Impl FullViewingKey::from_spending_key(SpendingKey, Network)

Remove From impl

zebra-chain/src/orchard/address.rs

@@ -66,7 +66,8 @@ mod tests {
 
         let spending_key = keys::SpendingKey::new(&mut OsRng);
 
-        let full_viewing_key = keys::FullViewingKey::from(spending_key);
+        let full_viewing_key =
+            keys::FullViewingKey::from_spending_key(spending_key, Network::Mainnet);
 
         // Default diversifier, where index = 0.
         let diversifier_key = keys::DiversifierKey::from(full_viewing_key);

zebra-chain/src/orchard/keys.rs

@@ -568,8 +568,6 @@ pub struct FullViewingKey {
     ivk_commit_randomness: IvkCommitRandomness,
 }
 
-// TODO: impl a From that accepts a Network?
-
 impl fmt::Debug for FullViewingKey {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("FullViewingKey")
@@ -598,20 +596,6 @@ impl fmt::Display for FullViewingKey {
     }
 }
 
-impl From<SpendingKey> for FullViewingKey {
-    fn from(sk: SpendingKey) -> FullViewingKey {
-        let spend_authorizing_key = SpendAuthorizingKey::from(sk);
-
-        Self {
-            // TODO: handle setting the Network better.
-            network: Network::default(),
-            spend_validating_key: SpendValidatingKey::from(spend_authorizing_key),
-            nullifier_deriving_key: NullifierDerivingKey::from(sk),
-            ivk_commit_randomness: IvkCommitRandomness::from(sk),
-        }
-    }
-}
-
 impl FromStr for FullViewingKey {
     type Err = SerializationError;
 
@@ -657,6 +641,21 @@ impl FullViewingKey {
         // let R = PRF^expand_K( [0x82] || I2LEOSP256(ak) || I2LEOSP256(nk) )
         prf_expand(K, t)
     }
+
+    /// Derive a full viewing key from a existing spending key and its network.
+    ///
+    /// https://zips.z.cash/protocol/nu5.pdf#addressesandkeys
+    /// https://zips.z.cash/protocol/nu5.pdf#orchardfullviewingkeyencoding
+    pub fn from_spending_key(sk: SpendingKey, network: Network) -> FullViewingKey {
+        let spend_authorizing_key = SpendAuthorizingKey::from(sk);
+
+        Self {
+            network,
+            spend_validating_key: SpendValidatingKey::from(spend_authorizing_key),
+            nullifier_deriving_key: NullifierDerivingKey::from(sk),
+            ivk_commit_randomness: IvkCommitRandomness::from(sk),
+        }
+    }
 }
 
 /// An outgoing viewing key, as described in [protocol specification

zebra-chain/src/orchard/keys/tests.rs

@@ -11,7 +11,8 @@ impl Arbitrary for TransmissionKey {
     fn arbitrary_with(_args: Self::Parameters) -> Self::Strategy {
         (any::<SpendingKey>())
             .prop_map(|spending_key| {
-                let full_viewing_key = FullViewingKey::from(spending_key);
+                let full_viewing_key =
+                    FullViewingKey::from_spending_key(spending_key, Network::Mainnet);
 
                 let diversifier_key = DiversifierKey::from(full_viewing_key);