1 files changed, 198 insertions, 0 deletions
diff --git a/src/auxpow.cpp b/src/auxpow.cpp
new file mode 100644
index 000000000..208a54bec
--- /dev/null
+++ b/src/auxpow.cpp
@@ -0,0 +1,198 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2011 Vince Durham
+// Copyright (c) 2009-2014 The Bitcoin developers
+// Copyright (c) 2014-2017 Daniel Kraft
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#include <auxpow.h>
+
+#include <compat/endian.h>
+#include <consensus/consensus.h>
+#include <consensus/merkle.h>
+#include <hash.h>
+#include <primitives/block.h>
+#include <script/script.h>
+#include <util.h>
+#include <utilstrencodings.h>
+
+#include <algorithm>
+#include <cassert>
+
+bool
+CAuxPow::check (const uint256& hashAuxBlock, int nChainId,
+                const Consensus::Params& params) const
+{
+    if (coinbaseTx.nIndex != 0)
+        return error("AuxPow is not a generate");
+
+    if (params.fStrictChainId && parentBlock.GetChainId () == nChainId)
+        return error("Aux POW parent has our chain ID");
+
+    if (vChainMerkleBranch.size() > 30)
+        return error("Aux POW chain merkle branch too long");
+
+    // Check that the chain merkle root is in the coinbase
+    const uint256 nRootHash
+      = CheckMerkleBranch (hashAuxBlock, vChainMerkleBranch, nChainIndex);
+    std::vector<unsigned char> vchRootHash(nRootHash.begin (), nRootHash.end ());
+    std::reverse (vchRootHash.begin (), vchRootHash.end ()); // correct endian
+
+    // Check that we are in the parent block merkle tree
+    if (CheckMerkleBranch(coinbaseTx.GetHash(), coinbaseTx.vMerkleBranch,
+                          coinbaseTx.nIndex)
+          != parentBlock.hashMerkleRoot)
+        return error("Aux POW merkle root incorrect");
+
+    const CScript script = coinbaseTx.tx->vin[0].scriptSig;
+
+    // Check that the same work is not submitted twice to our chain.
+    //
+
+    CScript::const_iterator pcHead =
+        std::search(script.begin(), script.end(), UBEGIN(pchMergedMiningHeader), UEND(pchMergedMiningHeader));
+
+    CScript::const_iterator pc =
+        std::search(script.begin(), script.end(), vchRootHash.begin(), vchRootHash.end());
+
+    if (pc == script.end())
+        return error("Aux POW missing chain merkle root in parent coinbase");
+
+    if (pcHead != script.end())
+    {
+        // Enforce only one chain merkle root by checking that a single instance of the merged
+        // mining header exists just before.
+        if (script.end() != std::search(pcHead + 1, script.end(), UBEGIN(pchMergedMiningHeader), UEND(pchMergedMiningHeader)))
+            return error("Multiple merged mining headers in coinbase");
+        if (pcHead + sizeof(pchMergedMiningHeader) != pc)
+            return error("Merged mining header is not just before chain merkle root");
+    }
+    else
+    {
+        // For backward compatibility.
+        // Enforce only one chain merkle root by checking that it starts early in the coinbase.
+        // 8-12 bytes are enough to encode extraNonce and nBits.
+        if (pc - script.begin() > 20)
+            return error("Aux POW chain merkle root must start in the first 20 bytes of the parent coinbase");
+    }
+
+
+    // Ensure we are at a deterministic point in the merkle leaves by hashing
+    // a nonce and our chain ID and comparing to the index.
+    pc += vchRootHash.size();
+    if (script.end() - pc < 8)
+        return error("Aux POW missing chain merkle tree size and nonce in parent coinbase");
+
+    uint32_t nSize;
+    memcpy(&nSize, &pc[0], 4);
+    nSize = le32toh (nSize);
+    const unsigned merkleHeight = vChainMerkleBranch.size ();
+    if (nSize != (1u << merkleHeight))
+        return error("Aux POW merkle branch size does not match parent coinbase");
+
+    uint32_t nNonce;
+    memcpy(&nNonce, &pc[4], 4);
+    nNonce = le32toh (nNonce);
+    if (nChainIndex != getExpectedIndex (nNonce, nChainId, merkleHeight))
+        return error("Aux POW wrong index");
+
+    return true;
+}
+
+int
+CAuxPow::getExpectedIndex (uint32_t nNonce, int nChainId, unsigned h)
+{
+  // Choose a pseudo-random slot in the chain merkle tree
+  // but have it be fixed for a size/nonce/chain combination.
