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About the challenge

The National Cipher Challenge has been run by the University of Southampton Mathematics Department since 2002 and has attracted a wide following. Fans and supporters include the (then Mayor of London) Boris Johnson; the Foreign Secretary William Hague; 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.

This special edition of the competition

With everyone across the country seemingly on sabbatical we thought some of you might like to try code-breaking so we are running a special edition of the Challenge from April 2nd to June 10th 2020.  

The stories take a long time to write, so we hope you will forgive us on this occasion for re-using an old Challenge. This 2020 Special Edition has been adapted from the third National Cipher Challenge, originally published in 2004. It is closely based on historic events, and the original texts can be found online in GitHub, though we would urge you not to look them up as that might spoil it. We have updated the story a little, changed the wording and will add one or two twists to the original to keep it interesting for those who took part before.


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.

Who is the competition for?

This special edition is for everyone. There are no prizes, and there are essentially no rules, other than the ones we need to make the website function. If you have any questions please contact Harry at [email protected]

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, a password, and some security questions in case you need to reset your password. Whether you are taking part alone or with others you will be asked to either create or join a team which you will use to submit your entries. You can find out more about this in the BOSS Trainer’s Manual. 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. Anyone who took part in the competition last Autumn can reuse their account from then. For everyone else we have tried to simplify the registration process, but if you get stuck drop us a line.

Your account will also allow you to join in on the BOSS Forum, where you can discuss a whole range of things connected to the competition, and quite a few that are totally unrelated.

Competition schedule

If all goes according to plan registration will open online on 30th March and the first episode will be published at 9am on Thursday April 2nd. 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. The main competition starts with episode 4 on 23rd April, with the remaining challenges published weekly until May 28th. NOTE: all times stated on the site refer to current UK time. The clocks change to British Summer time at around 2am on Sunday March 29th so our competition clock is set to BST.

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

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 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. You will be able to download certificates showing you how well you did in each round as well as your placing in the overall competition after 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, 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

We usually offer a range of generous prizes sponsored by GCHQ, IBM, Trinity College Cambridge and the School of Mathematics at the University of Southampton. This special edition of the competition is just for fun, so we hope you will find sufficient motivation in the challenges themselves. If you do get hooked on the National Cipher Challenge and are school age you can always come back and compete for the usual prizes in the Autumn.