| /* ********************************************************************* |
| * |
| * Sun elects to have this file available under and governed by the |
| * Mozilla Public License Version 1.1 ("MPL") (see |
| * http://www.mozilla.org/MPL/ for full license text). For the avoidance |
| * of doubt and subject to the following, Sun also elects to allow |
| * licensees to use this file under the MPL, the GNU General Public |
| * License version 2 only or the Lesser General Public License version |
| * 2.1 only. Any references to the "GNU General Public License version 2 |
| * or later" or "GPL" in the following shall be construed to mean the |
| * GNU General Public License version 2 only. Any references to the "GNU |
| * Lesser General Public License version 2.1 or later" or "LGPL" in the |
| * following shall be construed to mean the GNU Lesser General Public |
| * License version 2.1 only. However, the following notice accompanied |
| * the original version of this file: |
| * |
| * Version: MPL 1.1/GPL 2.0/LGPL 2.1 |
| * |
| * The contents of this file are subject to the Mozilla Public License Version |
| * 1.1 (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * http://www.mozilla.org/MPL/ |
| * |
| * Software distributed under the License is distributed on an "AS IS" basis, |
| * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License |
| * for the specific language governing rights and limitations under the |
| * License. |
| * |
| * 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 |
| * the Initial Developer. All Rights Reserved. |
| * |
| * Contributor(s): |
| * Stephen Fung <fungstep@hotmail.com>, Sun Microsystems Laboratories |
| * |
| * Alternatively, the contents of this file may be used under the terms of |
| * either the GNU General Public License Version 2 or later (the "GPL"), or |
| * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"), |
| * in which case the provisions of the GPL or the LGPL are applicable instead |
| * of those above. If you wish to allow use of your version of this file only |
| * under the terms of either the GPL or the LGPL, and not to allow others to |
| * use your version of this file under the terms of the MPL, indicate your |
| * decision by deleting the provisions above and replace them with the notice |
| * and other provisions required by the GPL or the LGPL. If you do not delete |
| * the provisions above, a recipient may use your version of this file under |
| * the terms of any one of the MPL, the GPL or the LGPL. |
| * |
| *********************************************************************** */ |
| /* |
| * Copyright (c) 2007, Oracle and/or its affiliates. All rights reserved. |
| * Use is subject to license terms. |
| */ |
| |
| #pragma ident "%Z%%M% %I% %E% SMI" |
| |
| #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; |
| int i, twowm1, mask; |
| |
| 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 { |
| mp_add_d(&k, -(out[i]), &k); |
| } |
| } 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; |
| |
| } |