Example #1
0
void XTR_FindPrimesAndGenerator(RandomNumberGenerator &rng, Integer &p, Integer &q, GFP2Element &g, unsigned int pbits, unsigned int qbits)
{
	assert(qbits > 9);	// no primes exist for pbits = 10, qbits = 9
	assert(pbits > qbits);

	const Integer minQ = Integer::Power2(qbits - 1);
	const Integer maxQ = Integer::Power2(qbits) - 1;
	const Integer minP = Integer::Power2(pbits - 1);
	const Integer maxP = Integer::Power2(pbits) - 1;

	Integer r1, r2;
	do
	{
		bool qFound = q.Randomize(rng, minQ, maxQ, Integer::PRIME, 7, 12);
		assert(qFound);
		bool solutionsExist = SolveModularQuadraticEquation(r1, r2, 1, -1, 1, q);
		assert(solutionsExist);
	} while (!p.Randomize(rng, minP, maxP, Integer::PRIME, CRT(rng.GetBit()?r1:r2, q, 2, 3), 3*q));
	assert(((p.Squared() - p + 1) % q).IsZero());

	GFP2_ONB<ModularArithmetic> gfp2(p);
	GFP2Element three = gfp2.ConvertIn(3), t;

	while (true)
	{
		g.c1.Randomize(rng, Integer::Zero(), p-1);
		g.c2.Randomize(rng, Integer::Zero(), p-1);
		t = XTR_Exponentiate(g, p+1, p);
		if (t.c1 == t.c2)
			continue;
		g = XTR_Exponentiate(g, (p.Squared()-p+1)/q, p);
		if (g != three)
			break;
	}
	assert(XTR_Exponentiate(g, q, p) == three);
}