Reply To: Challenge 10B
After finishing 10B on the 2nd January, I would just like to share the exacerbating journey that I went through to complete the cipher. At first, since this is my first time in the cipher challenge and since I was an individual participant, I would like to confess that I underestimated the difficulty of the cipher challenge, mainly 9B and 10B, which were the challenges were I didn’t get all the points. In 10B, I initially calculated the index of coincidence, which led me to think that it was a polyalphabetic cipher. The first alphanumeric cipher that came to my mind was a modified 6 by 6 playfair cipher, which would have the letters A-Z and the digits 0-9, and I tried to decrypt the cipher with frequency analysis and hill climbing. I kept thinking that until I saw case file 10.5, which led me to the conclusion that I was dealing with a modified foursquare cipher. After some more case files were released, especially the ones with the digraphs, I was able to fully complete the whole grid and create a code to decipher by the 26th January. However, after putting in the ciphertext and trying to decrypt it, I got an error. After that, I queried my grid and although it was actually right, I doubted myself, so I took a break for a couple of days. When I returned to the cipher with a fresh mind on the 2nd January, I realised that I had made a terrible mistake: I forgot to split the ciphertext into bigraphs! After splitting it into bigrams and decrypting the ciphertext, I had a fully complete decryption of the ciphertext, into a grammatically correct plaintext! Overall, despite regretting the mistakes I had initially made, I found the whole cipher challenge fun, and I cannot wait for the next challenge’s 10B cipher. Thank you to all those who made solving the cipher a fun experience. However, I am just curious how on earth one was supposed to decrypt the cipher without the first 7 case files, which I where I need your level of expertise Harry. If there was any participant who decrypted the cipher BEFORE CASE FILE 10.2 was released, then could you please explain on the forum your methods of reasoning and how you got there in the end.