Enforce Taproot script flags whenever WITNESS is set

3 files changed, 25 insertions, 20 deletions

diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 2e823c1211..c35d265f3c 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -9,6 +9,7 @@
 #include <consensus/merkle.h>
 #include <deploymentinfo.h>
 #include <hash.h> // for signet block challenge hash
+#include <script/interpreter.h>
 #include <util/system.h>
 
 #include <assert.h>
@@ -65,7 +66,10 @@ public:
         consensus.signet_blocks = false;
         consensus.signet_challenge.clear();
         consensus.nSubsidyHalvingInterval = 210000;
-        consensus.BIP16Exception = uint256S("0x00000000000002dc756eebf4f49723ed8d30cc28a5f108eb94b1ba88ac4f9c22");
+        consensus.script_flag_exceptions.emplace( // BIP16 exception
+            uint256S("0x00000000000002dc756eebf4f49723ed8d30cc28a5f108eb94b1ba88ac4f9c22"), SCRIPT_VERIFY_NONE);
+        consensus.script_flag_exceptions.emplace( // Taproot exception
+            uint256S("0x0000000000000000000f14c35b2d841e986ab5441de8c585d5ffe55ea1e395ad"), SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS);
         consensus.BIP34Height = 227931;
         consensus.BIP34Hash = uint256S("0x000000000000024b89b42a942fe0d9fea3bb44ab7bd1b19115dd6a759c0808b8");
         consensus.BIP65Height = 388381; // 000000000000000004c2b624ed5d7756c508d90fd0da2c7c679febfa6c4735f0
@@ -184,7 +188,8 @@ public:
         consensus.signet_blocks = false;
         consensus.signet_challenge.clear();
         consensus.nSubsidyHalvingInterval = 210000;
-        consensus.BIP16Exception = uint256S("0x00000000dd30457c001f4095d208cc1296b0eed002427aa599874af7a432b105");
+        consensus.script_flag_exceptions.emplace( // BIP16 exception
+            uint256S("0x00000000dd30457c001f4095d208cc1296b0eed002427aa599874af7a432b105"), SCRIPT_VERIFY_NONE);
         consensus.BIP34Height = 21111;
         consensus.BIP34Hash = uint256S("0x0000000023b3a96d3484e5abb3755c413e7d41500f8e2a5c3f0dd01299cd8ef8");
         consensus.BIP65Height = 581885; // 00000000007f6655f22f98e72ed80d8b06dc761d5da09df0fa1dc4be4f861eb6
@@ -323,7 +328,6 @@ public:
         consensus.signet_blocks = true;
         consensus.signet_challenge.assign(bin.begin(), bin.end());
         consensus.nSubsidyHalvingInterval = 210000;
-        consensus.BIP16Exception = uint256{};
         consensus.BIP34Height = 1;
         consensus.BIP34Hash = uint256{};
         consensus.BIP65Height = 1;
@@ -391,7 +395,6 @@ public:
         consensus.signet_blocks = false;
         consensus.signet_challenge.clear();
         consensus.nSubsidyHalvingInterval = 150;
-        consensus.BIP16Exception = uint256();
         consensus.BIP34Height = 1; // Always active unless overridden
         consensus.BIP34Hash = uint256();
         consensus.BIP65Height = 1;  // Always active unless overridden
diff --git a/src/consensus/params.h b/src/consensus/params.h
index 77bf7fd0d8..aca1995c36 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -7,7 +7,9 @@
 #define BITCOIN_CONSENSUS_PARAMS_H
 
 #include <uint256.h>
+
 #include <limits>
+#include <map>
 
 namespace Consensus {
 
@@ -70,8 +72,13 @@ struct BIP9Deployment {
 struct Params {
     uint256 hashGenesisBlock;
     int nSubsidyHalvingInterval;
-    /* Block hash that is excepted from BIP16 enforcement */
-    uint256 BIP16Exception;
+    /**
+     * Hashes of blocks that
+     * - are known to be consensus valid, and
+     * - buried in the chain, and
+     * - fail if the default script verify flags are applied.
+     */
+    std::map<uint256, uint32_t> script_flag_exceptions;
     /** Block height and hash at which BIP34 becomes active */
     int BIP34Height;
     uint256 BIP34Hash;
diff --git a/src/validation.cpp b/src/validation.cpp
index f21d6cdbf1..f465c96720 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1581,18 +1581,18 @@ static ThresholdConditionCache warningcache[VERSIONBITS_NUM_BITS] GUARDED_BY(cs_
 
 static unsigned int GetBlockScriptFlags(const CBlockIndex& block_index, const Consensus::Params& consensusparams)
 {
-    unsigned int flags = SCRIPT_VERIFY_NONE;
-
     // BIP16 didn't become active until Apr 1 2012 (on mainnet, and
     // retroactively applied to testnet)
     // However, only one historical block violated the P2SH rules (on both
-    // mainnet and testnet), so for simplicity, always leave P2SH
-    // on except for the one violating block.
-    if (consensusparams.BIP16Exception.IsNull() || // no bip16 exception on this chain
-        *Assert(block_index.phashBlock) != consensusparams.BIP16Exception) // this block isn't the historical exception
-    {
-        // Enforce WITNESS rules whenever P2SH is in effect
-        flags |= SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS;
+    // mainnet and testnet).
+    // Similarly, only one historical block violated the TAPROOT rules on
+    // mainnet.
+    // For simplicity, always leave P2SH+WITNESS+TAPROOT on except for the two
+    // violating blocks.
+    uint32_t flags{SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_TAPROOT};
+    const auto it{consensusparams.script_flag_exceptions.find(*Assert(block_index.phashBlock))};
+    if (it != consensusparams.script_flag_exceptions.end()) {
+        flags = it->second;
     }
 
     // Enforce the DERSIG (BIP66) rule
@@ -1610,11 +1610,6 @@ static unsigned int GetBlockScriptFlags(const CBlockIndex& block_index, const Co
         flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
     }
 
-    // Enforce Taproot (BIP340-BIP342)
-    if (DeploymentActiveAt(block_index, consensusparams, Consensus::DEPLOYMENT_TAPROOT)) {
-        flags |= SCRIPT_VERIFY_TAPROOT;
-    }
-
     // Enforce BIP147 NULLDUMMY (activated simultaneously with segwit)
     if (DeploymentActiveAt(block_index, consensusparams, Consensus::DEPLOYMENT_SEGWIT)) {
         flags |= SCRIPT_VERIFY_NULLDUMMY;