Reply To: Challenge 10A
Ok, so I’ve spent some time thinking about CF 10.1 and how it might relate to 10A. I’m not certain about any of this, but I thought it might be interesting to share some theories, and I may well be overthinking it.
A few things to note – title of the challenge, “MEA CULPA”, which is originally Latin and roughly translates to “my fault”. I feel like this could have multiple meanings – one could be the link to Babbage apologising to Charles in his letter for accusing Ternan.
After digging into the history, it was actually Johannes Trithemius who introduced the idea of the tabula recta (rows of shifted alphabets), which is the table later used in the Vigenère cipher.
Back to Mea Culpa- in early Latin, “apology” didn’t mean “sorry” in the modern sense, but more a defence/ justification/ explanation. And Trithemius lived in a time where scholars often had to justify why their work wasn’t heretical, dangerous, or immoral, very interesting given that he had gained a reputation as a necromancer. With that in mind, the guy in the image holding the abacus could plausibly be intended to represent Trithemius himself..
Given the length of the key in 10A, I think it’s more accurate to describe the cipher as Trithemius, which is equivalent to a Vigenère with the full alphabet as a progressive key (DEFGHIJKLMNOPQRSTUVWXYZABC). (Harry feel free to block out the key if that gives too much away.)
Now for the soldier climbing the ladder – Trithemius is a successive shift cipher, so can have either “ascending” or “descending” shifts in the alphabet from 0 to N where N is the length of the text. If the end of the alphabet is reached, start from the beginning. The shift in 10A is +3, I’m guessing up the ladder = positive shift through the alphabet.
Lastly – how is this image somehow more difficult to understand than the cipher itself… Nevertheless, I had fun going down a few rabbit holes, which I guess is half the point of these challenges anyway.