Hardfork: Fix Art Forz's time-traveller attack, where a 51% attack ca…

…n change difficulty at will.
freicoin · Feb 21, 2015 · beb2fa5 · beb2fa5 · peterzion45 · Nov 26, 2022
1 parent e43f25c
commit beb2fa5
Showing 1 changed file with 8 additions and 1 deletion.
diff --git a/src/pow.cpp b/src/pow.cpp
@@ -41,9 +41,16 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
         return pindexLast->nBits;
     }
 
+    // This fixes an issue where a 51% attack can change difficulty at will.
+    // Go back the full period unless it's the first retarget after genesis.
+    // Code courtesy of Art Forz
+    int blockstogoback = nInterval-1;
+    if ((pindexLast->nHeight+1) != nInterval)
+        blockstogoback = nInterval;
+
     // Go back by what we want to be 14 days worth of blocks
     const CBlockIndex* pindexFirst = pindexLast;
-    for (int i = 0; pindexFirst && i < Params().Interval()-1; i++)
+    for (int i = 0; pindexFirst && i < blockstogoback; i++)
         pindexFirst = pindexFirst->pprev;
     assert(pindexFirst);