openssl/doc/man1/rand.pod

=pod

=head1 NAME

openssl-rand,
rand - generate pseudo-random bytes

=head1 SYNOPSIS

B<openssl rand>
[B<-help>]
[B<-out> I<file>]
[B<-rand file...>]
[B<-writerand file>]
[B<-base64>]
[B<-hex>]
I<num>

=head1 DESCRIPTION

This command generates I<num> random bytes using a cryptographically
secure pseudo random number generator (CSPRNG).

The random bytes are generated using the L<RAND_bytes(3)> function,
which provides a security level of 256 bits, provided it managed to
seed itself successfully from a trusted operating system entropy source.
Otherwise, the command will fail with a nonzero error code.
For more details, see L<RAND_bytes(3)>, L<RAND(7)>, and L<RAND_DRBG(7)>.

=head1 OPTIONS

=over 4

=item B<-help>

Print out a usage message.

=item B<-out file>

Write to I<file> instead of standard output.

=item B<-rand file...>

A file or files containing random data used to seed the random number
generator.
Multiple files can be specified separated by an OS-dependent character.
The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
all others.
Explicitly specifying a seed file is in general not necessary, see the
L</NOTES> section for more information.

=item [B<-writerand file>]

Writes random data to the specified I<file> upon exit.
This can be used with a subsequent B<-rand> flag.

=item B<-base64>

Perform base64 encoding on the output.

=item B<-hex>

Show the output as a hex string.

=back

=head1 NOTES

Prior to OpenSSL 1.1.1, it was common for applications to store information
about the state of the random-number generator in a file that was loaded
at startup and rewritten upon exit. On modern operating systems, this is
generally no longer necessary as OpenSSL will seed itself from a trusted
entropy source provided by the operating system. The B<-rand>  and
B<-writerand>  flags are still supported for special platforms or
circumstances that might require them.

It is generally an error to use the same seed file more than once and
every use of B<-rand> should be paired with B<-writerand>.

=head1 SEE ALSO

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

=head1 COPYRIGHT

Copyright 2000-2020 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>.

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