Mercurial > dropbear

annotate libtommath/bn_mp_div_2.c @ 1861:2b3a8026a6ce

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Add re-exec for server This allows ASLR to re-randomize the address space for every connection, preventing some vulnerabilities from being exploitable by repeated probing. Overhead (memory and time) is yet to be confirmed. At present this is only enabled on Linux. Other BSD platforms with fexecve() would probably also work though have not been tested.
author Matt Johnston <matt@ucc.asn.au>
date Sun, 30 Jan 2022 10:14:56 +0800
parents 1051e4eea25a
children
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_DIV_2_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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6 /* b = a/2 */
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7 mp_err mp_div_2(const mp_int *a, mp_int *b)
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8 {
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9 int x, oldused;
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10 mp_digit r, rr, *tmpa, *tmpb;
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11 mp_err err;
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13 /* copy */
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14 if (b->alloc < a->used) {
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15 if ((err = mp_grow(b, a->used)) != MP_OKAY) {
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16 return err;
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17 }
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18 }
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20 oldused = b->used;
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21 b->used = a->used;
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22
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23 /* source alias */
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24 tmpa = a->dp + b->used - 1;
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26 /* dest alias */
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27 tmpb = b->dp + b->used - 1;
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29 /* carry */
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30 r = 0;
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31 for (x = b->used - 1; x >= 0; x--) {
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32 /* get the carry for the next iteration */
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33 rr = *tmpa & 1u;
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34
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35 /* shift the current digit, add in carry and store */
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36 *tmpb-- = (*tmpa-- >> 1) | (r << (MP_DIGIT_BIT - 1));
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37
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38 /* forward carry to next iteration */
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39 r = rr;
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40 }
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41
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42 /* zero excess digits */
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43 MP_ZERO_DIGITS(b->dp + b->used, oldused - b->used);
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44
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45 b->sign = a->sign;
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46 mp_clamp(b);
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47 return MP_OKAY;
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48 }
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49 #endif