Simple manual methods for encryption
One of the most basic methods for exchanging encrypted messages is a
substitution cipher. In its simplest form it uses a shifted alphabet.
This is often called a Caesar Cipher,
as it was used by Gaius Julius Caesar for communication with his generals.
It is also known as Strip Cipher, as some implementations use sliding
alphabets printed on strips (made of paper, plastic or wood).
Subsitution tables, matrix ciphers and some versions of the
One-Time Pad (OTP)
can also be seen as manual cipher methods.
Over the years, a wide variety of hand methods have been used,
with varying degrees of success. Some are really sophisticated, but most
are relatively simple and can be broken easily with pencil-and-paper methods
or computers. Below are some examples.