Mercurial > dropbear

annotate libtommath/bn_mp_reduce.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:
rev   line source
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
diff changeset
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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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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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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20
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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
1655
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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
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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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