bool ElGamal::BogusVerify(const BigInteger &M, const BigInteger &a, const BigInteger &b) const
{
// check a != 0 && a == (g^b * y^a + m) mod q
try
{
if(a.cmp(BigInteger::ZERO)==0)
return false;
// BigInteger a1 = a.mod(q);
// BigInteger b1 = b.mod(q);
BigInteger gbq = g.modExp(b,p,recip,nb);
BigInteger yaq = y.modExp(a,p,recip,nb);
/*
cout << "p = " << p << endl;
cout << "g = mod(" << g << ",p)" << endl;
cout << "a = " << a << endl;
cout << "b = " << b << endl;
cout << "y = " << y << endl;
cout << "gbq = " << gbq << endl;
cout << "yaq = " << yaq << endl;*/
BigInteger result;
result = gbq.modMulRecip(yaq,p,recip,nb);
// result = gbq.mul(yaq);
result = result.add(M);
// result = result.mod(p);
result = result.mod(q);
if(a.cmp(result)==0)
return true;
else
return false;
}
catch(ArithmeticException &)
{
}
return false;
}
BigInteger ElGamal::GetRandBetween(Random &rng, const BigInteger &min, const BigInteger &max)
{
BigInteger range = max.sub(min);
int nBits = range.bitLength();
BigInteger anInt;
do
{
anInt = BigInteger(nBits,rng);
}
while (anInt.cmp(range)>0);
anInt = anInt.add(min);
return anInt;
}
