Add decryption of the diversifier index for an address to the IVK.

Also correct a spelling error.

src/address.rs

@@ -32,7 +32,7 @@ impl Address {
         Address { d, pk_d }
     }
 
-    pub(crate) fn diversifer(&self) -> Diversifier {
+    pub(crate) fn diversifier(&self) -> Diversifier {
         self.d
     }
 

src/keys.rs

@@ -406,12 +406,6 @@ impl FullViewingKey {
 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct DiversifierKey([u8; 32]);
 
-impl From<&FullViewingKey> for DiversifierKey {
-    fn from(fvk: &FullViewingKey) -> Self {
-        fvk.derive_dk_ovk().0
-    }
-}
-
 /// The index for a particular diversifier.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct DiversifierIndex([u8; 11]);
@@ -437,6 +431,13 @@ impl From<[u8; 11]> for DiversifierIndex {
     }
 }
 
+impl DiversifierIndex {
+    /// Returns the raw bytes of the diversifier index.
+    pub fn to_bytes(&self) -> &[u8; 11] {
+        &self.0
+    }
+}
+
 impl DiversifierKey {
     /// Returns the diversifier at index 0.
     pub fn default_diversifier(&self) -> Diversifier {
@@ -556,7 +557,7 @@ pub struct IncomingViewingKey {
 impl From<&FullViewingKey> for IncomingViewingKey {
     fn from(fvk: &FullViewingKey) -> Self {
         IncomingViewingKey {
-            dk: fvk.into(),
+            dk: fvk.derive_dk_ovk().0,
             ivk: fvk.into(),
         }
     }
@@ -583,6 +584,18 @@ impl IncomingViewingKey {
         })
     }
 
+    /// Checks whether the given address was derived from this incoming viewing
+    /// key, and returns the diversifier index used to derive the address if
+    /// so. Returns `None` if the address was not derived from this key.
+    pub fn diversifier_index(&self, addr: &Address) -> Option<DiversifierIndex> {
+        let j = self.dk.diversifier_index(&addr.diversifier());
+        if &self.address_at(j) == addr {
+            Some(j)
+        } else {
+            None
+        }
+    }
+
     /// Returns the default payment address for this key.
     pub fn default_address(&self) -> Address {
         self.address(self.dk.default_diversifier())

src/note_encryption.rs

@@ -149,7 +149,7 @@ impl Domain for OrchardDomain {
     ) -> NotePlaintextBytes {
         let mut np = [0; NOTE_PLAINTEXT_SIZE];
         np[0] = 0x02;
-        np[1..12].copy_from_slice(note.recipient().diversifer().as_array());
+        np[1..12].copy_from_slice(note.recipient().diversifier().as_array());
         np[12..20].copy_from_slice(&note.value().to_bytes());
         np[20..52].copy_from_slice(note.rseed().to_bytes());
         np[52..].copy_from_slice(memo);