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zcashd/doc/release-notes.md

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(note: this is a temporary file, to be added-to by anybody, and moved to release-notes at release time)

Notable changes

Mnemonic Recovery Phrases

The zcashd wallet has been modified to support BIP 39, which describes how to derive the wallet's HD seed from a mnemonic phrase. The mnemonic phrase will be generated on load of the wallet, or the first time the wallet is unlocked, and is available via the z_exportwallet RPC call. All new addresses produced by the wallet are now derived from this seed using the HD wallet functionality described in ZIP 32 and ZIP 316. For users upgrading an existing Zcashd wallet, it is recommended that the wallet be backed up prior to upgrading to the 4.7.0 Zcashd release.

Following the upgrade to 4.7.0, Zcashd will require that the user confirm that they have backed up their new emergency recovery phrase, which may be obtained from the output of the z_exportwallet RPC call. This confirmation can be performed manually using the zcashd-wallet-tool utility that is supplied with this release (built or installed in the same directory as zcashd). The wallet will not allow the generation of new addresses until this confirmation has been performed. It is recommended that after this upgrade, that funds tied to preexisting addresses be migrated to newly generated addresses so that all wallet funds are recoverable using the emergency recovery phrase going forward. If you choose not to migrate funds in this fashion, you will continue to need to securely back up the entire wallet.dat file to ensure that you do not lose access to existing funds; EXISTING FUNDS WILL NOT BE RECOVERABLE USING THE EMERGENCY RECOVERY PHRASE UNLESS THEY HAVE BEEN MOVED TO A NEWLY GENERATED ADDRESS FOLLOWING THE 4.7.0 UPGRADE.

New RPC Methods

  • 'walletconfirmbackup' This newly created API checks a provided emergency recovery phrase against the wallet's emergency recovery phrase; if the phrases match then it updates the wallet state to allow the generation of new addresses. This backup confirmation workflow can be disabled by starting zcashd with -requirewalletbackup=false but this is not recommended unless you know what you're doing (and have otherwise backed up the wallet's recovery phrase anyway). For security reasons, this RPC method is not intended for use via zcash-cli but is provided to enable zcashd-wallet-tool and other third-party wallet interfaces to satisfy the backup confirmation requirement. Use of the walletconfirmbackup API via zcash-cli would risk that the recovery phrase being confirmed might be leaked via the user's shell history or the system process table; zcashd-wallet-tool is specifically provided to avoid this problem.
  • 'z_getbalanceforviewingkey' This newly created API allows a user to obtain balance information for funds visible to a Sapling or Unified full viewing key; if a Sprout viewing key is provided, this method allows retrieval of the balance only in the case that the wallet controls the corresponding spending key.

RPC Changes

  • The results of the 'dumpwallet' and 'z_exportwallet' RPC methods have been modified to now include the wallet's newly generated emergency recovery phrase as part of the exported data.

  • The results of the 'getwalletinfo' RPC have been modified to return two new fields: mnemonic_seedfp and legacy_seedfp, the latter of which replaces the field that was previously named seedfp.

Wallet

'z_sendmany'

  • The 'z_sendmany' RPC call no longer permits Sprout recipients in the list of recipient addresses. Transactions spending Sprout funds will still result in change being sent back into the Sprout pool, but no other Sprout->Sprout transactions will be constructed by the Zcashd wallet.

  • The restriction that prohibited Sprout->Sapling transactions has been lifted; however, since such transactions reveal the amount crossing pool boundaries, they must be explicitly enabled via a parameter to the 'z_sendmany' call.

  • A new string parameter, privacyPolicy, has been added to the list of arguments accepted by z_sendmany. This parameter enables the caller to control what kind of information they permit zcashd to reveal when creating the transaction. If the transaction can only be created by revealing more information than the given strategy permits, z_sendmany will return an error. The parameter defaults to LegacyCompat, which applies the most restrictive strategy FullPrivacy when a Unified Address is present as the sender or a recipient, and otherwise preserves existing behaviour (which corresponds to the AllowFullyTransparent policy).

  • Since Sprout outputs are no longer created (with the exception of change) 'z_sendmany' no longer generates payment disclosures (which were only available for Sprout outputs) when the -paymentdisclosure experimental feature flag is set.