You should keep in mind that the memset call is almost guarenteed to be inlined. So your code actually looks like this: void dosomethingsensitive(void)

You should keep in mind that the memset call is almost guarenteed to be inlined. So your code actually looks like this: void dosomethingsensitive(void) { uint8_t key[32]; /* ... */ int i; for (i = 0; i < 32; i++) key[i] = 0; key[0] = key[1] + 1; } Assuming the optimizer is sufficiently smart, then it'll remove that 'for' and it'll remove the addition after it in the same fashion.