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64 lines
1.6 KiB
64 lines
1.6 KiB
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*/
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#include "tomcrypt.h"
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/**
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@file mem_neq.c
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Compare two blocks of memory for inequality in constant time.
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Steffen Jaeckel
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*/
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/**
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Compare two blocks of memory for inequality in constant time.
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The usage is similar to that of standard memcmp, but you can only test
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if the memory is equal or not - you can not determine by how much the
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first different byte differs.
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This function shall be used to compare results of cryptographic
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operations where inequality means most likely usage of a wrong key.
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The execution time has therefore to be constant as otherwise
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timing attacks could be possible.
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@param a The first memory region
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@param b The second memory region
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@param len The length of the area to compare (octets)
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@return 0 when a and b are equal for len bytes, 1 they are not equal.
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*/
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int mem_neq(const void *a, const void *b, size_t len)
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{
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unsigned char ret = 0;
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const unsigned char* pa;
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const unsigned char* pb;
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LTC_ARGCHK(a != NULL);
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LTC_ARGCHK(b != NULL);
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pa = a;
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pb = b;
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while (len-- > 0) {
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ret |= *pa ^ *pb;
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++pa;
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++pb;
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}
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ret |= ret >> 4;
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ret |= ret >> 2;
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ret |= ret >> 1;
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ret &= 1;
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return ret;
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}
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/* ref: $Format:%D$ */
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/* git commit: $Format:%H$ */
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/* commit time: $Format:%ai$ */
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