Using Libraries (1)

Our Person class does not define an attribute accessor method for its password, and thus, others cannot ask for and retrieve it.

However, our person object could freely give them an encrypted version of it.

Actually, this is pretty similar to how authentication often works in real web applications:

Applications do not store your actual password in plain text (hopefully!) That way if, for some reason, they get hacked, attackers wouldn’t have your actual password. Instead they store an encrypted version of the password.

Anyhow, we now want to add a method encrypted_password to the Person class, which should return an encrypted version of the password that is stored in the instance variable @password.

Encryption is one of the things in programming that require very deep expert knowledge, and it is one of the things we definitely wouldn’t want to implement ourselves.

So far, all the Ruby features and methods that we have used are available right away when the Ruby runtime ruby executes your code. However, Ruby also comes with a ton of functionality that is not available (loaded) right away. Instead it is stored in so called libraries (which are just Ruby files, too), and we have to load them manually, in order to make them available.

To do this, we use the method require, and pass it the name of the library:

require 'digest'

Normally require statements should be placed at the very top of the file, so it is easy to see what libraries a particular piece of code (class) uses.

We are going to omit the initialize and name methods here, indicate the omission with the comment # ..., and just keep the password= attribute writer. In order to run this code make sure you keep all the methods.

require 'digest'

class Person
  # ...

  def password=(password)
    @password = password

  def encrypted_password

The library digest that we required includes a something called Digest::SHA2.

In programming a “digest” is an algorithm to convert one string into another in a way that the original string cannot be recovered later. However digesting the same string will always result in the same other, unique string. There are a good bunch of algorithms that do this, and “sha2” is the name of one of them.

Ok. For our example here we only need to understand that, once we have required the library digest, we can use the method Digest::SHA2.hexdigest, and it will encrypt (“digest”) the string that we pass to it.

If now run the following code:

person ="Ada")
person.password = "super secret"
puts person.encrypted_password

it will output


which is the digested form of the string "super secret". Every time you run the program you will see the same, unique string.