Cryptography and SSL/TLS Toolkit



openssl-rand - generate pseudo-random bytes


openssl rand [-help] [-out file] [-base64] [-hex] [-engine id] [-rand files] [-writerand file] [-provider name] [-provider-path path] [-propquery propq] num[K|M|G|T]


This command generates num random bytes using a cryptographically secure pseudo random number generator (CSPRNG). A suffix [K|M|G|T] may be appended to the num value to indicate the requested value be scaled as a multiple of KiB/MiB/GiB/TiB respectively. Note that suffixes are case sensitive, and that the suffixes represent binary multiples (K = 1024 bytes, M = 1024*1024 bytes, etc).

The string 'max' may be substituted for a numerical value in num, to request the maximum number of bytes the CSPRNG can produce per instantiation. Currently, this is restricted to 2^61 bytes as per NIST SP 800-90C.

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 EVP_RAND(7).



Print out a usage message.

-out file

Write to file instead of standard output.


Perform base64 encoding on the output.


Show the output as a hex string.

-engine id

See "Engine Options" in openssl(1). This option is deprecated.

-rand files, -writerand file

See "Random State Options" in openssl(1) for details.

-provider name
-provider-path path
-propquery propq

See "Provider Options" in openssl(1), provider(7), and property(7).


openssl(1), RAND_bytes(3), RAND(7), EVP_RAND(7)


The -engine option was deprecated in OpenSSL 3.0.

Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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