1=pod
2
3=head1 NAME
4
5RAND_load_file, RAND_write_file, RAND_file_name - PRNG seed file
6
7=head1 SYNOPSIS
8
9 #include <openssl/rand.h>
10
11 int RAND_load_file(const char *filename, long max_bytes);
12
13 int RAND_write_file(const char *filename);
14
15 const char *RAND_file_name(char *buf, size_t num);
16
17=head1 DESCRIPTION
18
19RAND_load_file() reads a number of bytes from file B<filename> and
20adds them to the PRNG. If B<max_bytes> is non-negative,
21up to B<max_bytes> are read;
22if B<max_bytes> is -1, the complete file is read.
23Do not load the same file multiple times unless its contents have
24been updated by RAND_write_file() between reads.
25Also, note that B<filename> should be adequately protected so that an
26attacker cannot replace or examine the contents.
27If B<filename> is not a regular file, then user is considered to be
28responsible for any side effects, e.g. non-anticipated blocking or
29capture of controlling terminal.
30
31RAND_write_file() writes a number of random bytes (currently 128) to
32file B<filename> which can be used to initialize the PRNG by calling
33RAND_load_file() in a later session.
34
35RAND_file_name() generates a default path for the random seed
36file. B<buf> points to a buffer of size B<num> in which to store the
37filename.
38
39On all systems, if the environment variable B<RANDFILE> is set, its
40value will be used as the seed file name.
41Otherwise, the file is called C<.rnd>, found in platform dependent locations:
42
43=over 4
44
45=item On Windows (in order of preference)
46
47 %HOME%, %USERPROFILE%, %SYSTEMROOT%, C:\
48
49=item On VMS
50
51 SYS$LOGIN:
52
53=item On all other systems
54
55 $HOME
56
57=back
58
59If C<$HOME> (on non-Windows and non-VMS system) is not set either, or
60B<num> is too small for the path name, an error occurs.
61
62=head1 RETURN VALUES
63
64RAND_load_file() returns the number of bytes read or -1 on error.
65
66RAND_write_file() returns the number of bytes written, or -1 if the
67bytes written were generated without appropriate seeding.
68
69RAND_file_name() returns a pointer to B<buf> on success, and NULL on
70error.
71
72=head1 SEE ALSO
73
74L<RAND_add(3)>,
75L<RAND_bytes(3)>,
76L<RAND(7)>
77
78=head1 COPYRIGHT
79
80Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
81
82Licensed under the OpenSSL license (the "License").  You may not use
83this file except in compliance with the License.  You can obtain a copy
84in the file LICENSE in the source distribution or at
85L<https://www.openssl.org/source/license.html>.
86
87=cut
88