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These notes form a brief introduction to using and cracking substitution ciphers and transposition ciphers, to accompany the teaching materials provided with the University of Southampton National Cipher Challenge. The website for the competition can be found at www.cipherchallenge.org.
This first set of resources is a full set of worksheets with teachers notes on a variety of ciphers. I developed these as part of an assignment whilst doing my PGCE. atbash_cipher.pdf
Write a encoded message using the Atbash Cipher. Pass it to the person si ng in front of you to decode. If someone was to intercept your message, how easy would it be for them to decipher the code, and read the message?
The Pigpen Cipher is a Subs tu on Cipher that was used by the Freemasons in the 18th Century. They subs tuted each le ©er of the alphabet with a picture. Using the diagram on the le L, can you decipher the two mathema cal words below? Discuss in pairs how the cipher works.
The following chart shows a Vigenere cipher, named after a French mathematician, Blaise Vigenere. This is an example of a polyalphabetic cipher, which differs from monoalphabetic ciphers like the Caesar
A cipher is a method of transforming a text in order to conceal its meaning. KEY PHRASE / KEY OBJECT A key phrase lets the sender tell the recipient what to use to decode a message.
Using frequency analysis, a sensible guess would be to try a shift which maps E to one of the most common ciphertext characters. Use any method (brute force, spotting patterns, frequency...
