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 in one of the Bitcoin development communities. Errors or suggestions related to documentation 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

The 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 will be introduced when sufficient numbers of miners switch to using Bitcoin Core 0.10.0 and other versions that create version 3 blocks. As described in draft BIP66, this soft fork change requires strict DER encoding for all ECDSA signatures used in transactions appearing in version 3 or later blocks. Transactions that do not use strict DER encoding have been non-standard since Bitcoin Core 0.8.0.

• Version 4 blocks will likely be introduced in the near-future as specified in draft BIP62. Possible changes include:

  • Reject version 4 blocks that include any version 2 transactions that don’t adhere to any of the version 2 transaction rules. These rules are not yet described in this documentation; see BIP62 for details.

  • A soft fork rollout of version 4 blocks identical to the rollout used for version 3 blocks (described briefly in BIP62 and in more detail in BIP34).

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 2014, it’s 25 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.

OP Codes

The op codes used in the pubkey scripts of standard transactions are:

• Various data pushing op codes 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 OP codes 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 op codes which can’t be modified without causing the pubkey script to fail. Placing non-data-pushing op codes in the signature script currently makes a transaction non-standard, and future consensus rules may forbid such transactions altogether. (Non-data-pushing op codes 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 as well as the alert keys for mainnet and testnet.

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.)

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 previously received by way of an inv message.

The response to a getdata message can be a tx message, block message, merkleblock 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 one or more block headers to a node which previously requested certain headers with a getheaders message.

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.

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.

The alert message warns nodes of problems that may affect them or the rest of the network. Each alert message is signed using a key controlled by respected community members, mostly Bitcoin Core developers.

To ensure all nodes can validate and forward alert messages, encapsulation is used. Developers create an alert using the data structure appropriate for the versions of the software they want to notify; then they serialize that data and sign it. The serialized data and its signature make up the outer alert message—allowing nodes which don’t understand the data structure to validate the signature and relay the alert to nodes which do understand it. The nodes which actually need the message can decode the serialized data to access the inner alert message.

The outer alert message has four fields:

Although designed to be easily upgraded, the format of the inner serialized alert has not changed since the alert message was first introduced in protocol version 311.

The annotated hexdump below shows an alert message. (The message header has been omitted.)

73 ................................. Bytes in encapsulated alert: 115
01000000 ........................... Version: 1
3766404f00000000 ................... RelayUntil: 1329620535
b305434f00000000 ................... Expiration: 1330917376

f2030000 ........................... ID: 1010
f1030000 ........................... Cancel: 1009
00 ................................. setCancel count: 0

10270000 ........................... MinVer: 10000
48ee0000 ........................... MaxVer: 61000
00 ................................. setUser_agent bytes: 0
64000000 ........................... Priority: 100

00 ................................. Bytes In Comment String: 0
46 ................................. Bytes in StatusBar String: 70
53656520626974636f696e2e6f72672f
666562323020696620796f7520686176
652074726f75626c6520636f6e6e6563
74696e67206166746572203230204665
627275617279 ....................... Status Bar String: "See [...]"
00 ................................. Bytes In Reserved String: 0

47 ................................. Bytes in signature: 71
30450221008389df45f0703f39ec8c1c
c42c13810ffcae14995bb648340219e3
53b63b53eb022009ec65e1c1aaeec1fd
334c6b684bde2b3f573060d5b70c3a46
723326e4e8a4f1 ..................... Signature

Alert key compromise: Bitcoin Core’s source code defines a particular set of alert parameters that can be used to notify users that the alert signing key has been compromised and that they should upgrade to get a new alert public key. Once a signed alert containing those parameters has been received, no other alerts can cancel or override it. See the ProcessAlert() function in the Bitcoin Core alert.cpp source code for the parameters of this message.

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 op code 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 op code 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

VerAck

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:0.9.2.1/

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

Bitcoin Core APIs

Hash Byte Order

Bitcoin Core RPCs accept and return hashes in the reverse of their normal byte order. For example, the Unix sha256sum command would display the SHA256(SHA256()) hash of mainnet block 300,000’s header as the following string:

5472ac8b1187bfcf91d6d218bbda1eb2405d7c55f1f8cc820000000000000000

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

020000005472ac8b1187bfcf91d6d218bbda1eb2405d7c55f1f8cc82000\
0000000000000ab0aaa377ca3f49b1545e2ae6b0667a08f42e72d8c24ae\
237140e28f14f3bb7c6bcc6d536c890019edd83ccf

However Bitcoin RPCs use the reverse byte order for hashes, so if you want to get information about block 300,000 using the getblock RPC, you need to reverse the byte order:

> 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 rational for the reversal is unknown, but it likely stems from Bitcoin’s use of hash digests (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.

