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annotate nss/lib/freebl/ecl/ec_naf.c @ 1:247cffdc9b89

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Add a pesodo config file for inlcude directories and library names
author Andre Heinecke <andre.heinecke@intevation.de>
date Mon, 28 Jul 2014 13:00:06 +0200
parents 1e5118fa0cb1
children
rev   line source
0
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1 /* This Source Code Form is subject to the terms of the Mozilla Public
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2 * License, v. 2.0. If a copy of the MPL was not distributed with this
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3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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4
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5 #include "ecl-priv.h"
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6
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7 /* Returns 2^e as an integer. This is meant to be used for small powers of
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8 * two. */
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9 int
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10 ec_twoTo(int e)
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11 {
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12 int a = 1;
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13 int i;
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14
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15 for (i = 0; i < e; i++) {
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16 a *= 2;
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17 }
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18 return a;
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19 }
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20
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21 /* Computes the windowed non-adjacent-form (NAF) of a scalar. Out should
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22 * be an array of signed char's to output to, bitsize should be the number
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23 * of bits of out, in is the original scalar, and w is the window size.
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24 * NAF is discussed in the paper: D. Hankerson, J. Hernandez and A.
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25 * Menezes, "Software implementation of elliptic curve cryptography over
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26 * binary fields", Proc. CHES 2000. */
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27 mp_err
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28 ec_compute_wNAF(signed char *out, int bitsize, const mp_int *in, int w)
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29 {
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30 mp_int k;
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31 mp_err res = MP_OKAY;
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32 int i, twowm1, mask;
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33
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34 twowm1 = ec_twoTo(w - 1);
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35 mask = 2 * twowm1 - 1;
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36
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37 MP_DIGITS(&k) = 0;
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38 MP_CHECKOK(mp_init_copy(&k, in));
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39
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40 i = 0;
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41 /* Compute wNAF form */
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42 while (mp_cmp_z(&k) > 0) {
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43 if (mp_isodd(&k)) {
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44 out[i] = MP_DIGIT(&k, 0) & mask;
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45 if (out[i] >= twowm1)
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46 out[i] -= 2 * twowm1;
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47
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48 /* Subtract off out[i]. Note mp_sub_d only works with
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49 * unsigned digits */
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50 if (out[i] >= 0) {
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51 mp_sub_d(&k, out[i], &k);
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52 } else {
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53 mp_add_d(&k, -(out[i]), &k);
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54 }
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55 } else {
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56 out[i] = 0;
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57 }
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58 mp_div_2(&k, &k);
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59 i++;
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60 }
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61 /* Zero out the remaining elements of the out array. */
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62 for (; i < bitsize + 1; i++) {
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63 out[i] = 0;
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64 }
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65 CLEANUP:
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66 mp_clear(&k);
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67 return res;
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68
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69 }
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