While you can learn a lot about classic encryption methods and their weaknesses under the menu item Ciphers, you here have the chance to encrypt a text in hex with the modern AES encryption method. Currently, this method is being regarded as safe – provided a "good" key is used.
You can have the Password Generator provide you with a safe password. On this site, you can also learn about what a "good" password is and how to remember a seemingly complicated password without a problem.
Try beating the computer at the Taxman game and prove your mathematical skills by getting to the top of the high score.