Off-site documentation such as the Bitcoin Wiki tends to use the terms big endian and little endian as shown in the table below, but they aren’t always consistent. Worse, these two different ways of representing a hash digest can confuse anyone who looks at the Bitcoin Core source code and finds a so-called “big endian” value being stored in a little-endian data type.

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 large number of Remote Procedure Calls (RPCs) using a HTTP JSON-RPC version 1.0 interface. Any program can access the RPCs using JSON-RPC, but Bitcoin Core also provides the bitcoin-cli command to wrap the JSON-RPC access for Command Line Interface (CLI) users. Most of the RPC examples in this documentation use bitcoin-cli for simplicity, so this subsection describes raw JSON-RPC interface and how the command-line interface translates it.

In order to start bitcoind, you will need to set a password for JSON-RPC in the bitcoin.conf file. See the Examples Page for details. JSON-RPC starts on port 8332 for mainnet and 18332 for testnet and regtest. By default, bitcoind doesn’t use a JSON-RPC user, but you can set one (see bitcoind --help).

The interface is not intended for public access and is only accessible from localhost by default.

RPCs are made using the standard JSON-RPC 1.0 syntax, which sends several standard arguments:

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

• “→” to indicate 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 RPC array.

• “Plain Text” names (like “RPC” above) are unnamed in the actual JSON-RPC

• literal names (like id above) are the strings that appear in the actual JSON-RPC

• Type (specifics) are the general JSON-RPC type and the specific Bitcoin Core type

• Required/Optional describe whether a field must be returned within its containing array or object. (So an optional object may still have required children.)

For example, here is the JSON-RPC requesting the hash of the latest block on the local best block chain:

{
    "jsonrpc": "1.0",
    "id": "Bitcoin developer documentation",
    "method": "getbestblockhash",
    "params": []
}

We can send that to a local Bitcoin Core running on testnet using cURL with the following command:

curl --user ':your_password' --data-binary '''
  {
      "jsonrpc": "1.0",
      "id":"Bitcoin developer documentation",
      "method": "getbestblockhash",
      "params": []
  }''' \
  -H 'content-type: text/plain;' http://127.0.0.1:18332/

The output will be sent using the standard JSON-RPC 1.0 format. For example (whitespace added):

{
    "result": "00000000bd68bfdf381efd5fff17c723d2bb645bcbb215a6e333d4204888e951",
    "error": null,
    "id": "Bitcoin developer documentation"
}

The standard JSON-RPC 1.0 result format is described below:

For an example of the error output, here’s the result after passing an invalid address to the sendtoaddress RPC (whitespace added):

{
    "result": null,
    "error": {
        "code": -5,
        "message": "Invalid Bitcoin address"
    },
    "id": "Bitcoin developer documentation"
}

The bitcoin-cli command can save command line users a lot of typing compared to using cURL or another HTTP-sending command. For example, to get the block hash we got before, we would use the following command:

bitcoin-cli getbestblockhash

For non-error output, bitcoin-cli will only display the value of the result field, and if it’s a string, bitcoin-cli will remove its JSON quotation marks. For example, the result for the command above:

00000000bd68bfdf381efd5fff17c723d2bb645bcbb215a6e333d4204888e951

For errors, bitcoin-cli will display only the error object. For example, the result of the invalid address command above as formatted by bitcoin-cli:

error: {"code":-5,"message":"Invalid Bitcoin address"}

Because bitcoin-cli abstracts away the parts of JSON-RPC we would need to repeatedly describe in each RPC description below, we describe the Bitcoin Core RPCs using bitcoin-cli. However, using an actual programming interface to the full JSON-RPC will serve you much better for automated tasks.

