openssl/doc/man3/RAND_load_file.pod

=pod

=head1 NAME

RAND_load_file, RAND_write_file, RAND_file_name - PRNG seed file

=head1 SYNOPSIS

 #include <openssl/rand.h>

 int RAND_load_file(const char *filename, long max_bytes);

 int RAND_write_file(const char *filename);

 const char *RAND_file_name(char *buf, size_t num);

=head1 DESCRIPTION

RAND_load_file() reads a number of bytes from file B<filename> and
adds them to the PRNG. If B<max_bytes> is non-negative,
up to B<max_bytes> are read;
if B<max_bytes> is -1, the complete file is read.
Do not load the same file multiple times unless its contents have
been updated by RAND_write_file() between reads.
Also, note that B<filename> should be adequately protected so that an
attacker cannot replace or examine the contents.
If B<filename> is not a regular file, then user is considered to be
responsible for any side effects, e.g. non-anticipated blocking or
capture of controlling terminal.

RAND_write_file() writes a number of random bytes (currently 128) to
file B<filename> which can be used to initialize the PRNG by calling
RAND_load_file() in a later session.

RAND_file_name() generates a default path for the random seed
file. B<buf> points to a buffer of size B<num> in which to store the
filename.

On all systems, if the environment variable B<RANDFILE> is set, its
value will be used as the seed file name.
Otherwise, the file is called C<.rnd>, found in platform dependent locations:

=over 4

=item On Windows (in order of preference)

 %HOME%, %USERPROFILE%, %SYSTEMROOT%, C:\

=item On VMS

 SYS$LOGIN:

=item On all other systems

 $HOME

=back

If C<$HOME> (on non-Windows and non-VMS system) is not set either, or
B<num> is too small for the path name, an error occurs.

=head1 RETURN VALUES

RAND_load_file() returns the number of bytes read or -1 on error.

RAND_write_file() returns the number of bytes written, or -1 if the
bytes written were generated without appropriate seeding.

RAND_file_name() returns a pointer to B<buf> on success, and NULL on
error.

=head1 SEE ALSO

L<RAND_add(3)>,
L<RAND_bytes(3)>,
L<RAND(7)>

=head1 COPYRIGHT

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut