include a Content-Type header set to text/plain and a Content-Length header set to the size of the request body.

The format of the request body and response data is based on version 1.0 of the JSON-RPC specification. Specifically, the HTTP POST data of a request must be a JSON object with the following format:

In the table above and in other tables describing RPC input and output, we use the following conventions

• “→” indicates an argument that is the child of a JSON array or JSON object. For example, “→ → Parameter” above means Parameter is the child of the params array which itself is a child of the Request object.

• Plain-text names like “Request” are unnamed in the actual JSON object

• Code-style names like params are literal strings that appear in the JSON object.

• “Type” is the JSON data type and the specific Bitcoin Core type.

• “Presence” indicates whether or not a field must be present within its containing array or object. Note that an optional object may still have required children.

The HTTP response data for a RPC request is a JSON object with the following format:

As an example, here is the JSON-RPC request object for the hash of the genesis block:

{
    "method": "getblockhash",
    "params": [0],
    "id": "foo"
}

The command to send this request using bitcoin-cli is:

bitcoin-cli getblockhash 0

Alternatively, we could POST this request using the cURL command-line program as follows:

curl --user ':my_secret_password' --data-binary '''
  {
      "method": "getblockhash",
      "params": [0],
      "id": "foo"
  }''' \
  --header 'Content-Type: text/plain;' localhost:8332

The HTTP response data for this request would be:

{
    "result": "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f",
    "error": null,
    "id": "foo"
}

Note: In order to minimize its size, the raw JSON response from Bitcoin Core doesn’t include any extraneous whitespace characters. Here we’ve added whitespace to make the object more readable. Speaking of which, bitcoin-cli also transforms the raw response to make it more human-readable. It:

• Adds whitespace indentation to JSON objects
• Expands escaped newline characters (“\n”) into actual newlines
• Returns only the value of the result field if there’s no error
• Strips the outer double-quotes around results of type string
• Returns only the error field if there’s an error

Continuing with the example above, the output from the bitcoin-cli command would be simply:

000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

If there’s an error processing a request, Bitcoin Core sets the result field to null and provides information about the error in the error field. For example, a request for the block hash at block height -1 would be met with the following response (again, whitespace added for clarity):

{
    "result": null,
    "error": {
        "code": -8,
        "message": "Block height out of range"
    },
    "id": "foo"
}

If bitcoin-cli encounters an error, it exits with a non-zero status code and outputs the error field as text to the process’s standard error stream:

error: {"code": -8, "message": "Block height out of range"}

Starting in Bitcoin Core version 0.7.0, the RPC interface supports request batching as described in version 2.0 of the JSON-RPC specification. To initiate multiple RPC requests within a single HTTP request, a client can POST a JSON array filled with Request objects. The HTTP response data is then a JSON array filled with the corresponding Response objects. Depending on your usage pattern, request batching may provide significant performance gains. The bitcoin-cli RPC client does not support batch requests.

To keep this documentation compact and readable, the examples for each of the available RPC calls will be given as bitcoin-cli commands:

bitcoin-cli [options] <method name> <param1> <param2> ...

This translates into an JSON-RPC Request object of the form:

{
    "method": "<method name>",
    "params": [ "<param1>", "<param2>", "..." ],
    "id": "foo"
}

[]proper money handling if you write programs using the JSON-RPC interface, you must ensure they handle high-precision real numbers correctly. See the Proper Money Handling Bitcoin Wiki article for details and example code.

Quick Reference

Block Chain RPCs

• GetBestBlockHash: returns the header hash of the most recent block on the best block chain.
• GetBlock: gets a block with a particular header hash from the local block database either as a JSON object or as a serialized block. Updated in 0.13.0
• GetBlockChainInfo: provides information about the current state of the block chain. Updated in 0.12.1
• GetBlockCount: returns the number of blocks in the local best block chain.
• GetBlockHash: returns the header hash of a block at the given height in the local best block chain.
• GetBlockHeader: gets a block header with a particular header hash from the local block database either as a JSON object or as a serialized block header. New in 0.12.0
• GetChainTips: returns information about the highest-height block (tip) of each local block chain.
• GetDifficulty: returns the proof-of-work difficulty as a multiple of the minimum difficulty.
• GetMemPoolAncestors: returns all in-mempool ancestors for a transaction in the mempool. New in 0.13.0
• GetMemPoolDescendants: returns all in-mempool descendants for a transaction in the mempool. New in 0.13.0
• GetMemPoolEntry: returns mempool data for given transaction (must be in mempool). New in 0.13.0
• GetMemPoolInfo: returns information about the node’s current transaction memory pool. Updated in 0.12.0
• GetRawMemPool: returns all transaction identifiers (TXIDs) in the memory pool as a JSON array, or detailed information about each transaction in the memory pool as a JSON object. Updated in 0.13.0
• GetTxOut: returns details about a transaction output. Only unspent transaction outputs (UTXOs) are guaranteed to be available.
• GetTxOutProof: returns a hex-encoded proof that one or more specified transactions were included in a block. New in 0.11.0
• GetTxOutSetInfo: returns statistics about the confirmed unspent transaction output (UTXO) set. Note that this call may take some time and that it only counts outputs from confirmed transactions—it does not count outputs from the memory pool.
• PreciousBlock: treats a block as if it were received before others with the same work. New in 0.14.0
• PruneBlockChain: prunes the blockchain up to a specified height or timestamp. New in 0.14.0
• VerifyChain: verifies each entry in the local block chain database.
• VerifyTxOutProof: verifies that a proof points to one or more transactions in a block, returning the transactions the proof commits to and throwing an RPC error if the block is not in our best block chain. New in 0.11.0

