Reply To: Challenge 4B
I don’t know how much I can say, but try pages 45-47 in the BOSS cryptanalyst handbook (https://www.cipherchallenge.org/wp-content/uploads/2023/09/BOSS-Cryptanalyst-Handbook-with-index-V3-1.pdf). That should hopefully tell you what you need to know (and as for lengths of the parts, see if the ciphertext is padded!)