zxcvbn をつかって Rails のパスワードバリデーションを強化してみる ref: http://qiita.com/items/5563519a8e7f2dbc427a

Gemfile

gem "zxcvbn-ruby", :require => 'zxcvbn'

ja.yml

ja:
  errors:
    messages:
      week_password: より複雑な%{attribute}を入力してください。あなたのパスワードは%{crack_time}で破られます。

shell

bundle

user.rb

  validates :password, zxcvbn: {score: 3}

zxcvbn_validator.rb

require 'zxcvbn'

class ZxcvbnValidator < ActiveModel::EachValidator
  attr_reader :record, :attribute, :value

  SCORE_RANGE = (1..4).freeze

  def initialize(options)
    unless SCORE_RANGE.include? options[:score]
      raise ArgumentError, ":range must be a #{SCORE_RANGE.to_s.gsub('..', ' to ')}"
    end

    super
  end

  def validate_each(record, attribute, value)
    @record, @attribute, @value = record, attribute, value

    @score = options[:score]
    add_error unless valid?
  end

  private

  def valid?
    @messages_options = {}
    week_keywords = []

    for key, val in @record.attributes
      next if %w[password password_confirmation encrypted_password].include?(key)
      next unless val.kind_of?(String)

      week_keywords.push val if val

      for splited_val in val.split(/[@._]/)
        week_keywords.push splited_val
      end
    end

    result = Zxcvbn.test(value, week_keywords)
    @messages_options[:crack_time] = display_time result.crack_time
    result.score >= @score
  end

  def add_error
    if message = options[:message]
      record.errors[attribute] << message
    else
      record.errors.add attribute, :week_password, @messages_options
    end
  end

  def display_time(seconds)
    minute  = 60
    hour    = minute * 60
    day     = hour * 24
    month   = day * 31
    year    = month * 12
    century = year * 100

    case
    when seconds < minute
      unit = 'x_seconds'
      count = 1 + seconds.ceil
    when seconds < hour
      unit = 'x_minutes'
      count = 1 + (seconds / minute).ceil
    when seconds < day
      unit = 'about_x_hours'
      count = 1 + (seconds / hour).ceil
    when seconds < month
      unit = 'x_days'
      count = 1 + (seconds / day).ceil
    when seconds < year
      unit = 'x_months'
      count = 1 + (seconds / month).ceil
    when seconds < century
      unit = 'x_years'
      count = 1 + (seconds / year).ceil
    end

    I18n.t "#{unit}.other", scope: [:datetime, :distance_in_words], count: count
  end

end