zcash_client_backend: Address compact_formats.proto comments

zcash_client_backend/CHANGELOG.md

@@ -44,7 +44,9 @@ and this library adheres to Rust's notion of
 - MSRV is now 1.51.0.
 - Bumped dependencies to `ff 0.11`, `group 0.11`, `bls12_381 0.6`, `jubjub 0.8`.
 - `zcash_client_backend::proto`:
-  - `compact_formats::CompactSpend` has been renamed to `CompactSaplingSpend`.
+  - `compact_formats::CompactSpend` has been renamed to `CompactSaplingSpend`,
+    and its `epk` field (and associated `set_epk` method) has been renamed to
+    `ephemeralKey` (and `set_ephemeralKey`).
   - `compact_formats::CompactOutput` has been renamed to `CompactSaplingOutput`.
 - `epk: jubjub::ExtendedPoint` has been replaced by
   `ephemeral_key: zcash_note_encryption::EphemeralKeyBytes` in various places:

zcash_client_backend/proto/compact_formats.proto

@@ -37,8 +37,8 @@ message CompactTx {
     // The transaction fee: present if server can provide. In the case of a
     // stateless server and a transaction with transparent inputs, this will be
     // unset because the calculation requires reference to prior transactions.
-    // in a pure-Sapling context, the fee will be calculable as:
-    //    valueBalance + (sum(vPubNew) - sum(vPubOld) - sum(tOut))
+    // If there are no transparent inputs, the fee will be calculable as:
+    //    valueBalanceSapling + valueBalanceOrchard + sum(vPubNew) - sum(vPubOld) - sum(tOut)
     uint32 fee = 3;
 
     repeated CompactSaplingSpend spends = 4;
@@ -52,11 +52,14 @@ message CompactSaplingSpend {
     bytes nf = 1;   // nullifier (see the Zcash protocol specification)
 }
 
-// output is a Sapling Output Description as described in section 7.4 of the
-// Zcash protocol spec. Total size is 948.
+// output encodes the `cmu` field, `ephemeralKey` field, and a 52-byte prefix of the
+// `encCiphertext` field of a Sapling Output Description. These fields are described in
+// section 7.4 of the Zcash protocol spec:
+// https://zips.z.cash/protocol/protocol.pdf#outputencodingandconsensus
+// Total size is 116 bytes.
 message CompactSaplingOutput {
     bytes cmu = 1;          // note commitment u-coordinate
-    bytes epk = 2;          // ephemeral public key
+    bytes ephemeralKey = 2; // ephemeral public key
     bytes ciphertext = 3;   // first 52 bytes of ciphertext
 }
 
@@ -66,5 +69,5 @@ message CompactOrchardAction {
     bytes nullifier = 1;        // [32] The nullifier of the input note
     bytes cmx = 2;              // [32] The x-coordinate of the note commitment for the output note
     bytes ephemeralKey = 3;     // [32] An encoding of an ephemeral Pallas public key
-    bytes encCiphertext = 4;    // [580] The encrypted contents of the note plaintext
+    bytes ciphertext = 4;       // [52] The first 52 bytes of the encCiphertext field
 }

zcash_client_backend/src/proto.rs

@@ -100,7 +100,7 @@ impl compact_formats::CompactSaplingOutput {
     ///
     /// [`CompactOutput.epk`]: #structfield.epk
     pub fn ephemeral_key(&self) -> Result<EphemeralKeyBytes, ()> {
-        self.epk[..]
+        self.ephemeralKey[..]
             .try_into()
             .map(EphemeralKeyBytes)
             .map_err(|_| ())
@@ -113,7 +113,7 @@ impl<A: sapling::Authorization> From<sapling::OutputDescription<A>>
     fn from(out: sapling::OutputDescription<A>) -> compact_formats::CompactSaplingOutput {
         let mut result = compact_formats::CompactSaplingOutput::new();
         result.set_cmu(out.cmu.to_repr().to_vec());
-        result.set_epk(out.ephemeral_key.as_ref().to_vec());
+        result.set_ephemeralKey(out.ephemeral_key.as_ref().to_vec());
         result.set_ciphertext(out.enc_ciphertext[..COMPACT_NOTE_SIZE].to_vec());
         result
     }

zcash_client_backend/src/welding_rig.rs

@@ -346,7 +346,7 @@ mod tests {
         cspend.set_nf(fake_nf);
         let mut cout = CompactSaplingOutput::new();
         cout.set_cmu(fake_cmu);
-        cout.set_epk(fake_epk);
+        cout.set_ephemeralKey(fake_epk);
         cout.set_ciphertext(vec![0; 52]);
         let mut ctx = CompactTx::new();
         let mut txid = vec![0; 32];
@@ -404,7 +404,7 @@ mod tests {
         cspend.set_nf(nf.0.to_vec());
         let mut cout = CompactSaplingOutput::new();
         cout.set_cmu(cmu);
-        cout.set_epk(epk);
+        cout.set_ephemeralKey(epk);
         cout.set_ciphertext(enc_ciphertext.as_ref()[..52].to_vec());
         let mut ctx = CompactTx::new();
         let mut txid = vec![0; 32];

zcash_client_sqlite/src/lib.rs

@@ -844,7 +844,7 @@ mod tests {
         // Create a fake CompactBlock containing the note
         let mut cout = CompactSaplingOutput::new();
         cout.set_cmu(cmu);
-        cout.set_epk(epk);
+        cout.set_ephemeralKey(epk);
         cout.set_ciphertext(enc_ciphertext.as_ref()[..52].to_vec());
         let mut ctx = CompactTx::new();
         let mut txid = vec![0; 32];
@@ -903,7 +903,7 @@ mod tests {
 
             let mut cout = CompactSaplingOutput::new();
             cout.set_cmu(cmu);
-            cout.set_epk(epk);
+            cout.set_ephemeralKey(epk);
             cout.set_ciphertext(enc_ciphertext.as_ref()[..52].to_vec());
             cout
         });
@@ -931,7 +931,7 @@ mod tests {
 
             let mut cout = CompactSaplingOutput::new();
             cout.set_cmu(cmu);
-            cout.set_epk(epk);
+            cout.set_ephemeralKey(epk);
             cout.set_ciphertext(enc_ciphertext.as_ref()[..52].to_vec());
             cout
         });