Sysrandom Gem Version Build Status ISC licensed

Secure random number generation for Ruby using system RNG facilities e.g. /dev/urandom, getrandom(2)


System/OS-level random number generators like /dev/urandom and getrandom(2) provide the best option for generating cryptographically secure random numbers.

Ruby's built-in SecureRandom does not provide this, but instead uses OpenSSL's userspace RNG. This has been a source of vulnerabilities in Ruby, and an open Ruby bug ticket contains much discussion on the issue with no clear path to resolution.

This gem aims to solve the problem.


In cryptography circles, the prevailing advice is to use OS RNG functionality, namely /dev/urandom or equivalent calls which use an OS-level CSPRNG to produce random numbers.

This gem provides an easy-to-install repackaging of the randombytes functionality from libsodium for the purpose of generating secure random numbers trustworthy for use in cryptographic contexts, such as generating cryptographic keys, initialization vectors, or nonces.

The following random number generators are utilized:

Platform RNG
Linux getrandom(2) if available, otherwise /dev/urandom
Windows RtlGenRandom CryptGenRandom without CryptoAPI deps
OpenBSD arc4random(3) with ChaCha20 CSPRNG (not RC4)
JRuby NativePRNGNonBlocking on Java 8, otherwise SHA1PRNG
Others /dev/urandom

Supported Platforms

Sysrandom is tested on the following Ruby implementations:

  • Ruby (MRI) 2.0, 2.1, 2.2, 2.3
  • JRuby


Add this line to your application's Gemfile:

gem 'sysrandom'

And then execute:

$ bundle

Or install it yourself as:

$ gem install sysrandom


Sysrandom aims to be API-compatible with Ruby's built-in SecureRandom class, but always prefers OS-level RNG wherever it's available:

>> Sysrandom.random_number(42)
=> 15
>> Sysrandom.random_bytes(32)
=> "\xD6J\xB3\xD2\x8B\x7F*9D\xB7\xF9\xEA\xE2\\\xAAH\tV#\xEC\x84\xE3E\r\x97\xB9\b\xFCH\x17\xA0\v"
>> Sysrandom.base64(32)
=> "WXPkxfAuLRpnI6Z4zFb4E+MIenx6w6vKhe01+rMPuIQ="
>> Sysrandom.urlsafe_base64(32)
=> "37rsMfR4X8g7Bb-uDJEekRHnB3r_7nO03cv52ilaWqE="
>> Sysrandom.hex(32)
=> "c950496ce200abf7d18eb1414e9206c6335f971a37d0394114f56439b59831ba"
>> Sysrandom.uuid
=> "391c6f52-8017-4838-9790-131a9b979c63"

Patching SecureRandom with Sysrandom

Since Sysrandom is SecureRandom-compatible, it can be patched in-place of SecureRandom if you prefer its RNG behavior.

To do this, require sysrandom/securerandom:

>> SecureRandom
=> SecureRandom
>> require "sysrandom/securerandom"
=> true
>> SecureRandom
=> Sysrandom
>> SecureRandom.hex(32)
=> "d1bbe8c1ab78fc2fe514c5623d913a27ffd2dcdc9e002f3b358bb01a996962f1"


  • Fork this repository on Github
  • Make your changes and send a pull request
  • If your changes look good, we'll merge them

Copyright (c) 2013-2017 Frank Denis, Tony Arcieri. See LICENSE.txt for further details.