Mercurial > dropbear

annotate libtommath/bn_mp_rshd.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:
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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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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
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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