Reply To: Challenge 10A
@P8S_EH
As stated earlier on the forum, you know you’re dealing with a Vigenère cipher, which will be something you have come across before in the challenges.
If you have done some IoC analysis, you might notice the peaks at length which are multiple of 13 (13,26, etc…) – see if you can infer anything from that and the hints posted above from others about the length/nature of the keyword
You can also use context around the challenges, like following the events of 9B you can reasonly infer that 10A could be a letter written by Charles Babbage to Dickens as an apology for accusing Ternan (which also links to the translated title of the challenge), which often start with “MYDEAR…” and ends with “CHARLES” which should be enough to get your started with some cribbing.