Add APIs for trial decrypting PCZT outputs

CHANGELOG.md

@@ -10,6 +10,9 @@ and this project adheres to Rust's notion of
 ### Added
 - Support for Partially-Created Zcash Transactions:
   - `orchard::builder::Builder::build_for_pczt`
+  - `orchard::note_encryption`:
+    - `OrchardDomain::for_pczt_action`
+    - `impl ShieldedOutput<OrchardDomain, ENC_CIPHERTEXT_SIZE> for orchard::pczt::Action`
   - `orchard::pczt` module.
 - `orchard::bundle::EffectsOnly`
 - `orchard::tree::MerklePath::{position, auth_path}`

src/note_encryption.rs

@@ -100,6 +100,13 @@ impl OrchardDomain {
         Self { rho: act.rho() }
     }
 
+    /// Constructs a domain that can be used to trial-decrypt a PCZT action's output note.
+    pub fn for_pczt_action(act: &crate::pczt::Action) -> Self {
+        Self {
+            rho: Rho::from_nf_old(act.spend().nullifier),
+        }
+    }
+
     /// Constructs a domain that can be used to trial-decrypt this action's output note.
     pub fn for_compact_action(act: &CompactAction) -> Self {
         Self { rho: act.rho() }
@@ -266,6 +273,20 @@ impl<T> ShieldedOutput<OrchardDomain, ENC_CIPHERTEXT_SIZE> for Action<T> {
     }
 }
 
+impl ShieldedOutput<OrchardDomain, ENC_CIPHERTEXT_SIZE> for crate::pczt::Action {
+    fn ephemeral_key(&self) -> EphemeralKeyBytes {
+        EphemeralKeyBytes(self.output().encrypted_note().epk_bytes)
+    }
+
+    fn cmstar_bytes(&self) -> [u8; 32] {
+        self.output().cmx().to_bytes()
+    }
+
+    fn enc_ciphertext(&self) -> &[u8; ENC_CIPHERTEXT_SIZE] {
+        &self.output().encrypted_note().enc_ciphertext
+    }
+}
+
 /// A compact Action for light clients.
 #[derive(Clone)]
 pub struct CompactAction {