Block height in coinbase as a new block rule

"Version 2" blocks are blocks that have nVersion=2 and
have the block height as the first item in their coinbase.
Block-height-in-the-coinbase is strictly enforced when
version=2 blocks are a supermajority in the block chain
(750 of the last 1,000 blocks on main net, 51 of 100 for
testnet). This does not affect old clients/miners at all,
which will continue producing nVersion=1 blocks, and
which will continue to be valid.

1 files changed, 27 insertions, 1 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 9e1b228b2a..fc57713129 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1554,6 +1554,19 @@ bool CBlock::AcceptBlock()
     if (!Checkpoints::CheckBlock(nHeight, hash))
         return error("AcceptBlock() : rejected by checkpoint lockin at %d", nHeight);
 
+    // Enforce block.nVersion=2 rule that the coinbase starts with serialized block height
+    if (nVersion > 1)
+    {
+        // if 750 of the last 1,000 blocks are version 2 or greater (51/100 if testnet):
+        if ((!fTestNet && CBlockIndex::IsSuperMajority(2, pindexPrev, 750, 1000)) ||
+            (fTestNet && CBlockIndex::IsSuperMajority(2, pindexPrev, 51, 100)))
+        {
+            CScript expect = CScript() << nHeight;
+            if (!std::equal(expect.begin(), expect.end(), vtx[0].vin[0].scriptSig.begin()))
+                return error("AcceptBlock() : block height mismatch in coinbase");
+        }
+    }
+
     // Write block to history file
     if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK)))
         return error("AcceptBlock() : out of disk space");
@@ -1575,6 +1588,18 @@ bool CBlock::AcceptBlock()
     return true;
 }
 
+bool CBlockIndex::IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned int nRequired, unsigned int nToCheck)
+{
+    unsigned int nFound = 0;
+    for (unsigned int i = 0; i < nToCheck && nFound < nRequired && pstart != NULL; i++)
+    {
+        if (pstart->nVersion >= minVersion)
+            ++nFound;
+        pstart = pstart->pprev;
+    }
+    return (nFound >= nRequired);
+}
+
 bool static ProcessBlock(CNode* pfrom, CBlock* pblock)
 {
     // Check for duplicate
@@ -3140,7 +3165,8 @@ void IncrementExtraNonce(CBlock* pblock, CBlockIndex* pindexPrev, unsigned int&
         hashPrevBlock = pblock->hashPrevBlock;
     }
     ++nExtraNonce;
-    pblock->vtx[0].vin[0].scriptSig = CScript() << pblock->nTime << CBigNum(nExtraNonce);
+    unsigned int nHeight = pindexPrev->nHeight+1; // Height first in coinbase required for block.version=2
+    pblock->vtx[0].vin[0].scriptSig = CScript() << nHeight << CBigNum(nExtraNonce);
     pblock->hashMerkleRoot = pblock->BuildMerkleTree();
 }