string_entropy

Outputs the information entropy, Shannon entropy, and metric entropy of any given ASCII_8BIT string.

More information on entropy:

• https://en.wikipedia.org/wiki/Entropy_%28information_theory%29
• https://en.wikibooks.org/wiki/An_Intuitive_Guide_to_the_Concept_of_Entropy_Arising_in_Various_Sectors_of_Science

Installation

Add this line to your application's Gemfile:

gem 'string_entropy'

And then execute:

$ bundle

Or install it yourself as:

$ gem install string_entropy

Usage

As an extension to the String class:

"password".entropy
=> 52.55884486664758

With the StringEntropy::Info class:

string_entropy = StringEntropy.info("password")
=> #<StringEntropy::Info:0x007fb864091590
 @count={"p"=>1.0, "a"=>1.0, "s"=>2.0, "w"=>1.0, "o"=>1.0, "r"=>1.0, "d"=>1.0},
 @frequency=
  {"p"=>0.125,
   "a"=>0.125,
   "s"=>0.25,
   "w"=>0.125,
   "o"=>0.125,
   "r"=>0.125,
   "d"=>0.125},
 @information_entropy=52.55884486664758,
 @metric_entropy=0.34375,
 @shannon_entropy=2.75,
 @shannon_formulas=
  ["H(X) = -[ ((0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))+(0.25 * Math.log2(0.25))+(0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))) ]",
   "H(X) = -[ ((-0.375)+(-0.375)+(-0.5)+(-0.375)+(-0.375)+(-0.375)+(-0.375)) ]",
   "H(X) = -[ (-2.75) ]",
   "H(X) = 2.75"],
 @string="password">

# Original string
string_entropy.string
=> "password"

# String encoding, currently only supports ASCII_8BIT
string_entropy.encoding
=> "ASCII-8BIT"

# The commonly described "entropy" of a string; Math.log2(total_possible_chars^string_length)
string_entropy.entropy
=> 52.55884486664758

# Alias for .entropy method
string_entropy.information_entropy
=> 52.55884486664758

# The Shannon entropy value
string_entropy.shannon_entropy
=> 2.75

# The metric entropy value (Shannon entropy divided by string length)
string_entropy.metric_entropy
=> 0.34375

# The count of each character
string_entropy.count
=> {
    "p" => 1.0,
    "a" => 1.0,
    "s" => 2.0,
    "w" => 1.0,
    "o" => 1.0,
    "r" => 1.0,
    "d" => 1.0
}

# The frequency/percentage of each character
string_entropy.frequency
=> {
    "p" => 0.125,
    "a" => 0.125,
    "s" => 0.25,
    "w" => 0.125,
    "o" => 0.125,
    "r" => 0.125,
    "d" => 0.125
}

# This is how the Shannon entropy is calculated
string_entropy.shannon_formulas
=> [
    [0] "H(X) = -[ ((0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))+(0.25 * Math.log2(0.25))+(0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))+(0.125 * Math.log2(0.125))) ]",
    [1] "H(X) = -[ ((-0.375)+(-0.375)+(-0.5)+(-0.375)+(-0.375)+(-0.375)+(-0.375)) ]",
    [2] "H(X) = -[ (-2.75) ]",
    [3] "H(X) = 2.75"
]

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Credits

Inspired by http://www.shannonentropy.netmark.pl.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/anothermh/string_entropy.

License

The gem is available as open source under the terms of the MIT License.