As a more complex example than the Caeser Cipher of ciphering messages and their use throughout history, the Vigenere Cipher can be used with older students (Years 5 & 6) to inspire an interest in security and cryptography. This cipher remained unbroken from 300 years after it was created by an Italian cryptologist (not Vigenere himself). I would use this as a catalyst for a lesson where students are guided into, then independently work to, create a cipher of their own, individually or in groups. Students can then test each other’s encryption codes and gain a first hand understanding of the need for strong security systems.

Attached are links to a wiki article and a tutorial video for the Vigenere cipher:

https://www.youtube.com/watch?v=zNO4PTlg62k

http://https://upload.wikimedia.org/wikipedia/commons/9/9a/Vigen%C3%A8re_square_shading.svg