Mercurial > dropbear

annotate libtommath/bn_mp_div_d.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_D_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 /* single digit division (based on routine from MPI) */
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7 mp_err mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
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8 {
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9 mp_int q;
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10 mp_word w;
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11 mp_digit t;
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12 mp_err err;
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13 int ix;
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14
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15 /* cannot divide by zero */
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16 if (b == 0u) {
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17 return MP_VAL;
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18 }
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19
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20 /* quick outs */
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21 if ((b == 1u) || MP_IS_ZERO(a)) {
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22 if (d != NULL) {
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23 *d = 0;
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24 }
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25 if (c != NULL) {
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26 return mp_copy(a, c);
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27 }
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28 return MP_OKAY;
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29 }
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30
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31 /* power of two ? */
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32 if ((b & (b - 1u)) == 0u) {
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33 ix = 1;
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34 while ((ix < MP_DIGIT_BIT) && (b != (((mp_digit)1)<<ix))) {
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35 ix++;
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36 }
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37 if (d != NULL) {
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38 *d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
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39 }
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40 if (c != NULL) {
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41 return mp_div_2d(a, ix, c, NULL);
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42 }
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43 return MP_OKAY;
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44 }
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45
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46 /* three? */
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47 if (MP_HAS(MP_DIV_3) && (b == 3u)) {
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48 return mp_div_3(a, c, d);
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49 }
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50
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51 /* no easy answer [c'est la vie]. Just division */
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52 if ((err = mp_init_size(&q, a->used)) != MP_OKAY) {
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53 return err;
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54 }
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56 q.used = a->used;
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57 q.sign = a->sign;
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58 w = 0;
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59 for (ix = a->used - 1; ix >= 0; ix--) {
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60 w = (w << (mp_word)MP_DIGIT_BIT) | (mp_word)a->dp[ix];
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61
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62 if (w >= b) {
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63 t = (mp_digit)(w / b);
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64 w -= (mp_word)t * (mp_word)b;
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65 } else {
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66 t = 0;
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67 }
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68 q.dp[ix] = t;
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69 }
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70
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71 if (d != NULL) {
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72 *d = (mp_digit)w;
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73 }
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74
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75 if (c != NULL) {
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76 mp_clamp(&q);
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77 mp_exch(&q, c);
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78 }
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79 mp_clear(&q);
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80
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81 return err;
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82 }
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84 #endif