You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
106 lines
2.4 KiB
106 lines
2.4 KiB
#include "ge.h"
|
|
#include "crypto_uint32.h"
|
|
|
|
static unsigned char equal(signed char b,signed char c)
|
|
{
|
|
unsigned char ub = b;
|
|
unsigned char uc = c;
|
|
unsigned char x = ub ^ uc; /* 0: yes; 1..255: no */
|
|
crypto_uint32 y = x; /* 0: yes; 1..255: no */
|
|
y -= 1; /* 4294967295: yes; 0..254: no */
|
|
y >>= 31; /* 1: yes; 0: no */
|
|
return y;
|
|
}
|
|
|
|
static unsigned char negative(signed char b)
|
|
{
|
|
unsigned long long x = b; /* 18446744073709551361..18446744073709551615: yes; 0..255: no */
|
|
x >>= 63; /* 1: yes; 0: no */
|
|
return x;
|
|
}
|
|
|
|
static void cmov(ge_precomp *t,ge_precomp *u,unsigned char b)
|
|
{
|
|
fe_cmov(t->yplusx,u->yplusx,b);
|
|
fe_cmov(t->yminusx,u->yminusx,b);
|
|
fe_cmov(t->xy2d,u->xy2d,b);
|
|
}
|
|
|
|
/* base[i][j] = (j+1)*256^i*B */
|
|
static ge_precomp base[32][8] = {
|
|
#include "base.h"
|
|
} ;
|
|
|
|
static void select(ge_precomp *t,int pos,signed char b)
|
|
{
|
|
ge_precomp minust;
|
|
unsigned char bnegative = negative(b);
|
|
unsigned char babs = b - (((-bnegative) & b) << 1);
|
|
|
|
ge_precomp_0(t);
|
|
cmov(t,&base[pos][0],equal(babs,1));
|
|
cmov(t,&base[pos][1],equal(babs,2));
|
|
cmov(t,&base[pos][2],equal(babs,3));
|
|
cmov(t,&base[pos][3],equal(babs,4));
|
|
cmov(t,&base[pos][4],equal(babs,5));
|
|
cmov(t,&base[pos][5],equal(babs,6));
|
|
cmov(t,&base[pos][6],equal(babs,7));
|
|
cmov(t,&base[pos][7],equal(babs,8));
|
|
fe_copy(minust.yplusx,t->yminusx);
|
|
fe_copy(minust.yminusx,t->yplusx);
|
|
fe_neg(minust.xy2d,t->xy2d);
|
|
cmov(t,&minust,bnegative);
|
|
}
|
|
|
|
/*
|
|
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
|
|
*/
|
|
|
|
void ge_scalarmult_base(ge_p3 *h,const unsigned char *a)
|
|
{
|
|
signed char e[64];
|
|
signed char carry;
|
|
ge_p1p1 r;
|
|
ge_p2 s;
|
|
ge_precomp t;
|
|
int i;
|
|
|
|
for (i = 0;i < 32;++i) {
|
|
e[2 * i + 0] = (a[i] >> 0) & 15;
|
|
e[2 * i + 1] = (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 = e[i] + 8;
|
|
carry >>= 4;
|
|
e[i] -= carry << 4;
|
|
}
|
|
e[63] += carry;
|
|
/* each e[i] is between -8 and 8 */
|
|
|
|
ge_p3_0(h);
|
|
for (i = 1;i < 64;i += 2) {
|
|
select(&t,i / 2,e[i]);
|
|
ge_madd(&r,h,&t); ge_p1p1_to_p3(h,&r);
|
|
}
|
|
|
|
ge_p3_dbl(&r,h); ge_p1p1_to_p2(&s,&r);
|
|
ge_p2_dbl(&r,&s); ge_p1p1_to_p2(&s,&r);
|
|
ge_p2_dbl(&r,&s); ge_p1p1_to_p2(&s,&r);
|
|
ge_p2_dbl(&r,&s); ge_p1p1_to_p3(h,&r);
|
|
|
|
for (i = 0;i < 64;i += 2) {
|
|
select(&t,i / 2,e[i]);
|
|
ge_madd(&r,h,&t); ge_p1p1_to_p3(h,&r);
|
|
}
|
|
}
|