randgen

randgen is a tool which generates random bytes using a pseudorandom number generator (PRNG).

Installation

From source

cargo install randgen

From binaries

The release page contains pre-built binaries for Linux, macOS and Windows.

How to build

Please see BUILD.adoc.

Usage

Basic usage

Generate 1 KiB of random bytes:

randgen 1KiB

Output formats

The following output formats are available:

• raw (encode the generated bytes as raw bytes)
• base64 (encode the generated bytes as base64)
• base64url (encode the generated bytes as URL-safe base64)
• hex (encode the generated bytes as hex string)

[!TIP] The result is output on a single line, so there is no line wrapping.

The default output format is raw. To change this, use -f option.

randgen -f base64 256

This has the same result as:

randgen 256 | base64 -w 0

Supported PRNGs and CSPRNGs

Supported PRNGs are:

• ISAAC RNGs (if enabled at compile time)
• Mersenne Twister RNGs (if enabled at compile time)
• PCG RNGs (if enabled at compile time)
• SFC RNGs (if enabled at compile time)
• Xorshift family
  • SplitMix64 RNG
  • Xorshift RNG (if enabled at compile time)
  • xoroshiro RNGs
  • xoshiro RNGs

Supported CSPRNGs are:

• ChaCha-based RNGs
• HC-128-based RNG (if enabled at compile time)

The default RNG is chacha12. To change this, use -r option.

randgen -r pcg64 "2 MB"

Providing a random seed

-s option allows you to specify a 64-bit unsigned integer random seed to be used when creating a new PRNG. If this option is not specified, the RNG seeded via random data from system sources such as the getrandom system call on Linux.

$ randgen -f hex -r sfc32 -s 8 32B
24f48cd0c3f6a1c6e8d7b4dcff9578864aced749e4eb1805dfba8b6e21d0cba0

This has the same result as:

$ randgen -r sfc32 -s 8 32B | xxd -c 0 -p
24f48cd0c3f6a1c6e8d7b4dcff9578864aced749e4eb1805dfba8b6e21d0cba0

Print the progress bar

When -p option is specified, randgen will print information showing the progress of the generation of random bytes.

randgen -p 4GiB > /dev/null

This is similar to the following example which uses pv(1):

randgen 4GiB | pv -s 4G > /dev/null

Generate shell completion

--generate-completion option generates shell completions to standard output.

The following shells are supported:

• bash
• elvish
• fish
• nushell
• powershell
• zsh

Example:

randgen --generate-completion bash > randgen.bash

Integration with other programs

Encode the generated bytes

To encode the generated bytes into an output format not supported by randgen, pipe the output of randgen to the input of another program.

For example, to encode the generated bytes as base32:

$ randgen -s 16 32B | base32
DYQZ33GRHUR5WIFRSBZVQ3ZPEFZASXB3SNTRUHR3NPITZBMDPZXQ====

Line wrapping

randgen does not wrap lines of the result.

To wrap lines of the result:

$ randgen -f base64url -s 256 128B | fold -w 76
0X82yjVU1_JLdDU07ywJ_7CAJBwRTEVS_i1-kRgR6HQsb9jFyQNuiFIBmrTucpwt-CZjZj90JYjE
6D2erJEn6f8ju9KBmLraVj55I9KQRxhh2BmJMrovQhEK9nU3Ysn-mOURovtVCE45dqKyWTHuWLV2
Hr1yramxGwVm88LXhA8=

This has the same result as:

$ randgen -s 256 128B | basenc --base64url
0X82yjVU1_JLdDU07ywJ_7CAJBwRTEVS_i1-kRgR6HQsb9jFyQNuiFIBmrTucpwt-CZjZj90JYjE
6D2erJEn6f8ju9KBmLraVj55I9KQRxhh2BmJMrovQhEK9nU3Ysn-mOURovtVCE45dqKyWTHuWLV2
Hr1yramxGwVm88LXhA8=

Comparison with similar things

The following generates 64 KiB of random bytes and encodes it as base64:

randgen -f base64 64KiB

This section describes how to do the same thing with other things.

OpenSSL

openssl-rand(1ssl) can be used for this purpose.

openssl rand -base64 64K

GnuPG

gpg --gen-random can be used for this purpose.

gpg --gen-random 1 65536 | base64

Kernel random number source devices

random(4) (/dev/random and /dev/urandom) can be used for this purpose.

head -c 65536 /dev/random | base64

[!CAUTION] Unlike randgen, these things wrap lines of the result.

Command-line options

Please see the following:

• randgen(1)

Source code

The upstream repository is available at https://github.com/sorairolake/randgen.git.

Changelog

Please see CHANGELOG.adoc.

Contributing

Please see CONTRIBUTING.adoc.

License

Copyright (C) 2025 Shun Sakai (see AUTHORS.adoc)

1. This program is distributed under the terms of either the Apache License 2.0 or the MIT License.
2. Some files are distributed under the terms of the Creative Commons Attribution 4.0 International Public License.

This project is compliant with version 3.3 of the REUSE Specification. See copyright notices of individual files for more details on copyright and licensing information.