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thirdparty/libtomcrypt/misc/mem_neq.c

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+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ */
+#include "tomcrypt.h"
+
+/**
+   @file mem_neq.c
+   Compare two blocks of memory for inequality in constant time.
+   Steffen Jaeckel
+*/
+
+/**
+   Compare two blocks of memory for inequality in constant time.
+
+   The usage is similar to that of standard memcmp, but you can only test
+   if the memory is equal or not - you can not determine by how much the
+   first different byte differs.
+
+   This function shall be used to compare results of cryptographic
+   operations where inequality means most likely usage of a wrong key.
+   The execution time has therefore to be constant as otherwise
+   timing attacks could be possible.
+
+   @param a     The first memory region
+   @param b     The second memory region
+   @param len   The length of the area to compare (octets)
+
+   @return 0 when a and b are equal for len bytes, 1 they are not equal.
+*/
+int mem_neq(const void *a, const void *b, size_t len)
+{
+   unsigned char ret = 0;
+   const unsigned char* pa;
+   const unsigned char* pb;
+
+   LTC_ARGCHK(a != NULL);
+   LTC_ARGCHK(b != NULL);
+
+   pa = a;
+   pb = b;
+
+   while (len-- > 0) {
+      ret |= *pa ^ *pb;
+      ++pa;
+      ++pb;
+   }
+
+   ret |= ret >> 4;
+   ret |= ret >> 2;
+   ret |= ret >> 1;
+   ret &= 1;
+
+   return ret;
+}
+
+/* ref:         HEAD -> master, tag: v1.18.2 */
+/* git commit:  7e7eb695d581782f04b24dc444cbfde86af59853 */
+/* commit time: 2018-07-01 22:49:01 +0200 */