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A Roman Conversion?
Age 16 to 18
Challenge Level 
This is the first of our challenge ciphers.
We recommend that you attempt them in order, as the solution of each challenge gives a small (and necessary!) hint for the next challenge.
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Stage 5 Cipher Challenge
Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?
More Secret Transmissions
In 'Secret Transmissions', Agent X could send four-digit codes error free. Can you devise an error-correcting system for codes with more than four digits?