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// xtr.cpp - originally written and placed in the public domain by Wei Dai
#include "pch.h"
#include "xtr.h"
#include "nbtheory.h"
#include "integer.h"
#include "algebra.h"
#include "modarith.h"
#include "algebra.cpp"
NAMESPACE_BEGIN(CryptoPP)
const GFP2Element & GFP2Element::Zero()
{
#if defined(CRYPTOPP_CXX11_STATIC_INIT)
static const GFP2Element s_zero;
return s_zero;
#else
return Singleton<GFP2Element>().Ref();
#endif
}
void XTR_FindPrimesAndGenerator(RandomNumberGenerator &rng, Integer &p, Integer &q, GFP2Element &g, unsigned int pbits, unsigned int qbits)
{
CRYPTOPP_ASSERT(qbits > 9); // no primes exist for pbits = 10, qbits = 9
CRYPTOPP_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;
top:
Integer r1, r2;
do
{
(void)q.Randomize(rng, minQ, maxQ, Integer::PRIME, 7, 12);
// Solution always exists because q === 7 mod 12.
(void)SolveModularQuadraticEquation(r1, r2, 1, -1, 1, q);
// I believe k_i, r1 and r2 are being used slightly different than the
// paper's algorithm. I believe it is leading to the failed asserts.
// Just make the assert part of the condition.
if(!p.Randomize(rng, minP, maxP, Integer::PRIME, CRT(rng.GenerateBit() ?
r1 : r2, q, 2, 3, EuclideanMultiplicativeInverse(p, 3)), 3 * q)) { continue; }
} while (((p % 3U) != 2) || (((p.Squared() - p + 1) % q).NotZero()));
// CRYPTOPP_ASSERT((p % 3U) == 2);
// CRYPTOPP_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;
}
if (XTR_Exponentiate(g, q, p) != three)
goto top;
// CRYPTOPP_ASSERT(XTR_Exponentiate(g, q, p) == three);
}
GFP2Element XTR_Exponentiate(const GFP2Element &b, const Integer &e, const Integer &p)
{
unsigned int bitCount = e.BitCount();
if (bitCount == 0)
return GFP2Element(-3, -3);
// find the lowest bit of e that is 1
unsigned int lowest1bit;
for (lowest1bit=0; e.GetBit(lowest1bit) == 0; lowest1bit++) {}
GFP2_ONB<MontgomeryRepresentation> gfp2(p);
GFP2Element c = gfp2.ConvertIn(b);
GFP2Element cp = gfp2.PthPower(c);
GFP2Element S[5] = {gfp2.ConvertIn(3), c, gfp2.SpecialOperation1(c)};
// do all exponents bits except the lowest zeros starting from the top
unsigned int i;
for (i = e.BitCount() - 1; i>lowest1bit; i--)
{
if (e.GetBit(i))
{
gfp2.RaiseToPthPower(S[0]);
gfp2.Accumulate(S[0], gfp2.SpecialOperation2(S[2], c, S[1]));
S[1] = gfp2.SpecialOperation1(S[1]);
S[2] = gfp2.SpecialOperation1(S[2]);
S[0].swap(S[1]);
}
else
{
gfp2.RaiseToPthPower(S[2]);
gfp2.Accumulate(S[2], gfp2.SpecialOperation2(S[0], cp, S[1]));
S[1] = gfp2.SpecialOperation1(S[1]);
S[0] = gfp2.SpecialOperation1(S[0]);
S[2].swap(S[1]);
}
}
// now do the lowest zeros
while (i--)
S[1] = gfp2.SpecialOperation1(S[1]);
return gfp2.ConvertOut(S[1]);
}
template class AbstractRing<GFP2Element>;
template class AbstractGroup<GFP2Element>;
NAMESPACE_END
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