redmine/db/migrate/20110223180953_salt_user_passwords.rb

class SaltUserPasswords < ActiveRecord::Migration[4.2]

  def self.up
    say_with_time "Salting user passwords, this may take some time..." do
      User.salt_unsalted_passwords!
    end
  end

  def self.down
    # Unsalted passwords can not be restored
    raise ActiveRecord::IrreversibleMigration, "Can't decypher salted passwords. This migration can not be rollback'ed."
  end
end