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 nonnegative, 21up to B<max_bytes> are read; 22if B<max_bytes> is -1, the complete file is read (unless the file 23is not a regular file, in that case a fixed number of bytes, 24256 in the current implementation, is attempted to be read). 25RAND_load_file() can read less than the complete file or the requested number 26of bytes if it doesn't fit in the return value type. 27Do not load the same file multiple times unless its contents have 28been updated by RAND_write_file() between reads. 29Also, note that B<filename> should be adequately protected so that an 30attacker cannot replace or examine the contents. 31If B<filename> is not a regular file, then user is considered to be 32responsible for any side effects, e.g. non-anticipated blocking or 33capture of controlling terminal. 34 35RAND_write_file() writes a number of random bytes (currently 128) to 36file B<filename> which can be used to initialize the PRNG by calling 37RAND_load_file() in a later session. 38 39RAND_file_name() generates a default path for the random seed 40file. B<buf> points to a buffer of size B<num> in which to store the 41filename. 42 43On all systems, if the environment variable B<RANDFILE> is set, its 44value will be used as the seed filename. 45Otherwise, the file is called C<.rnd>, found in platform dependent locations: 46 47=over 4 48 49=item On Windows (in order of preference) 50 51 %HOME%, %USERPROFILE%, %SYSTEMROOT%, C:\ 52 53=item On VMS 54 55 SYS$LOGIN: 56 57=item On all other systems 58 59 $HOME 60 61=back 62 63If C<$HOME> (on non-Windows and non-VMS system) is not set either, or 64B<num> is too small for the pathname, an error occurs. 65 66=head1 RETURN VALUES 67 68RAND_load_file() returns the number of bytes read or -1 on error. 69 70RAND_write_file() returns the number of bytes written, or -1 if the 71bytes written were generated without appropriate seeding. 72 73RAND_file_name() returns a pointer to B<buf> on success, and NULL on 74error. 75 76=head1 SEE ALSO 77 78L<RAND_add(3)>, 79L<RAND_bytes(3)>, 80L<RAND(7)> 81 82=head1 COPYRIGHT 83 84Copyright 2000-2025 The OpenSSL Project Authors. All Rights Reserved. 85 86Licensed under the Apache License 2.0 (the "License"). You may not use 87this file except in compliance with the License. You can obtain a copy 88in the file LICENSE in the source distribution or at 89L<https://www.openssl.org/source/license.html>. 90 91=cut 92