void cpSign(const vlPoint vlPrivateKey, const vlPoint k, const vlPoint vlMac, cpPair * sig) {
ecPoint q;
vlPoint tmp;
ecCopy(&q, &curve_point);
ecMultiply(&q, k);
gfPack(q.x, sig->r);
vlAdd(sig->r, vlMac);
vlRemainder(sig->r, prime_order);
if (sig->r[0] == 0) return;
vlMulMod(tmp, vlPrivateKey, sig->r, prime_order);
vlCopy(sig->s, k);
if (vlGreater(tmp, sig->s)) vlAdd(sig->s, prime_order);
vlSubtract(sig->s, tmp);
} /* cpSign */
int cpVerify(const vlPoint vlPublicKey, const vlPoint vlMac, cpPair * sig) {
ecPoint t1, t2;
vlPoint t3, t4;
ecCopy(&t1, &curve_point);
ecMultiply(&t1, sig->s);
ecUnpack(&t2, vlPublicKey);
ecMultiply(&t2, sig->r);
ecAdd(&t1, &t2);
gfPack(t1.x, t4);
vlRemainder(t4, prime_order);
vlCopy(t3, sig->r);
if (vlGreater(t4, t3)) vlAdd(t3, prime_order);
vlSubtract(t3, t4);
return vlEqual(t3, vlMac);
} /* cpVerify */
void ecUnpack (ecPoint *p, const vlPoint k)
/* unpacks a vlPoint into a curve point */
{
int yb;
vlPoint a;
vlCopy (a, k);
yb = a[0] ? a[1] & 1 : 0;
vlShortRshift (a, 1);
gfUnpack (p->x, a);
if (p->x[0] || yb) {
ecCalcY (p, yb);
} else {
p->y[0] = 0;
}
} /* ecUnpack */
