Add documentation specific to ZIP 212

src/main.cpp

@@ -966,10 +966,10 @@ bool ContextualCheckTransaction(
                     }
                 }
 
-                // ZIP 212: Check that the note plaintexts use the v2 note plaintext
+                // ZIP 212: after ZIP 212 any Sapling output of a coinbase tx that is
-                // version.
+                // decrypted to a note plaintext, MUST have note plaintext lead byte equal
-                // This check compels miners to switch to the new plaintext version
+                // to 0x02. This applies even during the grace period, and also applies to
-                // and overrides the grace period in plaintext_version_is_valid()
+                // funding stream outputs sent to shielded payment addresses, if any.
                 if (canopyActive != (encPlaintext->get_leadbyte() == 0x02)) {
                     return state.DoS(
                         DOS_LEVEL_BLOCK,

src/wallet/rpcwallet.cpp

@@ -3804,7 +3804,10 @@ UniValue z_viewtransaction(const UniValue& params, bool fHelp)
         auto wtxPrev = pwalletMain->mapWallet.at(op.hash);
 
         // We don't need to check the leadbyte here: if wtx exists in
-        // the wallet, it must have already passed the leadbyte check
+        // the wallet, it must have been successfully decrypted. This
+        // means the plaintext leadbyte was valid at the block height
+        // where the note was received.
+        // https://zips.z.cash/zip-0212#changes-to-the-process-of-receiving-sapling-notes
         auto decrypted = wtxPrev.DecryptSaplingNoteWithoutLeadByteCheck(op).get();
         auto notePt = decrypted.first;
         auto pa = decrypted.second;
@@ -3834,7 +3837,10 @@ UniValue z_viewtransaction(const UniValue& params, bool fHelp)
         bool isOutgoing;
 
         // We don't need to check the leadbyte here: if wtx exists in
-        // the wallet, it must have already passed the leadbyte check
+        // the wallet, it must have been successfully decrypted. This
+        // means the plaintext leadbyte was valid at the block height
+        // where the note was received.
+        // https://zips.z.cash/zip-0212#changes-to-the-process-of-receiving-sapling-notes
         auto decrypted = wtx.DecryptSaplingNoteWithoutLeadByteCheck(op);
         if (decrypted) {
             notePt = decrypted->first;

src/zcash/Note.cpp

@@ -369,7 +369,8 @@ boost::optional<SaplingNotePlaintext> SaplingNotePlaintext::plaintext_checks_wit
     const uint256 &cmu
 )
 {
-    // Check that epk is consistent with esk
+    // ZIP 212: The recipient MUST derive esk and check that epk is consistent with it.
+    // https://zips.z.cash/zip-0212#changes-to-the-process-of-receiving-sapling-notes
     uint256 expected_epk;
     if (!librustzcash_sapling_ka_derivepublic(plaintext.d.data(), esk.begin(), expected_epk.begin())) {
         return boost::none;