+  //
+  // This prevents the same work from being used twice for the
+  // same chain while reducing the chance that two chains clash
+  // for the same slot.
+
+  /* This computation can overflow the uint32 used.  This is not an issue,
+     though, since we take the mod against a power-of-two in the end anyway.
+     This also ensures that the computation is, actually, consistent
+     even if done in 64 bits as it was in the past on some systems.
+
+     Note that h is always <= 30 (enforced by the maximum allowed chain
+     merkle branch length), so that 32 bits are enough for the computation.  */
+
+  uint32_t rand = nNonce;
+  rand = rand * 1103515245 + 12345;
+  rand += nChainId;
+  rand = rand * 1103515245 + 12345;
+
+  return rand % (1u << h);
+}
+
+uint256
+CAuxPow::CheckMerkleBranch (uint256 hash,
+                            const std::vector<uint256>& vMerkleBranch,
+                            int nIndex)
+{
+  if (nIndex == -1)
+    return uint256 ();
+  for (std::vector<uint256>::const_iterator it(vMerkleBranch.begin ());
+       it != vMerkleBranch.end (); ++it)
+  {
+    if (nIndex & 1)
+      hash = Hash (BEGIN (*it), END (*it), BEGIN (hash), END (hash));
+    else
+      hash = Hash (BEGIN (hash), END (hash), BEGIN (*it), END (*it));
+    nIndex >>= 1;
+  }
+  return hash;
+}
+
+std::unique_ptr<CAuxPow>
+CAuxPow::createAuxPow (const CPureBlockHeader& header)
+{
+  assert (header.IsAuxpow ());
+
+  /* Build a minimal coinbase script input for merge-mining.  */
+  const uint256 blockHash = header.GetHash ();
+  std::vector<unsigned char> inputData(blockHash.begin (), blockHash.end ());
+  std::reverse (inputData.begin (), inputData.end ());
+  inputData.push_back (1);
+  inputData.insert (inputData.end (), 7, 0);
+
+  /* Fake a parent-block coinbase with just the required input
+     script and no outputs.  */
+  CMutableTransaction coinbase;
+  coinbase.vin.resize (1);
+  coinbase.vin[0].prevout.SetNull ();
+  coinbase.vin[0].scriptSig = (CScript () << inputData);
+  assert (coinbase.vout.empty ());
+  CTransactionRef coinbaseRef = MakeTransactionRef (coinbase);
+
+  /* Build a fake parent block with the coinbase.  */
+  CBlock parent;
+  parent.nVersion = 1;
+  parent.vtx.resize (1);
+  parent.vtx[0] = coinbaseRef;
+  parent.hashMerkleRoot = BlockMerkleRoot (parent);
+
+  /* Construct the auxpow object.  */
+  std::unique_ptr<CAuxPow> auxpow(new CAuxPow (coinbaseRef));
+  assert (auxpow->vChainMerkleBranch.empty ());
+  auxpow->nChainIndex = 0;
+  assert (auxpow->coinbaseTx.vMerkleBranch.empty ());
+  auxpow->coinbaseTx.nIndex = 0;
+  auxpow->parentBlock = parent;
+
+  return auxpow;
+}
+
+CPureBlockHeader&
+CAuxPow::initAuxPow (CBlockHeader& header)
+{
+  /* Set auxpow flag right now, since we take the block hash below when creating
+     the minimal auxpow for header.  */
+  header.SetAuxpowFlag(true);
+
+  std::unique_ptr<CAuxPow> apow = createAuxPow (header);
+  CPureBlockHeader& result = apow->parentBlock;
+  header.SetAuxpow (std::move (apow));
+
+  return result;
+}