Max-Reorg-Depth

src/chainparams.cpp

@@ -203,7 +203,9 @@ public:
                         //   (the tx=... number in the SetBestChain debug.log lines)
         	0.03  // * estimated number of transactions per second after that timestamp
         };
-
+        // Max-Reorg (51% attack prevention)
+        nMaxReorganizationDepth = 55; // 55 at 1 minute block timespan is +/- 55 minutes.
+        nMinReorganizationPeers = 3;
     }
 };
 
@@ -411,7 +413,7 @@ public:
 
         fDefaultConsistencyChecks = true;
         fRequireStandard = false;
-        fMineBlocksOnDemand = true; 
+        fMineBlocksOnDemand = true;
 
 //        checkpointData = (CCheckpointData) {
 //            {

src/chainparams.h

@@ -81,6 +81,9 @@ public:
     const CCheckpointData& Checkpoints() const { return checkpointData; }
     const ChainTxData& TxData() const { return chainTxData; }
     void UpdateVersionBitsParameters(Consensus::DeploymentPos d, int64_t nStartTime, int64_t nTimeout);
+    // Max-Reorg (51% attack prevention)
+    int MaxReorganizationDepth() const { return nMaxReorganizationDepth; }
+    int MinReorganizationPeers() const { return nMinReorganizationPeers; }
 protected:
     CChainParams() {}
 
@@ -99,6 +102,9 @@ protected:
     bool fMineBlocksOnDemand;
     CCheckpointData checkpointData;
     ChainTxData chainTxData;
+    // Max-Reorg (51% attack prevention)
+    int nMaxReorganizationDepth;
+    int nMinReorganizationPeers;
 };
 
 /**

src/consensus/validation.h

@@ -22,6 +22,8 @@ static const unsigned char REJECT_NONSTANDARD = 0x40;
 // static const unsigned char REJECT_DUST = 0x41; // part of BIP 61
 static const unsigned char REJECT_INSUFFICIENTFEE = 0x42;
 static const unsigned char REJECT_CHECKPOINT = 0x43;
+// Max-Reorg (51% attack prevention)
+static const unsigned char REJECT_MAXREORGDEPTH = 0x44;
 
 /** Capture information about block/transaction validation */
 class CValidationState {

src/init.cpp

@@ -364,6 +364,8 @@ std::string HelpMessage(HelpMessageMode mode)
     if (showDebug)
         strUsage += HelpMessageOpt("-feefilter", strprintf("Tell other nodes to filter invs to us by our mempool min fee (default: %u)", DEFAULT_FEEFILTER));
     strUsage += HelpMessageOpt("-loadblock=<file>", _("Imports blocks from external blk000??.dat file on startup"));
+    strUsage += HelpMessageOpt("-maxreorg=<n>", strprintf(_("Set the Maximum reorg depth (default: %u)"), defaultChainParams->MaxReorganizationDepth())); //#51-Attk-prevention
+    strUsage += HelpMessageOpt("-minreorgpeers=<n>", strprintf(_("Set the Minimum amount of peers required to not allow reorgs. Peers must be greater than. (default: %u)"), defaultChainParams->MinReorganizationPeers()));  //#51-Attk-prevention
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
     strUsage += HelpMessageOpt("-maxmempool=<n>", strprintf(_("Keep the transaction memory pool below <n> megabytes (default: %u)"), DEFAULT_MAX_MEMPOOL_SIZE));
     strUsage += HelpMessageOpt("-mempoolexpiry=<n>", strprintf(_("Do not keep transactions in the mempool longer than <n> hours (default: %u)"), DEFAULT_MEMPOOL_EXPIRY));

src/net_processing.cpp

@@ -1009,6 +1009,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                         // best equivalent proof of work) than the best header chain we know about.
                         send = mi->second->IsValid(BLOCK_VALID_SCRIPTS) && (pindexBestHeader != nullptr) &&
                             (pindexBestHeader->GetBlockTime() - mi->second->GetBlockTime() < nOneMonth) &&
+                            (chainActive.Height() - mi->second->nHeight < Params().MaxReorganizationDepth()) && //(51% attk prevention)
                             (GetBlockProofEquivalentTime(*pindexBestHeader, *mi->second, *pindexBestHeader, consensusParams) < nOneMonth);
                         if (!send) {
                             LogPrintf("%s: ignoring request from peer=%i for old block that isn't in the main chain\n", __func__, pfrom->GetId());

src/validation.cpp

@@ -42,6 +42,7 @@
 #include "validationinterface.h"
 #include "versionbits.h"
 #include "warnings.h"
+#include "net.h"
 
 #include <atomic>
 #include <sstream>
@@ -2942,6 +2943,13 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationSta
     assert(pindexPrev != nullptr);
     const int nHeight = pindexPrev->nHeight + 1;
 
+    //If this is a reorg, check that it is not too deep (51% attack prevention)
+    int nMaxReorgDepth = gArgs.GetArg("-maxreorg", Params().MaxReorganizationDepth());
+    int nMinReorgPeers = gArgs.GetArg("-minreorgpeers", Params().MinReorganizationPeers());
+    bool fGreaterThanMaxReorg = chainActive.Height() - nHeight >= nMaxReorgDepth;
+    if (fGreaterThanMaxReorg && g_connman && (int)g_connman->GetNodeCount(CConnman::CONNECTIONS_ALL) > nMinReorgPeers && !IsInitialBlockDownload())
+        return state.DoS(1, error("%s: forked chain older than max reorganization depth (height %d), with connections (count %d), and (initial download %s)", __func__, nHeight, g_connman ? g_connman->GetNodeCount(CConnman::CONNECTIONS_ALL) : -1, IsInitialBlockDownload() ? "true" : "false"), REJECT_MAXREORGDEPTH, "bad-fork-prior-to-maxreorgdepth");
+
     // Check proof of work
     const Consensus::Params& consensusParams = params.GetConsensus();
     if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))