Migrating to a new password encryption in devise, coming from authlogic

devise_migration.rb

class MigrateUserToDevise < ActiveRecord::Migration
  def self.up
    change_table :users do |t|
      t.string :encrypted_password, :null => false, :limit => 128
      # ...
    end
  end

  def self.down
  end
end

password_encryption_migration.rb

module Devise

  module PasswordEncryptionMigration

    def valid_password?(incoming_password)
      if using_authlogic_validation?
        Devise.secure_compare(authlogic_password_digest(incoming_password), self.crypted_password).tap do |validated|
          if validated
            self.password         = incoming_password
            self.crypted_password = nil
            self.save(:validate => false)
          end
        end
      else
        Devise.secure_compare(password_digest(incoming_password), self.encrypted_password)
      end
    end

    def using_authlogic_validation?
      self.encrypted_password.blank?
    end

    def authlogic_password_digest(password)
      if self.password_salt.present?
        Devise::Encryptors::AuthlogicSha512.digest(password, 20, self.password_salt, nil)
      end
    end

  end

end

user.rb

class User < ActiveRecord::Base

  # devise ...
  include Devise::PasswordEncryptionMigration

end