Merge pull request #615 from nuttycom/wallet/shield_to_ufvk

Shield funds to the internal Sapling key for a specified account.

zcash_client_backend/src/data_api/error.rs

@@ -2,6 +2,7 @@
 
 use std::error;
 use std::fmt;
+use zcash_address::unified::Typecode;
 use zcash_primitives::{
     consensus::BlockHeight,
     sapling::Node,
@@ -23,6 +24,9 @@ pub enum ChainInvalid {
 
 #[derive(Debug)]
 pub enum Error<NoteId> {
+    /// No account with the given identifier was found in the wallet.
+    AccountNotFound(AccountId),
+
     /// The amount specified exceeds the allowed range.
     InvalidAmount,
 
@@ -48,6 +52,9 @@ pub enum Error<NoteId> {
     /// does not correspond to root of the current commitment tree.
     InvalidWitnessAnchor(NoteId, BlockHeight),
 
+    /// No key of the given type was associated with the specified account.
+    KeyNotFound(AccountId, Typecode),
+
     /// The wallet must first perform a scan of the blockchain before other
     /// operations can be performed.
     ScanRequired,
@@ -79,6 +86,9 @@ impl ChainInvalid {
 impl<N: fmt::Display> fmt::Display for Error<N> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match &self {
+            Error::AccountNotFound(account) => {
+                write!(f, "Wallet does not contain account {}", u32::from(*account))
+            }
             Error::InvalidAmount => write!(
                 f,
                 "The value lies outside the valid range of Zcash amounts."
@@ -104,6 +114,9 @@ impl<N: fmt::Display> fmt::Display for Error<N> {
                 "Witness for note {} has incorrect anchor after scanning block {}",
                 id_note, last_height
             ),
+            Error::KeyNotFound(account, typecode) => {
+                write!(f, "No {:?} key was available for account {}", typecode, u32::from(*account))
+            }
             Error::ScanRequired => write!(f, "Must scan blocks first"),
             Error::Builder(e) => write!(f, "{:?}", e),
             Error::Protobuf(e) => write!(f, "{}", e),

zcash_client_backend/src/data_api/wallet.rs

@@ -12,8 +12,11 @@ use zcash_primitives::{
 };
 
 #[cfg(feature = "transparent-inputs")]
-use zcash_primitives::{
-    keys::OutgoingViewingKey, legacy::keys as transparent, legacy::keys::IncomingViewingKey,
+use {
+    zcash_address::unified::Typecode,
+    zcash_primitives::{
+        keys::OutgoingViewingKey, legacy::keys as transparent, legacy::keys::IncomingViewingKey,
+    },
 };
 
 use crate::{
@@ -418,11 +421,10 @@ where
 /// * `prover`: The TxProver to use in constructing the shielded transaction.
 /// * `sk`: The secp256k1 secret key that will be used to detect and spend transparent
 ///   UTXOs.
-/// * `extfvk`: The extended full viewing key that will be used to produce the
-///   Sapling address to which funds will be sent.
-/// * `account`: The ZIP32 account identifier associated with the the extended
-///   full viewing key. This procedure will return an error if this does not correctly
-///   correspond to `extfvk`.
+/// * `account`: The ZIP32 account identifier for the account to which funds will
+///   be shielded. Funds will be shielded to the internal (change) address associated with the
+///   most preferred shielded receiver corresponding to this account, or if no shielded
+///   receiver can be used for this account, this function will return an error.
 /// * `memo`: A memo to be included in the output to the (internal) recipient.
 ///   This can be used to take notes about auto-shielding operations internal
 ///   to the wallet that the wallet can use to improve how it represents those
@@ -437,7 +439,6 @@ pub fn shield_transparent_funds<E, N, P, D, R, U>(
     params: &P,
     prover: impl TxProver,
     sk: &transparent::AccountPrivKey,
-    extfvk: &ExtendedFullViewingKey,
     account: AccountId,
     memo: &MemoBytes,
     min_confirmations: u32,
@@ -448,11 +449,22 @@ where
     R: Copy + Debug,
     D: WalletWrite<Error = E, TxRef = R> + WalletWriteTransparent<UtxoRef = U>,
 {
-    // Check that the ExtendedSpendingKey we have been given corresponds to the
-    // ExtendedFullViewingKey for the account we are spending from.
-    if !wallet_db.is_valid_account_extfvk(account, extfvk)? {
-        return Err(E::from(Error::InvalidExtSk(account)));
-    }
+    // Obtain the UFVK for the specified account & use its internal change address
+    // as the destination for shielded funds.
+    let shielding_address = wallet_db
+        .get_unified_full_viewing_keys()
+        .and_then(|ufvks| {
+            ufvks
+                .get(&account)
+                .ok_or_else(|| E::from(Error::AccountNotFound(account)))
+                .and_then(|ufvk| {
+                    // TODO: select the most preferred shielded receiver once we have the ability to
+                    // spend Orchard funds.
+                    ufvk.sapling()
+                        .map(|dfvk| dfvk.change_address().1)
+                        .ok_or_else(|| E::from(Error::KeyNotFound(account, Typecode::Sapling)))
+                })
+        })?;
 
