bitcoin-bips/bip-0329.mediawiki

<pre>
  BIP: 329
  Layer: Applications
  Title: Wallet Labels Export Format
  Author: Craig Raw <craig@sparrowwallet.com>
  Comments-Summary: No comments yet.
  Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0329
  Status: Draft
  Type: Informational
  Created: 2022-08-23
  License: BSD-2-Clause
</pre>

==Abstract==

This document specifies a format for the export of labels that may be attached to various common types of records in a wallet.

==Copyright==

This BIP is licensed under the BSD 2-clause license.

==Motivation==

The export and import of funds across different Bitcoin wallet applications is well defined through standards such as BIP39, BIP32, BIP44 etc.
These standards are well supported and allow users to move easily between different wallets.
There is, however, no defined standard to transfer any labels the user may have applied to the transactions, addresses, public keys, inputs, outputs or xpubs in their wallet.
The UTXO model that Bitcoin uses makes these labels particularly valuable as they may indicate the source of funds, whether received externally or as a result of change from a prior transaction.
In both cases, care must be taken when spending to avoid undesirable leaks of private information.

Labels provide valuable guidance in this regard, and have even become mandatory when spending in several Bitcoin wallets.
Allowing users to import and export their labels in a standardized way ensures that they do not experience lock-in to a particular wallet application.
In addition, many wallets allow unspent outputs to be frozen or made unspendable within the wallet. Since this wallet-related metadata is similar to labels and not captured elsewhere, it is also included in this format.

==Rationale==

While there is currently no widely accepted format for exporting and importing labels, there are existing formats in use.
SLIP-0015<ref>[https://github.com/satoshilabs/slips/blob/master/slip-0015.md SLIP-0015]</ref> defines a format for exporting address and output labels, but requires encryption using a private key associated with the wallet seed, and thus cannot be used independently by coordinator wallets which cannot access private keys.
The Electrum wallet imports and exports address and transaction labels in a JSON format which could be used with other record types, but the format used is not self describing making record type identification difficult.

==Specification==

In order to be lightweight, human readable and well structured, this BIP uses a JSON format.
Further, the JSON Lines format is used (also called newline-delimited JSON)<ref>[https://jsonlines.org/ jsonlines.org]</ref>.
This allows a document to be split, streamed, or incrementally added to, and limits the potential for formatting errors to invalidate an entire import.
It is also a convenient format for command-line processing, which is often line-oriented.

Further to the JSON Lines specification, an export of labels from a wallet must be a UTF-8 encoded text file, containing one record per line consisting of a valid JSON object.
Lines are separated by <tt>\n</tt>. Multiline values are not permitted.
Each JSON object must contain 3 or 4 key/value pairs, defined as follows:

{| class="wikitable"
|-
! Key
! Description
|-
| <tt>type</tt>
| One of <tt>tx</tt>, <tt>addr</tt>, <tt>pubkey</tt>, <tt>input</tt>, <tt>output</tt> or <tt>xpub</tt>
|-
| <tt>ref</tt>
| Reference to the transaction, address, public key, input, output or extended public key
|-
| <tt>label</tt>
| The label applied to the reference
|-
| <tt>origin</tt>
| Optional key origin information referencing the wallet associated with the label
|-
| <tt>spendable</tt>
| One of <tt>true</tt> or <tt>false</tt>, denoting if an output should be spendable by the wallet
|}

The reference is defined for each <tt>type</tt> as follows:

{| class="wikitable"
|-
! Type
! Description
! Example
|-
| <tt>tx</tt>
| Transaction id in hexadecimal format
| <tt>f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd</tt>
|-
| <tt>addr</tt>
| Address in base58 or bech32 format
| <tt>bc1q34aq5drpuwy3wgl9lhup9892qp6svr8ldzyy7c</tt>
|-
| <tt>pubkey</tt>
| 32, 33 or 65 byte public key in hexadecimal format
| <tt>0283409659355b6d1cc3c32decd5d561abaac86c37a353b52895a5e6c196d6f448</tt>
|-
| <tt>input</tt>
| Transaction id and input index separated by a colon
| <tt>f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd:0</tt>
|-
| <tt>output</tt>
| Transaction id and output index separated by a colon
| <tt>f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd:1</tt>
|-
| <tt>xpub</tt>
| Extended public key as defined by BIP32
| <tt>xpub661MyMwAqRbcFtXgS5sYJABqqG9YLmC4Q1Rdap9gSE8Nq...</tt>
|}

Each JSON object must contain both <tt>type</tt> and <tt>ref</tt> properties. The <tt>label</tt>, <tt>origin</tt> and <tt>spendable</tt> properties are optional. If the <tt>label</tt> or <tt>spendable</tt> properties are omitted, the importing wallet should not alter these values. The <tt>spendable</tt> property should only appear where type is <tt>output</tt>.

If present, the optional <tt>origin</tt> property must contain an abbreviated output descriptor (as defined by BIP380<ref>[https://github.com/bitcoin/bips/blob/master/bip-0380.mediawiki BIP-0380]</ref>) describing a BIP32 compatible originating wallet, including all key origin information but excluding any actual keys, any child path elements, or a checksum.
This property should be used to disambiguate transaction labels from different wallets contained in the same export, particularly when exporting multiple accounts derived from the same seed.

Care should be taken when exporting due to the privacy sensitive nature of the data.
Encryption in transit over untrusted networks is highly recommended, and encryption at rest should also be considered.
Unencrypted exports should be deleted as soon as possible.
For security reasons no private key types are defined.

