Merge bitcoin#30681: Have miner account for timewarp mitigation, acti…

…vate on regtest, lower nPowTargetTimespan to 144 and add test

59ff17e miner: adjust clock to timewarp rule (Sjors Provoost)
e929054 Add timewarp attack mitigation test (Sjors Provoost)
e85f386 consensus: enable BIP94 on regtest (Sjors Provoost)
dd154b0 consensus: lower regtest nPowTargetTimespan to 144 (Sjors Provoost)

Pull request description:

  Because bitcoin#30647 reduced the timewarp attack threshold from 7200s to 600s, our miner code will fail to propose a block template (on testnet4) if the last block of the previous period has a timestamp two hours in the future. This PR fixes that and also adds a test.

  The non-test changes in the last commit should be in v28, otherwise miners have to patch it themselves. If necessary I can split that out into a separate PR, but I prefer to get the tests in as well.

  In order to add the test, we activate BIP94 on regtest.

  In order for the test to run faster, we reduce its difficulty retarget period to 144, the same number that's already used for softfork activation logic. Regtest does not actually adjust its difficulty, so this change has no effect (except for `getnetworkhashps`, see commit).

  An alternative approach would be to run this test on testnet4, by hardcoding its first 2015 in the test suite. But since the timewarp mitigation is a serious candidate for a future mainnet softfork, it seems better to just deploy it on regtest.

  The next commits add a test and fix the miner code.

  The `MAX_TIMEWARP` constant is moved to `consensus.h` so both validation and miner code have access to it.

ACKs for top commit:
  achow101:
    ACK 59ff17e
  fjahr:
    ACK 59ff17e
  glozow:
    ACK 59ff17e

Tree-SHA512: 50af9fdcba9b0d5c57e1efd5feffd870bd11b5318f1f8b0aabf684657f2d33ab108d5f00b1475fe0d38e8e0badc97249ef8dda20c7f47fcc1698bc1008798830

doc/release-notes-30647.md

@@ -0,0 +1,4 @@
+Tests
+-----
+
+- The BIP94 timewarp attack mitigation is now active on the `regtest` network

src/consensus/consensus.h

@@ -27,4 +27,11 @@ static const size_t MIN_SERIALIZABLE_TRANSACTION_WEIGHT = WITNESS_SCALE_FACTOR *
 /** Interpret sequence numbers as relative lock-time constraints. */
 static constexpr unsigned int LOCKTIME_VERIFY_SEQUENCE = (1 << 0);
 
+/**
+ * Maximum number of seconds that the timestamp of the first
+ * block of a difficulty adjustment period is allowed to
+ * be earlier than the last block of the previous period (BIP94).
+ */
+static constexpr int64_t MAX_TIMEWARP = 600;
+
 #endif // BITCOIN_CONSENSUS_CONSENSUS_H

src/consensus/params.h

@@ -108,6 +108,10 @@ struct Params {
     /** Proof of work parameters */
     uint256 powLimit;
     bool fPowAllowMinDifficultyBlocks;
+    /**
+      * Enfore BIP94 timewarp attack mitigation. On testnet4 this also enforces
+      * the block storm mitigation.
+      */
     bool enforce_BIP94;
     bool fPowNoRetargeting;
     int64_t nPowTargetSpacing;

src/kernel/chainparams.cpp

@@ -537,10 +537,10 @@ class CRegTestParams : public CChainParams
         consensus.SegwitHeight = 0; // Always active unless overridden
         consensus.MinBIP9WarningHeight = 0;
         consensus.powLimit = uint256{"7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"};
-        consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
+        consensus.nPowTargetTimespan = 24 * 60 * 60; // one day
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
-        consensus.enforce_BIP94 = false;
+        consensus.enforce_BIP94 = true;
         consensus.fPowNoRetargeting = true;
         consensus.nRuleChangeActivationThreshold = 108; // 75% for testchains
         consensus.nMinerConfirmationWindow = 144; // Faster than normal for regtest (144 instead of 2016)

src/node/miner.cpp

@@ -33,6 +33,14 @@ int64_t UpdateTime(CBlockHeader* pblock, const Consensus::Params& consensusParam
     int64_t nOldTime = pblock->nTime;
     int64_t nNewTime{std::max<int64_t>(pindexPrev->GetMedianTimePast() + 1, TicksSinceEpoch<std::chrono::seconds>(NodeClock::now()))};
 
+    if (consensusParams.enforce_BIP94) {
+        // Height of block to be mined.
+        const int height{pindexPrev->nHeight + 1};
+        if (height % consensusParams.DifficultyAdjustmentInterval() == 0) {
+            nNewTime = std::max<int64_t>(nNewTime, pindexPrev->GetBlockTime() - MAX_TIMEWARP);
+        }
+    }
+
     if (nOldTime < nNewTime) {
         pblock->nTime = nNewTime;
     }

src/validation.cpp

@@ -107,13 +107,6 @@ const std::vector<std::string> CHECKLEVEL_DOC {
  * */
 static constexpr int PRUNE_LOCK_BUFFER{10};
 
