mkpassphrase.rb

#!/usr/bin/env ruby

require 'optparse'

def exp_notation(n)
  Math.log10(n).floor
end

def main
  options = {}

  optparse = OptionParser.new do |opts|
    opts.banner = <<-EOB
Usage: #{0} [options] [number of words]

Generate a random passphrase from words in a dictionary.
EOB
    opts.on('-v', "--verbose", "Output the number of combinations from which this password was picked") {
      options[:verbose] = true
    }
    opts.on('-l', '--min-length=LENGTH', 'Set the minimum length for a constituent word (default: 3)') { |length|
      options[:min] = length.to_i
    }
    opts.on('-u', '--max-length=LENGTH', 'Set the maximum length for a constituent word (default: 9)') { |length|
      options[:max] = length.to_i
    }
    opts.on('-f', '--dictionary=DICT', 'Dictionary file to use (default: /usr/share/dict/words)') { |dict|
      options[:dict] = dict
    }
    opts.on('-x', '--exclude-easy-typos', 'Exclude repeated chars at word boundaries') {
      options[:exclude_duplicates_at_boundaries] = true
    }
    opts.on('-X', '--exclude-dupes-inside', 'Exclude repeated chars inside words') {
      options[:exclude_duplicates] = true
    }
    opts.on('-h', '--help', 'This help') {
      puts opts
      exit(1)
    }
  end
  optparse.parse!

  n=(ARGV[0] || 4).to_i
  min = options[:min] || 3
  max = options[:max] || 9
  dict = options[:dict] || '/usr/share/dict/words'

  lines = File.open(dict).readlines.map {|line| line.chomp.downcase }.uniq.select {|word|
    word.length >= min && word.length <= max && (!options[:exclude_duplicates] || !word.match(/([a-z])\1/))
  }
  words = []
  last_word = ''
  n.times do
    word = lines[rand(lines.length)]
    if options[:exclude_duplicates_at_boundaries] && last_word[-1] == word.first
      continue
    end
    words << word
    last_word = word
  end
  passphrase = words.join(' ').downcase
  print passphrase

  if options[:verbose]
    puts " (10e#{exp_notation(27 ** passphrase.length)}c 10e#{exp_notation(lines.length ** words.length)}w)"
  else
    puts
  end
end

main if $0 == __FILE__