Control RPCs

• GetInfo: prints various information about the node and the network. Deprecated
• Help: lists all available public RPC commands, or gets help for the specified RPC. Commands which are unavailable will not be listed, such as wallet RPCs if wallet support is disabled.
• Stop: safely shuts down the Bitcoin Core server.

Generating RPCs

• Generate: nearly instantly generates blocks. New in 0.11.0, Updated in 0.13.0
• GenerateToAddress: mines blocks immediately to a specified address. New in 0.13.0

Mining RPCs

• GetBlockTemplate: gets a block template or proposal for use with mining software.
• GetMiningInfo: returns various mining-related information. Updated in 0.14.0
• GetNetworkHashPS: returns the estimated current or historical network hashes per second based on the last n blocks.
• PrioritiseTransaction: adds virtual priority or fee to a transaction, allowing it to be accepted into blocks mined by this node (or miners which use this node) with a lower priority or fee. (It can also remove virtual priority or fee, requiring the transaction have a higher priority or fee to be accepted into a locally-mined block.)
• SubmitBlock: accepts a block, verifies it is a valid addition to the block chain, and broadcasts it to the network. Extra parameters are ignored by Bitcoin Core but may be used by mining pools or other programs.

Network RPCs

• AddNode: attempts to add or remove a node from the addnode list, or to try a connection to a node once. Updated in 0.14.0
• ClearBanned: clears list of banned nodes. New in 0.12.0
• DisconnectNode: immediately disconnects from a specified node. New in 0.12.0
• GetAddedNodeInfo: returns information about the given added node, or all added nodes (except onetry nodes). Only nodes which have been manually added using the addnode RPC will have their information displayed. Updated in 0.14.0
• GetConnectionCount: returns the number of connections to other nodes.
• GetNetTotals: returns information about network traffic, including bytes in, bytes out, and the current time. Updated in 0.12.0
• GetNetworkInfo: returns information about the node’s connection to the network. Updated in 0.13.0
• GetPeerInfo: returns data about each connected network node. Updated in 0.13.0
• ListBanned: lists all banned IPs/Subnets. New in 0.12.0
• Ping: sends a P2P ping message to all connected nodes to measure ping time. Results are provided by the getpeerinfo RPC pingtime and pingwait fields as decimal seconds. The P2P ping message is handled in a queue with all other commands, so it measures processing backlog, not just network ping.
• SetBan: attempts add or remove a IP/Subnet from the banned list. New in 0.12.0
• SetNetworkActive: disables/enables all P2P network activity. New in 0.14.0

Raw Transaction RPCs

• CreateRawTransaction: creates an unsigned serialized transaction that spends a previous output to a new output with a P2PKH or P2SH address. The transaction is not stored in the wallet or transmitted to the network.
• FundRawTransaction: adds inputs to a transaction until it has enough in value to meet its out value. New in 0.12.0, Updated in 0.14.0
• DecodeRawTransaction: decodes a serialized transaction hex string into a JSON object describing the transaction. Updated in 0.13.0
• DecodeScript: decodes a hex-encoded P2SH redeem script.
• GetRawTransaction: gets a hex-encoded serialized transaction or a JSON object describing the transaction. By default, Bitcoin Core only stores complete transaction data for UTXOs and your own transactions, so the RPC may fail on historic transactions unless you use the non-default txindex=1 in your Bitcoin Core startup settings. Updated in 0.14.0
• SendRawTransaction: validates a transaction and broadcasts it to the peer-to-peer network.
• SignRawTransaction: signs a transaction in the serialized transaction format using private keys stored in the wallet or provided in the call.

Utility RPCs

• CreateMultiSig: creates a P2SH multi-signature address.
• EstimateFee: estimates the transaction fee per kilobyte that needs to be paid for a transaction to be included within a certain number of blocks. Updated in 0.14.0Deprecated
• EstimatePriority: estimates the priority that a transaction needs in order to be included within a certain number of blocks as a free high-priority transaction. Deprecated
• GetMemoryInfo: returns information about memory usage.
• ValidateAddress: returns information about the given Bitcoin address. Updated in 0.13.0
• VerifyMessage: verifies a signed message.

Wallet RPCs

Note: the wallet RPCs are only available if Bitcoin Core was built with wallet support, which is the default.

