Mercurial > dropbear

annotate libtommath/bn_s_mp_mul_digs.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_MUL_DIGS_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 /* multiplies |a| * |b| and only computes upto digs digits of result
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7 * HAC pp. 595, Algorithm 14.12 Modified so you can control how
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8 * many digits of output are created.
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9 */
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10 mp_err s_mp_mul_digs(const mp_int *a, const mp_int *b, mp_int *c, int digs)
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11 {
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12 mp_int t;
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13 mp_err err;
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14 int pa, pb, ix, iy;
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15 mp_digit u;
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16 mp_word r;
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17 mp_digit tmpx, *tmpt, *tmpy;
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19 /* can we use the fast multiplier? */
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20 if ((digs < MP_WARRAY) &&
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21 (MP_MIN(a->used, b->used) < MP_MAXFAST)) {
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22 return s_mp_mul_digs_fast(a, b, c, digs);
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23 }
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24
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25 if ((err = mp_init_size(&t, digs)) != MP_OKAY) {
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26 return err;
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27 }
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28 t.used = digs;
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29
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30 /* compute the digits of the product directly */
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31 pa = a->used;
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32 for (ix = 0; ix < pa; ix++) {
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33 /* set the carry to zero */
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34 u = 0;
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35
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36 /* limit ourselves to making digs digits of output */
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37 pb = MP_MIN(b->used, digs - ix);
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38
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39 /* setup some aliases */
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40 /* copy of the digit from a used within the nested loop */
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41 tmpx = a->dp[ix];
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42
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43 /* an alias for the destination shifted ix places */
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44 tmpt = t.dp + ix;
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46 /* an alias for the digits of b */
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47 tmpy = b->dp;
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48
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49 /* compute the columns of the output and propagate the carry */
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50 for (iy = 0; iy < pb; iy++) {
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51 /* compute the column as a mp_word */
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52 r = (mp_word)*tmpt +
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53 ((mp_word)tmpx * (mp_word)*tmpy++) +
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54 (mp_word)u;
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55
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56 /* the new column is the lower part of the result */
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57 *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
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58
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59 /* get the carry word from the result */
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60 u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
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61 }
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62 /* set carry if it is placed below digs */
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63 if ((ix + iy) < digs) {
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64 *tmpt = u;
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65 }
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66 }
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68 mp_clamp(&t);
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69 mp_exch(&t, c);
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71 mp_clear(&t);
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72 return MP_OKAY;
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73 }
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74 #endif