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v0.27.0: detect AACS-scrambled units by raw TS sync, not flag bits

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Rename is_unit_encrypted -> is_aacs_scrambled and decide encryption from the unit's MPEG-TS sync bytes (destroyed by the encrypted body) instead of the TP_extra copy-control (byte 0) or TS scrambling-control (byte 7) flags, which discs do not set reliably. One shared predicate now backs the decrypt gate and out-of-band key validation, so callers agree on what 'encrypted' means. Decryption restores the syncs, so a decrypted unit reads as clear and there is no flag to clear.
This commit is contained in:
MattJackson
2026-06-03 07:35:50 -07:00
parent c8eb42b490
commit b518860d9c
8 changed files with 138 additions and 132 deletions
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src/decrypt.rs
+11 -10
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@@ -185,12 +185,13 @@ pub fn decrypt_sectors(
let chunks: Vec<&mut [u8]> = buf.chunks_mut(unit_len).collect();
let nunits = chunks.len();
// Per-unit decrypt closure. The is_unit_encrypted check is
// a byte-0 heuristic; on a misfire we snapshot+restore via
// the original bytes so non-m2ts (e.g. MPLS/CLPI nav files)
// survive. See test `nav_file_unit_survives_decrypt_attempt`.
// Per-unit decrypt closure. The is_aacs_scrambled check reads the
// raw TS syncs; a non-m2ts unit (e.g. MPLS/CLPI nav file) can look
// scrambled and trigger a decrypt attempt, so on a verify miss we
// snapshot+restore the original bytes so it survives. See test
// `nav_file_unit_survives_decrypt_attempt`.
let decrypt_one = |chunk: &mut [u8]| {
if chunk.len() == unit_len && aacs::is_unit_encrypted(chunk) {
if chunk.len() == unit_len && aacs::is_aacs_scrambled(chunk) {
let original: Vec<u8> = chunk.to_vec();
if !aacs::decrypt_unit_full(chunk, &uk, rdk.as_ref()) {
chunk.copy_from_slice(&original);
@@ -232,11 +233,11 @@ pub fn decrypt_sectors(
mod tests {
use super::*;
/// Regression for the 0.18.1 nav-file scramble bug. A non-m2ts unit whose
/// first byte has the top 2 bits set (here: the ASCII letter 'M' that
/// MPLS files start with, 0x4D = 0b01001101) trips `is_unit_encrypted`,
/// gets AES-decrypted with the unit key, fails the TS-sync verification,
/// and must be restored to its original bytes — not left scrambled.
/// Regression for the 0.18.1 nav-file scramble bug. A non-m2ts unit (here
/// an MPLS file: starts "MPLS", carries no TS syncs) reads as scrambled
/// under `is_aacs_scrambled`, gets AES-decrypted with the unit key, fails
/// the TS-sync verification, and must be restored to its original bytes —
/// not left scrambled.
#[test]
fn nav_file_unit_survives_decrypt_attempt() {
let mut unit = vec![0u8; aacs::ALIGNED_UNIT_LEN];