==Importing==

* An importing wallet may ignore records it does not store, and truncate labels if necessary. A suggested default for maximum label length is 255 characters, and an importing wallet should consider warning the user if truncation is applied.
* Wallets importing public key records may derive addresses from them to match against known wallet addresses.
* Wallets importing extended public keys may match them against signers, for example in a multisig setup.

==Backwards Compatibility==

The nature of this format makes it naturally extensible to handle other record types.
However, importing wallets complying to this specification should ignore types not defined here.

==Test Vectors==

The following fragment represents a wallet label export:
<pre>
{ "type": "tx", "ref": "f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd", "label": "Transaction", "origin": "wpkh([d34db33f/84'/0'/0'])" }
{ "type": "addr", "ref": "bc1q34aq5drpuwy3wgl9lhup9892qp6svr8ldzyy7c", "label": "Address" }
{ "type": "pubkey", "ref": "0283409659355b6d1cc3c32decd5d561abaac86c37a353b52895a5e6c196d6f448", "label": "Public Key" }
{ "type": "input", "ref": "f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd:0", "label": "Input" }
{ "type": "output", "ref": "f91d0a8a78462bc59398f2c5d7a84fcff491c26ba54c4833478b202796c8aafd:1", "label": "Output", "spendable": false }
{ "type": "xpub", "ref": "xpub661MyMwAqRbcFtXgS5sYJABqqG9YLmC4Q1Rdap9gSE8NqtwybGhePY2gZ29ESFjqJoCu1Rupje8YtGqsefD265TMg7usUDFdp6W1EGMcet8", "label": "Extended Public Key" }
{ "type": "tx", "ref": "f546156d9044844e02b181026a1a407abfca62e7ea1159f87bbeaa77b4286c74", "label": "Account #1 Transaction", "origin": "wpkh([d34db33f/84'/0'/1'])" }
</pre>

==Additional Fields==

If the goal is solely to move labels between cooperating wallets,
then the above values are the minimum needed. However, wallet data
exports can serve other purposes. Many values associated with
addresses, transactions and outputs are already on hand for the
wallet generating the export, and yet would be hard or impossible
for importing tools to reconstruct.

All of the following values are optional for the exporter to provide,
but should be given if they are readily available.

=== Transactions ===

* <tt>height</tt>: An integer giving the block height where this fully confirmed transaction can be found. For transactions that are confirmed by less than 6 blocks, omit this field or provide a value of zero.  (Background: Until it is fully confirmed, the "height" of a transaction is in flux and may vary due to chain reorgs. However, the consumer of the labels, may not know the current block height, so it cannot know if the height is "real" (firm, fixed) or just transitory. Therefore, it is important to omit the height unless the generating wallet considers the transaction to be confirmed.)

* <tt>time</tt>: ISO-8601 formatted timestamp of the block given by the "height" field, preferably in UTC, although ISO-8601 can represent local times. Example: <tt>2025-01-23T11:40:35Z</tt>.

* <tt>fee</tt>: Integer giving the number of Satoshis that went to the miner for this transaction.

* <tt>value</tt>: Signed integer giving the number of Satoshis that came into the wallet by this transaction. Will be negative when sats leave the wallet. Could be zero if it is a consolidation transaction that moves from old UTXO to new. 

* <tt>rate</tt>: Exchange rate at time of transaction. This is the value of a Bitcoin, expressed in another currency, at the time of the transaction, based on user preferences for data source. Multiple currencies can be given. Keys are ISO 4217 currency codes where possible. Example: <tt>"rate": { "USD":  105620.00 }</tt>

=== Address, Inputs, and Outputs ===

* <tt>keypath</tt>: The data needed to build full descriptor down to the specific address.  This extends <tt>origin</tt> with the final two components that are unhardened (in the typical case, assuming BIP-84).  Provide string <tt>/1/123</tt> for <tt>wpkh([d34db33f/84'/0'/0'/1/123])</tt>. If the first character is not <tt>/</tt>, then it should be interpreted as a full descriptor, independant of <tt>origin</tt> (if any).

=== Inputs and Outputs ===

* <tt>value</tt>: Integer with the number of Satoshis (<tt>nValue</tt>) of the input or output.

* <tt>fmv</tt>: Fair market value of the input/output relative to some other currency, typically fiat. The value should be a mapping, from currency code to decimal number. Example: <tt>"fmv": { "USD":  1233.45 }</tt>. Most situations will have only a single currency value, and it represents the real price of the goods/services expressed in some fiat currency. This is not an exchange *rate*, but an absolute value. By dividing by the <tt>value</tt> (above), it is possible to calculate an effective change rate for the transaction.

* <tt>height</tt> and <tt>time</tt>: Same definition as defined in Transactions.

=== Address ===

* <tt>heights</tt>: a list of block heights that contain any activity related to this address, include outputs that deposit to the address, and transactions that spend UTXOs of this address. Omit heights for transactions that are not fully confirmed. An empty array indicates the address is unused for confirmed transactions.

== Comment on Types in JSON ==

JSON can serialize a number of basic types, including string, integer
and boolean (true/false).  Decimal values (<tt>123.45</tt>) can
also be serialized, but some parsing libraries may interpret them as floating
point values, which is generally not what we want in financial applications.
When hand-crafting JSON data, be careful not to write <tt>"false"</tt> (with quotes),
since that is a string with 5 characters and not a boolean.

==Reference Implementation==

* [https://github.com/Labelbase/python-bip329 Python-BIP329 package]

==References==

<references />