What is a Transposition Cipher?

A transposition cipher is a cipher in which the letters of the plaintext are not replaced but are simply moved. There have been examples involving all sorts of cunning devices, often rotated or flipped halfway through writing the message.

A large number of ciphers include both a substitution and a transposition element. This includes the majority of modern block-ciphers.

The most famous transposition cipher is also one of the earliest, known to have been used by Spartan generals at least 2,500 years ago.

The Scytale

The Scytale was the name of a staff carried by officers in the Spartan army. It was a precise diameter, the same for all officers. A belt would be wound around the scytale in a helical pattern and the secret message written along the length of the staff in as many rows as were needed. When the belt was unwound the letters would appear as an incomprehensible jumble but the message could be easily read by anyone knowing the trick who had a staff of exactly the same size.

The belt could be worn by a messenger with the message on the inside, making the method steganographic as well as cryptographic.