Litecoin: Fix zeitgeist2 attack thanks to Lolcust and ArtForz. 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.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/pow.cpp b/src/pow.cpp
index 52c826d72..c629ee4a4 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -41,8 +41,14 @@ unsigned int GetNextWorkRequired(const CBlockIndex* pindexLast, const CBlockHead
         return pindexLast->nBits;
     }
 
+    // Litecoin: 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 = params.DifficultyAdjustmentInterval()-1;
+    if ((pindexLast->nHeight+1) != params.DifficultyAdjustmentInterval())
+        blockstogoback = params.DifficultyAdjustmentInterval();
+
     // Go back by what we want to be 14 days worth of blocks
-    int nHeightFirst = pindexLast->nHeight - (params.DifficultyAdjustmentInterval()-1);
+    int nHeightFirst = pindexLast->nHeight - blockstogoback;
     assert(nHeightFirst >= 0);
     const CBlockIndex* pindexFirst = pindexLast->GetAncestor(nHeightFirst);
     assert(pindexFirst);