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annotate libtommath/bn_mp_reduce.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:
rev   line source
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_REDUCE_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 /* reduces x mod m, assumes 0 < x < m**2, mu is
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7 * precomputed via mp_reduce_setup.
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8 * From HAC pp.604 Algorithm 14.42
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9 */
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10 mp_err mp_reduce(mp_int *x, const mp_int *m, const mp_int *mu)
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11 {
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12 mp_int q;
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13 mp_err err;
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14 int um = m->used;
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15
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16 /* q = x */
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17 if ((err = mp_init_copy(&q, x)) != MP_OKAY) {
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18 return err;
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19 }
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21 /* q1 = x / b**(k-1) */
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22 mp_rshd(&q, um - 1);
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23
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24 /* according to HAC this optimization is ok */
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25 if ((mp_digit)um > ((mp_digit)1 << (MP_DIGIT_BIT - 1))) {
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26 if ((err = mp_mul(&q, mu, &q)) != MP_OKAY) {
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27 goto CLEANUP;
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28 }
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29 } else if (MP_HAS(S_MP_MUL_HIGH_DIGS)) {
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30 if ((err = s_mp_mul_high_digs(&q, mu, &q, um)) != MP_OKAY) {
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31 goto CLEANUP;
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32 }
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33 } else if (MP_HAS(S_MP_MUL_HIGH_DIGS_FAST)) {
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34 if ((err = s_mp_mul_high_digs_fast(&q, mu, &q, um)) != MP_OKAY) {
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35 goto CLEANUP;
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36 }
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37 } else {
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38 err = MP_VAL;
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39 goto CLEANUP;
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40 }
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41
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42 /* q3 = q2 / b**(k+1) */
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43 mp_rshd(&q, um + 1);
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44
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45 /* x = x mod b**(k+1), quick (no division) */
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46 if ((err = mp_mod_2d(x, MP_DIGIT_BIT * (um + 1), x)) != MP_OKAY) {
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47 goto CLEANUP;
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48 }
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49
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50 /* q = q * m mod b**(k+1), quick (no division) */
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51 if ((err = s_mp_mul_digs(&q, m, &q, um + 1)) != MP_OKAY) {
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52 goto CLEANUP;
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53 }
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54
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55 /* x = x - q */
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56 if ((err = mp_sub(x, &q, x)) != MP_OKAY) {
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57 goto CLEANUP;
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58 }
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59
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60 /* If x < 0, add b**(k+1) to it */
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61 if (mp_cmp_d(x, 0uL) == MP_LT) {
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62 mp_set(&q, 1uL);
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63 if ((err = mp_lshd(&q, um + 1)) != MP_OKAY) {
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64 goto CLEANUP;
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65 }
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66 if ((err = mp_add(x, &q, x)) != MP_OKAY) {
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67 goto CLEANUP;
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68 }
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69 }
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70
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71 /* Back off if it's too big */
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72 while (mp_cmp(x, m) != MP_LT) {
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73 if ((err = s_mp_sub(x, m, x)) != MP_OKAY) {
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74 goto CLEANUP;
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75 }
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76 }
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77
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78 CLEANUP:
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79 mp_clear(&q);
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80
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81 return err;
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82 }
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83 #endif