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diff --git a/doc/release-notes-16528.md b/doc/release-notes-16528.md new file mode 100644 index 0000000000..0a7a31cc9d --- /dev/null +++ b/doc/release-notes-16528.md @@ -0,0 +1,120 @@ +Wallet +------ + +### Experimental Descriptor Wallets + +Please note that Descriptor Wallets are still experimental and not all expected functionality +is available. Additionally there may be some bugs and current functions may change in the future. +Bugs and missing functionality can be reported to the [issue tracker](https://github.com/bitcoin/bitcoin/issues). + +0.21 introduces a new type of wallet - Descriptor Wallets. Descriptor Wallets store +scriptPubKey information using descriptors. This is in contrast to the Legacy Wallet +structure where keys are used to generate scriptPubKeys and addresses. Because of this +shift to being script based instead of key based, many of the confusing things that Legacy +Wallets do are not possible with Descriptor Wallets. Descriptor Wallets use a definition +of "mine" for scripts which is simpler and more intuitive than that used by Legacy Wallets. +Descriptor Wallets also uses different semantics for watch-only things and imports. + +As Descriptor Wallets are a new type of wallet, their introduction does not affect existing wallets. +Users who already have a Bitcoin Core wallet can continue to use it as they did before without +any change in behavior. Newly created Legacy Wallets (which is the default type of wallet) will +behave as they did in previous versions of Bitcoin Core. + +The differences between Descriptor Wallets and Legacy Wallets are largely limited to non user facing +things. They are intended to behave similarly except for the import/export and watchonly functionality +as described below. + +#### Creating Descriptor Wallets + +Descriptor Wallets are not created by default. They must be explicitly created using the +`createwallet` RPC or via the GUI. A `descriptors` option has been added to `createwallet`. +Setting `descriptors` to `true` will create a Descriptor Wallet instead of a Legacy Wallet. + +In the GUI, a checkbox has been added to the Create Wallet Dialog to indicate that a +Descriptor Wallet should be created. + +Without those options being set, a Legacy Wallet will be created instead. Additionally the +Default Wallet created upon first startup of Bitcoin Core will be a Legacy Wallet. + +#### `IsMine` Semantics + +`IsMine` refers to the function used to determine whether a script belongs to the wallet. +This is used to determine whether an output belongs to the wallet. `IsMine` in Legacy Wallets +returns true if the wallet would be able to sign an input that spends an output with that script. +Since keys can be involved in a variety of different scripts, this definition for `IsMine` can +lead to many unexpected scripts being considered part of the wallet. + +With Descriptor Wallets, descriptors explicitly specify the set of scripts that are owned by +the wallet. Since descriptors are deterministic and easily enumerable, users will know exactly +what scripts the wallet will consider to belong to it. Additionally the implementation of `IsMine` +in Descriptor Wallets is far simpler than for Legacy Wallets. Notably, in Legacy Wallets, `IsMine` +allowed for users to take one type of address (e.g. P2PKH), mutate it into another address type +(e.g. P2WPKH), and the wallet would still detect outputs sending to the new address type +even without that address being requested from the wallet. Descriptor Wallets does not +allow for this and will only watch for the addresses that were explicitly requested from the wallet. + +These changes to `IsMine` will make it easier to reason about what scripts the wallet will +actually be watching for in outputs. However for the vast majority of users, this change is +largely transparent and will not have noticeable effect. + +#### Imports and Exports + +In Legacy Wallets, raw scripts and keys could be imported to the wallet. Those imported scripts +and keys are treated separately from the keys generated by the wallet. This complicates the `IsMine` +logic as it has to distinguish between spendable and watchonly. + +Descriptor Wallets handle importing scripts and keys differently. Only complete descriptors can be +imported. These descriptors are then added to the wallet as if it were a descriptor generated by +the wallet itself. This simplifies the `IsMine` logic so that it no longer has to distinguish +between spendable and watchonly. As such, the watchonly model for Descriptor Wallets is also +different and described in more detail in the next section. + +To import into a Descriptor Wallet, a new `importdescriptors` RPC has been added that uses a syntax +similar to that of `importmulti`. + +As Legacy Wallets and Descriptor Wallets use different mechanisms for storing and importing scripts and keys +the existing import RPCs have been disabled for descriptor wallets. +New export RPCs for Descriptor Wallets have not yet been added. + +The following RPCs are disabled for Descriptor Wallets: + +* importprivkey +* importpubkey +* importaddress +* importwallet +* dumpprivkey +* dumpwallet +* importmulti +* addmultisigaddress +* sethdseed + +#### Watchonly Wallets + +A Legacy Wallet contains both private keys and scripts that were being watched. +Those watched scripts would not contribute to your normal balance. In order to see the watchonly +balance and to use watchonly things in transactions, an `include_watchonly` option was added +to many RPCs that would allow users to do that. However it is easy to forget to include this option. + +Descriptor Wallets move to a per-wallet watchonly model. Instead an entire wallet is considered to be +watchonly depending on whether it was created with private keys disabled. This eliminates the need +to distinguish between things that are watchonly and things that are not within a wallet itself. + +This change does have a caveat. If a Descriptor Wallet with private keys *enabled* has +a multiple key descriptor without all of the private keys (e.g. `multi(...)` with only one private key), +then the wallet will fail to sign and broadcast transactions. Such wallets would need to use the PSBT +workflow but the typical GUI Send, `sendtoaddress`, etc. workflows would still be available, just +non-functional. + +This issue is worsened if the wallet contains both single key (e.g. `wpkh(...)`) descriptors and such +multiple key descriptors as some transactions could be signed and broadast and others not. This is +due to some transactions containing only single key inputs, while others would contain both single +key and multiple key inputs, depending on which are available and how the coin selection algorithm +selects inputs. However this is not considered to be a supported use case; multisigs +should be in their own wallets which do not already have descriptors. Although users cannot export +descriptors with private keys for now as explained earlier. + +#### BIP 44/49/84 Support + +The change to using descriptors changes the default derivation paths used by Bitcoin Core +to adhere to BIP 44/49/84. Descriptors with different derivation paths can be imported without +issue. |