/*
* h = a * B
* where a = a[0]+256*a[1]+...+256^31 a[31]
* B is the Ed25519 base point (x,4/5) with x positive.
*
* Preconditions:
* a[31] <= 127
*/
public static void ge_scalarmult(Ge_p3 h, byte[] a, Ge_p3 A)
{
byte[] e = new byte[64];
byte carry;
Ge_p1p1 r = new Ge_p1p1();
Ge_p2 s = new Ge_p2();
Ge_p3 t0 = new Ge_p3();
Ge_p3 t1 = new Ge_p3();
Ge_p3 t2 = new Ge_p3();
Ge_cached t = new Ge_cached();
Ge_cached[] pre = new Ge_cached[8];
for (int count = 0; count < pre.Length; count++)
{
pre[count] = new Ge_cached();
}
int i;
for (i = 0; i < 32; ++i)
{
e[2 * i + 0] = (byte)((((uint)a[i]) >> 0) & 15);
e[2 * i + 1] = (byte)((((uint)a[i]) >> 4) & 15);
}
/* each e[i] is between 0 and 15 */
/* e[63] is between 0 and 7 */
carry = 0;
for (i = 0; i < 63; ++i)
{
e[i] += carry;
carry = (byte)(e[i] + 8);
carry >>= 4;
e[i] -= (byte)(carry << 4);
}
e[63] += carry;
/* each e[i] is between -8 and 8 */
// Precomputation:
Ge_p3_to_cached.ge_p3_to_cached(pre[0], A); // A
Ge_p3_dbl.ge_p3_dbl(r, A);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t0, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[1], t0); // 2A
Ge_add.ge_add(r, A, pre[1]);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t1, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[2], t1); // 3A
Ge_p3_dbl.ge_p3_dbl(r, t0);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t0, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[3], t0); // 4A
Ge_add.ge_add(r, A, pre[3]);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t2, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[4], t2); // 5A
Ge_p3_dbl.ge_p3_dbl(r, t1);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t1, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[5], t1); // 6A
Ge_add.ge_add(r, A, pre[5]);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t1, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[6], t1); // 7A
Ge_p3_dbl.ge_p3_dbl(r, t0);
Ge_p1p1_to_p3.ge_p1p1_to_p3(t0, r);
Ge_p3_to_cached.ge_p3_to_cached(pre[7], t0); // 8A
Ge_p3_0.ge_p3_0(h);
for (i = 63; i > 0; i--)
{
select(t, pre, e[i]);
Ge_add.ge_add(r, h, t);
Ge_p1p1_to_p2.ge_p1p1_to_p2(s, r);
Ge_p2_dbl.ge_p2_dbl(r, s); Ge_p1p1_to_p2.ge_p1p1_to_p2(s, r);
Ge_p2_dbl.ge_p2_dbl(r, s); Ge_p1p1_to_p2.ge_p1p1_to_p2(s, r);
Ge_p2_dbl.ge_p2_dbl(r, s); Ge_p1p1_to_p2.ge_p1p1_to_p2(s, r);
Ge_p2_dbl.ge_p2_dbl(r, s); Ge_p1p1_to_p3.ge_p1p1_to_p3(h, r);
}
select(t, pre, e[0]);
Ge_add.ge_add(r, h, t);
Ge_p1p1_to_p3.ge_p1p1_to_p3(h, r);
}
/*
* r = a * A + b * B
* where a = a[0]+256*a[1]+...+256^31 a[31].
* and b = b[0]+256*b[1]+...+256^31 b[31].
* B is the Ed25519 base point (x,4/5) with x positive.
*/
public static void ge_double_scalarmult_vartime(Ge_p2 r, byte[] a, Ge_p3 A, byte[] b)
{
sbyte[] aslide = new sbyte[256];
sbyte[] bslide = new sbyte[256];
Ge_cached[] Ai = new Ge_cached[8]; /* A,3A,5A,7A,9A,11A,13A,15A */
for (int count = 0; count < 8; count++)
{
Ai[count] = new Ge_cached();
}
Ge_p1p1 t = new Ge_p1p1();
Ge_p3 u = new Ge_p3();
Ge_p3 A2 = new Ge_p3();
int i;
slide(aslide, a);
slide(bslide, b);
Ge_p3_to_cached.ge_p3_to_cached(Ai[0], A);
Ge_p3_dbl.ge_p3_dbl(t, A); Ge_p1p1_to_p3.ge_p1p1_to_p3(A2, t);
Ge_add.ge_add(t, A2, Ai[0]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[1], u);
Ge_add.ge_add(t, A2, Ai[1]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[2], u);
Ge_add.ge_add(t, A2, Ai[2]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[3], u);
Ge_add.ge_add(t, A2, Ai[3]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[4], u);
Ge_add.ge_add(t, A2, Ai[4]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[5], u);
Ge_add.ge_add(t, A2, Ai[5]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[6], u);
Ge_add.ge_add(t, A2, Ai[6]); Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t); Ge_p3_to_cached.ge_p3_to_cached(Ai[7], u);
Ge_p2_0.ge_p2_0(r);
for (i = 255; i >= 0; --i)
{
if (aslide[i] != 0 || bslide[i] != 0)
{
break;
}
}
for (; i >= 0; --i)
{
Ge_p2_dbl.ge_p2_dbl(t, r);
if (aslide[i] > 0)
{
Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t);
Ge_add.ge_add(t, u, Ai[aslide[i] / 2]);
}
else if (aslide[i] < 0)
{
Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t);
Ge_sub.ge_sub(t, u, Ai[(-aslide[i]) / 2]);
}
if (bslide[i] > 0)
{
Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t);
Ge_madd.ge_madd(t, u, Bi[bslide[i] / 2]);
}
else if (bslide[i] < 0)
{
Ge_p1p1_to_p3.ge_p1p1_to_p3(u, t);
Ge_msub.ge_msub(t, u, Bi[(-bslide[i]) / 2]);
}
Ge_p1p1_to_p2.ge_p1p1_to_p2(r, t);
}
}