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Further DoS prevention: Verify signatures last

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Loop over all inputs doing inexpensive validity checks first,
and then loop over them a second time doing expensive signature
checks. This helps prevent possible CPU exhaustion attacks
where an attacker tries to make a victim waste time checking
signatures for invalid transactions.
This commit is contained in:
Gavin Andresen 2012-05-16 11:26:56 -04:00
parent 7a15109c04
commit 4add41a2a6
1 changed files with 16 additions and 5 deletions
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21
src/main.cpp
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@ -1142,17 +1142,28 @@ bool CTransaction::ConnectInputs(MapPrevTx inputs,
if (pindex->nBlockPos == txindex.pos.nBlockPos && pindex->nFile == txindex.pos.nFile)
return error("ConnectInputs() : tried to spend coinbase at depth %d", pindexBlock->nHeight - pindex->nHeight);
// Check for negative or overflow input values
nValueIn += txPrev.vout[prevout.n].nValue;
if (!MoneyRange(txPrev.vout[prevout.n].nValue) || !MoneyRange(nValueIn))
return DoS(100, error("ConnectInputs() : txin values out of range"));
}
// The first loop above does all the inexpensive checks.
// Only if ALL inputs pass do we perform expensive ECDSA signature checks.
// Helps prevent CPU exhaustion attacks.
for (unsigned int i = 0; i < vin.size(); i++)
{
COutPoint prevout = vin[i].prevout;
assert(inputs.count(prevout.hash) > 0);
CTxIndex& txindex = inputs[prevout.hash].first;
CTransaction& txPrev = inputs[prevout.hash].second;
// Check for conflicts (double-spend)
// This doesn't trigger the DoS code on purpose; if it did, it would make it easier
// for an attacker to attempt to split the network.
if (!txindex.vSpent[prevout.n].IsNull())
return fMiner ? false : error("ConnectInputs() : %s prev tx already used at %s", GetHash().ToString().substr(0,10).c_str(), txindex.vSpent[prevout.n].ToString().c_str());
// Check for negative or overflow input values
nValueIn += txPrev.vout[prevout.n].nValue;
if (!MoneyRange(txPrev.vout[prevout.n].nValue) || !MoneyRange(nValueIn))
return DoS(100, error("ConnectInputs() : txin values out of range"));
// Skip ECDSA signature verification when connecting blocks (fBlock=true)
// before the last blockchain checkpoint. This is safe because block merkle hashes are
// still computed and checked, and any change will be caught at the next checkpoint.