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About the challenge

The National Cipher Challenge has been run by the University of Southampton Mathematics Department since 2002 and since then has attracted a number of fans. These include two Foreign Secretaries; the media scientists Adam Hart-Davis and Simon Singh; Newsnight editor Mark Urban who has a passion for military history;  comedy writer James Cary who wrote Bluestone 42 and the Radio 4 comedy Hut 33, and the star of that show (and many others),  Robert Bathurst  whose aunt worked at Bletchley in the war. We have also had the pleasure of introducing the Cipher Challenge team from Saint Anne’s School in Southampton to the Duke of Edinburgh who, remembering his work in the second world war immediately fell in love with the competition and gave Harry a reading list for the summer. The real fans though are the competitors who take part every year until they are too old, by which time it is too late and they are hooked. Many of them go on to careers in cyber security and others follow other paths using the mathematics and computing skills they learned tackling our fiendish challenges.

If I were to name one thing which has undoubtedly influenced my academic drive, interests and overall career to date, it would be the National Cipher Challenge. Since being introduced to cryptography and the challenge in Year 8, it has been my one passion and driving force in pursuing further education in maths.

Julian Bhardwaj

Julian went on to study Discrete Mathematics and made it to the Grand Final of the UK National Cyber Security Championship in 2013, following in the footsteps of the 2008 National Cipher Challenge winner, Jonathan Millican, who was crowned winner of the UK National Cyber Security Championship the previous year. Naomi Andrew, who operates under a code name as one of the Elves on the site, took part from Year 8 until she was sadly too old to compete, but managed to stay involved as a student at Southampton. She is now studying for her PhD here and we like to think the Cipher Challenge had an important part to play in that journey:

It was fun seeing a different side of maths to what I was learning in class, and the elation of finally understanding a difficult cipher is a feeling that’s hard to beat. The challenge was my first taste of how much there is to maths, and more than 10 years later the subject continues to amaze and excite me!

Naomi Andrew

Even if you can’t or don’t want to take part in the competition there is a lot here for you to enjoy. You can find guides to programming and codebreaking, some free lessons to use in the classroom or as an extra-curricula activity, links to a wide range of resources, and to past competitions that are still available for you to enjoy.

The lesson PowerPoints are great to use with any year group – easy to understand with passages written in code for them to practise using the decryption methods, with little input needed from the teacher. Would recommend – especially if you are starting a Codebreaking club before the competition begins like me.

Sam Barlow, Queen Anne’s School, Caversham

We love the world of codes and ciphers and hope that, with a little encouragement, you will too.

“It was said by Niels Ferguson, one of the leading cryptographers of his generation, that cryptography was “just about the most fun you can have with mathematics”. We agree with that sentiment and hope that the Cipher Challenge will convince you too.

About the Challenge

Welcome to the National Cipher Challenge, a nationwide, online codebreaking competition, which will run again from October 10th 2019 to January 9th 2020.  If you have any questions please contact Harry at [email protected].

The competition is structured as a series of encrypted messages which tell a story. This year we travel back in time to the space race, and join Harry as he and his team struggle to uncover a saboteur working in the heart of NASA. Who are they, what do they want and can you stop them before time runs out? It is truly a Countdown to Catastrophe.

Who is the competition for?

The competition is aimed at school and sixth form students of mathematics and computer science, and is a great extension activity (or a fantastic maths club project) that can be tackled by them in teams or on their own.

How to register and join in

There is no charge to register or take part, and all you need to get involved is a reasonably modern web browser. We publish news about the competition at, and you can also keep up to date with competition news by following us on Twitter.

Entrants can take part alone or in teams of any size. To take part you will need to register for an account on the website, and we will ask you for a username (which we will use to identify you on the forum, where you can discuss a whole range of things connected to the competition, and quite a few that are totally unrelated). You will then be asked to create or join a team which you will use to submit your entires. If you ask to join an existing team then we will email your request to the team captain and let you know the outcome. If your request is turned down, don’t worry, you can request to join another team, or set up your own.

When setting up the team we ask you to say whether or not you are eligible for a prize. The rules are below. If you are eligible we will ask you for some information about your school, including the name and email address of a teacher contact. We need this in case you win a prize, but please do ask them first. If you are home educated then state that in the School name box and give the name and email address of an adult we can contact if we need to. We will not publish your name or the contact information of your teacher without your (or their) permission, but of course if you win a prize we will want to tell the world about your success!

If you want others to join your team let them know and they can submit a request through their team page which is linked under their user name at the top right of every page.  The names of everyone on a team will be on the certificate and we will publish the team name on the leaderboards so you can see how everyone is getting on.


You can download lessons and notes on codebreaking from the resources page on the competition website. This is the competition library and, alongside the materials we have produced you will find links to books, online videos and help guides that contain everything you need to be a successful code-breaker. You can even build your own cipher machines, including the simple cipher wheel and the more complicated Pringle Can Enigma Machine.

The history of the competition

The National Cipher Challenge has been run by the Mathematics department at the University of Southampton since 2002. It regularly attracts entries from teams from over 700 UK schools and colleges, together with a number of schools overseas who are in it for the fun. They are not eligible for prizes, but that doesn’t seem to put them off!

Competition schedule

Registration will open online on 30th September and the first episode will be published at 3pm on Thursday October 10th. The first three episodes are designed as a warm up, and while we will publish leader boards, the marks for those challenges won’t count towards the final competition standings. There will be a break for half term from and the main competition starts with episode 4 on 7th November, with the remaining challenges published weekly until December 12th. NOTE: all times stated on the site refer to current UK time. The clocks change back from British Summer time to GMT at around 2am on Sunday October 27th and our competition clock resets with that.

You can find a schedule for the release of challenges on the Challenge page

As usual we apologise in advance if your school holidays clash with the schedule. It is impossible to set the schedule to avoid them all, but there is nothing to stop you doing the challenge during the break, you only need a web browser and your brain!

Scoring the Challenge

There are two parallel competitions, part A and part B, and you can take part in one or both (or neither, but why would you?) Competition B carries the prizes and is scored for speed and accuracy. We use the Damerau-Levenshtein distance to determine how accurate you are and break up the time into bands each worth a certain number of points. For each round you can submit more than once, and we mark each of your submissions. We then take your most accurate submission and award the appropriate time points to give a pair of numbers (accuracy out of 100, time points) and then use this to rank team entries. Accuracy is ALWAYS more important than speed. Speed does matter, but you do not have to rush to download the first challenges immediately as you have a day or two in which you can still get top marks. In later challenges speed will become important, and the full schedule of marks is published on the Challenge pages so you can see how quickly you will need to get started in each round.

Challenge A is intended for less experienced code breakers, so typically the challenges are a bit easier. There are no prizes for Challenge A, but you can download certificates showing you how well you did in each round.

The first three challenges should be thought of as a “warm-up” exercise and will not count in the final leader board rankings or for the award of main prizes, however it is still worth tackling them as they give excellent practice and they do develop the storyline. You will be able to download certificates recording your team’s performance at each stage.

Rewards and Prizes

As usual we are indebted to our sponsors for their support. GCHQ, IBM, Trinity College Cambridge and the School of Mathematics at the University of Southampton will each provide a main prize, to be announced before the competition starts on October 10th. We also have a new sponsor providing 9 additional round prizes to be awarded to schools at each stage of the competition. Keep your eyes on the home page for details.