Long Road Computer Science and Maths A level students have been taking part in a national code-breaking challenge set up by the University of Southampton Mathematics department – and sponsored by GCHQ! Year 2 students Emma Rooney (Computer Science, Maths, Further Maths and Physics – left in photo) and Hatesh Saini (Computer Science, Maths and Media – right in photo) explain what’s involved:
Emma: Each week during term-time we’ve been set a challenge based on a story. We’ve had to decrypt each message by a deadline.
Hatesh: The clues are on the page – and some text contains hidden messages. To start with we were using basic substitution techniques with, for example, one letter standing in for another. We’ve then had to use transpositional techniques where we use grids – this might involve swapping columns and rows. We’ve made use of the Vigenère cipher, a polyalphabetic cipher based on the letters of a keyword.
Emma: Another method – one of the hardest to decrypt – is the Vernam cipher, which is based on the principle that each plaintext character from a message is ‘mixed’ with one character from a key stream. You use a ‘one-time’ pad with a new key each time and use a table to produce output.
Hatesh: We’re on week 6 at the moment – there are 8 in total. The problem is posted at about 3pm on Thursdays.
Emma: I have to wait until after my classes to get to work as I’m in lessons then! The overall winner gets £1000.
Both students are working hard to get into competitive universities:
Hatesh: I’m hoping to study Computer Science at the University of York or Aston University.
Emma: I want to study Maths / Computer Science at the University of Southampton or the University of Warwick.
Main photo: A format of one-time pad, as used in the Vernam Cipher. This example was used by the U.S. National Security Agency, code named DIANA. The table on the right is an aid for converting between plaintext and ciphertext using the characters at left as the key.