Warning: 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. New in 0.9.0
• GetBlock: gets a block with a particular header hash from the local block database either as a JSON object or as a serialized block.
• GetBlockChainInfo: provides information about the current state of the block chain. New in 0.9.2, Updated in 0.10.0
• 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.
• GetChainTips: returns information about the highest-height block (tip) of each local block chain. New in 0.10.0
• GetDifficulty: returns the proof-of-work difficulty as a multiple of the minimum difficulty.
• GetMemPoolInfo: returns information about the node’s current transaction memory pool. New in 0.10.0
• 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.
• GetTxOut: returns details about a transaction output. Only unspent transaction outputs (UTXOs) are guaranteed to be available.
• 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.
• VerifyChain: verifies each entry in the local block chain database.

Control RPCs

• GetInfo: prints various information about the node and the network. Updated in 0.10.0, 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 (in regtest mode only) New in master
• GetGenerate: returns true if the node is set to generate blocks using its CPU.
• SetGenerate: enables or disables hashing to attempt to find the next block. Updated in master

Mining RPCs

• GetBlockTemplate: gets a block template or proposal for use with mining software.
• GetMiningInfo: returns various mining-related information. Updated in master
• 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.) New in 0.10.0
• 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.
• 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.
• GetConnectionCount: returns the number of connections to other nodes.
• GetNetTotals: returns information about network traffic, including bytes in, bytes out, and the current time.
• GetNetworkInfo: returns information about the node’s connection to the network. New in 0.9.2, Updated in 0.10.0
• GetPeerInfo: returns data about each connected network node. Updated in 0.10.0
• 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.

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.
• DecodeRawTransaction: decodes a serialized transaction hex string into a JSON object describing the transaction.
• 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.
• 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. New in 0.10.0
• 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. New in 0.10.0
• ValidateAddress: returns information about the given Bitcoin address.
• 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.

• 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.
• 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.
• GetAccount: returns the name of the account associated with the given address.
• GetAddressesByAccount: returns a list of every address assigned to a particular account.
• 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.
• 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 0.10.0
• GetUnconfirmedBalance: returns the wallet’s total unconfirmed balance.
• GetWalletInfo: provides information about the wallet. New in 0.9.2
• 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. New in 0.10.0
• 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. Updated in 0.10.0
• 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. Updated in 0.10.0
• ListReceivedByAddress: lists the total number of bitcoins received by each address. Updated in 0.10.0
• 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. Updated in 0.10.0
• ListTransactions: returns the most recent transactions that affect the wallet. Updated in 0.10.0
• ListUnspent: returns an array of unspent transaction outputs belonging to this wallet. Updated in 0.10.0
• 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.
• SendFrom: spends an amount from a local account to a bitcoin address.
• 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.
• 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.
• 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

• GetHashesPerSec: was removed in Bitcoin Core master (unreleased). It returned a recent hashes per second performance measurement when the node was generating blocks.
• GetWork: was removed in Bitcoin Core 0.10.0.

RPCs

Warning: 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.

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.

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.

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—references to previous outputs

Parameter #2—P2PKH or P2SH addresses and amounts

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 0.10.0

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

bitcoin-cli -testnet decoderawtransaction 0100000001268a9ad7bfb2\
1d3c086f0ff28f73a064964aa069ebb69a9e437da85c7e55c7d7000000006b48\
3045022100ee69171016b7dd218491faf6e13f53d40d64f4b40123a2de52560f\
eb95de63b902206f23a0919471eaa1e45a0982ed288d374397d30dff541b2dd4\
5a4c3d0041acc0012103a7c1fd1fdec50e1cf3f0cc8cb4378cd8e9a2cee8ca9b\
3118f3db16cbbcf8f326ffffffff0350ac6002000000001976a91456847befbd\
2360df0e35b4e3b77bae48585ae06888ac80969800000000001976a9142b1495\
0b8d31620c6cc923c5408a701b1ec0a02088ac002d3101000000001976a9140d\
fc8bafc8419853b34d5e072ad37d1a5159f58488ac00000000

Result:

