/* this =this^e mod p using side-channel resistant Montgomery Ladder, for short e */
public void skpow(BIG e, FF p)
{
int i, b, n = p.length;
FF R0 = new FF(n);
FF R1 = new FF(n);
FF ND = p.invmod2m();
mod(p);
R0.one();
R1.copy(this);
R0.nres(p);
R1.nres(p);
for (i = 8 * ROM.MODBYTES - 1; i >= 0; i--)
{
b = e.bit(i);
copy(R0);
modmul(R1, p, ND);
cswap(R0, R1, b);
R0.modsqr(p, ND);
R1.copy(this);
cswap(R0, R1, b);
}
copy(R0);
redc(p, ND);
}
/* double exponentiation r=x^e.y^f mod p */
public void pow2(BIG e, FF y, BIG f, FF p)
{
int i, eb, fb, n = p.length;
FF xn = new FF(n);
FF yn = new FF(n);
FF xy = new FF(n);
FF ND = p.invmod2m();
xn.copy(this);
yn.copy(y);
xn.nres(p);
yn.nres(p);
xy.copy(xn);
xy.modmul(yn, p, ND);
one();
nres(p);
for (i = 8 * ROM.MODBYTES - 1; i >= 0; i--)
{
eb = e.bit(i);
fb = f.bit(i);
modsqr(p, ND);
if (eb == 1)
{
if (fb == 1)
{
modmul(xy, p, ND);
}
else
{
modmul(xn, p, ND);
}
}
else
{
if (fb == 1)
{
modmul(yn, p, ND);
}
}
}
redc(p, ND);
}
/* raise to an integer power - right-to-left method */
public void power(int e, FF p)
{
int n = p.length;
FF w = new FF(n);
FF ND = p.invmod2m();
bool f = true;
w.copy(this);
w.nres(p);
if (e == 2)
{
copy(w);
modsqr(p, ND);
}
else
{
for (; ;)
{
if (e % 2 == 1)
{
if (f)
{
copy(w);
}
else
{
modmul(w, p, ND);
}
f = false;
}
e >>= 1;
if (e == 0)
{
break;
}
w.modsqr(p, ND);
}
}
redc(p, ND);
}
/* this=this^e mod p, faster but not side channel resistant */
public void pow(FF e, FF p)
{
int i, b, n = p.length;
FF w = new FF(n);
FF ND = p.invmod2m();
w.copy(this);
one();
nres(p);
w.nres(p);
for (i = 8 * ROM.MODBYTES * n - 1; i >= 0; i--)
{
modsqr(p, ND);
b = e.v[i / 256].bit(i % 256);
if (b == 1)
{
modmul(w, p, ND);
}
}
redc(p, ND);
}
