The art and skill of concealing messages was a common activity in Shakespeare’s days. Just like today, it was vital to protect sensitive information so that it wouldn't fall into the wrong hands. Sometimes your life would depend on effective cryptography.

 

One famous example is the fate of Mary, Queen of Scots, whose destiny was sealed because of bad cryptology. Her intercepted letters sent from jail were deciphered, and eventually she was beheaded because of their content. Read more about the "Babington Plot" on Wikipedia:

 

 

http://en.wikipedia.org/wiki/Babington_Plot