////Option 2 : Spender knows my private key
BitcoinSecret secret = new BitcoinSecret("...", Network.Mainnet);
var sig = spending.SignInput(secret, scriptCoin);
var p2pkhProof = PayToPubkeyHashTemplate
.GenerateScriptSig(sig, secret.PrivateKey.PubKey);
selectIf = OpcodeType.OP_0; //go to else
scriptSig = p2pkhProof + selectIf + redeemBytes;
spending.Inputs[0].ScriptSig = scriptSig;