explicit_memset(3) - NetBSD Manual Pages

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EXPLICIT_MEMSET(3)      NetBSD Library Functions Manual     EXPLICIT_MEMSET(3)


NAME

     explicit_memset -- guarantee writing a byte to a byte string


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <string.h>

     void *
     explicit_memset(void *b, int c, size_t len);


DESCRIPTION

     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.


RETURN VALUES

     The explicit_memset() function returns the original value of b.


EXAMPLES

     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));
           }


SEE ALSO

     consttime_memequal(3), memset(3)


HISTORY

     The explicit_memset() function appeared in NetBSD 7.0.

NetBSD 7.0                      August 28, 2013                     NetBSD 7.0