/*
* mpbrndodd_w
* generates a random odd number in the range 1 < r < b-1
* needs workspace of (size) words
*/
void mpbrndodd_w(const mpbarrett* b, randomGeneratorContext* rc, mpw* result, mpw* wksp)
{
size_t msz = mpmszcnt(b->size, b->modl);
mpcopy(b->size, wksp, b->modl);
mpsubw(b->size, wksp, 1);
do
{
rc->rng->next(rc->param, (byte*) result, MP_WORDS_TO_BYTES(b->size));
result[0] &= (MP_ALLMASK >> msz);
mpsetlsb(b->size, result);
while (mpge(b->size, result, wksp))
{
mpsub(b->size, result, wksp);
mpsetlsb(b->size, result);
}
} while (mpleone(b->size, result));
}
/*
* needs workspace of (8*size+2) words
*/
void mpprndconone_w(mpbarrett* p, randomGeneratorContext* rc, size_t bits, int t, const mpbarrett* q, const mpnumber* f, mpnumber* r, int cofactor, mpw* wksp)
{
/*
* Generate a prime p with n bits such that p mod q = 1, and p = qr+1 where r = 2s
*
* Conditions: q > 2 and size(q) < size(p) and size(f) <= size(p)
*
* Conditions: r must be chosen so that r is even, otherwise p will be even!
*
* if cofactor == 0, then s will be chosen randomly
* if cofactor == 1, then make sure that q does not divide r, i.e.:
* q cannot be equal to r, since r is even, and q > 2; hence if q <= r make sure that GCD(q,r) == 1
* if cofactor == 2, then make sure that s is prime
*
* Optional input f: if f is not null, then search p so that GCD(p-1,f) = 1
*/
mpbinit(p, MP_BITS_TO_WORDS(bits + MP_WBITS - 1));
if (p->modl != (mpw*) 0)
{
size_t sbits = bits - mpbits(q->size, q->modl) - 1;
mpbarrett s;
mpbzero(&s);
mpbinit(&s, MP_BITS_TO_WORDS(sbits + MP_WBITS - 1));
while (1)
{
mpprndbits(&s, sbits, 0, (mpnumber*) 0, (mpnumber*) 0, rc, wksp);
if (cofactor == 1)
{
mpsetlsb(s.size, s.modl);
/* if (q <= s) check if GCD(q,s) != 1 */
if (mplex(q->size, q->modl, s.size, s.modl))
{
/* we can find adequate storage for computing the gcd in s->wksp */
mpsetx(s.size, wksp, q->size, q->modl);
mpgcd_w(s.size, s.modl, wksp, wksp+s.size, wksp+2*s.size);
if (!mpisone(s.size, wksp+s.size))
continue;
}
}
else if (cofactor == 2)
{
mpsetlsb(s.size, s.modl);
}
if (cofactor == 2)
{
/* do a small prime product trial division test on r */
if (!mppsppdiv_w(&s, wksp))
continue;
}
/* multiply q*s */
mpmul(wksp, s.size, s.modl, q->size, q->modl);
/* s.size + q.size may be greater than p.size by 1, but the product will fit exactly into p */
mpsetx(p->size, p->modl, s.size+q->size, wksp);
/* multiply by two and add 1 */
mpmultwo(p->size, p->modl);
mpaddw(p->size, p->modl, 1);
/* test if the product actually contains enough bits */
if (mpbits(p->size, p->modl) < bits)
continue;
/* do a small prime product trial division test on p */
if (!mppsppdiv_w(p, wksp))
continue;
/* if we have an f, do the congruence test */
if (f != (mpnumber*) 0)
{
mpcopy(p->size, wksp, p->modl);
mpsubw(p->size, wksp, 1);
mpsetx(p->size, wksp, f->size, f->data);
mpgcd_w(p->size, wksp, wksp+p->size, wksp+2*p->size, wksp+3*p->size);
if (!mpisone(p->size, wksp+2*p->size))
continue;
}
/* if cofactor is two, test if s is prime */
if (cofactor == 2)
{
mpbmu_w(&s, wksp);
if (!mppmilrab_w(&s, rc, mpptrials(sbits), wksp))
continue;
}
/* candidate has passed so far, now we do the probabilistic test on p */
mpbmu_w(p, wksp);
if (!mppmilrab_w(p, rc, t, wksp))
continue;
mpnset(r, s.size, s.modl);
mpmultwo(r->size, r->data);
mpbfree(&s);
return;
}
}
}