• AbandonTransaction: marks an in-wallet transaction and all its in-wallet descendants as abandoned. This allows their inputs to be respent. New in 0.12.0
• AddWitnessAddress: adds a witness address for a script (with pubkey or redeemscript known). New in 0.13.0
• AddMultiSigAddress: adds a P2SH multisig address to the wallet.
• BackupWallet: safely copies wallet.dat to the specified file, which can be a directory or a path with filename.
• BumpFee: replaces an unconfirmed wallet transaction that signaled RBF with a new transaction that pays a higher fee. New in 0.14.0
• DumpPrivKey: returns the wallet-import-format (WIP) private key corresponding to an address. (But does not remove it from the wallet.)
• DumpWallet: creates or overwrites a file with all wallet keys in a human-readable format.
• EncryptWallet: encrypts the wallet with a passphrase. This is only to enable encryption for the first time. After encryption is enabled, you will need to enter the passphrase to use private keys.
• GetAccountAddress: returns the current Bitcoin address for receiving payments to this account. If the account doesn’t exist, it creates both the account and a new address for receiving payment. Once a payment has been received to an address, future calls to this RPC for the same account will return a different address. Deprecated
• GetAccount: returns the name of the account associated with the given address.
• GetAddressesByAccount: returns a list of every address assigned to a particular account. Deprecated
• GetBalance: gets the balance in decimal bitcoins across all accounts or for a particular account.
• GetNewAddress: returns a new Bitcoin address for receiving payments. If an account is specified, payments received with the address will be credited to that account.
• GetRawChangeAddress: returns a new Bitcoin address for receiving change. This is for use with raw transactions, not normal use.
• GetReceivedByAccount: returns the total amount received by addresses in a particular account from transactions with the specified number of confirmations. It does not count coinbase transactions. Deprecated
• GetReceivedByAddress: returns the total amount received by the specified address in transactions with the specified number of confirmations. It does not count coinbase transactions.
• GetTransaction: gets detailed information about an in-wallet transaction. Updated in 0.12.0
• GetUnconfirmedBalance: returns the wallet’s total unconfirmed balance.
• GetWalletInfo: provides information about the wallet.
• ImportAddress: adds an address or pubkey script to the wallet without the associated private key, allowing you to watch for transactions affecting that address or pubkey script without being able to spend any of its outputs.
• ImportMulti: imports addresses or scripts (with private keys, public keys, or P2SH redeem scripts) and optionally performs the minimum necessary rescan for all imports. New in 0.14.0
• ImportPrunedFunds: imports funds without the need of a rescan. Meant for use with pruned wallets. New in 0.13.0
• ImportPrivKey: adds a private key to your wallet. The key should be formatted in the wallet import format created by the dumpprivkey RPC.
• ImportWallet: imports private keys from a file in wallet dump file format (see the dumpwallet RPC). These keys will be added to the keys currently in the wallet. This call may need to rescan all or parts of the block chain for transactions affecting the newly-added keys, which may take several minutes.
• KeyPoolRefill: fills the cache of unused pre-generated keys (the keypool).
• ListAccounts: lists accounts and their balances. Deprecated
• ListAddressGroupings: lists groups of addresses that may have had their common ownership made public by common use as inputs in the same transaction or from being used as change from a previous transaction.
• ListLockUnspent: returns a list of temporarily unspendable (locked) outputs.
• ListReceivedByAccount: lists the total number of bitcoins received by each account. Deprecated
• ListReceivedByAddress: lists the total number of bitcoins received by each address.
• ListSinceBlock: gets all transactions affecting the wallet which have occurred since a particular block, plus the header hash of a block at a particular depth.
• ListTransactions: returns the most recent transactions that affect the wallet. Updated in 0.12.1
• ListUnspent: returns an array of unspent transaction outputs belonging to this wallet. Updated in 0.13.0
• LockUnspent: temporarily locks or unlocks specified transaction outputs. A locked transaction output will not be chosen by automatic coin selection when spending bitcoins. Locks are stored in memory only, so nodes start with zero locked outputs and the locked output list is always cleared when a node stops or fails.
• Move: moves a specified amount from one account in your wallet to another using an off-block-chain transaction. Deprecated
• RemovePrunedFunds: deletes the specified transaction from the wallet. Meant for use with pruned wallets and as a companion to importprunedfunds. New in 0.13.0
• SendFrom: spends an amount from a local account to a bitcoin address. Deprecated
• SendMany: creates and broadcasts a transaction which sends outputs to multiple addresses.
• SendToAddress: spends an amount to a given address.
• SetAccount: puts the specified address in the given account. Deprecated
• SetTxFee: sets the transaction fee per kilobyte paid by transactions created by this wallet.
• SignMessage: signs a message with the private key of an address.
• SignMessageWithPrivKey: signs a message with a given private key. New in 0.13.0
• WalletLock: removes the wallet encryption key from memory, locking the wallet. After calling this method, you will need to call walletpassphrase again before being able to call any methods which require the wallet to be unlocked.
• WalletPassphrase: stores the wallet decryption key in memory for the indicated number of seconds. Issuing the walletpassphrase command while the wallet is already unlocked will set a new unlock time that overrides the old one.
• WalletPassphraseChange: changes the wallet passphrase from ‘old passphrase’ to ‘new passphrase’.

