ref: a7a315bff61bff58a9c918294f53c1e87d7ae7bb
dir: /sys/src/libsec/port/curve25519_dh.c/
#include "os.h"
#include <mp.h>
#include <libsec.h>
static uchar nine[32] = {9};
static uchar zero[32] = {0};
void
curve25519_dh_new(uchar x[32], uchar y[32])
{
uchar b;
/* new public/private key pair */
genrandom(x, 32);
b = x[31];
x[0] &= ~7; /* clear bit 0,1,2 */
x[31] = 0x40 | (b & 0x7f); /* set bit 254, clear bit 255 */
curve25519(y, x, nine);
/* bit 255 is always 0, so make it random */
y[31] |= b & 0x80;
}
int
curve25519_dh_finish(uchar x[32], uchar y[32], uchar z[32])
{
/* remove the random bit */
y[31] &= 0x7f;
/* calculate dhx key */
curve25519(z, x, y);
memset(x, 0, 32);
memset(y, 0, 32);
return tsmemcmp(z, zero, 32) != 0;
}