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annotate libtommath/bn_s_mp_mul_digs.c @ 1930:299f4f19ba19

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Add /usr/sbin and /sbin to default root PATH When dropbear is used in a very restricted environment (such as in a initrd), the default user shell is often also very restricted and doesn't take care of setting the PATH so the user ends up with the PATH set by dropbear. Unfortunately, dropbear always sets "/usr/bin:/bin" as default PATH even for the root user which should have /usr/sbin and /sbin too. For a concrete instance of this problem, see the "Remote Unlocking" section in this tutorial: https://paxswill.com/blog/2013/11/04/encrypted-raspberry-pi/ It speaks of a bug in the initramfs script because it's written "blkid" instead of "/sbin/blkid"... this is just because the scripts from the initramfs do not expect to have a PATH without the sbin directories and because dropbear is not setting the PATH appropriately for the root user. I'm thus suggesting to use the attached patch to fix this misbehaviour (I did not test it, but it's easy enough). It might seem anecdotic but multiple Kali users have been bitten by this. From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403
author Raphael Hertzog <hertzog@debian.org>
date Mon, 09 Jul 2018 16:27:53 +0200
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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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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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