Tuesday, 19 May 2020

Stage 5 Cipher Challenge

Exams begin in 4 weeks but I seem to want to do everything BUT revise for them. Today I started a cipher challenge I found on NRICH and was so excited to get the first clue. I made a frequency chart using Excel and found the letter E pretty quick and then, with some deduction, found a few more letters. It got to a certain point where it was easy to guess the entire thing. This is it:

Well done, you've cracked this code! Have you worked out how this message has been enciphered? The letter 'a' was passed to 'd', 'e' 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, must 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 decrypted message. The neat message will be slightly harder, good luck!
Now I need to figure out how to force myself to revise and get A LOT of schoolwork done. Wish me luck !

Stage 5 Cipher Challenge

Exams begin in 4 weeks but I seem to want to do everything BUT revise for them. Today I started a cipher challenge I found on NRICH and was ...