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121 lines
6.7 KiB
121 lines
6.7 KiB
Wallet
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------
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### Experimental Descriptor Wallets
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Please note that Descriptor Wallets are still experimental and not all expected functionality
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is available. Additionally there may be some bugs and current functions may change in the future.
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Bugs and missing functionality can be reported to the [issue tracker](https://github.com/bitcoin/bitcoin/issues).
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0.21 introduces a new type of wallet - Descriptor Wallets. Descriptor Wallets store
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scriptPubKey information using descriptors. This is in contrast to the Legacy Wallet
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structure where keys are used to generate scriptPubKeys and addresses. Because of this
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shift to being script based instead of key based, many of the confusing things that Legacy
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Wallets do are not possible with Descriptor Wallets. Descriptor Wallets use a definition
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of "mine" for scripts which is simpler and more intuitive than that used by Legacy Wallets.
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Descriptor Wallets also uses different semantics for watch-only things and imports.
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As Descriptor Wallets are a new type of wallet, their introduction does not affect existing wallets.
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Users who already have a Bitcoin Core wallet can continue to use it as they did before without
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any change in behavior. Newly created Legacy Wallets (which is the default type of wallet) will
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behave as they did in previous versions of Bitcoin Core.
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The differences between Descriptor Wallets and Legacy Wallets are largely limited to non user facing
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things. They are intended to behave similarly except for the import/export and watchonly functionality
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as described below.
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#### Creating Descriptor Wallets
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Descriptor Wallets are not created by default. They must be explicitly created using the
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`createwallet` RPC or via the GUI. A `descriptors` option has been added to `createwallet`.
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Setting `descriptors` to `true` will create a Descriptor Wallet instead of a Legacy Wallet.
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In the GUI, a checkbox has been added to the Create Wallet Dialog to indicate that a
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Descriptor Wallet should be created.
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Without those options being set, a Legacy Wallet will be created instead. Additionally the
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Default Wallet created upon first startup of Bitcoin Core will be a Legacy Wallet.
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#### `IsMine` Semantics
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`IsMine` refers to the function used to determine whether a script belongs to the wallet.
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This is used to determine whether an output belongs to the wallet. `IsMine` in Legacy Wallets
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returns true if the wallet would be able to sign an input that spends an output with that script.
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Since keys can be involved in a variety of different scripts, this definition for `IsMine` can
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lead to many unexpected scripts being considered part of the wallet.
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With Descriptor Wallets, descriptors explicitly specify the set of scripts that are owned by
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the wallet. Since descriptors are deterministic and easily enumerable, users will know exactly
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what scripts the wallet will consider to belong to it. Additionally the implementation of `IsMine`
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in Descriptor Wallets is far simpler than for Legacy Wallets. Notably, in Legacy Wallets, `IsMine`
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allowed for users to take one type of address (e.g. P2PKH), mutate it into another address type
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(e.g. P2WPKH), and the wallet would still detect outputs sending to the new address type
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even without that address being requested from the wallet. Descriptor Wallets does not
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allow for this and will only watch for the addresses that were explicitly requested from the wallet.
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These changes to `IsMine` will make it easier to reason about what scripts the wallet will
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actually be watching for in outputs. However for the vast majority of users, this change is
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largely transparent and will not have noticeable effect.
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#### Imports and Exports
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In Legacy Wallets, raw scripts and keys could be imported to the wallet. Those imported scripts
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and keys are treated separately from the keys generated by the wallet. This complicates the `IsMine`
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logic as it has to distinguish between spendable and watchonly.
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Descriptor Wallets handle importing scripts and keys differently. Only complete descriptors can be
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imported. These descriptors are then added to the wallet as if it were a descriptor generated by
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the wallet itself. This simplifies the `IsMine` logic so that it no longer has to distinguish
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between spendable and watchonly. As such, the watchonly model for Descriptor Wallets is also
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different and described in more detail in the next section.
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To import into a Descriptor Wallet, a new `importdescriptors` RPC has been added that uses a syntax
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similar to that of `importmulti`.
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As Legacy Wallets and Descriptor Wallets use different mechanisms for storing and importing scripts and keys
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the existing import RPCs have been disabled for descriptor wallets.
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New export RPCs for Descriptor Wallets have not yet been added.
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The following RPCs are disabled for Descriptor Wallets:
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* importprivkey
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* importpubkey
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* importaddress
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* importwallet
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* dumpprivkey
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* dumpwallet
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* importmulti
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* addmultisigaddress
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* sethdseed
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#### Watchonly Wallets
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A Legacy Wallet contains both private keys and scripts that were being watched.
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Those watched scripts would not contribute to your normal balance. In order to see the watchonly
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balance and to use watchonly things in transactions, an `include_watchonly` option was added
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to many RPCs that would allow users to do that. However it is easy to forget to include this option.
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Descriptor Wallets move to a per-wallet watchonly model. Instead an entire wallet is considered to be
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watchonly depending on whether it was created with private keys disabled. This eliminates the need
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to distinguish between things that are watchonly and things that are not within a wallet itself.
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This change does have a caveat. If a Descriptor Wallet with private keys *enabled* has
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a multiple key descriptor without all of the private keys (e.g. `multi(...)` with only one private key),
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then the wallet will fail to sign and broadcast transactions. Such wallets would need to use the PSBT
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workflow but the typical GUI Send, `sendtoaddress`, etc. workflows would still be available, just
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non-functional.
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This issue is worsened if the wallet contains both single key (e.g. `wpkh(...)`) descriptors and such
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multiple key descriptors as some transactions could be signed and broadast and others not. This is
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due to some transactions containing only single key inputs, while others would contain both single
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key and multiple key inputs, depending on which are available and how the coin selection algorithm
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selects inputs. However this is not considered to be a supported use case; multisigs
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should be in their own wallets which do not already have descriptors. Although users cannot export
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descriptors with private keys for now as explained earlier.
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#### BIP 44/49/84 Support
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The change to using descriptors changes the default derivation paths used by Bitcoin Core
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to adhere to BIP 44/49/84. Descriptors with different derivation paths can be imported without
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issue.
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