Mercurial > dropbear

annotate libtommath/bn_s_mp_add.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_S_MP_ADD_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 /* low level addition, based on HAC pp.594, Algorithm 14.7 */
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7 mp_err s_mp_add(const mp_int *a, const mp_int *b, mp_int *c)
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8 {
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9 const mp_int *x;
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10 mp_err err;
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11 int olduse, min, max;
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12
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13 /* find sizes, we let |a| <= |b| which means we have to sort
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14 * them. "x" will point to the input with the most digits
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15 */
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16 if (a->used > b->used) {
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17 min = b->used;
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18 max = a->used;
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19 x = a;
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20 } else {
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21 min = a->used;
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22 max = b->used;
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23 x = b;
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24 }
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26 /* init result */
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27 if (c->alloc < (max + 1)) {
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28 if ((err = mp_grow(c, max + 1)) != MP_OKAY) {
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29 return err;
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30 }
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31 }
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33 /* get old used digit count and set new one */
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34 olduse = c->used;
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35 c->used = max + 1;
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36
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37 {
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38 mp_digit u, *tmpa, *tmpb, *tmpc;
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39 int i;
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41 /* alias for digit pointers */
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42
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43 /* first input */
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44 tmpa = a->dp;
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45
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46 /* second input */
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47 tmpb = b->dp;
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49 /* destination */
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50 tmpc = c->dp;
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51
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52 /* zero the carry */
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53 u = 0;
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54 for (i = 0; i < min; i++) {
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55 /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */
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56 *tmpc = *tmpa++ + *tmpb++ + u;
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57
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58 /* U = carry bit of T[i] */
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59 u = *tmpc >> (mp_digit)MP_DIGIT_BIT;
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60
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61 /* take away carry bit from T[i] */
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62 *tmpc++ &= MP_MASK;
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63 }
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64
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65 /* now copy higher words if any, that is in A+B
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66 * if A or B has more digits add those in
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67 */
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68 if (min != max) {
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69 for (; i < max; i++) {
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70 /* T[i] = X[i] + U */
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71 *tmpc = x->dp[i] + u;
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73 /* U = carry bit of T[i] */
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74 u = *tmpc >> (mp_digit)MP_DIGIT_BIT;
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75
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76 /* take away carry bit from T[i] */
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77 *tmpc++ &= MP_MASK;
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78 }
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79 }
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80
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81 /* add carry */
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82 *tmpc++ = u;
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83
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84 /* clear digits above oldused */
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85 MP_ZERO_DIGITS(tmpc, olduse - c->used);
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86 }
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87
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88 mp_clamp(c);
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89 return MP_OKAY;
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90 }
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91 #endif