/// <summary>
/// Generation of SignatureHash. This method is responsible for removal of transaction metadata. It's necessary signature can't sign itself.
/// </summary>
/// <param name="script">Spending instructions</param>
/// <param name="txTo">Instance of transaction</param>
/// <param name="nIn">Input number</param>
/// <param name="nHashType">Hash type flag</param>
/// <returns></returns>
public static uint256 SignatureHash(CScript script, CTransaction txTo, int nIn, int nHashType)
{
Contract.Requires<ArgumentOutOfRangeException>(nIn < txTo.vin.Length, "nIn out of range.");
// Init a copy of transaction
var txTmp = new CTransaction(txTo);
// In case concatenating two scripts ends up with two codeseparators,
// or an extra one at the end, this prevents all those possible incompatibilities.
script.RemoveInstruction(instruction.OP_CODESEPARATOR);
// Blank out other inputs' signatures
for (int i = 0; i < txTmp.vin.Length; i++)
{
txTmp.vin[i].scriptSig = new CScript();
}
txTmp.vin[nIn].scriptSig = script;
// Blank out some of the outputs
if ((nHashType & 0x1f) == (int)sigflag.SIGHASH_NONE)
{
// Wildcard payee
txTmp.vout = new CTxOut[0];
// Let the others update at will
for (int i = 0; i < txTmp.vin.Length; i++)
{
if (i != nIn)
{
txTmp.vin[i].nSequence = 0;
}
}
}
else if ((nHashType & 0x1f) == (int)sigflag.SIGHASH_SINGLE)
{
// Only lock-in the txout payee at same index as txin
int nOut = nIn;
if (nOut >= txTmp.vout.Length)
{
StringBuilder sb = new StringBuilder();
sb.AppendFormat("ERROR: SignatureHash() : nOut={0} out of range\n", nOut);
throw new ArgumentOutOfRangeException("nOut", sb.ToString());
}
Array.Resize(ref txTmp.vout, nOut + 1);
for (int i = 0; i < nOut; i++)
{
txTmp.vout[i] = new CTxOut();
}
// Let the others update at will
for (int i = 0; i < txTmp.vin.Length; i++)
{
if (i != nIn)
{
txTmp.vin[i].nSequence = 0;
}
}
}
// Blank out other inputs completely, not recommended for open transactions
if ((nHashType & (int)sigflag.SIGHASH_ANYONECANPAY) != 0)
{
txTmp.vin[0] = txTmp.vin[nIn];
Array.Resize(ref txTmp.vin, 1);
}
// Concatenate and hash
var txBytes = (byte[])txTmp;
var nHashTypeBytes = BitConverter.GetBytes(nHashType);
return CryptoUtils.ComputeHash256(ref txBytes, ref nHashTypeBytes);
}