Removed RPCs

• GetGenerate: was removed in Bitcoin Core 0.13.0.
• GetHashesPerSec: was removed in Bitcoin Core 0.11.0.
• GetWork: was removed in Bitcoin Core 0.10.0.
• SetGenerate: was removed in Bitcoin Core 0.13.0.

RPCs

the block chain and memory pool can include arbitrary data which several of the commands below will return in hex format. If you convert this data to another format in an executable context, it could be used in an exploit. For example, displaying a pubkey script as ASCII text in a webpage could add arbitrary Javascript to that page and create a cross-site scripting (XSS) exploit. To avoid problems, please treat block chain and memory pool data as an arbitrary input from an untrusted source.

AbandonTransaction

Added in Bitcoin Core 0.12.0

The abandontransaction RPC marks an in-wallet transaction and all its in-wallet descendants as abandoned. This allows their inputs to be respent.

Parameter #1—a transaction identifier (TXID)

Result—null on success

Example from Bitcoin Core 0.13.1

Abandons the transaction on your node.

bitcoin-cli abandontransaction fa3970c341c9f5de6ab13f128cbfec58d732e736a505fe32137ad551c799ecc4

Result (no output from bitcoin-cli because result is set to null).

See also

• SendRawTransaction: validates a transaction and broadcasts it to the peer-to-peer network.

AddMultiSigAddress

Requires wallet support.

The addmultisigaddress RPC adds a P2SH multisig address to the wallet.

Parameter #1—the number of signatures required

Parameter #2—the full public keys, or addresses for known public keys

Parameter #3—the account name

Result—a P2SH address printed and stored in the wallet

Example from Bitcoin Core 0.10.0

Adding a 2-of-3 P2SH multisig address to the “test account” by mixing two P2PKH addresses and one full public key:

bitcoin-cli -testnet addmultisigaddress \
  2 \
  '''
    [
      "mjbLRSidW1MY8oubvs4SMEnHNFXxCcoehQ",
      "02ecd2d250a76d204011de6bc365a56033b9b3a149f679bc17205555d3c2b2854f",
      "mt17cV37fBqZsnMmrHnGCm9pM28R1kQdMG"
    ]
  ''' \
  'test account'

Result:

2MyVxxgNBk5zHRPRY2iVjGRJHYZEp1pMCSq

(New P2SH multisig address also stored in wallet.)

See also

• CreateMultiSig: creates a P2SH multi-signature address.
• DecodeScript: decodes a hex-encoded P2SH redeem script.
• Pay-To-Script-Hash (P2SH)

AddNode

The addnode RPC attempts to add or remove a node from the addnode list, or to try a connection to a node once.

Parameter #1—hostname/IP address and port of node to add or remove

Parameter #2—whether to add or remove the node, or to try only once to connect

Result—null plus error on failed remove

Example from Bitcoin Core 0.10.0

Try connecting to the following node.

bitcoin-cli -testnet addnode 192.0.2.113:18333 onetry

Result (no output from bitcoin-cli because result is set to null).

See also

• GetAddedNodeInfo: returns information about the given added node, or all added nodes (except onetry nodes). Only nodes which have been manually added using the addnode RPC will have their information displayed.

AddWitnessAddress

Added in Bitcoin Core 0.13.0

Requires wallet support. Requires an unlocked wallet or an unencrypted wallet.

The addwitnessaddress RPC adds a witness address for a script (with pubkey or redeem script known).

Parameter #1—the witness address

Result—the witness script

Example from Bitcoin Core 0.13.1

bitcoin-cli addwitnessaddress 1BRo7qrYHMPrzdBDzfjmzteBdYAyTMXW75

Result:

The RPC is disabled by default on mainnet as long as Segregated Witness has not been activated. -walletprematurewitness enables the RPC.

3LfAujMsBHgQKoxLn59dVbeYPmfUrHSAQb

See also

• BIP-141 - Segregated Witness
• BIP-142 - Address Format for Segregated Witness

BackupWallet

Requires wallet support.

The backupwallet RPC safely copies wallet.dat to the specified file, which can be a directory or a path with filename.

Parameter #1—destination directory or filename

Result—null or error

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet backupwallet /tmp/backup.dat

See also

• DumpWallet: creates or overwrites a file with all wallet keys in a human-readable format.
• ImportWallet: imports private keys from a file in wallet dump file format (see the dumpwallet RPC). These keys will be added to the keys currently in the wallet. This call may need to rescan all or parts of the block chain for transactions affecting the newly-added keys, which may take several minutes.



BumpFee

Added in Bitcoin Core 0.14.0

Requires wallet support. Wallet must be unlocked.

The bumpfee RPC replaces an unconfirmed wallet transaction that signaled RBF with a new transaction that pays a higher fee. The increased fee is deducted from the change output. The command fails if the change output is too small to increase the fee or if the wallet or mempool contains a transaction that spends one of the transaction’s outputs. The -walletrbf option needs to be enabled (default is false).

