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annotate libtommath/bn_s_mp_sqr_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_SQR_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 /* the jist of squaring...
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7 * you do like mult except the offset of the tmpx [one that
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8 * starts closer to zero] can't equal the offset of tmpy.
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9 * So basically you set up iy like before then you min it with
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10 * (ty-tx) so that it never happens. You double all those
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11 * you add in the inner loop
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12
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13 After that loop you do the squares and add them in.
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14 */
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15
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16 mp_err s_mp_sqr_fast(const mp_int *a, mp_int *b)
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17 {
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18 int olduse, pa, ix, iz;
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19 mp_digit W[MP_WARRAY], *tmpx;
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20 mp_word W1;
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21 mp_err err;
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22
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23 /* grow the destination as required */
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24 pa = a->used + a->used;
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25 if (b->alloc < pa) {
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26 if ((err = mp_grow(b, pa)) != MP_OKAY) {
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27 return err;
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28 }
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29 }
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30
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31 /* number of output digits to produce */
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32 W1 = 0;
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33 for (ix = 0; ix < pa; ix++) {
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34 int tx, ty, iy;
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35 mp_word _W;
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36 mp_digit *tmpy;
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37
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38 /* clear counter */
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39 _W = 0;
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40
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41 /* get offsets into the two bignums */
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42 ty = MP_MIN(a->used-1, ix);
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43 tx = ix - ty;
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44
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45 /* setup temp aliases */
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46 tmpx = a->dp + tx;
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47 tmpy = a->dp + ty;
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48
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49 /* this is the number of times the loop will iterrate, essentially
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50 while (tx++ < a->used && ty-- >= 0) { ... }
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51 */
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52 iy = MP_MIN(a->used-tx, ty+1);
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53
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54 /* now for squaring tx can never equal ty
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55 * we halve the distance since they approach at a rate of 2x
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56 * and we have to round because odd cases need to be executed
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57 */
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58 iy = MP_MIN(iy, ((ty-tx)+1)>>1);
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59
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60 /* execute loop */
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61 for (iz = 0; iz < iy; iz++) {
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62 _W += (mp_word)*tmpx++ * (mp_word)*tmpy--;
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63 }
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64
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65 /* double the inner product and add carry */
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66 _W = _W + _W + W1;
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67
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68 /* even columns have the square term in them */
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69 if (((unsigned)ix & 1u) == 0u) {
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70 _W += (mp_word)a->dp[ix>>1] * (mp_word)a->dp[ix>>1];
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71 }
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72
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73 /* store it */
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74 W[ix] = (mp_digit)_W & MP_MASK;
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75
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76 /* make next carry */
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77 W1 = _W >> (mp_word)MP_DIGIT_BIT;
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78 }
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79
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80 /* setup dest */
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81 olduse = b->used;
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82 b->used = a->used+a->used;
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83
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84 {
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85 mp_digit *tmpb;
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86 tmpb = b->dp;
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87 for (ix = 0; ix < pa; ix++) {
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88 *tmpb++ = W[ix] & MP_MASK;
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89 }
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90
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91 /* clear unused digits [that existed in the old copy of c] */
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92 MP_ZERO_DIGITS(tmpb, olduse - ix);
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93 }
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94 mp_clamp(b);
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95 return MP_OKAY;
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96 }
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97 #endif