-/**
- * Maximum number of seconds that the timestamp of the first
- * block of a difficulty adjustment period is allowed to
- * be earlier than the last block of the previous period (BIP94).
- */
-static constexpr int64_t MAX_TIMEWARP = 600;
-
 GlobalMutex g_best_block_mutex;
 std::condition_variable g_best_block_cv;
 uint256 g_best_block;
@@ -4189,7 +4182,7 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidatio
     if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
         return state.Invalid(BlockValidationResult::BLOCK_INVALID_HEADER, "time-too-old", "block's timestamp is too early");
 
-    // Testnet4 only: Check timestamp against prev for difficulty-adjustment
+    // Testnet4 and regtest only: Check timestamp against prev for difficulty-adjustment
     // blocks to prevent timewarp attacks (see https://github.com/bitcoin/bitcoin/pull/15482).
     if (consensusParams.enforce_BIP94) {
         // Check timestamp for the first block of each difficulty adjustment

test/functional/mining_basic.py

@@ -28,12 +28,16 @@
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
+    assert_greater_than_or_equal,
     assert_raises_rpc_error,
     get_fee,
 )
 from test_framework.wallet import MiniWallet
 
 
+DIFFICULTY_ADJUSTMENT_INTERVAL = 144
+MAX_FUTURE_BLOCK_TIME = 2 * 3600
+MAX_TIMEWARP = 600
 VERSIONBITS_TOP_BITS = 0x20000000
 VERSIONBITS_DEPLOYMENT_TESTDUMMY_BIT = 28
 DEFAULT_BLOCK_MIN_TX_FEE = 1000  # default `-blockmintxfee` setting [sat/kvB]
@@ -115,6 +119,46 @@ def test_blockmintxfee_parameter(self):
             assert tx_below_min_feerate['txid'] not in block_template_txids
             assert tx_below_min_feerate['txid'] not in block_txids
 
+    def test_timewarp(self):
+        self.log.info("Test timewarp attack mitigation (BIP94)")
+        node = self.nodes[0]
+
+        self.log.info("Mine until the last block of the retarget period")
+        blockchain_info = self.nodes[0].getblockchaininfo()
+        n = DIFFICULTY_ADJUSTMENT_INTERVAL - blockchain_info['blocks'] % DIFFICULTY_ADJUSTMENT_INTERVAL - 2
+        t = blockchain_info['time']
+
+        for _ in range(n):
+            t += 600
+            self.nodes[0].setmocktime(t)
+            self.generate(self.wallet, 1, sync_fun=self.no_op)
+
+        self.log.info("Create block two hours in the future")
+        self.nodes[0].setmocktime(t + MAX_FUTURE_BLOCK_TIME)
+        self.generate(self.wallet, 1, sync_fun=self.no_op)
+        assert_equal(node.getblock(node.getbestblockhash())['time'], t + MAX_FUTURE_BLOCK_TIME)
+
+        self.log.info("First block template of retarget period can't use wall clock time")
+        self.nodes[0].setmocktime(t)
+        # The template will have an adjusted timestamp, which we then modify
+        tmpl = node.getblocktemplate(NORMAL_GBT_REQUEST_PARAMS)
+        assert_greater_than_or_equal(tmpl['curtime'], t + MAX_FUTURE_BLOCK_TIME - MAX_TIMEWARP)
+
+        block = CBlock()
+        block.nVersion = tmpl["version"]
+        block.hashPrevBlock = int(tmpl["previousblockhash"], 16)
+        block.nTime = tmpl["curtime"]
+        block.nBits = int(tmpl["bits"], 16)
+        block.nNonce = 0
+        block.vtx = [create_coinbase(height=int(tmpl["height"]))]
+        block.solve()
+        assert_template(node, block, None)
+
+        bad_block = copy.deepcopy(block)
+        bad_block.nTime = t
+        bad_block.solve()
+        assert_raises_rpc_error(-25, 'time-timewarp-attack', lambda: node.submitheader(hexdata=CBlockHeader(bad_block).serialize().hex()))
+
     def run_test(self):
         node = self.nodes[0]
         self.wallet = MiniWallet(node)
@@ -322,6 +366,7 @@ def chain_tip(b_hash, *, status='headers-only', branchlen=1):
         assert_equal(node.submitblock(hexdata=block.serialize().hex()), 'duplicate')  # valid
 
         self.test_blockmintxfee_parameter()
+        self.test_timewarp()
 
 
 if __name__ == '__main__':

test/functional/rpc_blockchain.py

@@ -58,7 +58,7 @@
 TIME_RANGE_MTP = TIME_GENESIS_BLOCK + (HEIGHT - 6) * TIME_RANGE_STEP
 TIME_RANGE_TIP = TIME_GENESIS_BLOCK + (HEIGHT - 1) * TIME_RANGE_STEP
 TIME_RANGE_END = TIME_GENESIS_BLOCK + HEIGHT * TIME_RANGE_STEP
-DIFFICULTY_ADJUSTMENT_INTERVAL = 2016
+DIFFICULTY_ADJUSTMENT_INTERVAL = 144
 
 
 class BlockchainTest(BitcoinTestFramework):