Parameter #1—The TXID of the transaction

Parameter #2—Additional options

Result—information about the new transaction

Example from Bitcoin Core 0.14.1

bitcoin-cli -testnet bumpfee d4a33e0cabaz723149e1fcab4e033a40173\
88a644c65370e3cb06ba2f0e13975\
'{
    "totalFee": 4000,
    "replaceable": false
}'

Result:

{
	"txid": "37a55ce49636977k79bcb04ee1143573b570b1743e09660e79e7ec3320968ca54",
	"origfee": 0.00002450,
	"fee": 0.00004000,
	"errors": ""
}

See also

• CreateRawTransaction: creates an unsigned serialized transaction that spends a previous output to a new output with a P2PKH or P2SH address. The transaction is not stored in the wallet or transmitted to the network.
• FundRawTransaction: adds inputs to a transaction until it has enough in value to meet its out value.
• SignRawTransaction: signs a transaction in the serialized transaction format using private keys stored in the wallet or provided in the call.
• SendRawTransaction: validates a transaction and broadcasts it to the peer-to-peer network.
• Serialized Transaction Format

ClearBanned

Added in Bitcoin Core 0.12.0

The clearbanned RPC clears list of banned nodes.

Parameters: none

Result—null on success

Example from Bitcoin Core 0.13.1

Clears the ban list.

bitcoin-cli clearbanned

Result (no output from bitcoin-cli because result is set to null).

See also

• ListBanned: lists all banned IPs/Subnets.
• SetBan: attempts add or remove a IP/Subnet from the banned list.

CreateMultiSig

The createmultisig RPC creates a P2SH multi-signature address.

Parameter #1—the number of signatures required

Parameter #2—the full public keys, or addresses for known public keys

Result—P2SH address and hex-encoded redeem script

Example from Bitcoin Core 0.10.0

Creating a 2-of-3 P2SH multisig address by mixing two P2PKH addresses and one full public key:

bitcoin-cli -testnet createmultisig 2 '''
  [
    "mjbLRSidW1MY8oubvs4SMEnHNFXxCcoehQ",
    "02ecd2d250a76d204011de6bc365a56033b9b3a149f679bc17205555d3c2b2854f",
    "mt17cV37fBqZsnMmrHnGCm9pM28R1kQdMG"
  ]
'''

Result:

{
  "address" : "2MyVxxgNBk5zHRPRY2iVjGRJHYZEp1pMCSq",
  "redeemScript" : "522103ede722780d27b05f0b1169efc90fa15a601a32fc6c3295114500c586831b6aaf2102ecd2d250a76d204011de6bc365a56033b9b3a149f679bc17205555d3c2b2854f21022d609d2f0d359e5bc0e5d0ea20ff9f5d3396cb5b1906aa9c56a0e7b5edc0c5d553ae"
}

See also

• AddMultiSigAddress: adds a P2SH multisig address to the wallet.
• DecodeScript: decodes a hex-encoded P2SH redeem script.
• Pay-To-Script-Hash (P2SH)

CreateRawTransaction

The createrawtransaction RPC creates an unsigned serialized transaction that spends a previous output to a new output with a P2PKH or P2SH address. The transaction is not stored in the wallet or transmitted to the network.

Parameter #1—Inputs

Parameter #2—P2PKH or P2SH addresses and amounts

Parameter #3—locktime

Result—the unsigned raw transaction in hex

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet createrawtransaction '''
  [
    {
      "txid": "1eb590cd06127f78bf38ab4140c4cdce56ad9eb8886999eb898ddf4d3b28a91d",
      "vout" : 0
    }
  ]''' '{ "mgnucj8nYqdrPFh2JfZSB1NmUThUGnmsqe": 0.13 }'

Result (wrapped):

01000000011da9283b4ddf8d89eb996988b89ead56cecdc44041ab38bf787f12\
06cd90b51e0000000000ffffffff01405dc600000000001976a9140dfc8bafc8\
419853b34d5e072ad37d1a5159f58488ac00000000

See also

• DecodeRawTransaction: decodes a serialized transaction hex string into a JSON object describing the transaction.
• SignRawTransaction: signs a transaction in the serialized transaction format using private keys stored in the wallet or provided in the call.
• SendRawTransaction: validates a transaction and broadcasts it to the peer-to-peer network.
• Serialized Transaction Format

DecodeRawTransaction

The decoderawtransaction RPC decodes a serialized transaction hex string into a JSON object describing the transaction.

Parameter #1—serialized transaction in hex

Result—the decoded transaction

Example from Bitcoin Core 0.13.1

Decode a signed one-input, three-output transaction:

bitcoin-cli decoderawtransaction 0100000001bafe2175b9d7b3041ebac\
529056b393cf2997f7964485aa382ffa449ffdac02a000000008a47304402201\
3d212c22f0b46bb33106d148493b9a9723adb2c3dd3a3ebe3a9c9e3b95d8cb00\
220461661710202fbab550f973068af45c294667fc4dc526627a7463eb23ab39\
e9b01410479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815\
b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08\
ffb10d4b8ffffffff01b0a86a00000000001976a91401b81d5fa1e55e069e3cc\
2db9c19e2e80358f30688ac00000000

Result:

