Tuesday morning, I'm in the car with my son, and the topic of steganography comes up. Eli is an adventurous kid – he loves playing games involving treasure and discovery with his mates. No prize for guessing how fascinated he was with the concept of hiding secret messages in plain sight.

He wanted to learn a few steganography techniques, of course. I told him about some of the obvious ones. Despite my experience with steganography in the past, I struggled coming up with simple techniques he could put into practice without the help of a computer. Determined to figure something out, I explained Acrostic Steganography. Eli loved the idea. Now he could write letters to his friends containing secret messages.