friendly_guid.rb

class FriendlyGuid
  attr_reader :mask

  def initialize(mask)
    @mask = mask
  end

  def guid(id)
    (id.to_i ^ mask).to_s(36)
  end

  def id(guid)
    guid.to_i(36) ^ mask
  end
end

if __FILE__ == $0
  mask = Random.new.rand(2**64)
  id = Random.new.rand(2**64)
  f = FriendlyGuid.new(mask)
  puts "mask = #{mask}"
  puts "id = #{id}"
  g = f.guid(id)
  puts "guid = #{g}"
  puts "id = #{f.id(g)}"
end

output.txt

mask = 1000723141368662252
id = 2465229093246480629
guid = q6parhf03kt5
id = 2465229093246480629