{
    "txid": "52309405287e737cf412fc42883d65a392ab950869fae80b2a5f1e33326aca46",
    "hash": "52309405287e737cf412fc42883d65a392ab950869fae80b2a5f1e33326aca46",
    "size": 223,
    "vsize": 223,
    "version": 1,
    "locktime": 0,
    "vin": [
        {
            "txid": "2ac0daff49a4ff82a35a4864797f99f23c396b0529c5ba1e04b3d7b97521feba",
            "vout": 0,
            "scriptSig": {
                "asm": "3044022013d212c22f0b46bb33106d148493b9a9723adb2c3dd3a3ebe3a9c9e3b95d8cb00220461661710202fbab550f973068af45c294667fc4dc526627a7463eb23ab39e9b[ALL] 0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8",
                "hex": "473044022013d212c22f0b46bb33106d148493b9a9723adb2c3dd3a3ebe3a9c9e3b95d8cb00220461661710202fbab550f973068af45c294667fc4dc526627a7463eb23ab39e9b01410479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8"
            },
            "sequence": 4294967295
        }
    ],
    "vout": [
        {
            "value": 0.06990000,
            "n": 0,
            "scriptPubKey": {
            "asm": "OP_DUP OP_HASH160 01b81d5fa1e55e069e3cc2db9c19e2e80358f306 OP_EQUALVERIFY OP_CHECKSIG",
                "hex": "76a91401b81d5fa1e55e069e3cc2db9c19e2e80358f30688ac",
                "reqSigs": 1,
                "type": "pubkeyhash",
                "addresses": [
                    "1A6Ei5cRfDJ8jjhwxfzLJph8B9ZEthR9Z"
                ]
            }
        }
    ]
}

See also

• CreateRawTransaction: creates an unsigned serialized transaction that spends a previous output to a new output with a P2PKH or P2SH address. The transaction is not stored in the wallet or transmitted to the network.
• SignRawTransaction: signs a transaction in the serialized transaction format using private keys stored in the wallet or provided in the call.
• SendRawTransaction: validates a transaction and broadcasts it to the peer-to-peer network.

DecodeScript

The decodescript RPC decodes a hex-encoded P2SH redeem script.

Parameter #1—a hex-encoded redeem script

Result—the decoded script

Example from Bitcoin Core 0.10.0

A 2-of-3 P2SH multisig pubkey script:

bitcoin-cli -testnet decodescript 522103ede722780d27b05f0b1169ef\
c90fa15a601a32fc6c3295114500c586831b6aaf2102ecd2d250a76d204011de\
6bc365a56033b9b3a149f679bc17205555d3c2b2854f21022d609d2f0d359e5b\
c0e5d0ea20ff9f5d3396cb5b1906aa9c56a0e7b5edc0c5d553ae

Result:

{
    "asm" : "2 03ede722780d27b05f0b1169efc90fa15a601a32fc6c3295114500c586831b6aaf 02ecd2d250a76d204011de6bc365a56033b9b3a149f679bc17205555d3c2b2854f 022d609d2f0d359e5bc0e5d0ea20ff9f5d3396cb5b1906aa9c56a0e7b5edc0c5d5 3 OP_CHECKMULTISIG",
    "reqSigs" : 2,
    "type" : "multisig",
    "addresses" : [
        "mjbLRSidW1MY8oubvs4SMEnHNFXxCcoehQ",
        "mo1vzGwCzWqteip29vGWWW6MsEBREuzW94",
        "mt17cV37fBqZsnMmrHnGCm9pM28R1kQdMG"
    ],
    "p2sh" : "2MyVxxgNBk5zHRPRY2iVjGRJHYZEp1pMCSq"
}

See also

• CreateMultiSig: creates a P2SH multi-signature address.
• Pay-To-Script-Hash (P2SH)

DisconnectNode

Added in Bitcoin Core 0.12.0

The disconnectnode RPC immediately disconnects from a specified node.

Parameter #1—hostname/IP address and port of node to disconnect

Result—null on success or error on failed disconnect

Example from Bitcoin Core 0.14.1

Disconnects following node from your node.

bitcoin-cli -testnet disconnectnode 192.0.2.113:18333

Result (no output from bitcoin-cli because result is set to null).

See also

• AddNode: attempts to add or remove a node from the addnode list, or to try a connection to a node once.
• GetAddedNodeInfo: returns information about the given added node, or all added nodes (except onetry nodes). Only nodes which have been manually added using the addnode RPC will have their information displayed.

DumpPrivKey

Requires wallet support. Requires an unlocked wallet or an unencrypted wallet.

The dumpprivkey RPC returns the wallet-import-format (WIF) private key corresponding to an address. (But does not remove it from the wallet.)

Parameter #1—the address corresponding to the private key to get

Result—the private key

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet dumpprivkey moQR7i8XM4rSGoNwEsw3h4YEuduuP6mxw7

Result:

cTVNtBK7mBi2yc9syEnwbiUpnpGJKohDWzXMeF4tGKAQ7wvomr95

See also

• ImportPrivKey: adds a private key to your wallet. The key should be formatted in the wallet import format created by the dumpprivkey RPC.
• DumpWallet: creates or overwrites a file with all wallet keys in a human-readable format.