     let (latest_scanned_height, latest_anchor) = wallet_db
         .get_target_and_anchor_heights(min_confirmations)
@@ -461,11 +473,6 @@ where
     let account_pubkey = sk.to_account_pubkey();
     let ovk = OutgoingViewingKey(account_pubkey.internal_ovk().as_bytes());
 
-    // derive own shielded address from the provided extended full viewing key
-    // TODO: this should become the internal change address derived from
-    // the wallet's UFVK
-    let z_address = extfvk.default_address().1;
-
     // derive the t-address for the extpubkey at the minimum valid child index
     let (taddr, child_index) = account_pubkey
         .derive_external_ivk()
@@ -497,11 +504,16 @@ where
     }
 
     // there are no sapling notes so we set the change manually
-    builder.send_change_to(ovk, z_address.clone());
+    builder.send_change_to(ovk, shielding_address.clone());
 
     // add the sapling output to shield the funds
     builder
-        .add_sapling_output(Some(ovk), z_address.clone(), amount_to_shield, memo.clone())
+        .add_sapling_output(
+            Some(ovk),
+            shielding_address.clone(),
+            amount_to_shield,
+            memo.clone(),
+        )
         .map_err(Error::Builder)?;
 
     let (tx, tx_metadata) = builder.build(&prover).map_err(Error::Builder)?;
@@ -515,7 +527,7 @@ where
         account,
         outputs: vec![SentTransactionOutput {
             output_index,
-            recipient_address: &RecipientAddress::Shielded(z_address),
+            recipient_address: &RecipientAddress::Shielded(shielding_address),
             value: amount_to_shield,
             memo: Some(memo.clone()),
         }],

zcash_primitives/CHANGELOG.md

@@ -108,6 +108,11 @@ and this library adheres to Rust's notion of
   refactored to become a member function of a new `DiversifiableFullViewingKey`
   type, which represents the ability to derive IVKs, OVKs, and addresses, but
   not child viewing keys.
+- `zcash_primitives::sapling::keys::DiversifiableFullViewingKey::change_address`
+  has been added as a convenience method for obtaining the change address
+  at the default diversifier. This address **MUST NOT** be encoded and exposed
+  to users. User interfaces should instead mark these notes as "change notes" or
+  "internal wallet operations".
 - A new module `zcash_primitives::legacy::keys` has been added under the
   `transparent-inputs` feature flag to support types related to supporting
   transparent components of unified addresses and derivation of OVKs for

zcash_primitives/src/sapling/keys.rs

@@ -292,6 +292,16 @@ impl DiversifiableFullViewingKey {
         zip32::sapling_default_address(&self.fvk, &self.dk)
     }
 
+    /// Returns the internal address corresponding to the smallest valid diversifier index,
+    /// along with that index.
+    ///
+    /// This address **MUST NOT** be encoded and exposed to end users. User interfaces
+    /// should instead mark these notes as "change notes" or "internal wallet operations".
+    pub fn change_address(&self) -> (zip32::DiversifierIndex, PaymentAddress) {
+        let internal_dfvk = self.derive_internal();
+        zip32::sapling_default_address(&internal_dfvk.fvk, &internal_dfvk.dk)
+    }
+
     /// Attempts to decrypt the given address's diversifier with this full viewing key.
     ///
     /// This method extracts the diversifier from the given address and decrypts it as a