Add NoteCommitment.extract_u()

zebra-chain/src/notes/sapling.rs

@@ -109,6 +109,15 @@ impl ZcashDeserialize for NoteCommitment {
     }
 }
 
+impl NoteCommitment {
+    /// Hash Extractor for Jubjub (?)
+    ///
+    /// https://zips.z.cash/protocol/protocol.pdf#concreteextractorjubjub
+    pub fn extract_u(self) -> jubjub::Fq {
+        self.0.get_u()
+    }
+}
+
 /// The decrypted form of encrypted Sapling notes on the blockchain.
 pub struct NotePlaintext {
     diversifier: Diversifier,

zebra-chain/src/transaction/tests/arbitrary.rs

@@ -106,7 +106,7 @@ impl Arbitrary for Output {
             .prop_map(
                 |(cv, cm, ephemeral_key_bytes, enc_ciphertext, out_ciphertext, zkproof)| Self {
                     cv,
-                    cm_u: cm.0.get_u(),
+                    cm_u: cm.extract_u(),
                     ephemeral_key: jubjub::AffinePoint::from_bytes(ephemeral_key_bytes).unwrap(),
                     enc_ciphertext,
                     out_ciphertext,