DumpWallet

Requires wallet support. Requires an unlocked wallet or an unencrypted wallet.

The dumpwallet RPC creates or overwrites a file with all wallet keys in a human-readable format.

Parameter #1—a filename

Result—null or error

Example from Bitcoin Core 0.10.0

Create a wallet dump and then print its first 10 lines.

bitcoin-cli -testnet dumpwallet /tmp/dump.txt
head /tmp/dump.txt

Results (only showing the first 10 lines):

# Wallet dump created by Bitcoin v0.9.1.0-g026a939-beta (Tue, 8 Apr 2014 12:04:06 +0200)
# * Created on 2014-04-29T20:46:09Z
# * Best block at time of backup was 227221 (0000000026ede4c10594af8087748507fb06dcd30b8f4f48b9cc463cabc9d767),
#   mined on 2014-04-29T21:15:07Z

cTtefiUaLfXuyBXJBBywSdg8soTEkBNh9yTi1KgoHxUYxt1xZ2aA 2014-02-05T15:44:03Z label=test1 # addr=mnUbTmdAFD5EAg3348Ejmonub7JcWtrMck
cQNY9v93Gyt8KmwygFR59bDhVs3aRDkuT8pKaCBpop82TZ8ND1tH 2014-02-05T16:58:41Z reserve=1 # addr=mp4MmhTp3au21HPRz5waf6YohGumuNnsqT
cNTEPzZH9mjquFFADXe5S3BweNiHLUKD6PvEKEsHApqjX4ZddeU6 2014-02-05T16:58:41Z reserve=1 # addr=n3pdvsxveMBkktjsGJixfSbxacRUwJ9jQW
cTVNtBK7mBi2yc9syEnwbiUpnpGJKohDWzXMeF4tGKAQ7wvomr95 2014-02-05T16:58:41Z change=1 # addr=moQR7i8XM4rSGoNwEsw3h4YEuduuP6mxw7
cNCD679B4xi17jb4XeLpbRbZCbYUugptD7dCtUTfSU4KPuK2DyKT 2014-02-05T16:58:41Z reserve=1 # addr=mq8fzjxxVbAKxUGPwaSSo3C4WaUxdzfw3C

See also

• BackupWallet: safely copies wallet.dat to the specified file, which can be a directory or a path with filename.
• ImportWallet: imports private keys from a file in wallet dump file format (see the dumpwallet RPC). These keys will be added to the keys currently in the wallet. This call may need to rescan all or parts of the block chain for transactions affecting the newly-added keys, which may take several minutes.

EncryptWallet

Requires wallet support.

The encryptwallet RPC encrypts the wallet with a passphrase. This is only to enable encryption for the first time. After encryption is enabled, you will need to enter the passphrase to use private keys.

if using this RPC on the command line, remember that your shell probably saves your command lines (including the value of the passphrase parameter). In addition, there is no RPC to completely disable encryption. If you want to return to an unencrypted wallet, you must create a new wallet and restore your data from a backup made with the dumpwallet RPC.

Parameter #1—a passphrase

Result—a notice (with program shutdown)

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet encryptwallet "test"

Result:

wallet encrypted; Bitcoin server stopping, restart to run with encrypted
wallet. The keypool has been flushed, you need to make a new backup.

See also

• WalletPassphrase: stores the wallet decryption key in memory for the indicated number of seconds. Issuing the walletpassphrase command while the wallet is already unlocked will set a new unlock time that overrides the old one.
• WalletLock: removes the wallet encryption key from memory, locking the wallet. After calling this method, you will need to call walletpassphrase again before being able to call any methods which require the wallet to be unlocked.
• WalletPassphraseChange: changes the wallet passphrase from ‘old passphrase’ to ‘new passphrase’.

EstimateFee

The estimatefee RPC estimates the transaction fee per kilobyte that needs to be paid for a transaction to be included within a certain number of blocks.

Parameter #1—how many blocks the transaction may wait before being included

Result—the fee the transaction needs to pay per kilobyte

Examples from Bitcoin Core 0.14.1

bitcoin-cli estimatefee 6

Result:

0.00162556

Requesting data the node can’t calculate (out of range):

bitcoin-cli estimatefee 100

Result:

-1

See also

• SetTxFee: sets the transaction fee per kilobyte paid by transactions created by this wallet.

EstimatePriority

Added in Bitcoin Core 0.10.0.

The estimatepriority RPC estimates the priority (coin age) that a transaction needs in order to be included within a certain number of blocks as a free high-priority transaction. This should not to be confused with the prioritisetransaction RPC which will remain supported for adding fee deltas to transactions.

estimatepriority has been removed and will no longer be available in the next major release (planned for Bitcoin Core 0.15.0). Use the RPC listed in the “See Also” subsection below instead.

Transaction priority is relative to a transaction’s byte size.

Parameter #1—how many blocks the transaction may wait before being included as a free high-priority transaction

Result—the priority a transaction needs

Examples from Bitcoin Core 0.10.0

bitcoin-cli estimatepriority 6

Result:

718158904.10958910

Requesting data the node can’t calculate yet:

bitcoin-cli estimatepriority 100

Result:

-1.00000000

See also

• EstimateFee: estimates the transaction fee per kilobyte that needs to be paid for a transaction to be included within a certain number of blocks. Deprecated



FundRawTransaction

Requires wallet support.

