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.