Matthew Jackson
6e14fc0c0c
Security - Remove the unsafe Vec::set_len over recycled sector buffers — UB reachable from safe code (GHSA-j8ww-f5fg-9pmh, low). Uses Vec::resize; pooling unchanged. CI / tooling - clippy on stable with the MSRV single-sourced from Cargo.toml; cargo-deny dependency-audit gate with first-party git sources allowed (#15); audience-based comment-guard (#17). Docs - README (keydb ownership, BD-J parser count), drive-access transport/reset notes, mux timeline module-doc links.
1.8 KiB
AACS 2.1 FMTS forensic segment map (src/aacs/segment.rs)
Background moved out of the module's rustdoc to keep the doc comments within the comment-guard's prose caps.
Terminology
The index carried by each segment record (1..32) is NOT the AACS 2.1
Media Key Variant — that is the 65536-value device selector in the MKB
that decides which set of index keys a device receives, a layer this
module does not deal with. All the index keys belong to one variant, whose
number is unknown and irrelevant to the segment map. Decrypting a segment
with the ordinary CPS Unit Key yields garbage — broken HEVC reference
frames (empirically: Could not find ref with POC … on a plain unit-key
rip).
Measurements from a retail AACS 2.1 disc
index is the 1..32 forensic index tag, NOT a sequential segment id:
measured on a retail 2.1 disc it cycles 1,2,…,32,1,2,… across records in
file order — 24 full cycles of 32 plus a final partial cycle of 24 = 792
records. Source-packet numbers are the 192-byte BDAV packet index: byte
offset = spn * 192. Each segment is ~2560 packets (~480 KB) = 80 aligned
units, spread across the entire 54 GB feature (one roughly every 67 MB).
Inside a segment the 80 units interleave in two stride-2 halves: applying the segment's index key decrypts ~40 of them to clean TS and garbles the other ~40 (a second interleaved half, unidentified), which the demux then drops — leaving one coherent stream. Confirmed by decoding a retail disc with a full set of 32 index keys.
index_to_key_idx
The fmts_key_ranges callback maps a segment's index to a position in the
key pool, e.g. |i| i as usize when the pool is laid out as
[base, idx1, idx2, …].
See also docs/segment-key.md for the on-disc key store these indices
select from.