Is the regularity shown in this encoded message noise or structure?
Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?
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?
This is the fourth 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.