The fundrawtransaction RPC adds inputs to a transaction until it has enough in value to meet its out value. This will not modify existing inputs, and will add one change output to the outputs. Note that inputs which were signed may need to be resigned after completion since in/outputs have been added. The inputs added will not be signed, use signrawtransaction for that. All existing inputs must have their previous output transaction be in the wallet.

Parameter #1—The hex string of the raw transaction

Parameter #2—Additional options

Result—information about the created transaction

Example from Bitcoin Core 0.13.1

bitcoin-cli -testnet fundrawtransaction 01000000011da9283b4ddf8d\
89eb996988b89ead56cecdc44041ab38bf787f1206cd90b51e0000000000ffff\
ffff01405dc600000000001976a9140dfc8bafc8419853b34d5e072ad37d1a51\
59f58488ac00000000 
'{
    "changeAddress": "15gJiApWFGTN2iTteQwQbqasdT6dwGWwv6",
    "changePosition" : 1,
    "includeWatching" : false,
    "lockUnspents" : true,
    "feeRate" : 0.0001
}'

Result:

{
	"hex": "01000000011da9283b4ddf8d89eb996988b89ead56cecdc44041ab38bf787f1206cd90b51e0000000000ffffffff01405dc600000000001976a9140dfc8bafc8419853b34d5e072ad37d1a5159f58488ac00000000",
	"fee": 0.0000245,
	"changepos": 2
}

See also

• CreateRawTransaction: creates an unsigned serialized transaction that spends a previous output to a new output with a P2PKH or P2SH address. The transaction is not stored in the wallet or transmitted to the network.
• DecodeRawTransaction: decodes a serialized transaction hex string into a JSON object describing the transaction.
• SignRawTransaction: signs a transaction in the serialized transaction format using private keys stored in the wallet or provided in the call.
• SendRawTransaction: validates a transaction and broadcasts it to the peer-to-peer network.
• Serialized Transaction Format

Generate

Requires wallet support.

The generate RPC nearly instantly generates blocks.

Parameter #1—the number of blocks to generate

Parameter #2—the maximum number of iterations to try

Result—the generated block header hashes

Example from Bitcoin Core 0.13.1

Using regtest mode (also works in normal mode), generate 2 blocks:

bitcoin-cli -regtest generate 2 500000

Result:

[
    "36252b5852a5921bdfca8701f936b39edeb1f8c39fffe73b0d8437921401f9af",
    "5f2956817db1e386759aa5794285977c70596b39ea093b9eab0aa4ba8cd50c06"
]

See also

• GenerateToAddress: mines blocks immediately to a specified address.
• GetMiningInfo: returns various mining-related information.
• GetBlockTemplate: gets a block template or proposal for use with mining software.

GenerateToAddress

Added in Bitcoin Core 0.13.0

Requires wallet support.

The generatetoaddress RPC mines blocks immediately to a specified address.

Parameter #1—the number of blocks to generate

Parameter #2—an address (P2PKH or P2SH)

Parameter #3—the maximum number of iterations to try

Result—the generated block header hashes

Example from Bitcoin Core 0.13.1

Using regtest mode, generate 2 blocks with maximal 500000 iterations:

bitcoin-cli -regtest generatetoaddress 2 "1BRo7qrYHMPrzdBDzfjmzt\
eBdYAyTMXW75" 500000

Result:

[
    "36252b5852a5921bdfca8701f936b39edeb1f8c39fffe73b0d8437921401f9af",
    "5f2956817db1e386759aa5794285977c70596b39ea093b9eab0aa4ba8cd50c06"
]

See also

• Generate: nearly instantly generates blocks.
• GetMiningInfo: returns various mining-related information.
• GetBlockTemplate: gets a block template or proposal for use with mining software.

GetAccountAddress

Requires wallet support.

The getaccountaddress RPC returns the current Bitcoin address for receiving payments to this account. If the account doesn’t exist, it creates both the account and a new address for receiving payment. Once a payment has been received to an address, future calls to this RPC for the same account will return a different address.

getaccountaddress will be removed in a later version of Bitcoin Core. Use the RPCs listed in the See Also subsection below instead.

Parameter #1—an account name

Result—a bitcoin address

Example from Bitcoin Core 0.10.0

Get an address for the default account:

bitcoin-cli -testnet getaccountaddress ""

Result:

msQyFNYHkFUo4PG3puJBbpesvRCyRQax7r

See also

• GetNewAddress: returns a new Bitcoin address for receiving payments. If an account is specified, payments received with the address will be credited to that account.
• GetRawChangeAddress: returns a new Bitcoin address for receiving change. This is for use with raw transactions, not normal use.
• GetAddressesByAccount: returns a list of every address assigned to a particular account.

GetAccount

Requires wallet support.

The getaccount RPC returns the name of the account associated with the given address.

Parameter #1—a Bitcoin address