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PoolOfEntropy is a pseudo random number generator (PRNG) based on secure hashes, intended to bring back the feeling of 'personal agency' that some gamers may feel when rolling their own dice. An instance of the PoolOfEntropy class could be assigned to a player, or to each die in a game, and it can be influenced (similar to throwing a die differently), or personalised by feeding in arbitrary data (e.g. a picture of the player, a favourite saying). It can handle these influences whilst remaining unbiased and fair on each roll.

PoolOfEntropy is probably secure when used appropriately, and in a very limited sense. However, cryptographic security is not its purpose. The core purpose is for playing with random number generation and non-standard sources of entropy. The choice of name is supposed to reflect this.

If you are looking for a secure PRNG in Ruby, good for generating session codes or server-side secrets, use the standard library SecureRandom.

If you think that rolling all your dice on an anonymous server has removed a little bit of soul from your game sessions, or if you want to generate unbiased random numbers using input from your laptop's microphone or mobile's accellerometer as a source, then PoolOfEntropy might be for you.


Add this line to your application's Gemfile:

gem 'pool_of_entropy'

And then execute:

$ bundle

Or install it yourself as:

$ gem install pool_of_entropy


Create a new generator:

pool = PoolOfEntropy.new


pool = PoolOfEntropy.new :size => 24


pool = PoolOfEntropy.new :size => 24, :blank => true

The :size parameter sets the amount of randomness that the pool can store, in multiples of 512 bits (or 64 bytes). The default size of 1 is fastest, and has a good distribution of values statistically. Larger pool sizes (up to 256) will calculate a little slower, but can be used to buffer more entropy from the #add_to_pool method.

Setting :blank to true starts the pool with the entire pool zero, so that repeatedly using the generator in exactly the same way will return the same values.

Get a random number.

Not feeding the generator with any customisation means it is completely deterministic based on current internal state. The analogy here might be "trusting to Fate":

pool.rand( 20 )

Influence the next random number (but not any others).

This is analogous to shaking or throwing dice in a certain way. Only the next result from rand() is affected:

pool.modify_next( 'Shake the die.' )
pool.rand( 20 )

# Also
pool.modify_next( 'Shake the die.' ).rand( 20 )

# This next result will not be influenced,
# we re-join the deterministic sequence of the PRNG:

Influence the next three random numbers.

Data supplied to modify_next is put in a queue, first in, first out:

pool.modify_next( 'Shake the die lots.' )
pool.modify_next( 'Roll the die cautiously.' )
pool.modify_next( 'Drop the die from a great height and watch it bounce.' )

pool.rand  # influenced by 'Shake the die lots.'
pool.rand  # etc

pool.rand #  . . . and back to main sequence

Influence all random numbers from this point forward.

This is analogous to having a personal style of throwing dice, or perhaps a different environment to throw them in.

pool.modify_all( 'Gawds help me in my hour of need!' )

# All these are modified in same way
pool.rand( 20 )
pool.rand( 20 )

# The two modifier types "stack", and this is modified twice
pool.modify_next( 'And I really mean it!' ).rand( 20 )

Remove modfiers.

# Just the "all" modifier
pool.modify_all( nil )

# Insert a pause into the "next" queue
pool.modify_next( nil )

# Re-set "next" and "all" modifiers

Alter internal state of pool.

This mixes in any entropy in the supplied data, and changes the deterministic sequence going forward. This is analogous to long-term alterations to dice, the environment, or person throwing the dice.

pool.add_to_pool( 'Purple is my favourite colour.' )

All the inputs can be any length String, from any source. If the data contains any "true randomness" (however you want to define it, and however the String is formatted), then PoolOfEntropy will process that (using SHA-512) into unbiased results.

If you care about your own source of randomness being more "important" than the initial state of the PRNG or its deterministic progression, then make use of the modifiers and/or add data to the pool frequently.

More information


  1. Fork it ( http://github.com/neilslater/pool_of_entropy/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request