bool BankTool::isCoinDoubleSpent(const Coin &coin1, const Coin &coin2) const {
// throw an exception if these coins do not share the same S value
if(coin1.getSPrime() != coin2.getSPrime())
{
throw CashException(CashException::CE_UNKNOWN_ERROR,
"[BankTool::checkIfCoinDoubleSpent] Coins do not share same serial "
"coin point and are not valid candidates for checking double "
"spending.");
}
// if contract hashes are same, then both coins were spent in the same
// transaction so the coin was not double spent
return (coin1.getR() != coin2.getR());
}
ZZ BankTool::identifyDoubleSpender(const Coin& coin1, const ZZ &tPrime2,
const ZZ& rValue2) const {
// Should probably check that the R values are different
ZZ mod = coin1.getCashGroup()->getModulus();
ZZ order = coin1.getCashGroup()->getOrder();
ZZ t1 = coin1.getTPrime();
ZZ t2 = tPrime2;
ZZ r1 = coin1.getR();
ZZ r2 = rValue2;
if (r2 > r1) {
NTL::swap(r2, r1);
NTL::swap(t2, t1);
}
ZZ exp = InvMod(r1 - r2, order);
ZZ num = PowerMod(t2, r1, mod);
ZZ denom = InvMod(PowerMod(t1, r2, mod), mod);
ZZ base = MulMod(num, denom, mod);
ZZ publicKeyUser = PowerMod(base, exp, mod);
return publicKeyUser;
}
ZZ BankTool::identifyDoubleSpender(const Coin& coin1, const Coin& coin2) const {
return identifyDoubleSpender(coin1, coin2.getTPrime(), coin2.getR());
}
