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Probably a Code?

Is the regularity shown in this encoded message noise or structure?

Stage 5 Cipher Challenge

Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?

More Secret Transmissions

Age 16 to 18
Challenge Level

In Secret Transmissions, the check digits were in position 1, 2 and 4 of the 7 digits, and the message digits were in position 3, 5, 6 and 7.

Digits 1, 3, 5 and 7 contained an even number of 1s.

Digits 2, 3, 6 and 7 contained an even number of 1s.

Digits 4, 5, 6 and 7 contained an even number of 1s.


What do you notice about the position of the check digits in the message?
Where might you put the next check digit in a longer message?
How can you determine which message digits 'belong' to each check digit?