annotate libtommath/bn_mp_montgomery_calc_normalization.c @ 1861:2b3a8026a6ce

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
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_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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6 /*
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7 * shifts with subtractions when the result is greater than b.
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8 *
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9 * The method is slightly modified to shift B unconditionally upto just under
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10 * the leading bit of b. This saves alot of multiple precision shifting.
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11 */
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12 mp_err mp_montgomery_calc_normalization(mp_int *a, const mp_int *b)
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13 {
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14 int x, bits;
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15 mp_err err;
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16
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17 /* how many bits of last digit does b use */
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18 bits = mp_count_bits(b) % MP_DIGIT_BIT;
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19
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20 if (b->used > 1) {
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21 if ((err = mp_2expt(a, ((b->used - 1) * MP_DIGIT_BIT) + bits - 1)) != MP_OKAY) {
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22 return err;
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23 }
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24 } else {
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25 mp_set(a, 1uL);
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26 bits = 1;
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27 }
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29
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30 /* now compute C = A * B mod b */
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31 for (x = bits - 1; x < (int)MP_DIGIT_BIT; x++) {
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32 if ((err = mp_mul_2(a, a)) != MP_OKAY) {
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33 return err;
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34 }
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35 if (mp_cmp_mag(a, b) != MP_LT) {
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36 if ((err = s_mp_sub(a, b, a)) != MP_OKAY) {
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37 return err;
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38 }
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39 }
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40 }
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41
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42 return MP_OKAY;
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43 }
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44 #endif