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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.

Wallet Updates

The zcashd wallet has been modified to alter the way that change is handled. In the case that funds are being spent from a unified account, change is sent to a wallet-internal change address for that account instead of sending change amounts back to the original address where a note being spent was received. The rationale for this change is that it improves the security that is provided to the user of the wallet when supplying incoming viewing keys to third parties; previously, an incoming viewing key could effectively be used to detect when a note was spent (hence violating the "incoming" restriction) by observing change outputs that were sent back to the address where the spent note was originally received.

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_getnewaccount This API allows for creation of new BIP 44 / ZIP 32 accounts using HD derivation from the wallet's mnemonic seed. Each account represents a separate spending authority and source of funds. A single account may contain funds in the Sapling and Orchard shielded pools, as well as funds held in transparent addresses.
  • z_getaddressforaccount This API allows for creation of diversified unified addresses under a single account. Each call to this API will, by default, create a new diversified unified address containing p2pkh, Sapling, and Orchard receivers. Additional arguments to this API may be provided to request the address to be created with a user-specified set of receiver types and diversifier index.
  • z_getbalanceforaccount This API makes it possible to obtain balance information on a per-account basis.
  • 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. This API has been added to supplement (and largely supplant) z_getbalance. Querying for balance by a single address returns only the amount received by that address, and omits value sent to other diversified addresses derived from the same full viewing key; by using z_getbalanceforviewingkey it is possible to obtain a correct balance that includes all amounts controlled by a single spending key, including both those sent to external diversified addresses and to wallet-internal change addresses.
  • z_listunifiedreceivers This API allows the caller to extract the individual component receivers from a unified address. This is useful if one needs to provide a bare Sapling or p2pkh address to a service that does not yet support unified addresses.

RPC Changes

  • The result type for the listaddresses endpoint has been modified:
    • The keypool source type has been removed; it was reserved but not used.
    • In the sapling address results, the zip32AccountId attribute has been removed in favor of zip32KeyPath. This is to allow distinct key paths to be reported for addresses derived from the legacy account under different child spending authorities, as are produced by z_getnewaddress.
  • 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.
  • A new pool attribute has been added to each element returned by z_listunspent to indicate which value pool the unspent note controls funds in.
  • z_listreceivedbyaddress a pool attribute has been added to each result to indicate what pool the received funds are held in.
  • z_viewtransaction has been updated to include attributes that provide information about Orchard components of the transaction. Also, the type attribute for spend and output values has been deprecated and replaced by the pool attribute.
  • z_getnotescount now also returns information for Orchard notes.
  • The output format of z_exportwallet has been changed. The exported file now includes the mnemonic seed for the wallet, and HD keypaths are now exported for transparent addresses when available.
  • The result value for z_importviewingkey now includes an address_type field that replaces the now-deprecated type key.

'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.

RPC Deprecations

  • z_getnewaddress has been deprecated in favor of z_getnewaccount and z_getaddressforaccount.
  • z_listaddresses has been deprecated. Use listaddresses instead.
  • z_getbalance has been deprecated. Use z_getbalanceforviewingkey instead. See the discussion of how change is now handled under the Wallet heading for additional background.
  • z_gettotalbalance has been deprecated. Use z_getbalanceforaccount instead.
  • dumpwallet has been deprecated. Use z_exportwallet instead.

Platform Support

  • Debian 9 has been removed from the list of supported platforms.