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aacs: extract mkb.rs (MKB record format, MkbType, finders)

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Relocate the shared MKB machinery into a single mkb module: the record
framing walker + MkbRecord view (from variant), the MkbType/AacsVersion
classification, the MKB-file utilities, and the record-body finders (from
keys). Fixes the inversion where the MKB parser lived in the 2.1-only
variant module. variant.rs keeps its local MkbRecord-based mkb_find_mk_dv
(name collision with the raw one; unified in the dedup follow-up).

Relocation only. Proven byte-identical to the pre-refactor state via the
function-body logic hash (imports normalized out); 2210 tests green.
This commit is contained in:
Matthew Jackson
2026-07-04 13:55:06 -07:00
parent f55d8f7acd
commit f55f11d043
5 changed files with 344 additions and 325 deletions
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src/aacs/variant.rs
+1 -66
View File
@@ -73,6 +73,7 @@
//! variant path.
use super::crypto::{aes_ecb_decrypt, aes_g};
use super::mkb::*;
use super::types::DeviceKey;
// ── Public constants ──────────────────────────────────────────────────────
@@ -86,65 +87,6 @@ pub const KEY_CORRECTION_DATA_PLACEHOLDER: [u8; 16] = [0u8; 16];
// ── MKB record walking ────────────────────────────────────────────────────
/// A single MKB record produced by [`walk_mkb`].
#[derive(Debug, Clone)]
pub struct MkbRecord {
/// Byte offset of the record within the MKB.
pub offset: usize,
/// Record type byte.
pub rec_type: u8,
/// Record length in bytes (includes the 4-byte header).
pub rec_len: usize,
/// Record body (the bytes after the 4-byte header).
pub body: Vec<u8>,
}
/// Walk an MKB into a flat list of records.
///
/// MKB record framing per AACS: 1 byte type, 3 bytes BE length
/// INCLUDING the 4-byte header, followed by payload. The walker stops
/// at the first `(type=0, len=0)` end marker or at end of buffer.
pub fn walk_mkb(mkb: &[u8]) -> Vec<MkbRecord> {
mkb_records(mkb)
.map(|(offset, rec_type, rec_len)| MkbRecord {
offset,
rec_type,
rec_len,
body: mkb[offset + 4..offset + rec_len].to_vec(),
})
.collect()
}
/// THE single MKB record-framing walker: yields `(offset, rec_type, rec_len)`
/// for each record — a 4-byte header (type byte + big-endian 24-bit length)
/// then the body — stopping at the `00 000000` end marker or a
/// malformed/out-of-bounds length. Lazy (no body clone), so a find-one-record
/// caller never materialises the multi-MB cvalue table. [`walk_mkb`] and every
/// MKB record walk in `aacs::keys` are built on this, so the framing rules — and
/// any future fix to them — live in exactly one place (they had drifted across
/// six hand-rolled copies).
pub(crate) fn mkb_records(mkb: &[u8]) -> impl Iterator<Item = (usize, u8, usize)> + '_ {
let mut pos = 0usize;
std::iter::from_fn(move || {
if pos + 4 > mkb.len() {
return None;
}
let rec_type = mkb[pos];
let rec_len = ((mkb[pos + 1] as usize) << 16)
| ((mkb[pos + 2] as usize) << 8)
| (mkb[pos + 3] as usize);
if rec_type == 0 && rec_len == 0 {
return None;
}
if rec_len < 4 || pos + rec_len > mkb.len() {
return None;
}
let here = pos;
pos += rec_len;
Some((here, rec_type, rec_len))
})
}
/// True iff `records` contains at least one Media Key Variant record.
///
/// The real AACS 2.1 Variant markers — confirmed against a live variant MKB —
@@ -226,13 +168,6 @@ pub struct ProcessingKeyMatch {
pub cvalue_index: usize,
}
fn mkb_find_body(records: &[MkbRecord], rec_type: u8) -> Option<&[u8]> {
records
.iter()
.find(|r| r.rec_type == rec_type && !r.body.is_empty())
.map(|r| r.body.as_slice())
}
fn mkb_find_mk_dv(records: &[MkbRecord]) -> Option<[u8; 16]> {
let r = records
.iter()