{
    "txid" : "ef7c0cbf6ba5af68d2ea239bba709b26ff7b0b669839a63bb01c2cb8e8de481e",
    "version" : 1,
    "locktime" : 0,
    "vin" : [
        {
            "txid" : "d7c7557e5ca87d439e9ab6eb69a04a9664a0738ff20f6f083c1db2bfd79a8a26",
            "vout" : 0,
            "scriptSig" : {
                "asm" : "3045022100ee69171016b7dd218491faf6e13f53d40d64f4b40123a2de52560feb95de63b902206f23a0919471eaa1e45a0982ed288d374397d30dff541b2dd45a4c3d0041acc001 03a7c1fd1fdec50e1cf3f0cc8cb4378cd8e9a2cee8ca9b3118f3db16cbbcf8f326",
                "hex" : "483045022100ee69171016b7dd218491faf6e13f53d40d64f4b40123a2de52560feb95de63b902206f23a0919471eaa1e45a0982ed288d374397d30dff541b2dd45a4c3d0041acc0012103a7c1fd1fdec50e1cf3f0cc8cb4378cd8e9a2cee8ca9b3118f3db16cbbcf8f326"
            },
            "sequence" : 4294967295
        }
    ],
    "vout" : [
        {
            "value" : 0.39890000,
            "n" : 0,
            "scriptPubKey" : {
                "asm" : "OP_DUP OP_HASH160 56847befbd2360df0e35b4e3b77bae48585ae068 OP_EQUALVERIFY OP_CHECKSIG",
                "hex" : "76a91456847befbd2360df0e35b4e3b77bae48585ae06888ac",
                "reqSigs" : 1,
                "type" : "pubkeyhash",
                "addresses" : [
                    "moQR7i8XM4rSGoNwEsw3h4YEuduuP6mxw7"
                ]
            }
        },
        {
            "value" : 0.10000000,
            "n" : 1,
            "scriptPubKey" : {
                "asm" : "OP_DUP OP_HASH160 2b14950b8d31620c6cc923c5408a701b1ec0a020 OP_EQUALVERIFY OP_CHECKSIG",
                "hex" : "76a9142b14950b8d31620c6cc923c5408a701b1ec0a02088ac",
                "reqSigs" : 1,
                "type" : "pubkeyhash",
                "addresses" : [
                    "mjSk1Ny9spzU2fouzYgLqGUD8U41iR35QN"
                ]
            }
        },
        {
            "value" : 0.20000000,
            "n" : 2,
            "scriptPubKey" : {
                "asm" : "OP_DUP OP_HASH160 0dfc8bafc8419853b34d5e072ad37d1a5159f584 OP_EQUALVERIFY OP_CHECKSIG",
                "hex" : "76a9140dfc8bafc8419853b34d5e072ad37d1a5159f58488ac",
                "reqSigs" : 1,
                "type" : "pubkeyhash",
                "addresses" : [
                    "mgnucj8nYqdrPFh2JfZSB1NmUThUGnmsqe"
                ]
            }
        }
    ]
}

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)

DumpPrivKey

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

The dumpprivkey RPC returns the wallet-import-format (WIP) 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.

Warning: 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

Added in Bitcoin Core 0.10.0.

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 0.10.0

bitcoin-cli estimatefee 6

Result:

0.00026809

Requesting data the node can’t calculate yet:

bitcoin-cli estimatefee 100

Result:

-1.00000000

See also

• 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.
• 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 that a transaction needs in order to be included within a certain number of blocks as a free high-priority transaction.

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.

Generate

Requires wallet support.

The generate RPC nearly instantly generates blocks (in regtest mode only)

Parameter #1—the number of blocks to generate

Result—the generated block header hashes

Examples from Bitcoin Core master (commit c2fa0846)

Using regtest mode, generate 2 blocks:

bitcoin-cli -regtest generate 2

Result:

[
    "36252b5852a5921bdfca8701f936b39edeb1f8c39fffe73b0d8437921401f9af",
    "5f2956817db1e386759aa5794285977c70596b39ea093b9eab0aa4ba8cd50c06"
]

See also

• SetGenerate: returns true if the node is set to generate blocks using its CPU.
• 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.

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

Result—an account name

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getaccount mjSk1Ny9spzU2fouzYgLqGUD8U41iR35QN

Result:

doc test

See also

• GetAddressesByAccount: returns a list of every address assigned to a particular account.

GetAddedNodeInfo

The getaddednodeinfo RPC 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.

Parameter #1—whether to display connection information

Parameter #2—what node to display information about

Result—a list of added nodes

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getaddednodeinfo true

Result (real hostname and IP address replaced):

[
    {
        "addednode" : "bitcoind.example.com:18333",
        "connected" : true,
        "addresses" : [
            {
                "address" : "192.0.2.113:18333",
                "connected" : "outbound"
            }
        ]
    }
]

See also

• AddNode: attempts to add or remove a node from the addnode list, or to try a connection to a node once.
• GetPeerInfo: returns data about each connected network node.

GetAddressesByAccount

Requires wallet support.

