Mercurial > dropbear

annotate libtommath/bn_mp_div_2d.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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1 #include "tommath_private.h"
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2 #ifdef BN_MP_DIV_2D_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 /* shift right by a certain bit count (store quotient in c, optional remainder in d) */
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7 mp_err mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d)
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8 {
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9 mp_digit D, r, rr;
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10 int x;
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11 mp_err err;
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12
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13 /* if the shift count is <= 0 then we do no work */
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14 if (b <= 0) {
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15 err = mp_copy(a, c);
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16 if (d != NULL) {
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17 mp_zero(d);
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18 }
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19 return err;
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20 }
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21
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22 /* copy */
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23 if ((err = mp_copy(a, c)) != MP_OKAY) {
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24 return err;
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25 }
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26 /* 'a' should not be used after here - it might be the same as d */
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27
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28 /* get the remainder */
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29 if (d != NULL) {
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30 if ((err = mp_mod_2d(a, b, d)) != MP_OKAY) {
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31 return err;
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32 }
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33 }
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34
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35 /* shift by as many digits in the bit count */
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36 if (b >= MP_DIGIT_BIT) {
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37 mp_rshd(c, b / MP_DIGIT_BIT);
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38 }
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39
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40 /* shift any bit count < MP_DIGIT_BIT */
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41 D = (mp_digit)(b % MP_DIGIT_BIT);
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42 if (D != 0u) {
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43 mp_digit *tmpc, mask, shift;
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45 /* mask */
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46 mask = ((mp_digit)1 << D) - 1uL;
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48 /* shift for lsb */
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49 shift = (mp_digit)MP_DIGIT_BIT - D;
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51 /* alias */
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52 tmpc = c->dp + (c->used - 1);
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54 /* carry */
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55 r = 0;
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56 for (x = c->used - 1; x >= 0; x--) {
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57 /* get the lower bits of this word in a temp */
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58 rr = *tmpc & mask;
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59
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60 /* shift the current word and mix in the carry bits from the previous word */
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61 *tmpc = (*tmpc >> D) | (r << shift);
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62 --tmpc;
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63
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64 /* set the carry to the carry bits of the current word found above */
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65 r = rr;
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66 }
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67 }
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68 mp_clamp(c);
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69 return MP_OKAY;
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70 }
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71 #endif