Solution by SenorGPT on 2025-12-17 17:01: Java `.jar` crackme. Using JADX, I recovered `checkValidity()` which scores the 10-character key by counting how many characters satisfy `(ch & 3) == 0` (i.e., ASCII divisible by 4). A key is valid if the score is exactly 4. I also wrote a small Python keygen to generate valid keys.