The getaddressesbyaccount RPC returns a list of every address assigned to a particular account.

Parameter #1—the account name

Result—a list of addresses

Example from Bitcoin Core 0.10.0

Get the addresses assigned to the account “doc test”:

bitcoin-cli -testnet getaddressesbyaccount "doc test"

Result:

[
    "mjSk1Ny9spzU2fouzYgLqGUD8U41iR35QN",
    "mft61jjkmiEJwJ7Zw3r1h344D6aL1xwhma",
    "mmXgiR6KAhZCyQ8ndr2BCfEq1wNG2UnyG6"
]

See also

• GetAccount: returns the name of the account associated with the given address.
• GetBalance: gets the balance in decimal bitcoins across all accounts or for a particular account.

GetBalance

Requires wallet support.

The getbalance RPC gets the balance in decimal bitcoins across all accounts or for a particular account.

Parameter #1—an account name

Parameter #2—the minimum number of confirmations

Parameter #3—whether to include watch-only addresses

Result—the balance in bitcoins

Examples from Bitcoin Core 0.10.0

Get the balance for the “test1” account, including transactions with at least one confirmation and those spent to watch-only addresses in that account.

bitcoin-cli -testnet getbalance "test1" 1 true

Result:

1.99900000

See also

• ListAccounts: lists accounts and their balances.
• 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.
• GetReceivedByAddress: returns the total amount received by the specified address in transactions with the specified number of confirmations. It does not count coinbase transactions.

GetBestBlockHash

Added in Bitcoin Core 0.9.0

The getbestblockhash RPC returns the header hash of the most recent block on the best block chain.

Parameters: none

Result—hash of the tip from the best block chain

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getbestblockhash

Result:

0000000000075c58ed39c3e50f99b32183d090aefa0cf8c324a82eea9b01a887

See also

• GetBlock: gets a block with a particular header hash from the local block database either as a JSON object or as a serialized block.
• GetBlockHash: returns the header hash of a block at the given height in the local best block chain.

GetBlock

The getblock RPC gets a block with a particular header hash from the local block database either as a JSON object or as a serialized block.

Parameter #1—header hash

Parameter #2—JSON or hex output

Result (if format was false)—a serialized block

Result (if format was true or omitted)—a JSON block

Example from Bitcoin Core 0.10.0

Get a block in raw hex:

bitcoin-cli -testnet getblock \
            000000000fe549a89848c76070d4132872cfb6efe5315d01d7ef77e4900f2d39 \
            false

Result (wrapped):

02000000df11c014a8d798395b5059c722ebdf3171a4217ead71bf6e0e99f4c7\
000000004a6f6a2db225c81e77773f6f0457bcb05865a94900ed11356d0b7522\
8efb38c7785d6053ffff001d005d437001010000000100000000000000000000\
00000000000000000000000000000000000000000000ffffffff0d03b4770301\
64062f503253482fffffffff0100f9029500000000232103adb7d8ef6b63de74\
313e0cd4e07670d09a169b13e4eda2d650f529332c47646dac00000000

Get the same block in JSON:

bitcoin-cli -testnet getblock \
            000000000fe549a89848c76070d4132872cfb6efe5315d01d7ef77e4900f2d39 \
            true

Result:

{
    "hash" : "000000000fe549a89848c76070d4132872cfb6efe5315d01d7ef77e4900f2d39",
    "confirmations" : 88029,
    "size" : 189,
    "height" : 227252,
    "version" : 2,
    "merkleroot" : "c738fb8e22750b6d3511ed0049a96558b0bc57046f3f77771ec825b22d6a6f4a",
    "tx" : [
        "c738fb8e22750b6d3511ed0049a96558b0bc57046f3f77771ec825b22d6a6f4a"
    ],
    "time" : 1398824312,
    "nonce" : 1883462912,
    "bits" : "1d00ffff",
    "difficulty" : 1.00000000,
    "chainwork" : "000000000000000000000000000000000000000000000000083ada4a4009841a",
    "previousblockhash" : "00000000c7f4990e6ebf71ad7e21a47131dfeb22c759505b3998d7a814c011df",
    "nextblockhash" : "00000000afe1928529ac766f1237657819a11cfcc8ca6d67f119e868ed5b6188"
}

See also

• GetBlockHash: returns the header hash of a block at the given height in the local best block chain.
• GetBestBlockHash: returns the header hash of the most recent block on the best block chain.

