Skip verifying transaction signatures during initial block-chain download

src/main.cpp

@@ -810,6 +810,9 @@ bool CTransaction::ConnectInputs(CTxDB& txdb, map<uint256, CTxIndex>& mapTestPoo
                                  CBlockIndex* pindexBlock, int64& nFees, bool fBlock, bool fMiner, int64 nMinFee)
 {
     // Take over previous transactions' spent pointers
+    // fBlock is true when this is called from AcceptBlock when a new best-block is added to the blockchain
+    // fMiner is true when called from the internal bitcoin miner
+    // ... both are false when called from CTransaction::AcceptToMemoryPool
     if (!IsCoinBase())
     {
         int64 nValueIn = 0;
@@ -863,9 +866,13 @@ bool CTransaction::ConnectInputs(CTxDB& txdb, map<uint256, CTxIndex>& mapTestPoo
                     if (pindex->nBlockPos == txindex.pos.nBlockPos && pindex->nFile == txindex.pos.nFile)
                         return DoS(10, error("ConnectInputs() : tried to spend coinbase at depth %d", pindexBlock->nHeight - pindex->nHeight));
 
-            // Verify signature
-            if (!VerifySignature(txPrev, *this, i))
-                return DoS(100,error("ConnectInputs() : %s VerifySignature failed", GetHash().ToString().substr(0,10).c_str()));
+            // Skip ECDSA signature verification when connecting blocks (fBlock=true) during initial download
+            // (before the last blockchain checkpoint). This is safe because block merkle hashes are
+            // still computed and checked, and any change will be caught at the next checkpoint.
+            if (!(fBlock && IsInitialBlockDownload()))
+                // Verify signature
+                if (!VerifySignature(txPrev, *this, i))
+                    return DoS(100,error("ConnectInputs() : %s VerifySignature failed", GetHash().ToString().substr(0,10).c_str()));
 
             // Check for conflicts (double-spend)
             // This doesn't trigger the DoS code on purpose; if it did, it would make it easier