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annotate libtommath/bn_s_mp_mul_high_digs_fast.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
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1692
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1 #include "tommath_private.h"
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2 #ifdef BN_S_MP_MUL_HIGH_DIGS_FAST_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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5
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6 /* this is a modified version of fast_s_mul_digs that only produces
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7 * output digits *above* digs. See the comments for fast_s_mul_digs
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8 * to see how it works.
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9 *
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10 * This is used in the Barrett reduction since for one of the multiplications
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11 * only the higher digits were needed. This essentially halves the work.
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12 *
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13 * Based on Algorithm 14.12 on pp.595 of HAC.
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14 */
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15 mp_err s_mp_mul_high_digs_fast(const mp_int *a, const mp_int *b, mp_int *c, int digs)
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16 {
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17 int olduse, pa, ix, iz;
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18 mp_err err;
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19 mp_digit W[MP_WARRAY];
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20 mp_word _W;
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21
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22 /* grow the destination as required */
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23 pa = a->used + b->used;
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24 if (c->alloc < pa) {
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25 if ((err = mp_grow(c, pa)) != MP_OKAY) {
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26 return err;
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27 }
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28 }
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29
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30 /* number of output digits to produce */
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31 pa = a->used + b->used;
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32 _W = 0;
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33 for (ix = digs; ix < pa; ix++) {
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34 int tx, ty, iy;
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35 mp_digit *tmpx, *tmpy;
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36
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37 /* get offsets into the two bignums */
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38 ty = MP_MIN(b->used-1, ix);
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39 tx = ix - ty;
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40
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41 /* setup temp aliases */
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42 tmpx = a->dp + tx;
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43 tmpy = b->dp + ty;
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44
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45 /* this is the number of times the loop will iterrate, essentially its
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46 while (tx++ < a->used && ty-- >= 0) { ... }
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47 */
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48 iy = MP_MIN(a->used-tx, ty+1);
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49
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50 /* execute loop */
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51 for (iz = 0; iz < iy; iz++) {
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52 _W += (mp_word)*tmpx++ * (mp_word)*tmpy--;
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53 }
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54
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55 /* store term */
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56 W[ix] = (mp_digit)_W & MP_MASK;
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57
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58 /* make next carry */
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59 _W = _W >> (mp_word)MP_DIGIT_BIT;
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60 }
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61
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62 /* setup dest */
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63 olduse = c->used;
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64 c->used = pa;
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65
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66 {
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67 mp_digit *tmpc;
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68
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69 tmpc = c->dp + digs;
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70 for (ix = digs; ix < pa; ix++) {
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71 /* now extract the previous digit [below the carry] */
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72 *tmpc++ = W[ix];
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73 }
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74
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75 /* clear unused digits [that existed in the old copy of c] */
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76 MP_ZERO_DIGITS(tmpc, olduse - ix);
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77 }
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78 mp_clamp(c);
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79 return MP_OKAY;
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80 }
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81 #endif