Decrypting MKBv81 disc with libaacs

[prozistka]

Hello!

This thread is not asking for solution but some background knowledge.
I'm trying to understand how AACSv1 works and there is a strange phenomenon for me.
I have an MKBv81 disc and a driver with LibreDrive enabled.

• The disc is MKBv81
• The AACS version of my driver is v81 too
• The current keydb.cfg does not contain VUK of this specific disc
• The keydb.cfg does not contain HC for MKBv81

The following is what I encountered

• VLC can play this disc perfectly with only libaacs
• Xreveal with low version 2.4.x can decrypt the disc perfectly
• Xreveal(Free) with current version 2.7.0 cannot decrypt the disc

Here are some questions.

• Why VLC (or libaacs) can decrypt my disc without HC for MKBv81? From what I've known, one need a valid HC to decrypt a disc with specific MKB version.
• Following the previous question, is it because of LibreDrive such that I can decrypt the disc without HC?
• If I want to calculate VUK of this specific disc, is there any advice except DVDFab since my goal is understanding AACSv1?

The following is the information from makemkv:

Drive Information
OS device name: F:
Current profile: BD-ROM
Manufacturer: BUFFALO
Product: Optical Drive
Revision: BU10
Serial number: ############
Firmware date: 2117-05-30 17:28
Bus encryption flags: 1F
Highest AACS version: 81

LibreDrive Information
Status: Enabled
Drive platform: MT1959
Firmware type: Original (unpatched)
Firmware version: 0.BU10O
DVD all regions: Yes
BD raw data read: Yes
BD raw metadata read: Yes
Unrestricted read speed: Yes

Disc Information
Label: ###################
Timestamp: ##################
Protection: AACS v81
Data capacity: 3.8 Gb
Disc type: BD-ROM
Number of layers: 1
Channel bit length: 74,5 nm (25.0 GB max. per layer)