Mercurial > dropbear

annotate libtomcrypt/src/misc/mem_neq.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 6dba84798cd5
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1471
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
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2 *
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3 * LibTomCrypt is a library that provides various cryptographic
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4 * algorithms in a highly modular and flexible manner.
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5 *
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6 * The library is free for all purposes without any express
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7 * guarantee it works.
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8 */
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9 #include "tomcrypt.h"
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10
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11 /**
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12 @file mem_neq.c
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13 Compare two blocks of memory for inequality in constant time.
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14 Steffen Jaeckel
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15 */
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16
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17 /**
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18 Compare two blocks of memory for inequality in constant time.
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19
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20 The usage is similar to that of standard memcmp, but you can only test
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21 if the memory is equal or not - you can not determine by how much the
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22 first different byte differs.
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23
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24 This function shall be used to compare results of cryptographic
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25 operations where inequality means most likely usage of a wrong key.
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26 The execution time has therefore to be constant as otherwise
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27 timing attacks could be possible.
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28
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29 @param a The first memory region
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30 @param b The second memory region
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31 @param len The length of the area to compare (octets)
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32
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33 @return 0 when a and b are equal for len bytes, 1 they are not equal.
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34 */
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35 int mem_neq(const void *a, const void *b, size_t len)
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36 {
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37 unsigned char ret = 0;
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38 const unsigned char* pa;
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39 const unsigned char* pb;
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40
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41 LTC_ARGCHK(a != NULL);
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42 LTC_ARGCHK(b != NULL);
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43
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44 pa = a;
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45 pb = b;
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46
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47 while (len-- > 0) {
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48 ret |= *pa ^ *pb;
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49 ++pa;
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50 ++pb;
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51 }
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52
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53 ret |= ret >> 4;
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54 ret |= ret >> 2;
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55 ret |= ret >> 1;
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56 ret &= 1;
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57
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58 return ret;
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59 }
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60
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61 /* ref: $Format:%D$ */
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62 /* git commit: $Format:%H$ */
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63 /* commit time: $Format:%ai$ */