From 6bbe0906a8f521b436071f5c08533f3763d230c0 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Wed, 30 Jun 2021 22:22:05 +0100
Subject: [PATCH] ZIP 203: Enforce coinbase nExpiryHeight consensus rule from
 NU5

---
 src/gtest/test_checktransaction.cpp |  2 +-
 src/main.cpp                        | 27 +++++++++++++++++++++++----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/src/gtest/test_checktransaction.cpp b/src/gtest/test_checktransaction.cpp
index df36cb9ec..ce9944985 100644
--- a/src/gtest/test_checktransaction.cpp
+++ b/src/gtest/test_checktransaction.cpp
@@ -769,7 +769,7 @@ TEST(ChecktransactionTests, OverwinterExpiryHeight) {
         CTransaction tx(mtx);
         MockCValidationState state;
         EXPECT_CALL(state, DoS(100, false, REJECT_INVALID, "bad-tx-expiry-height-too-high", false)).Times(1);
-        CheckTransactionWithoutProofVerification(tx, state);
+        ContextualCheckTransaction(tx, state, Params(), 1, true);
     }
 
     {
diff --git a/src/main.cpp b/src/main.cpp
index 6e2790496..dc0396e35 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1136,11 +1136,25 @@ bool ContextualCheckTransaction(
 
         if (tx.IsCoinBase()) {
             // TODO: Check that Orchard coinbase outputs can be decrypted with the all-zeros OVK
+        } else {
+            // ZIP 203: From NU5, the upper limit on nExpiryHeight is removed for coinbase
+            // transactions.
+            if (tx.nExpiryHeight >= TX_EXPIRY_HEIGHT_THRESHOLD) {
+                return state.DoS(100, error("CheckTransaction(): expiry height is too high"),
+                                 REJECT_INVALID, "bad-tx-expiry-height-too-high");
+            }
         }
     } else {
         // Rules that apply generally before NU5. These were previously
         // noncontextual checks that became contextual after NU5 activation.
 
+        if (tx.nExpiryHeight >= TX_EXPIRY_HEIGHT_THRESHOLD) {
+            return state.DoS(
+                dosLevelPotentiallyRelaxing,
+                error("CheckTransaction(): expiry height is too high"),
+                REJECT_INVALID, "bad-tx-expiry-height-too-high");
+        }
+
         // Check that Orchard transaction components are not present prior to
         // NU5. NOTE: This is an internal zcashd consistency check; it does not
         // correspond to a consensus rule in the protocol specification, but is
@@ -1406,10 +1420,6 @@ bool CheckTransactionWithoutProofVerification(const CTransaction& tx, CValidatio
             return state.DoS(100, error("CheckTransaction(): unknown tx version group id"),
                     REJECT_INVALID, "bad-tx-version-group-id");
         }
-        if (tx.nExpiryHeight >= TX_EXPIRY_HEIGHT_THRESHOLD) {
-            return state.DoS(100, error("CheckTransaction(): expiry height is too high"),
-                            REJECT_INVALID, "bad-tx-expiry-height-too-high");
-        }
     }
     auto orchard_bundle = tx.GetOrchardBundle();
 
@@ -4673,6 +4683,15 @@ bool ContextualCheckBlock(
         }
     }
 
+    // ZIP 203: From NU5 onwards, nExpiryHeight is set to the block height in coinbase
+    // transactions.
+    if (consensusParams.NetworkUpgradeActive(nHeight, Consensus::UPGRADE_NU5)) {
+        if (block.vtx[0].nExpiryHeight != nHeight) {
+            return state.DoS(100, error("%s: block height mismatch in nExpiryHeight", __func__),
+                             REJECT_INVALID, "bad-cb-height");
+        }
+    }
+
     if (consensusParams.NetworkUpgradeActive(nHeight, Consensus::UPGRADE_CANOPY)) {
         // Funding streams are checked inside ContextualCheckTransaction.
         // This empty conditional branch exists to enforce this ZIP 207 consensus rule: