v0.25.13: DrmScheme dispatcher + AACS 2.1 framework + libredrive cleanup

- Introduce DrmScheme enum (Css/Aacs10/Aacs20/Aacs21) + drm module with
  uniform detect/load dispatch across all four protection schemes.
- Land AACS 2.1 Media Key Variant framework in aacs::variants: chain
  derivation, MKB record types 0x82/0x83, bit-0x02 SoftKCD and bit-0x04
  online-challenge detection. Aacs21 dispatcher arm wired but commented
  out pending validation against a Variant-scheme disc.
- Replace aacs2: bool with AacsVersion enum across ContentCertificate,
  UnitKeyFile, ResolvedKeys. resolve_keys splits into _v1/_v2/_v21.
- Delete the libredrive raw-read VID shortcut from do_handshake; the
  drive enforces the AGID requirement regardless of firmware-upload
  state, so the shortcut spuriously dispatched E7017 instead of
  surfacing the real downstream walls.

CHANGELOG.md

@@ -1,5 +1,70 @@
 # Changelog
 
+## 0.25.13 (2026-05-21)
+
+### Added
+
+- **`DrmScheme` top-level dispatcher.** New `drm` module with a
+  `DrmScheme` enum (`Css`, `Aacs10`, `Aacs20`, `Aacs21`) and a
+  `detect` + `load` pair that uniformly handles all four content
+  protection schemes. Replaces the inlined dispatch in
+  `disc::encrypt::resolve_encryption` and the scattered CSS routing
+  in `disc::mod`. Both CSS call sites now route through the same
+  entry point.
+- **AACS 2.1 Media Key Variant framework.** New `aacs::variants`
+  module implementing the Media Key Variant derivation chain
+  (`Kp + C → Kmp → ⊕KCD → Kpnew → Km → VUK`), Variant-scheme MKB
+  record parsing (record types `0x82` / `0x83`), bit-0x02 SoftKCD
+  and bit-0x04 online-challenge detection with dedicated error
+  variants. Wired into `DrmScheme::Aacs21` but the dispatcher arm
+  is commented out pending validation against a Variant-scheme
+  disc. Per-manufacturer Key Correction Data must be supplied by
+  the integrator; `KEY_CORRECTION_DATA_PLACEHOLDER` is the empty
+  placeholder slot.
+- **`AacsVersion` enum.** Replaces the `aacs2: bool` field on
+  `ContentCertificate`, `UnitKeyFile`, and `ResolvedKeys`.
+  `parse_unit_key_ro` and `parse_content_cert` now take/emit the
+  enum. `resolve_keys` is split into `resolve_keys_v1`,
+  `resolve_keys_v2`, and `resolve_keys_v21` (the last not reachable
+  from the dispatcher today).
+
+### Fixed
+
+- **Libredrive raw-read VID shortcut deleted.** v0.25.11 introduced a
+  `do_handshake` branch that, on libredrive-active drives, skipped the
+  AACS cert handshake and issued `READ_DISC_STRUCTURE` format 0x80
+  with AGID=0 directly. The hypothesis was that firmware-uploaded
+  drives would serve VID without auth. Empirical test on rip1 (BU40N
+  + Barbie UHD, 2026-05-21) showed the drive returns
+  `0x05 / 0x6F / 0x02` (`ILLEGAL_REQUEST / Copy protection key
+  exchange failure: KEY NOT ESTABLISHED`) to that CDB regardless of
+  firmware-upload state. The AACS spec requires a successful
+  `REPORT_KEY` / `SEND_KEY` exchange to establish an AGID before
+  format 0x80 returns VID; that requirement is enforced by the drive
+  itself and isn't bypassed by libredrive firmware. The shortcut
+  fired for every libredrive-active drive, so v0.25.11 / v0.25.12
+  Barbie scans were stuck at E7017 instead of progressing to the
+  real wall (no DK walks MKB v77).
+- `Disc::do_handshake` now always routes through `do_handshake_cert`.
+  `Drive::is_libredrive_active()` and the Mt1959 MMkv+LbDr marker
+  detection are kept as informational signals (logged in the
+  `handshake_entry` warn line) but no longer steer the auth path.
+- `read_volume_id_libredrive` deleted (~50 LOC).
+
+The corollary: AACS resolution on HRL-burned drives + UHD discs now
+fails honestly. Either cert auth succeeds (firmware-upload may or
+may not bypass the HRL — that's the new empirical question) and we
+hit the actual DK wall (E7018 "No DK that walks this MKB" for v77+
+UHD without a v77+ DK in keydb), or cert auth fails and we surface
+E7015. Both are real verdicts; E7017's previous spurious dispatch
+is gone.
+
+## 0.25.12 (2026-05-21)
+
+No libfreemkv source changes — unified sync bump for autorip's
+`aacs_failure_message` two-line wording rewrite. See the autorip
+v0.25.12 release for details.
+
 ## 0.25.11 (2026-05-21)
 
 ### Added

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "libfreemkv"
-version = "0.25.12"
+version = "0.25.13"
 edition = "2024"
 rust-version = "1.86"
 license = "AGPL-3.0-only"

src/aacs/keys.rs

@@ -3,6 +3,38 @@
 use super::decrypt::aes_ecb_decrypt;
 use super::keydb::{DeviceKey, KeyDb};
 
+// ── AACS version ────────────────────────────────────────────────────────────
+
+/// AACS protection generation a disc carries.
+///
+/// The content cert byte distinguishes V10 (`0x00`) from V20 (`0x01`). V21
+/// cannot be detected from the cert alone — a V21 disc carries a V20 cert
+/// and is upgraded to `V21` only after the MKB walk turns up record types
+/// `0x82` / `0x83` (Media Key Variant Data and Variant Number).
+///
+/// Key-storage stride in `Unit_Key_RO.inf` is 48 bytes for V10 and 64
+/// bytes for V20 / V21.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AacsVersion {
+    /// AACS 1.0 — original BD-ROM.
+    V10,
+    /// AACS 2.0 — UHD-BD, classical Media Key derivation.
+    V20,
+    /// AACS 2.1 — UHD-BD with Media Key Variant chain on top of V20.
+    V21,
+}
+
+impl AacsVersion {
+    /// Stride (in bytes) between successive encrypted unit keys in
+    /// `Unit_Key_RO.inf`.
+    fn unit_key_stride(self) -> usize {
+        match self {
+            AacsVersion::V10 => 48,
+            AacsVersion::V20 | AacsVersion::V21 => 64,
+        }
+    }
+}
+
 // ── VUK derivation ──────────────────────────────────────────────────────────
 
 /// Derive VUK from Media Key and Volume ID.
@@ -33,8 +65,8 @@ pub struct UnitKeyFile {
     pub num_bdmv_dir: u8,
     /// Whether SKB MKB is used
     pub use_skb_mkb: bool,
-    /// Whether this is AACS 2.0
+    /// AACS generation this file's stride matches
-    pub aacs2: bool,
+    pub version: AacsVersion,
     /// Encrypted unit keys (CPS unit number, encrypted key)
     pub encrypted_keys: Vec<(u32, [u8; 16])>,
     /// Title → CPS unit index mapping (title_idx → unit_key_idx)
@@ -76,8 +108,8 @@ pub fn disc_hash_hex(hash: &[u8; 20]) -> String {
 ///   [uk_pos..uk_pos+2]   BE16: num_unit_keys
 ///   [uk_pos+48..]        encrypted keys, 16 bytes each
 ///                         AACS 1.0: 48-byte stride
-///                         AACS 2.0: 64-byte stride (48 + 16 extra)
+///                         AACS 2.0 / 2.1: 64-byte stride (48 + 16 extra)
-pub fn parse_unit_key_ro(data: &[u8], aacs2: bool) -> Option<UnitKeyFile> {
+pub fn parse_unit_key_ro(data: &[u8], version: AacsVersion) -> Option<UnitKeyFile> {
     if data.len() < 20 {
         return None;
     }
@@ -103,14 +135,14 @@ pub fn parse_unit_key_ro(data: &[u8], aacs2: bool) -> Option<UnitKeyFile> {
             app_type,
             num_bdmv_dir,
             use_skb_mkb,
-            aacs2,
+            version,
             encrypted_keys: Vec::new(),
             title_cps_unit: Vec::new(),
         });
     }
 
     // Stride between keys
-    let stride = if aacs2 { 64 } else { 48 };
+    let stride = version.unit_key_stride();
 
     // Validate size
     let keys_start = uk_pos + 48; // first key at uk_pos + 48
@@ -155,7 +187,7 @@ pub fn parse_unit_key_ro(data: &[u8], aacs2: bool) -> Option<UnitKeyFile> {
         app_type,
         num_bdmv_dir,
         use_skb_mkb,
-        aacs2,
+        version,
         encrypted_keys,
         title_cps_unit,
     })
@@ -210,18 +242,11 @@ pub fn derive_media_key_from_pk(mkb: &[u8], processing_keys: &[[u8; 16]]) -> Opt
 /// Validate a processing key against a cvalue/UV pair.
 /// Returns the Media Key if valid.
 ///
-/// Implements libaacs `_validate_pk` (aacs.c:98-133) per sgx.fail
+/// Steps:
-/// Appendix D.2 step 25:
 ///   1. `mk = AES-128D(pk, cvalue)`
-///   2. `mk[12..16] ^= uv` (4 bytes XOR into the LAST 4 bytes only)
+///   2. `mk[12..16] ^= uv` (4 bytes XOR into the last 4 bytes only)
 ///   3. `dec_vd = AES-128D(mk, mk_dv)`
 ///   4. If `dec_vd[0..8] == 01 23 45 67 89 AB CD EF` → valid.
-///
-/// Previous implementation XOR'd the full 16-byte cvalue back into mk
-/// (extra step not in libaacs), skipped the uv XOR entirely, and used
-/// AES-128E + 12-zero-byte check instead of AES-128D + magic. Net effect
-/// was that correct processing keys were rejected whenever `uv != 0`,
-/// which is essentially every real disc.
 fn validate_processing_key(
     pk: &[u8; 16],
     cvalue: &[u8],
@@ -237,8 +262,7 @@ fn validate_processing_key(
     cv.copy_from_slice(&cvalue[..16]);
     let mut mk = aes_ecb_decrypt(pk, &cv);
 
-    // Step 2: XOR uv into the LAST 4 bytes of mk (mk[12..16]).
+    // Step 2: XOR uv into the last 4 bytes of mk (mk[12..16]).
-    // sgx.fail D.2 step 25 and libaacs aacs.c:118-120.
     for a in 0..4 {
         mk[12 + a] ^= uv[a];
     }
@@ -319,13 +343,6 @@ fn mkb_find_subdiff_records(mkb: &[u8]) -> Option<Vec<u8>> {
 /// signature. To stay correct on both lines we prefer `0x07` first (the
 /// AACS 2.x layout used by every modern UHD disc) and fall back to
 /// `0x05` for AACS 1.0 MKBs.
-///
-/// References:
-///   - libaacs `mkb_cvalues` (mkb.c:190-193) uses `0x05` exclusively.
-///   - sgx.fail Appendix D.5 walks an AACS 2.x MKB and confirms cvalues
-///     at `0x07`.
-///   - Empirically confirmed against our `aacs2-mkb-samples/`
-///     (Wicked / Civil War / Barbie v77 MKBs): cvalues at `0x07`.
 fn mkb_find_cvalues(mkb: &[u8]) -> Option<Vec<u8>> {
     if let Some(body) = find_record_body(mkb, 0x07) {
         return Some(body);
@@ -585,8 +602,12 @@ pub struct ContentCert {
     pub bus_encryption: bool,
     /// Content Certificate ID (6 bytes)
     pub cc_id: [u8; 6],
-    /// AACS version: false = AACS 1.0, true = AACS 2.0
+    /// AACS generation indicated by the certificate type byte.
-    pub aacs2: bool,
+    ///
+    /// Cert type `0x00` → [`AacsVersion::V10`]; any other value →
+    /// [`AacsVersion::V20`]. The certificate alone cannot distinguish
+    /// V20 from V21 — Variant detection happens after the MKB walk.
+    pub version: AacsVersion,
 }
 
 /// Parse a Content Certificate (ContentXXX.cer) file.
@@ -599,7 +620,11 @@ pub fn parse_content_cert(data: &[u8]) -> Option<ContentCert> {
     //   [0] certificate type (0x00 = AACS1, 0x01 = AACS2)
     //   [1] bus_encryption_enabled (bit 0)
     //   [2..8] cc_id (6 bytes)
-    let aacs2 = data[0] != 0x00;
+    let version = if data[0] == 0x00 {
+        AacsVersion::V10
+    } else {
+        AacsVersion::V20
+    };
     let bus_encryption = (data[1] & 0x01) != 0;
     let mut cc_id = [0u8; 6];
     cc_id.copy_from_slice(&data[2..8]);
@@ -607,7 +632,7 @@ pub fn parse_content_cert(data: &[u8]) -> Option<ContentCert> {
     Some(ContentCert {
         bus_encryption,
         cc_id,
-        aacs2,
+        version,
     })
 }
 
@@ -624,44 +649,172 @@ pub struct ResolvedKeys {
     pub unit_keys: Vec<(u32, [u8; 16])>,
     /// Title → CPS unit index mapping
     pub title_cps_unit: Vec<u16>,
-    /// Whether AACS 2.0
+    /// AACS generation that drove the resolution
-    pub aacs2: bool,
+    pub version: AacsVersion,
     /// Whether bus encryption is enabled (from Content Certificate)
     pub bus_encryption: bool,
     /// Which resolution path succeeded (1=KEYDB, 2=KEYDB derived, 3=PK, 4=DK)
     pub key_source: u8,
 }
 
-/// Resolve all AACS keys for a disc given:
+/// Inputs shared by every classical-path resolver. References only —
-///   - Unit_Key_RO.inf raw data
+/// callers retain ownership of all buffers.
-///   - Content Certificate raw data (optional, for AACS version detection)
+pub struct ResolveContext<'a> {
-///   - Volume ID (from SCSI handshake)
+    /// `Unit_Key_RO.inf` raw bytes.
-///   - KEYDB
+    pub unit_key_ro: &'a [u8],
-///
+    /// Content Certificate raw bytes (optional — used for bus-encryption flag).
-/// Tries in order:
+    pub content_cert: Option<&'a [u8]>,
-///   1. Disc hash → KEYDB → VUK (fast path)
+    /// 16-byte Volume ID from SCSI handshake. `[0u8; 16]` is the
-///   2. KEYDB media key + volume ID → VUK (if disc hash not in KEYDB but MK is)
+    /// "no VID" sentinel and disables paths 2/3/4.
-///   3. MKB + processing keys → media key → VUK (full derivation)
+    pub volume_id: &'a [u8; 16],
-pub fn resolve_keys(
+    /// Key database.
-    unit_key_ro_data: &[u8],
+    pub keydb: &'a KeyDb,
-    content_cert_data: Option<&[u8]>,
+    /// MKB raw bytes (optional — paths 3/4 require it).
-    volume_id: &[u8; 16],
+    pub mkb: Option<&'a [u8]>,
-    keydb: &KeyDb,
+}
-    mkb_data: Option<&[u8]>,
-) -> Option<ResolvedKeys> {
-    // Detect AACS version
-    let aacs2 = content_cert_data
-        .and_then(parse_content_cert)
-        .map(|cc| cc.aacs2)
-        .unwrap_or(false);
 
-    let bus_encryption = content_cert_data
+/// AACS 1.0 key resolution. Parses `Unit_Key_RO.inf` with 48-byte
+/// stride. Tries paths 1 → 4 in order.
+pub fn resolve_keys_v1(ctx: &ResolveContext<'_>) -> Option<ResolvedKeys> {
+    resolve_keys_classical(ctx, AacsVersion::V10)
+}
+
+/// AACS 2.0 key resolution. Parses `Unit_Key_RO.inf` with 64-byte
+/// stride. Tries paths 1 → 4 in order. When paths 3/4 succeed against
+/// an MKB carrying Variant records (`0x82` / `0x83`), the result's
+/// `version` is upgraded to [`AacsVersion::V21`] — derivation still
+/// runs through the classical V2 path; the V21-specific Variant chain
+/// is wired separately via [`resolve_keys_v21`].
+pub fn resolve_keys_v2(ctx: &ResolveContext<'_>) -> Option<ResolvedKeys> {
+    let mut resolved = resolve_keys_classical(ctx, AacsVersion::V20)?;
+    if let Some(mkb) = ctx.mkb {
+        let recs = super::variants::walk_mkb(mkb);
+        if super::variants::is_variant_mkb(&recs) {
+            resolved.version = AacsVersion::V21;
+        }
+    }
+    Some(resolved)
+}
+
+/// AACS 2.1 key resolution via the Media Key Variant chain.
+///
+/// This is wired but not reachable from the production dispatcher — the
+/// Variant chain still requires an integrator-supplied Key Correction
+/// Data constant (see [`super::variants::KEY_CORRECTION_DATA_PLACEHOLDER`])
+/// and an empirically-validated `VARIANTS[uv]` table. Until both are
+/// available, [`super::variants::derive_media_key_variant`] returns
+/// errors that this wrapper logs and converts to `None`.
+///
+/// The chain still passes the disc hash → KEYDB path (1) and the
+/// KEYDB-derived MK+VID path (2) before attempting variant derivation;
+/// V21 discs already in the keydb behave identically to V20.
+pub fn resolve_keys_v21(ctx: &ResolveContext<'_>) -> Option<ResolvedKeys> {
+    // Paths 1 and 2 are version-agnostic — try them first via the
+    // classical V20-stride parser.
+    let uk_file = parse_unit_key_ro(ctx.unit_key_ro, AacsVersion::V20)?;
+    let hash_hex = disc_hash_hex(&uk_file.disc_hash);
+    let bus_encryption = ctx
+        .content_cert
         .and_then(parse_content_cert)
         .map(|cc| cc.bus_encryption)
         .unwrap_or(false);
 
-    // Parse Unit_Key_RO.inf
+    let build = |vuk: [u8; 16], key_source: u8| -> ResolvedKeys {
-    let uk_file = parse_unit_key_ro(unit_key_ro_data, aacs2)?;
+        let unit_keys: Vec<(u32, [u8; 16])> = uk_file
+            .encrypted_keys
+            .iter()
+            .map(|(num, enc_key)| (*num, decrypt_unit_key(&vuk, enc_key)))
+            .collect();
+        ResolvedKeys {
+            disc_hash: uk_file.disc_hash,
+            vuk,
+            unit_keys,
+            title_cps_unit: uk_file.title_cps_unit.clone(),
+            version: AacsVersion::V21,
+            bus_encryption,
+            key_source,
+        }
+    };
+
+    tracing::warn!(
+        target: "freemkv::disc",
+        phase = "resolve_keys_v21_start",
+        bus_encryption,
+        disc_hash = %hash_hex,
+        mkb_present = ctx.mkb.is_some(),
+        "resolve_keys_v21: starting"
+    );
+
+    if let Some(entry) = ctx.keydb.find_disc(&hash_hex) {
+        if let Some(vuk) = entry.vuk {
+            return Some(build(vuk, 1));
+        }
+    }
+
+    if *ctx.volume_id == [0u8; 16] {
+        tracing::warn!(
+            target: "freemkv::disc",
+            phase = "resolve_keys_v21_no_vid",
+            "VID unavailable; v21 derivation requires VID"
+        );
+        return None;
+    }
+
+    for entry in ctx.keydb.disc_entries.values() {
+        if let (Some(mk), Some(did)) = (entry.media_key, entry.disc_id) {
+            if did == *ctx.volume_id {
+                return Some(build(derive_vuk(&mk, ctx.volume_id), 2));
+            }
+        }
+    }
+
+    // Variant chain — walk MKB, derive Km via the Media Key Variant
+    // chain, then derive VUK off Km and the disc's VID.
+    let mkb = ctx.mkb?;
+    let recs = super::variants::walk_mkb(mkb);
+    match super::variants::derive_media_key_variant(
+        &recs,
+        &ctx.keydb.device_keys,
+        &super::variants::KEY_CORRECTION_DATA_PLACEHOLDER,
+        ctx.volume_id,
+    ) {
+        Ok((_km, kvu)) => {
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "resolve_keys_v21_variant_ok",
+                "Media Key Variant chain produced Km + Kvu"
+            );
+            Some(build(kvu, 4))
+        }
+        Err(e) => {
+            tracing::warn!(
+                target: "freemkv::disc",
+                phase = "resolve_keys_v21_variant_err",
+                error_code = %e,
+                "Media Key Variant chain failed"
+            );
+            None
+        }
+    }
+}
+
+/// Resolve all AACS keys for a disc using the classical (single-stage
+/// Media Key derivation) paths. Used by both V10 and V20.
+///
+/// Tries in order:
+///   1. Disc hash → KEYDB → VUK (fast path, no VID required)
+///   2. KEYDB media key + volume ID → VUK
+///   3. MKB + processing keys → media key → VUK
+///   4. MKB + device keys → processing key → media key → VUK
+fn resolve_keys_classical(ctx: &ResolveContext<'_>, version: AacsVersion) -> Option<ResolvedKeys> {
+    let bus_encryption = ctx
+        .content_cert
+        .and_then(parse_content_cert)
+        .map(|cc| cc.bus_encryption)
+        .unwrap_or(false);
+
+    // Parse Unit_Key_RO.inf at the version-appropriate stride.
+    let uk_file = parse_unit_key_ro(ctx.unit_key_ro, version)?;
 
     let hash_hex = disc_hash_hex(&uk_file.disc_hash);
 
@@ -677,7 +830,7 @@ pub fn resolve_keys(
             vuk,
             unit_keys,
             title_cps_unit: uk_file.title_cps_unit.clone(),
-            aacs2,
+            version,
             bus_encryption,
             key_source,
         }
@@ -686,15 +839,15 @@ pub fn resolve_keys(
     tracing::warn!(
         target: "freemkv::disc",
         phase = "resolve_keys_start",
-        aacs2,
+        version = ?version,
         bus_encryption,
         disc_hash = %hash_hex,
-        mkb_present = mkb_data.is_some(),
+        mkb_present = ctx.mkb.is_some(),
         "resolve_keys: starting"
     );
 
     // Path 1: Look up VUK by disc hash in KEYDB
-    if let Some(entry) = keydb.find_disc(&hash_hex) {
+    if let Some(entry) = ctx.keydb.find_disc(&hash_hex) {
         tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path1_hit_entry", "disc hash found in keydb");
         if let Some(vuk) = entry.vuk {
             return Some(build(vuk, 1));
@@ -710,7 +863,7 @@ pub fn resolve_keys(
     // sentinel "no VID" — short-circuit here so we don't surface a
     // misleading "all paths failed" log when really the math is
     // structurally impossible.
-    if *volume_id == [0u8; 16] {
+    if *ctx.volume_id == [0u8; 16] {
         tracing::warn!(
             target: "freemkv::disc",
             phase = "resolve_keys_no_vid",
@@ -721,19 +874,19 @@ pub fn resolve_keys(
 
     // Path 2: Find entry with matching VID → derive VUK from MK + VID
     let mut path2_mk_did_count = 0usize;
-    for entry in keydb.disc_entries.values() {
+    for entry in ctx.keydb.disc_entries.values() {
         if let (Some(mk), Some(did)) = (entry.media_key, entry.disc_id) {
             path2_mk_did_count += 1;
-            if did == *volume_id {
+            if did == *ctx.volume_id {
                 tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path2_hit", "MK+VID entry matched volume_id");
-                return Some(build(derive_vuk(&mk, volume_id), 2));
+                return Some(build(derive_vuk(&mk, ctx.volume_id), 2));
             }
         }
     }
     tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path2_miss", mk_did_entries = path2_mk_did_count, "no MK+VID entry matched volume_id");
 
     // Path 3: MKB + processing keys → media key → VUK
-    if let Some(mkb) = mkb_data {
+    if let Some(mkb) = ctx.mkb {
         let mk_dv = mkb_find_mk_dv(mkb);
         let subdiff = mkb_find_subdiff_records(mkb);
         let cvalues = mkb_find_cvalues(mkb);
@@ -748,18 +901,18 @@ pub fn resolve_keys(
             "MKB record scan results"
         );
 
-        if let Some(mk) = derive_media_key_from_pk(mkb, &keydb.processing_keys) {
+        if let Some(mk) = derive_media_key_from_pk(mkb, &ctx.keydb.processing_keys) {
             tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path3_hit", "media key derived from processing key");
-            return Some(build(derive_vuk(&mk, volume_id), 3));
+            return Some(build(derive_vuk(&mk, ctx.volume_id), 3));
         }
-        tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path3_miss", pk_count = keydb.processing_keys.len(), "PK derivation failed");
+        tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path3_miss", pk_count = ctx.keydb.processing_keys.len(), "PK derivation failed");
 
         // Path 4: MKB + device keys → processing key → media key → VUK
-        if let Some(mk) = derive_media_key_from_dk(mkb, &keydb.device_keys) {
+        if let Some(mk) = derive_media_key_from_dk(mkb, &ctx.keydb.device_keys) {
             tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path4_hit", "media key derived from device key");
-            return Some(build(derive_vuk(&mk, volume_id), 4));
+            return Some(build(derive_vuk(&mk, ctx.volume_id), 4));
         }
-        tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path4_miss", dk_count = keydb.device_keys.len(), "DK derivation failed");
+        tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_path4_miss", dk_count = ctx.keydb.device_keys.len(), "DK derivation failed");
     } else {
         tracing::warn!(target: "freemkv::disc", phase = "resolve_keys_no_mkb", "no MKB data available; paths 3/4 skipped");
     }
@@ -974,10 +1127,10 @@ mod tests {
             data[key2_pos + i] = 0xBB;
         }
 
-        let parsed = parse_unit_key_ro(&data, false).unwrap();
+        let parsed = parse_unit_key_ro(&data, AacsVersion::V10).unwrap();
         assert_eq!(parsed.app_type, 1);
         assert_eq!(parsed.num_bdmv_dir, 1);
-        assert!(!parsed.aacs2);
+        assert_eq!(parsed.version, AacsVersion::V10);
         assert_eq!(parsed.encrypted_keys.len(), 2);
         assert_eq!(parsed.encrypted_keys[0].0, 1); // CPS unit 1
         assert_eq!(parsed.encrypted_keys[0].1, [0xAA; 16]);
@@ -1197,7 +1350,14 @@ mod tests {
         );
         keydb.processing_keys.push([0u8; 16]);
 
-        let result = resolve_keys(&uk_ro, None, &zero_vid, &keydb, None);
+        let ctx = ResolveContext {
+            unit_key_ro: &uk_ro,
+            content_cert: None,
+            volume_id: &zero_vid,
+            keydb: &keydb,
+            mkb: None,
+        };
+        let result = resolve_keys_v1(&ctx);
         assert!(
             result.is_none(),
             "resolve_keys with VID=0 and no matching disc-hash entry must return None"
@@ -1230,8 +1390,16 @@ mod tests {
             },
         );
 
-        let resolved = resolve_keys(&uk_ro, None, &[0u8; 16], &keydb, None)
+        let vid = [0u8; 16];
-            .expect("path 1 must run regardless of VID availability");
+        let ctx = ResolveContext {
+            unit_key_ro: &uk_ro,
+            content_cert: None,
+            volume_id: &vid,
+            keydb: &keydb,
+            mkb: None,
+        };
+        let resolved =
+            resolve_keys_v1(&ctx).expect("path 1 must run regardless of VID availability");
         assert_eq!(resolved.vuk, known_vuk);
         assert_eq!(resolved.key_source, 1);
     }
@@ -1243,14 +1411,14 @@ mod tests {
         data[0] = 0x00; // AACS 1.0
         data[1] = 0x00; // no bus encryption
         let cc = parse_content_cert(&data).unwrap();
-        assert!(!cc.aacs2);
+        assert_eq!(cc.version, AacsVersion::V10);
         assert!(!cc.bus_encryption);
 
         // AACS 2.0 with bus encryption
         data[0] = 0x01; // AACS 2.0
         data[1] = 0x01; // bus encryption enabled
         let cc = parse_content_cert(&data).unwrap();
-        assert!(cc.aacs2);
+        assert_eq!(cc.version, AacsVersion::V20);
         assert!(cc.bus_encryption);
     }
 }

src/aacs/mod.rs

@@ -17,6 +17,7 @@ pub mod decrypt;
 pub mod handshake;
 pub mod keydb;
 pub mod keys;
+pub mod variants;
 
