openssl-rand, rand - generate pseudo-random bytes
openssl rand [-help] [-out file] [-rand
file...] [-writerand file] [-base64] [-hex]
num
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).
- -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.
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.
RAND_bytes(3), RAND(7), RAND_DRBG(7)
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>.
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