GetBlockChainInfo

Added in Bitcoin Core 0.9.2

The getblockchaininfo RPC provides information about the current state of the block chain.

Parameters: none

Result—A JSON object providing information about the block chain

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getblockchaininfo

Result:

{
    "chain" : "test",
    "blocks" : 315280,
    "headers" : 315280,
    "bestblockhash" : "000000000ebb17fb455e897b8f3e343eea1b07d926476d00bc66e2c0342ed50f",
    "difficulty" : 1.00000000,
    "verificationprogress" : 1.00000778,
    "chainwork" : "0000000000000000000000000000000000000000000000015e984b4fb9f9b350"
}

See also

• GetMiningInfo: returns various mining-related information.
• GetNetworkInfo: returns information about the node’s connection to the network.
• GetWalletInfo: provides information about the wallet.

GetBlockCount

The getblockcount RPC returns the number of blocks in the local best block chain.

Parameters: none

Result—the number of blocks in the local best block chain

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getblockcount

Result:

315280

See also

• GetBlockHash: returns the header hash of a block at the given height in the local 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.

GetBlockHash

The getblockhash RPC returns the header hash of a block at the given height in the local best block chain.

Parameter—a block height

Result—the block header hash

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getblockhash 240886

Result:

00000000a0faf83ab5799354ae9c11da2a2bd6db44058e03c528851dee0a3fff

See also

• GetBlock: gets a block with a particular header hash from the local block database either as a JSON object or as a serialized block.
• GetBestBlockHash: returns the header hash of the most recent block on the best block chain.

GetBlockTemplate

The getblocktemplate RPC gets a block template or proposal for use with mining software. For more information, please see the following resources:

• Bitcoin Wiki GetBlockTemplate
• BIP22
• BIP23

See also

• SetGenerate: enables or disables hashing to attempt to find the next block.
• GetMiningInfo: returns various mining-related information.
• 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.
• 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.)

GetChainTips

Added in Bitcoin Core 0.10.0.

The getchaintips RPC returns information about the highest-height block (tip) of each local block chain.

Parameters: none

Result—an array of block chain tips

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getchaintips

[
    {
        "height" : 312647,
        "hash" : "000000000b1be96f87b31485f62c1361193304a5ad78acf47f9164ea4773a843",
        "branchlen" : 0,
        "status" : "active"
    },
    {
        "height" : 282072,
        "hash" : "00000000712340a499b185080f94b28c365d8adb9fc95bca541ea5e708f31028",
        "branchlen" : 5,
        "status" : "valid-fork"
    },
    {
        "height" : 281721,
        "hash" : "000000006e1f2a32199629c6c1fbd37766f5ce7e8c42bab0c6e1ae42b88ffe12",
        "branchlen" : 1,
        "status" : "valid-headers"
    },
]

See also

• 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.
• GetBlockChainInfo: provides information about the current state of the block chain.

GetConnectionCount

The getconnectioncount RPC returns the number of connections to other nodes.

Parameters: none

Result—the number of connections to other nodes

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getconnectioncount

Result:

14

See also

• GetNetTotals: returns information about network traffic, including bytes in, bytes out, and the current time.
• GetPeerInfo: returns data about each connected network node.
• GetNetworkInfo: returns information about the node’s connection to the network.

GetDifficulty

The getdifficulty RPC

Parameters: none

Result—the current difficulty

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getdifficulty

Result:

1.00000000

See also

• GetNetworkHashPS: returns the estimated current or historical network hashes per second based on the last n blocks.
• GetMiningInfo: returns various mining-related information.

GetGenerate

Requires wallet support.

The getgenerate RPC returns true if the node is set to generate blocks using its CPU.

Parameters: none

Result—whether the server is set to generate blocks

Example from Bitcoin Core 0.10.0

bitcoin-cli -testnet getgenerate

Result:

false

See also

• SetGenerate: enables or disables hashing to attempt to find the next block.
• GetMiningInfo: returns various mining-related information.
• GetHashesPerSec: was removed in Bitcoin Core master (unreleased). It returned a recent hashes per second performance measurement when the node was generating blocks.

GetHashesPerSec

Requires wallet support.

The gethashespersec RPC was removed in Bitcoin Core master (unreleased). It returned a recent hashes per second performance measurement when the node was generating blocks.

Parameters: none

Result—the number of hashes your computer generated per second