I really need help for this case, that's the hardest I've tried. I'm stuck, not so far from the answer I think but right now I'm becoming a little bit crazy. Spoiler: MAYBE HUGE SPOILERS = what I did in 25.2 I know it's a rolling XOR-based cypher. I first transcript the HEX to binary, then with ASCII tables I transcript my binary to what I assume to be the key. For example, the first part of the data is HEX 73 : in binary I have 01110011. So I took the bin before this one and got 01110010 => I choose this one as a key and get 00000001. Which is pure non-sense for me. I've tried different orders (n+1 or n-1 for the key), still with absurd results. I've tried different transcriptions, BIN, HEX, Unicode... but I never had a nice plaintext box. I've used several websites like asciitohex; r12a.github.io/uniview/ ; darkfader.net/toolbox/convert/ but I still don't get it... Can I have a huge nudge here or by PM please ? Also I have to notice that english is not my native language.