Or more generally, is it irrelevant when the respective VUK is presented to MakeMKV for "direct" decryption? (Assuming MakeMKV would also use VUK to "directly" decrypt an AACS 1.0 encrypted backup when one is found in keydb.cfg.)
In other words, is it (currently?) only relevant for AACS 1.0 encrypted backup because MakeMKV will use data in the file to compute the VUK needed (or for maybe some alternative "approach" of decryption)? (I'm not interested in finding out the "secret" of MakeMKV -- if there is such thing. I'm just interested in like under what circumstances the discatt.dat matters.)
Because I just tested libaacs (the "real" one) and MakeMKV/libmmbd with an encrypted AACS 2.0 UHD BD backup without discatt.dat, and to my surprise, they both seem to work fine in decrypting it. Just want to know whether my "theory" is correct, or if I'm missing something.
P.S. I notice that at least for the decrypted backup of the same disc, the discatt.dat seems to have quite some amount of (significant?) data that is found in the one of the encrypted backup omitted. I have yet to check one in a regular BD / AACS 1.0 backup, but is that what would happen when that piece data wasn't used in the decryption process? Or does it always get omitted in a decrypted backup because it is considered "no longer relevant"?