Reply To: Challenge 10B
@Chinchinchilla
Take a look at Case File 10.9, it effectively gives you the opening of the plaintext. From there, you can fill in the blanks to recover the full opening sentence which gives you a lot more context to work with.
To fill in more of the grid, one way is to write the ciphertext out in digraphs and put the corresponding plaintext letters underneath, leaving blanks where you’re unsure (Eg: 7C -> R, XS -> E…) and then reverse engineer to fill in the missing squares in the grid. You can also write some code to automate this.
Probably a more useful thing- it’s also worth thinking of how the grids are filled, so if you can guess the keyword, you can make a reasonable assumption looking at Case File 10.10 that it starts with the keyword (no repeats), followed by the start of the alphabet in order.
Hope this helps