The HD DVD Title Key File (VTKF*.AACS) stores 64 title-key entries of 36 bytes
each — 1-byte BIFO + 3 reserved + 16-byte encrypted key + 16-byte binding MAC —
per AACS "HD DVD and DVD Pre-recorded Book" Table 3-8, confirmed byte-exact
against real discs (Freedom VTKF090, Dukes VTKF000: every 36-byte slot has
BIFO=0x80, a clean key, and a 0xFF binding MAC).
The parser used a 32-byte stride (a 12-byte pad in place of the 16-byte binding
MAC) with flag-based termination. That aligns entry #1 (key at offset 132, where
both strides agree) but drifts +4 bytes per entry after it and never terminates
(the previous entry's 0xFF MAC reads as a set present-flag), so it recovered a
correct key only for single-CPS-unit discs and garbage for CPS unit >=2. Every
multi-title HD DVD (Freedom, Harry Potter) was affected.
Fix: 36-byte stride, iterate the fixed 64 slots, take slots whose BIFO AV_FLG
(bit 7) is set, key at offset 4, slot index = CPS unit (skip empty slots rather
than terminate so a gap can't renumber later keys), and never read the trailing
16-byte TKF MAC as a key. Tests rebuilt on the real layout, including a full
64-entry file.
Also correct the VTKF-selection TODO in mod.rs: the AACS HD DVD Book gives the
selector explicitly (match the TKF's PLAYLIST_NAME field to the active
playlist), not the "validate against an encrypted unit" placeholder.
Reconciled against the new HD DVD reference (freemkv.org/docs/hddvd/); the spec
source is archived in freemkv-private/spec/.
Matthew Jackson
2274423a6f