Mercurial > dropbear

annotate libtommath/bn_mp_rshd.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
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f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_RSHD_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 /* shift right a certain amount of digits */
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7 void mp_rshd(mp_int *a, int b)
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8 {
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9 int x;
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10 mp_digit *bottom, *top;
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12 /* if b <= 0 then ignore it */
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13 if (b <= 0) {
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14 return;
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15 }
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16
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17 /* if b > used then simply zero it and return */
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18 if (a->used <= b) {
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19 mp_zero(a);
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20 return;
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21 }
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23 /* shift the digits down */
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24
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25 /* bottom */
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26 bottom = a->dp;
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28 /* top [offset into digits] */
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29 top = a->dp + b;
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30
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31 /* this is implemented as a sliding window where
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32 * the window is b-digits long and digits from
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33 * the top of the window are copied to the bottom
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34 *
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35 * e.g.
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36
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37 b-2 | b-1 | b0 | b1 | b2 | ... | bb | ---->
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38 /\ | ---->
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39 \-------------------/ ---->
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40 */
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41 for (x = 0; x < (a->used - b); x++) {
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42 *bottom++ = *top++;
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43 }
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44
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45 /* zero the top digits */
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46 MP_ZERO_DIGITS(bottom, a->used - x);
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47
f52919ffd3b1 update ltm to 1.1.0 and enable FIPS 186.4 compliant key-generation (#79)
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parents: 1470
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48 /* remove excess digits */
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49 a->used -= b;
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50 }
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51 #endif