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HD Multisig derivation standard

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+<pre>
+  BIP: 48
+  Layer: Applications
+  Title: Multi-Script Hierarchy for Multi-Sig Wallets
+  Author: Fontaine <dentondevelopment@protonmail.com>
+  Comments-Summary: No comments
+  Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0048
+  Status: Proposed
+  Type: Standards Track
+  Created: 2020-12-16
+  License: MIT
+</pre>
+
+==Abstract==
+
+This BIP defines a logical hierarchy for deterministic multi-sig wallets based on an algorithm
+described in BIP-0067 (BIP67 from now on), 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.
+
+==Copyright==
+
+This BIP falls under the MIT License.
+
+==Motivation==
+
+The motivation of this BIP is to define the existing industry wide practice of utilizing  m/48'
+derivation paths in hierarchical deterministic multi-sig wallets so that other developers may
+benefit from a standard. This BIP allows for future script types to easily be appended to the
+specification so that a new BIP is not required for every future script type.
+
+The hierarchy proposed in this paper is quite comprehensive. It allows the handling of
+multiple accounts, external and internal chains per account, multiple script types and
+millions of addresses per chain.
+
+This paper was inspired from BIP44.
+
+==Backwards compatibility==
+
+Currently a number of wallets utilize the ‎<code>m/48'</code> derivation scheme for HD multi-sig accounts.
+This BIP is intended to maintain the *existing* real world use of the ‎<code>m/48'</code> derivation.
+No breaking changes are made so as to avoid "loss of funds" to existing users.
+Wallet's which currently support the ‎<code>m/48'</code> derivation will not need to make any changes
+to comply with this BIP.
+
+==Specification==
+
+===Key sorting===
+
+Any wallet that supports BIP48 inherently supports deterministic key sorting as per BIP67 so that all possible
+multi-signature addresses/scripts are derived from deterministically sorted public keys.
+
+===Path levels===
+
+We define the following 6 levels in BIP32 path:
+
+<pre>
+m / purpose' / coin_type' / account' / script_type' / 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 48' 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.
+
+===Script===
+
+This level splits the key space into two separate <code>script_type</code>(s). To provide
+forward compatibility for future script types this specification can be easily extended.
+
+Currently the only script types covered by this BIP are Native Segwit (p2wsh) and
+Nested Segwit (p2sh-p2wsh).
+
+The following path represents Nested Segwit (p2sh-p2wsh) mainnet, account 0:
+<code>1'</code>: Nested Segwit (p2sh-p2wsh) <code>m/48'/0'/0'/1'</code></br>
+
+The following path represents Native Segwit (p2wsh) mainnet, account 0:
+<code>2'</code>: Native Segwit (p2wsh) <code>m/48'/0'/0'/2'</code></br>
+
+The recommended default for wallets is pay to witness script hash <code>m/48'/0'/0'/2'</code>.
+
+To add new script types submit a PR to this specification and include it in the list above:
+<code>X'</code>: Future script type <code>m/48'/0'/0'/X'</code></br>
+
+===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
+|script
+|chain
+|address
+|path
+|-
+|mainnet
+|first
+|p2wsh
+|external
+|first
+|m / 48' / 0' / 0' / 2' / 0 / 0
+|-
+|mainnet
+|first
+|p2wsh
+|external
+|second
+|m / 48' / 0' / 0' / 2' / 0 / 1
+|-
+|mainnet
+|first
+|p2wsh
+|change
+|first
+|m / 48' / 0' / 0' / 2' / 1 / 0
+|-
+|mainnet
+|first
+|p2wsh
+|change
+|second
+|m / 48' / 0' / 0' / 2' / 1 / 1
+|-
+|mainnet
+|second
+|p2wsh
+|external
+|first
+|m / 48' / 0' / 1' / 2' / 0 / 0
+|-
+|mainnet
+|second
+|p2wsh
+|external
+|second
+|m / 48' / 0' / 1' / 2' / 0 / 1
+|-
+|testnet
+|first
+|p2sh-p2wsh
+|external
+|first
+|m / 48' / 1' / 0' / 1' / 0 / 0
+|-
+|testnet
+|first
+|p2wsh
+|external
+|second
+|m / 48' / 1' / 0' / 2' / 0 / 1
+|-
+|testnet
+|first
+|p2wsh
+|change
+|first
+|m / 48' / 1' / 0' / 2' / 1 / 0
+|-
+|testnet
+|first
+|p2wsh
+|change
+|second
+|m / 48' / 1' / 0' / 2' / 1 / 1
+|-
+|testnet
+|second
+|p2wsh
+|external
+|first
+|m / 48' / 1' / 1' / 2' / 0 / 0
+|-
+|testnet
+|second
+|p2wsh
+|external
+|second
+|m / 48' / 1' / 1' / 2' / 0 / 1
+|-
+|testnet
+|second
+|p2wsh
+|change
+|first
+|m / 48' / 1' / 1' / 2' / 1 / 0
+|-
+|testnet
+|second
+|p2wsh
+|change
+|second
+|m / 48' / 1' / 1' / 2' / 1 / 1
+|}
+
+
+==Reference==
+
+* [[bip-0067.mediawiki|BIP67 - Deterministic Pay-to-script-hash multi-signature addresses through public key sorting]]
+* [[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]]