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Do not allow overwriting unspent transactions (BIP 30)

Introduce the following network rule:
 * a block is not valid if it contains a transaction whose hash
   already exists in the block chain, unless all that transaction's
   outputs were already spent before said block.

Warning: this is effectively a network rule change, with potential
risk for forking the block chain. Leaving this unfixed carries the
same risk however, for attackers that can cause a reorganisation
in part of the network.

Thanks to Russell O'Connor and Ben Reeves.
Pieter Wuille 9 years ago
1 changed files with 24 additions and 2 deletions
  1. 24

+ 24
- 2
src/main.cpp View File

@@ -976,8 +976,10 @@ bool CTransaction::DisconnectInputs(CTxDB& txdb)

// Remove transaction from index
if (!txdb.EraseTxIndex(*this))
return error("DisconnectInputs() : EraseTxPos failed");
// This can fail if a duplicate of this transaction was in a chain that got
// reorganized away. This is only possible if this transaction was completely
// spent, so erasing it would be a no-op anway.

return true;
@@ -1256,6 +1258,26 @@ bool CBlock::ConnectBlock(CTxDB& txdb, CBlockIndex* pindex)
if (!CheckBlock())
return false;

// Do not allow blocks that contain transactions which 'overwrite' older transactions,
// unless those are already completely spent.
// If such overwrites are allowed, coinbases and transactions depending upon those
// can be duplicated to remove the ability to spend the first instance -- even after
// being sent to another address.
// See BIP30 and for more information.
// This logic is not necessary for memory pool transactions, as AcceptToMemoryPool
// already refuses previously-known transaction id's entirely.
// This rule applies to all blocks whose timestamp is after March 15, 2012, 0:00 UTC.
// On testnet it is enabled as of februari 20, 2012, 0:00 UTC.
if (pindex->nTime > 1331769600 || (fTestNet && pindex->nTime > 1329696000))
BOOST_FOREACH(CTransaction& tx, vtx)
CTxIndex txindexOld;
if (txdb.ReadTxIndex(tx.GetHash(), txindexOld))
BOOST_FOREACH(CDiskTxPos &pos, txindexOld.vSpent)
if (pos.IsNull())
return false;

// To avoid being on the short end of a block-chain split,
// don't do secondary validation of pay-to-script-hash transactions
// until blocks with timestamps after paytoscripthashtime (see init.cpp for default).