### view src/jdk.crypto.ec/share/native/libsunec/impl/ec_naf.c @ 17286:65464a307408

Added tag jdk-9+181 for changeset bd66ea2fdde3
author prr Thu, 03 Aug 2017 18:56:59 +0000 b49a0af85821
line wrap: on
line source
```/*
* Use is subject to license terms.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*
* or visit www.oracle.com if you need additional information or have any
* questions.
*/

/* *********************************************************************
*
* The Original Code is the elliptic curve math library.
*
* The Initial Developer of the Original Code is
* Sun Microsystems, Inc.
* Portions created by the Initial Developer are Copyright (C) 2003
*
* Contributor(s):
*   Stephen Fung <fungstep@hotmail.com>, Sun Microsystems Laboratories
*
*********************************************************************** */

#include "ecl-priv.h"

/* Returns 2^e as an integer. This is meant to be used for small powers of
* two. */
int
ec_twoTo(int e)
{
int a = 1;
int i;

for (i = 0; i < e; i++) {
a *= 2;
}
return a;
}

/* Computes the windowed non-adjacent-form (NAF) of a scalar. Out should
* be an array of signed char's to output to, bitsize should be the number
* of bits of out, in is the original scalar, and w is the window size.
* NAF is discussed in the paper: D. Hankerson, J. Hernandez and A.
* Menezes, "Software implementation of elliptic curve cryptography over
* binary fields", Proc. CHES 2000. */
mp_err
ec_compute_wNAF(signed char *out, int bitsize, const mp_int *in, int w)
{
mp_int k;
mp_err res = MP_OKAY;

twowm1 = ec_twoTo(w - 1);
mask = 2 * twowm1 - 1;

MP_DIGITS(&k) = 0;
MP_CHECKOK(mp_init_copy(&k, in));

i = 0;
/* Compute wNAF form */
while (mp_cmp_z(&k) > 0) {
if (mp_isodd(&k)) {
out[i] = MP_DIGIT(&k, 0) & mask;
if (out[i] >= twowm1)
out[i] -= 2 * twowm1;

/* Subtract off out[i].  Note mp_sub_d only works with
* unsigned digits */
if (out[i] >= 0) {
mp_sub_d(&k, out[i], &k);
} else {
}
} else {
out[i] = 0;
}
mp_div_2(&k, &k);
i++;
}
/* Zero out the remaining elements of the out array. */
for (; i < bitsize + 1; i++) {
out[i] = 0;
}
CLEANUP:
mp_clear(&k);
return res;

}```