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<pre> | ||
BIP: multipath-descs | ||
Layer: Applications | ||
Title: Multipath Descriptor Key Expressions | ||
Author: Andrew Chow <andrew@achow101.com> | ||
Comments-Summary: No comments yet. | ||
Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-multipath-descs | ||
Status: Draft | ||
Type: Informational | ||
Created: 2022-07-26 | ||
License: BSD-2-Clause | ||
</pre> | ||
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==Abstract== | ||
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This document specifies a modification to Key Expressions of Descriptors that are described in BIP 380. | ||
This modification allows Key Expressions to indicate BIP 32 derivation path steps that can have multiple values. | ||
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==Copyright== | ||
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This BIP is licensed under the BSD 2-clause license. | ||
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==Motivation== | ||
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Descriptors can describe the scripts that are used in a wallet, but wallets often require at least two descriptors for all of the scripts that they watch for. | ||
Wallets typically have one descriptor for producing receiving addresses, and the other for change addresses. | ||
These descriptors are often extremely similar - they produce the same types of scripts, derive keys from the same master key, and use derivation paths that are almost identical. | ||
The only differences are in the derivation path where one of the steps will be different between the descriptors. | ||
Thus it is useful to have a notation to represent both descriptors as a single descriptor where one of the derivation steps is a pair of values. | ||
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==Specification== | ||
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For extended keys and their derivations paths in a Key Expression, BIP 380 states: | ||
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* <tt>xpub</tt> encoded extended public key or <tt>xprv</tt> encoded extended private key (as defined in BIP 32) | ||
** Followed by zero or more <tt>/NUM</tt> or <tt>/NUMh</tt> path elements indicating BIP 32 derivation steps to be taken after the given extended key. | ||
** Optionally followed by a single <tt>/*</tt> or <tt>/*h</tt> final step to denote all direct unhardened or hardened children. | ||
This is modifed to state: | ||
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* <tt>xpub</tt> encoded extended public key or <tt>xprv</tt> encoded extended private key (as defined in BIP 32) | ||
** Followed by zero or more <tt>/NUM</tt> or <tt>/NUMh</tt> path elements indicating BIP 32 derivation steps to be taken after the given extended key. | ||
** Followed by zero or one <tt>/<NUM;NUM</tt> (<tt>NUM</tt> may be followed by <tt>h</tt> to indicated a hardened step) path element indicating a tuple of BIP 32 derivation steps to be taken after the given extended key. | ||
*** Followed by zero or more <tt>;NUM</tt> or <tt>;NUMh</tt> additional tuple values of BIP 32 derivation steps | ||
*** Followed by a single <tt>></tt> | ||
** Followed by zero or more <tt>/NUM</tt> or <tt>/NUMh</tt> path elements indicating BIP 32 derivation steps to be taken after the given extended key. | ||
** Optionally followed by a single <tt>/*</tt> or <tt>/*h</tt> final step to denote all direct unhardened or hardened children. | ||
When a <tt>/<NUM;NUM;...;NUM></tt> is encountered, parsers should produce multiple descriptors where the first descriptor uses the first <tt>NUM</tt>, and a second descriptor uses the second <tt>NUM</tt>, and so on, until each <tt>NUM</tt> is accounted for. | ||
Descriptors that contain multiple Key Expressions that each have a <tt>/<NUM;NUM;...;NUM></tt> must have tuples of exactly the same length. | ||
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The common use case for this is to represent descriptors for producing receiving and change addresses. | ||
When interpreting for this use case, wallets should use the first descriptor for producing receiving addresses, and the second descriptor for producing change addresses. | ||
For this use case, the element will commonly be the value <tt>/<0;1></tt> | ||
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==Test Vectors== | ||
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TBD | ||
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==Backwards Compatibility== | ||
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This is an addition to the Key Expressions defined in BIP 380. | ||
Key Expressions using the format described in BIP 380 are compatible with this modification and parsers that implement this will still be able to parse such descriptors. | ||
However as this is an addition to Key Expressions, older parsers will not be able to understand such descriptors. | ||
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This modification to Key Expressions uses two new characters: <tt><</tt> and <tt>;</tt>. | ||
These are part of the descriptor character set and so are covered by the checksum algorithm. | ||
As these are previously unused characters, old parsers will not accidentally mistake them for indicating something else. | ||
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==Reference Implementation== | ||
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https://github.com/bitcoin/bitcoin/pull/22838 |