[Cryptography] [Crypto-practicum] Secure erasure in C.

[Ray Dillinger]

On 09/07/2016 05:27 PM, Ron Garret wrote:
> On Sep 7, 2016, at 5:08 PM, Ray Dillinger <bear at sonic.net> wrote:
>> On 09/07/2016 04:23 PM, Ron Garret wrote:

>>> void erase(volatile char *buf, size_t len) {
>> ....
>>
>> everything that starts with this line doesn't work, because
>> passing a (non-volatile) 'char *' to a 'volatile char *' is
>> an error.  Something can't be made volatile by a cast; it
>> can only be done when declaring the variable (or buffer).
> 
> OK, so then why not:
> 
> void erase_non_volatile(char* buf, size_t len) {
>   volatile char* buf1 = buf;
>   erase(buf1, len);
> }

You can initialize a volatile pointer from a non-volatile
pointer, but that's because the pointer itself is volatile
when created.  You want to initialize a pointer at a
volatile _object_ from a pointer at a non-volatile _object_,
which is different.

I don't think that's allowed unless the non-volatile
object is 'static' in the first place, like a procedure
or a static variable.  IME nothing can become 'volatile'
unless its location can be fixed at compile time.  But
now I have to go read the standard again because I may
be remembering that incorrectly.  It would be very nice
if it's allowed.

				Bear

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