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diff --git a/Multisig Derivation Standard.mediawiki b/Multisig Derivation Standard.mediawiki new file mode 100644 index 0000000..6d11c6e --- /dev/null +++ b/Multisig Derivation Standard.mediawiki @@ -0,0 +1,237 @@ +<pre> + BIP: Number not assigned + Layer: Applications + Title: Modern Hierarchy for Deterministic Multisignature Wallets + Author: Robert Spigler <RobertSpigler@ProtonMail.ch> + Comments-Summary: No comments + Comments-URI: + Status: Proposed + Type: Standards Track + Created: 2020-03-11 +</pre> + +===Copyright=== + +This BIP is licensed under the 2-clause BSD license. + +==Abstract== + +This BIP defines a sane hierarchy for deterministic multisig wallets based on an algorithm described in BIP-0032 (BIP32 from now on), purpose scheme described in +BIP-0043 (BIP43 from now on), and multi-account hierarchy described in BIP-0044 (BIP44 from now on). + +This BIP is a particular application of BIP43. + +==Motivation== + +With the increase of more user friendly (offline) multisignature wallets, and adoption of new technologies such as +[https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md the descriptor language] and [https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki +BIP-0174 (Partially Signed Bitcoin Transactions)] it is necessary to create a common derivation scheme that makes use of all new technologies. + +There are many issues with the current standards. As background, BIP 44/49/84 specifies: + +<pre> +m / purpose' / coin_type' / account' / change / address_index +</pre> + +where the BIP43 <code>purpose'</code> path is separate for each script (P2PKH, P2WPKH-in-P2SH, and P2WPKH respectively). However, these per-script derivations +are made redundant with descriptors, which describe a collection of output scripts. Note also that these are single sig derivations (which souldn't be reused for +multisig). + +Standardization is needed for multisig derivation paths. There are some in existence, but all have issues. For example, BIP45 specifies: + +<pre> +m / purpose' / cosigner_index / change / address_index +</pre> + +Like BIP44/49/84, BIP45 unecessarily demands a single script type (here, P2SH). In addition, BIP45 sets <code>cosigner_index</code> in order to sort the +<code>purpose'</code> public keys of each cosigner. This too is redundant, as descriptors can set the order of the public keys with <code>multi</code> or have +them sorted lexicographically (as described in [https://github.com/bitcoin/bips/blob/master/bip-0067.mediawiki BIP67) with <code>sortedmulti</code>. Sorting +public keys between cosigners in order to create the full derivation path, prior to sending the key record to the coordinator to create the descriptor, merely adds +additional unnecessary communication rounds. + +There is an additional multisig derivation path in use "BIP"48 (there is no real standard), which specifies: + +<pre> +m / purpose' / coin_type' / account' / script_type' / change / address_index +</pre> + +Rather than having a separate BIP per script type after P2SH (BIP45), vendors decided to insert <code>script_type'</code> into the derivation path (where +P2SH-P2WSH=1, P2WSH=2, Future_Script=3, etc). As described previously, this is unnecessary, as the descriptor sets the script. While it attempts to reduce +maintainence work by getting rid of new BIPs-per-script, it still requires maintaining an updated, redundant, script_type list. + +The hierarchy proposed in this paper is quite comprehensive. It allows the handling of multiple accounts, external and internal chains per account, and millions +of addresses per chain. + +Any script that is supported by descriptors (and the specific wallet implementation) is compatible with this BIP. + +This paper was inspired from BIP44. + +==Key sorting== + +Any wallet that supports descriptors inherently supports deterministic key sorting as per BIP67 (through the <code>sortedmulti</code> function) so that all +possible multisignature addresses/scripts are derived from deterministically sorted public keys. + +==Path levels== + +You should not be mixing keys and scripts. We define the following 5 levels in the BIP32 path: + +<pre> +m / purpose' / coin_type' / account' / change / address_index +</pre> + +<code>h</code> or <code>'</code> in the path indicates that BIP32 hardened derivation is used. + +Each level has a special meaning, described in the chapters below. + +===Purpose=== + +Purpose is a constant set to XY' following the BIP43 recommendation. +It indicates that the subtree of this node is used according to this specification. + +Hardened derivation is used at this level. + +===Coin type=== + +One master node (seed) can be used for multiple Bitcoin networks. +Sharing the same space for various networks has some disadvantages. + +Avoiding reusing addresses across networks and improving privacy issues. + +Coin type <code>0</code> for mainnet and <code>1</code> for testnet. + +Hardened derivation is used at this level. + +===Account=== + +This level splits the key space into independent user identities, following the BIP44 pattern, so the wallet never mixes the coins across different accounts. + +Users can use these accounts to organize the funds in the same fashion as bank accounts; for donation purposes (where all addresses are considered public), for +saving purposes, for common expenses, etc. + +Accounts are numbered from index 0 in sequentially increasing manner. +This number is used as child index in BIP32 derivation. + +Hardened derivation is used at this level. + +===Change=== + +Constant 0 is used for external chain and constant 1 for internal chain (also known as change addresses). External chain is used for addresses that are meant to be +visible outside of the wallet (e.g. for receiving payments). Internal chain is used for addresses which are not meant to be visible outside of the wallet and is +used for return transaction change. + +Public derivation is used at this level. + +===Index=== + +Addresses are numbered from index 0 in sequentially increasing manner. +This number is used as child index in BIP32 derivation. + +Public derivation is used at this level. + +==Examples== + +{| +|network +|account +|chain +|address +|path +|- +|mainnet +|first +|external +|first +|m / XY' / 0' / 0' / 0 / 0 +|- +|mainnet +|first +|external +|second +|m / XY' / 0' / 0' / 0 / 1 +|- +|mainnet +|first +|change +|first +|m / XY' / 0' / 0' / 1 / 0 +|- +|mainnet +|first +|change +|second +|m / XY' / 0' / 0' / 1 / 1 +|- +|mainnet +|second +|external +|first +|m / XY' / 0' / 1' / 0 / 0 +|- +|mainnet +|second +|external +|second +|m / XY' / 0' / 1' / 0 / 1 +|- +|testnet +|first +|external +|first +|m / XY' / 1' / 0' / 0 / 0 +|- +|testnet +|first +|external +|second +|m / XY' / 1' / 0' / 0 / 1 +|- +|testnet +|first +|change +|first +|m / XY' / 1' / 0' / 1 / 0 +|- +|testnet +|first +|change +|second +|m / XY' / 1' / 0' / 1 / 1 +|- +|testnet +|second +|external +|first +|m / XY' / 1' / 1' / 0 / 0 +|- +|testnet +|second +|external +|second +|m / XY' / 1' / 1' / 0 / 1 +|- +|testnet +|second +|change +|first +|m / XY' / 1' / 1' / 1 / 0 +|- +|testnet +|second +|change +|second +|m / XY' / 1' / 1' / 1 / 1 +|} + +==Acknowledgement== + + +==References== + +Original mailing list thread: TBD + +* [[bip-0032.mediawiki|BIP32 - Hierarchical Deterministic Wallets]] +* [[bip-0043.mediawiki|BIP43 - Purpose Field for Deterministic Wallets]] +* [[bip-0044.mediawiki|BIP44 - Multi-Account Hierarchy for Deterministic Wallets]] +* [[https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md - Output Descriptors]] +* [[bip-0174.mediawiki|BIP174 - Partially Signed Bitcoin Transaction Format]] +* [[bip-0067.mediawiki|BIP67 - Deterministic Pay-to-script-hash multi-signature addresses through public key sorting]] |