Mercurial > dropbear

annotate libtommath/bn_mp_reduce.c @ 1861:2b3a8026a6ce

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Add re-exec for server This allows ASLR to re-randomize the address space for every connection, preventing some vulnerabilities from being exploitable by repeated probing. Overhead (memory and time) is yet to be confirmed. At present this is only enabled on Linux. Other BSD platforms with fexecve() would probably also work though have not been tested.
author Matt Johnston <matt@ucc.asn.au>
date Sun, 30 Jan 2022 10:14:56 +0800
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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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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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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parents: 1470
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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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parents: 1470
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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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parents: 1470
diff changeset
69 }
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parents: 1470
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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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parents: 1470
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74 goto CLEANUP;
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parents: 1470
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75 }
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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76 }
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77
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parents:
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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