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79 lines
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79 lines
3.5 KiB
Plaintext
<pre>
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BIP: 383
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Layer: Applications
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Title: Multisig Output Script Descriptors
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Author: Pieter Wuille <pieter@wuille.net>
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Andrew Chow <andrew@achow101.com>
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Comments-Summary: No comments yet.
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Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0383
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Status: Draft
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Type: Informational
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Created: 2021-06-27
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License: BSD-2-Clause
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</pre>
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==Abstract==
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This document specifies <tt>multi()</tt>, and <tt>sortedmulti()</tt> output script descriptors.
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Both functions take a threshold and one or more public keys and produce a multisig output script.
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<tt>multi()</tt> specifies the public keys in the output script in the order given in the descriptor while <tt>sortedmulti()</tt> sorts the public keys lexicographically when the output script is produced.
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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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The most common complex script used in Bitcoin is a threshold multisig.
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These expressions allow specifying multisig scripts as a descriptor.
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==Specification==
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Two new script expressions are defined: <tt>multi()</tt>, and <tt>sortedmulti()</tt>.
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Both expressions produce the scripts of the same template and take the same arguments.
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They are written as <tt>multi(k,KEY_1,KEY_2,...,KEY_n)</tt>.
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<tt>k</tt> is the threshold - the number of keys that must sign the input for the script to be valid.
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<tt>KEY_1,KEY_2,...,KEY_n</tt> are the key expressions for the multisig. <tt>k</tt> must be less than or equal to <tt>n</tt>.
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<tt>multi()</tt> and <tt>sortedmulti()</tt> expressions can be used as a top level expression, or inside of either a <tt>sh()</tt> or <tt>wsh()</tt> descriptor.
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Depending on the higher level descriptors, there may be restrictions on the type of public keys that can be included.
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Depending on the higher level descriptors, there are also restrictions on the number of keys that can be present, i.e. the maximum value of <tt>n</tt>.
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When used at the top level, there can only be at most 3 keys.
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When used inside of a <tt>sh()</tt> expression, there can only be most 15 compressed public keys (this is limited by the P2SH script limit).
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Otherwise the maximum number of keys is 20.
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The output script produced also depends on the value of <tt>k</tt>. If <tt>k</tt> is less than or equal to 16:
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<pre>
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OP_k KEY_1 KEY_2 ... KEY_n OP_CHECKMULTISIG
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</pre>
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if <tt>k</tt> is greater than 16:
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<pre>
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k KEY_1 KEY_2 ... KEY_n OP_CHECKMULTISIG
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</pre>
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===<tt>sortedmulti()</tt>===
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The only change for <tt>sortedmulti()</tt> is that the keys are sorted lexicographically prior to the creation of the output script.
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This sorting is on the keys that are to be put into the output script, i.e. after all extended keys are derived.
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===Multiple Extended Keys</tt>===
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When one or more the key expressions in a <tt>multi()</tt> or <tt>sortedmulti()</tt> expression are extended keys, the derived keys use the same child index.
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This changes the keys in lockstep and allows for output scripts to be indexed in the same way that the derived keys are indexed.
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==Test Vectors==
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TBD
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==Backwards Compatibility==
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<tt>multi()</tt>, and <tt>sortedmulti()</tt> descriptors use the format and general operation specified in [[bip-0380.mediawiki|380]].
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As these are a wholly new descriptors, they are not compatible with any implementation.
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However the scripts produced are standard scripts so existing software are likely to be familiar with them.
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==Reference Implemntation==
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<tt>multi()</tt>, and <tt>multi()</tt> descriptors have been implemented in Bitcoin Core since version 0.17.
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