The National Cipher Challenge

Stephen Bond

The National Cipher Challenge Paul Wingfield (1990) & James Lloyd (2005)

Dr Paul Wingfield Dr James Lloyd.

September 2021 marks the twentieth anniversary of an outreach initiative that is notable in being open to anyone at secondary school: the National Cipher Challenge, run by the University of Southampton School of Mathematics, which is in Trinity’s Link Area of Hampshire. Trinity has supported this annual cryptography competition for schools since 2005, when I as Admissions Tutor and Professor Joan Lasenby (Engineering; 1978) proposed that the College sponsor a prize alongside IBM, GCHQ and the British Computer Society. The Challenge is open to anyone in full-time education who is 18 or under on 31 August of the year in which the competition finishes. Its format is straightforward. Entrants may compete singly or in teams. Between the start of the school year and Christmas the competitors attempt to break a series of cryptograms published weekly on the competition website. The initial puzzles are comparatively simple, but in later challenges the cryptograms become much harder to break. Prizes are awarded on the basis of how accurate submitted solutions are and how quickly the entrant(s) have broken the ciphers. The prize winners and other randomly selected entrants are then invited to a day held at Bletchley Park consisting of a special lunch, lectures on mathematical and cryptographic topics, and the prize-giving ceremony. Over the years, the Cipher Challenge has brought Trinity into contact with a wide variety of students from a huge range of schools across the UK, many of which are remote and would be extremely unlikely to receive a visit from a Fellow or member of the Schools Liaison team. What all of these students have had in common is simply a thirst for intellectual endeavour of the sort that lies at the heart of Trinity’s educational mission. A significant number of the Challenge’s prize winners have in fact come to study Maths, Natural Sciences and Computer Science at Trinity; indeed, in the 2011 Challenge the Trinity College prize was won by a two-woman team from Dartford Grammar School for Girls: Natalie Behague and Florence Salter, both of whom came to the College in 2012 to read Maths – a remarkable double success in a subject that tends to be maledominated. Some Trinity prize winners are now quite far advanced in their careers. The

2004 overall winner of the Challenge, James Lloyd (from Portsmouth Grammar School), studied Maths here and returned to complete a PhD in Machine Learning. Below James gives an account of how winning the Challenge and his time at Trinity have shaped his subsequent career path.

What I enjoyed the most about the cipher challenge was the thrill of discovering patterns, but then building tools to speed up or automate the pattern discovery process. The sudden excitement of an “aha” moment and the satisfaction of watching a well-oiled machine do its thing. And now, luckily for me, I get to build machines to automate pattern discovery for a living. After the cipher challenge I studied mathematics at Trinity College, Cambridge, and my experience from the challenge certainly helped by giving me a head start in programming and optimisation algorithms. During my study I specialised towards statistics, i.e. one of the ways to formally study pattern discovery, continuing to an M.Phil in statistics. Along the way I spent some of my holidays working at a hedge fund (searching for patterns in financial data) but after an enjoyable internship I joined the Boston Consulting Group (BCG) as a strategy consultant.

Part of my reasoning for joining BCG was a desire not to be typecast as a “mathmo”, but I soon realised that I rather enjoyed being a mathematical specialist, so I contacted my M. Phil. advisor, Richard Samworth (Director of the Statistical Laboratory and Fellow of St John’s), and asked what PhDs might be a good fit for me. After speaking with some of the people Richard recommended to me, it was ultimately David Spiegelhalter (a Professor in the Statistical Laboratory and Fellow of Churchill) who tipped me off about the existence of the Machine Learning Group in the Engineering Department at Cambridge. I discovered I could study my favourite flavours of statistics at the time (Bayesian and nonparametric) whilst also working on artificial intelligence, which sounded rather exciting.

Studying for a PhD with Zoubin Ghahramani (another Fellow of St John’s) in the Machine Learning Group was a great decision. I loved going deep into areas of mathematics and getting to the forefront of human knowledge, I got involved in some fun side projects (I helped write a musical using statistics and machine learning) and I got to meet plenty of smart and interesting people, including my wife (also a Trinitarian). And fundamentally, my work was all about automating the process of discovering and understanding patterns.