Knuthy Obfuscation (Optimus Prime)

obfuscation.rb

# app/models/concerns/obfuscation.rb

# ID obfuscation using Optimus algorithm
# TODO if we want to use this with more classes, it'd
# be best to make sure we use a different random seed
# for each model.
# Do something like this: http://jes.al/2014/11/creating-rails-concern-accepts-argumentsparameters/
module Obfuscation
  extend ActiveSupport::Concern

  module ClassMethods
    def obfuscate_id(n)
      OPTIMUS.encode(n.to_i)
    end

    def deobfuscate_id(str)
      OPTIMUS.decode(str.to_i)
    end

    def find_by_obfuscated_id(id)
      find_by(id: OPTIMUS.decode(id.to_i))
    end

    def find_by_obfuscated_id!(id)
      find_by!(id: OPTIMUS.decode(id.to_i))
    end
  end

  def obfuscated_id
    OPTIMUS.encode(id.to_i)
  end

  def to_param
    respond_to?(:title) && title.present? ? "#{obfuscated_id}-#{title.parameterize}" : obfuscated_id.to_s
  end
end

optimus.rb

# lib/util/optimus.rb

# Donald Knuth's two-way fast hashing algorithm
# More info: https://jenssegers.com/67/id-transformation-with-optimus
# Based on: https://github.com/jenssegers/optimus
# Generate prime, inverse, and random xor with `php vendor/bin/optimus spark` (must have above installed via PHP composer)
# Numeric alternative to: http://hashids.org/ruby/
module Optimus
  class Optimus
    MAX_INT = 2147483647 # based on Postgres' integer/int4 maximum

    def initialize(prime, inverse, xor = 0)
      raise ArgumentError, "prime must be an integer" unless (prime.is_a?(Numeric) && prime.integer?)
      raise ArgumentError, "inverse must be an integer" unless (inverse.is_a?(Numeric) && inverse.integer?)
      raise ArgumentError, "xor must be an integer" unless (xor.is_a?(Numeric) && xor.integer?)

      @prime = prime.to_i
      @inverse = inverse.to_i
      @xor = xor.to_i
    end

    def encode(value)
      raise ArgumentError, "Value to encode must be an integer" unless (value.is_a?(Numeric) && value.integer?)
      ((value.to_i * @prime) & MAX_INT) ^ @xor
    end

    def decode(value)
      raise ArgumentError, "Value to decode must be an integer" unless (value.is_a?(Numeric) && value.integer?)
      ((value.to_i ^ @xor) * @inverse) & MAX_INT
    end
  end
end

optimus_primes.rb

# config/initializers/optimus_primes.rb

OPTIMUS = Optimus::Optimus.new(ENV['optimus_prime'].to_i, ENV['optimus_inverse'].to_i, ENV['optimus_random'].to_i)