Steganography (Greek for 'covered writing') is a science that is quite different from cryptography. In cryptography, the sender encodes the message so that it will be unintelligible. In steganography, the sender does not try to encode the message because the message is sent secretly, and if no one other than the receiver sees the message there's little need to encode it. Steganography may be considered an alternate branch of cryptology, in some respects, though it stands firmly on its own in others.

The first recorded use of steganography comes from China during the 11th century. Diplomats would write messages on very thin silk and then roll it into a small ball. The ball could be hidden easily on the messenger (it was often swallowed). Another ancient story of steganography involves a rich Greek who shaved the head of his spy, tattooed a message onto his scalp and then allowed the hair to grow back. Once the slave had a full head of hair again, he was sent to one of the Master's friends with instructions to shave the slave's head upon arrival. Both of these methods do conceal that a message is present - but they also require a courier, which is something not easily accessible.

One popular way to conceal messages is to use a Cardano Grille. Named after its inventor, Girolama Cardano (who also helped with a polyalphabetic cipher), the Cardano Grille system is something you're probably already familiar with. Basically, each recipient has a piece of paper with several holes cut it. When the 'grille' (the piece of paper with holes) is placed over an innocuous looking messages the holes in the grille line up with words in the larger message and produces the desired hidden message. People intercepting the message will be none the wiser because the words that the grille sees have been used in a larger message that takes up the entire page. Providing that the sender is a decent wordsmith with a good imagination, even difficult messages can be sent with the grille while the larger message will still be literate and sound meaningful.

The Cardano grille is perhaps the safest way to transmit concealing messages if performed correctly. Unfortunately, it does not lend itself well to large concealed messages when creating literate text from the bits and pieces of the secret message becomes very difficult. An alternative to the Cardano method is the so-called jargon code.