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Probably a Code?

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

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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?

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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?

A Roman Conversion?

Age 16 to 18 Challenge Level:

Have you managed to solve the entire Stage 5 Cipher Challenge? Solutions are now closed, but perhaps you want to take up the full challenge.


Successful solvers of this part were


Amy, England
Khishigbadral Ganzorigt, Li Po Chun United World College, Hong Kong
Ibrahim EL-Serafy, Slough Grammar School, England
Ben James, Wilson's School, United Kingdon
Mahdokht Mohamady, Farzanegan of Kermanshah
Patrick, Woodbridge School, England
Narika and Juhi, Claremont High School Academy Trust, England
Jasmine Velani, Salcombe Preparatory
Luke, Cottenham Village College, England
Louis, Parkside School, England
Rhea from England
Matthew from Wilson's School, England
An Anonymous Solver, from Somewhere
Jospeh, from Hong Kong
Adam, from England

Well done to you all!

The solution is as follows

Well done, you've cracked this code! Have you worked out how this message has been enciphered? The letter 'a' was mapped to 'd', 'b' to 'e' etc. This is called a Caesar shift, with a shift of three letters in this case. We also made things a bit easier by leaving punctuation and the spaces between the words in. How did you decipher this? You may have tried looking for repeated three letter words such as 'the', or counted how many of each letter appeared in the ciphertext and guessed that the most common letter corresponds to 'e'. This second method is the basis of a method called frequency analysis and is very useful for monoalphabetic ciphers. If you know how to program, you can save yourself a lot of time by writing some code to do it for you! Don't worry if you don't though, there are lots of ways you can do it. The 'find and replace' tool in a word processing program can be very useful, just make sure you don't change again the letters you've already replaced! One way around this is to turn the whole message into lower case, and then use capitals for the decrpyted message. The next message will be slightly harder, good luck!

Caesar shift +3