explicit_memset
—
guarantee writing a byte to a byte string
Standard C Library (libc, -lc)
#include <string.h>
void *
explicit_memset
(void
*b, int c,
size_t len);
The explicit_memset
() function writes
len bytes of value c (converted to
an unsigned char) to the string b. It is guaranteed not
to be optimized away by the compiler even if b is no
longer used and is about to be freed or go out of scope.
The explicit_memset
() function returns the original
value of b.
Create a buffer on the stack for a secret key, use it, and then zero it in
memory before throwing it away.
void
f(void)
{
uint8_t key[32];
crypto_random(key, sizeof(key));
do_crypto_stuff(key, sizeof(key));
...
explicit_memset(key, 0, sizeof(key));
}
The explicit_memset
() function appeared in
NetBSD 7.0.