Mercurial > dropbear

annotate libtommath/bn_s_mp_mul_digs.c @ 1715:3974f087d9c0

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Disallow leading lines before the ident for server (#102) Per RFC4253 4.2 clients must be able to process other lines of data before the version string, server behavior is not defined neither with MUST/SHOULD nor with MAY. If server process up to 50 lines too - it may cause too long hanging session with invalid/evil client that consume host resources and potentially may lead to DDoS on poor embedded boxes. Let's require first line from client to be version string and fail early if it's not - matches both RFC and real OpenSSH behavior.
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 15 Jun 2020 18:22:18 +0500
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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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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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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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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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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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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67
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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