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208 lines
6.8 KiB
208 lines
6.8 KiB
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BIP: BIP-0044
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Title: Multi-Account Hierarchy for Deterministic Wallets
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Authors: Marek Palatinus <slush@satoshilabs.com>
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Pavol Rusnak <stick@satoshilabs.com>
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Status: Draft
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Type: Standards Track
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Created: 2014-04-24
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------------------------------------------------------------
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[[abstract]]
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Abstract
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~~~~~~~~
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This BIP defines a logical hierarchy for deterministic wallets based on
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an algorithm described in BIP-0032 (BIP32 from now on) and purpose
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scheme described in BIP-0043 (BIP43 from now on).
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This BIP is a particular application of BIP43.
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[[motivation]]
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Motivation
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~~~~~~~~~~
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The hierarchy proposed in this paper is quite comprehensive. It allows
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the handling of multiple coins, multiple accounts, external and internal
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chains per account and millions of addresses per chain.
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[[path-levels]]
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Path levels
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~~~~~~~~~~~
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We define the following 5 levels in BIP32 path:
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-------------------------------------------------------------
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m / purpose' / coin_type' / account' / change / address_index
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-------------------------------------------------------------
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Apostrophe in the path indicates that BIP32 hardened derivation is used.
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Each level has a special meaning, described in the chapters below.
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[[purpose]]
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Purpose
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^^^^^^^
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Purpose is a constant set to 44' (or 0x8000002C) following the BIP43
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recommendation. It indicates that the subtree of this node is used
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according to this specification.
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Hardened derivation is used at this level.
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[[coin-type]]
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Coin type
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^^^^^^^^^
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One master node (seed) can be used for unlimited number of independent
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cryptocoins such as Bitcoin, Litecoin or Namecoin. However, sharing the
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same space for various cryptocoins has some disadvantages.
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This level creates a separate subtree for every cryptocoin, avoiding
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reusing addresses across cryptocoins and improving privacy issues.
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Coin type is a constant, set for each cryptocoin. Cryptocoin developers
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may ask for registering unused number for their project.
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The list of already allocated coin types is in the chapter "Registered
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coin types" below.
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Hardened derivation is used at this level.
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[[account]]
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Account
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^^^^^^^
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This level splits the key space into independent user identities, so the
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wallet never mixes the coins across different accounts.
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Users can use these accounts to organize the funds in the same fashion
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as bank accounts; for donation purposes (where all addresses are
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considered public), for saving purposes, for common expenses etc.
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Accounts are numbered from index 0 in sequentially increasing manner.
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This number is used as child index in BIP32 derivation.
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Hardened derivation is used at this level.
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Software should prevent a creation of an account if a previous account
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does not have a transaction history (meaning none of its addresses have
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been used before).
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Software needs to discover all used accounts after importing the seed
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from an external source. Such an algorithm is described in "Account
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discovery" chapter.
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[[change]]
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Change
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^^^^^^
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Constant 0 is used for external chain and constant 1 for internal chain
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(also known as change addresses). External chain is used for addresses
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that are meant to be visible outside of the wallet (e.g. for receiving
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payments). Internal chain is used for addresses which are not meant to
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be visible outside of the wallet and is used for return transaction
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change.
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Public derivation is used at this level.
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[[index]]
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Index
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^^^^^
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Addresses are numbered from index 0 in sequentially increasing manner.
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This number is used as child index in BIP32 derivation.
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Public derivation is used at this level.
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[[account-discovery]]
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Account discovery
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~~~~~~~~~~~~~~~~~
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When the master seed is imported from an external source the software
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should start to discover the accounts in the following manner:
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1. derive the first account's node (index = 0)
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2. derive the external chain node of this account
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3. scan addresses of the external chain; respect the gap limit
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described below
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4. if no transactions are found on the external chain, stop discovery
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5. if there are some transactions, increase the account index and go to
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step 1
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This algorithm is successful because software should disallow creation
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of new accounts if previous one has no transaction history, as described
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in chapter "Account" above.
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Please note that the algorithm works with the transaction history, not
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account balances, so you can have an account with 0 total coins and the
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algorithm will still continue with discovery.
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[[address-gap-limit]]
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Address gap limit
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^^^^^^^^^^^^^^^^^
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Address gap limit is currently set to 20. If the software hits 20 unused
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addresses in a row, it expects there are no used addresses beyond this
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point and stops searching the address chain.
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Wallet software should warn when the user is trying to exceed the gap
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limit on an external chain by generating a new address.
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[[registered-coin-types]]
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Registered coin types
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~~~~~~~~~~~~~~~~~~~~~
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These are the registered coin types for usage in level 2 of BIP44
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described in chapter "Coin type" above.
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All these constants are used as hardened derivation.
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[cols=",,",options="header",]
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|==============================
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|index |hexa |coin
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|0 |0x80000000 |Bitcoin
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|1 |0x80000001 |Bitcoin Testnet
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|==============================
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[[examples]]
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Examples
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~~~~~~~~
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[cols=",,,,",options="header",]
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|====================================================================
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|coin |account |chain |address |path
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|Bitcoin |first |external |first |m / 44' / 0' / 0' / 0 / 0
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|Bitcoin |first |external |second |m / 44' / 0' / 0' / 0 / 1
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|Bitcoin |first |change |first |m / 44' / 0' / 0' / 1 / 0
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|Bitcoin |first |change |second |m / 44' / 0' / 0' / 1 / 1
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|Bitcoin |second |external |first |m / 44' / 0' / 1' / 0 / 0
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|Bitcoin |second |external |second |m / 44' / 0' / 1' / 0 / 1
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|Bitcoin |second |change |first |m / 44' / 0' / 1' / 1 / 0
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|Bitcoin |second |change |second |m / 44' / 0' / 1' / 1 / 1
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|Bitcoin Testnet |first |external |first |m / 44' / 1' / 0' / 0 / 0
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|Bitcoin Testnet |first |external |second |m / 44' / 1' / 0' / 0 / 1
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|Bitcoin Testnet |first |change |first |m / 44' / 1' / 0' / 1 / 0
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|Bitcoin Testnet |first |change |second |m / 44' / 1' / 0' / 1 / 1
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|Bitcoin Testnet |second |external |first |m / 44' / 1' / 1' / 0 / 0
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|Bitcoin Testnet |second |external |second |m / 44' / 1' / 1' / 0 / 1
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|Bitcoin Testnet |second |change |first |m / 44' / 1' / 1' / 1 / 0
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|Bitcoin Testnet |second |change |second |m / 44' / 1' / 1' / 1 / 1
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|====================================================================
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[[compatible-wallets]]
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Compatible wallets
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~~~~~~~~~~~~~~~~~~
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* https://mytrezor.com[myTREZOR web wallet]
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(https://github.com/trezor/webwallet[source])
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[[reference]]
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Reference
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~~~~~~~~~
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* link:bip-0032.mediawiki[BIP32 - Hierarchical Deterministic Wallets]
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* link:bip-0043.mediawiki[BIP43 - Purpose Field for Deterministic
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Wallets]
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