From c87debb0486349a04088fb91ec0bbc8a2d8c1d1b Mon Sep 17 00:00:00 2001
From: instagibbs <gsanders87@gmail.com>
Date: Thu, 9 Jun 2016 13:23:11 -0400
Subject: [PATCH] Add parentChainPowLimit, check in CheckBitcoinProof

---
 src/chainparams.cpp    | 7 +++++++
 src/consensus/params.h | 1 +
 src/pow.cpp            | 2 +-
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 4bf40a63ff..4552dc0180 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -61,6 +61,12 @@ public:
         consensus.BIP65Height = 388381; // 000000000000000004c2b624ed5d7756c508d90fd0da2c7c679febfa6c4735f0
         consensus.BIP66Height = 363725; // 00000000000000000379eaa19dce8c9b722d46ae6a57c2f1a988119488b50931
         consensus.powLimit = uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
+        // Peg-ins Bitcoin headers must have higher difficulty target than this field
+        // This value must be sufficiently small to not preclude realistic parent
+        // chain difficulty during network lifespan yet sufficiently large to
+        // deny peg-in DoS attacks due to our inability to ban after failed
+        // IsBitcoinBlock RPC checks.
+        consensus.parentChainPowLimit = uint256S("00000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = false;
@@ -166,6 +172,7 @@ public:
         consensus.BIP65Height = 1351; // BIP65 activated on regtest (Used in rpc activation tests)
         consensus.BIP66Height = 1251; // BIP66 activated on regtest (Used in rpc activation tests)
         consensus.powLimit = uint256S("7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
+        consensus.parentChainPowLimit = uint256S("7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks
         consensus.nPowTargetSpacing = 10 * 60;
         consensus.fPowAllowMinDifficultyBlocks = true;
diff --git a/src/consensus/params.h b/src/consensus/params.h
index 6240e82857..a6d00987ce 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -56,6 +56,7 @@ struct Params {
     BIP9Deployment vDeployments[MAX_VERSION_BITS_DEPLOYMENTS];
     /** Proof of work parameters */
     uint256 powLimit;
+    uint256 parentChainPowLimit;
     bool fPowAllowMinDifficultyBlocks;
     bool fPowNoRetargeting;
     int64_t nPowTargetSpacing;
diff --git a/src/pow.cpp b/src/pow.cpp
index 73d5699431..68fe276238 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -46,7 +46,7 @@ bool CheckBitcoinProof(uint256 hash, unsigned int nBits)
     bnTarget.SetCompact(nBits, &fNegative, &fOverflow);
 
     // Check range
-    if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(Params().GetConsensus().powLimit))
+    if (fNegative || bnTarget == 0 || fOverflow || bnTarget > UintToArith256(Params().GetConsensus().parentChainPowLimit))
         return false;
 
     // Check proof of work matches claimed amount