A working cipher machine: a maths EPQ idea
A title to start from
Can a working model cipher machine show why rotor ciphers were strong, and where they were weak?
Why it works as an EPQ
Building a paper or software rotor machine makes the permutation mathematics concrete, and attacking your own machine tests it.
Scope and difficulty
Solid. Solid. One or two rotors; attack with frequency analysis and known plaintext.
The maths
Builds on these A Level topics: Probability · Proof.
You would learn:
- Permutations
- Counting key spaces
- Frequency analysis
One possible plan
- Research how rotor machines work.
- Build a paper or software machine.
- Count its key space and attack it with your own methods.
- Evaluate its strengths and weaknesses.
Pitfalls
- Copying existing code.
- No mathematics of the permutations.
Where to start reading
- The Code Book (Simon Singh)
- Search for: rotor cipher permutation composition
Making something? Read the artefact guide first: an artefact still needs a research-based written report.
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