Mercurial > dropbear

annotate libtomcrypt/src/misc/mem_neq.c @ 1857:6022df862942

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Use DSCP for IP QoS traffic classes The previous TOS values are deprecated and not used by modern traffic classifiers. This sets AF21 for "interactive" traffic (with a tty). Non-tty traffic sets AF11 - that indicates high throughput but is not lowest priority (which would be CS1 or LE). This differs from the CS1 used by OpenSSH, it lets interactive git over SSH have higher priority than background least effort traffic. Dropbear's settings here should be suitable with the diffservs used by CAKE qdisc.
author Matt Johnston <matt@ucc.asn.au>
date Tue, 25 Jan 2022 17:32:20 +0800
parents 6dba84798cd5
children
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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: $Format:%ai$ */