NAME

       openssl-rand, rand - generate pseudo-random bytes

SYNOPSIS

       openssl rand [-help] [-out file] [-rand file...]  [-writerand file] [-base64] [-hex] num

DESCRIPTION

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

       The random bytes are generated using the 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 RAND_bytes(3),
       RAND(7), and RAND_DRBG(7).

OPTIONS

       -help
           Print out a usage message.

       -out file
           Write to file instead of standard output.

       -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 ; for MS-Windows, , for
           OpenVMS, and : for all others.  Explicitly specifying a seed file is in general not necessary, see
           the "NOTES" section for more information.

       [-writerand file]
           Writes random data to the specified file upon exit.  This can be used with a subsequent -rand flag.

       -base64
           Perform base64 encoding on the output.

       -hex
           Show the output as a hex string.

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 -rand  and -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 -rand should be paired
       with -writerand.

SEE ALSO

       RAND_bytes(3), RAND(7), RAND_DRBG(7)

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
       <https://www.openssl.org/source/license.html>.