 // Explicit re-exports — only items needed by external consumers and sibling crate modules.
 // AES primitives (aes_ecb_encrypt, aes_ecb_decrypt, aes_cbc_decrypt) are pub(crate) in decrypt.rs.
@@ -26,7 +27,13 @@ pub use decrypt::{
 };
 pub use keydb::{DeviceKey, DiscEntry, HostCert, KeyDb};
 pub use keys::{
-    ContentCert, ResolvedKeys, UnitKeyFile, decrypt_unit_key, derive_media_key_from_dk,
+    AacsVersion, ContentCert, ResolveContext, ResolvedKeys, UnitKeyFile, decrypt_unit_key,
-    derive_media_key_from_pk, derive_vuk, disc_hash, disc_hash_hex, mkb_version,
+    derive_media_key_from_dk, derive_media_key_from_pk, derive_vuk, disc_hash, disc_hash_hex,
-    parse_content_cert, parse_unit_key_ro, read_mkb_from_drive, resolve_keys,
+    mkb_version, parse_content_cert, parse_unit_key_ro, read_mkb_from_drive, resolve_keys_v1,
+    resolve_keys_v2, resolve_keys_v21,
+};
+pub use variants::{
+    KEY_CORRECTION_DATA_PLACEHOLDER, MediaKeyVariantError, MkbRecord, ProcessingKeyMatch,
+    derive_media_key_variant, is_variant_mkb, variant_data_record, variant_key_data, variant_nonce,
+    walk_mkb, walk_processing_key,
 };

src/aacs/variants.rs

@@ -0,0 +1,679 @@
+//! AACS Media Key Variant chain.
+//!
+//! On AACS 2.1 the Media Key derivation gains a second stage on top of
+//! the classical subset-difference walk. The classical walk yields a
+//! Media Key Precursor (Kmp) rather than the final Media Key; the
+//! Precursor combines with disc-supplied Variant Key Data (VKD) and an
+//! integrator-supplied Key Correction Data (KCD) constant to produce
+//! the Media Key.
+//!
+//! This module is wiring only — `resolve_keys` is not aware of it. The
+//! entry point is [`derive_media_key_variant`]. The Variant scheme is
+//! detected via the new MKB record types `0x82` (Encrypted Media Key
+//! Variant Data + Variant Key Data) and `0x83` (Variant Number). When
+//! a disc carries neither, callers should fall back to the classical
+//! single-stage derivation in [`super::keys`].
+//!
+//! The chain follows the published spec:
+//!
+//! ```text
+//! Kmp     = AES-128D(Kp, C) XOR uv
+//! Kpnew   = Kmp XOR KCD
+//! Kvn     = AES-G(Kp, Nonce) & 0xFFFF   (low 16 bits, BE)
+//! VKD_idx = Kvn XOR VARIANTS[uv]
+//! VKD     = vkd_table[VKD_idx * 16 .. +16]
+//! Km      = AES-128D(Kpnew, VKD) XOR uv
+//! ```
+//!
+//! Two condition bits on `Kmp[15]` route off the hardcoded-KCD path
+//! (Soft Correction and Online Challenge). The chain refuses to run in
+//! either case — callers must handle those modes out of band.
+
+use super::decrypt::aes_ecb_decrypt;
+use super::keydb::DeviceKey;
+
+// ── Public constants ──────────────────────────────────────────────────────
+
+/// Placeholder Key Correction Data. Sixteen zero bytes.
+///
+/// Integrators MUST supply a non-placeholder KCD via the `kcd` argument
+/// to [`derive_media_key_variant`]; the chain refuses to operate when
+/// the supplied KCD compares equal to this placeholder.
+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> {
+    let mut out = Vec::new();
+    let mut pos = 0;
+    while pos + 4 <= mkb.len() {
+        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 {
+            break;
+        }
+        if rec_len < 4 || pos + rec_len > mkb.len() {
+            break;
+        }
+        let body = mkb[pos + 4..pos + rec_len].to_vec();
+        out.push(MkbRecord {
+            offset: pos,
+            rec_type,
+            rec_len,
+            body,
+        });
+        pos += rec_len;
+    }
+    out
+}
+
+/// True iff `records` contains at least one Media Key Variant record
+/// (type `0x82` or `0x83`).
+pub fn is_variant_mkb(records: &[MkbRecord]) -> bool {
+    records.iter().any(|r| matches!(r.rec_type, 0x82 | 0x83))
+}
+
+/// Body of the Encrypted Media Key Variant Data record (type `0x82`).
+pub fn variant_data_record(records: &[MkbRecord]) -> Option<&[u8]> {
+    records
+        .iter()
+        .find(|r| r.rec_type == 0x82)
+        .map(|r| r.body.as_slice())
+}
+
+/// 16-byte Nonce from the Variant Number record (type `0x83`). Returns
+/// the first 16 bytes of the body.
+pub fn variant_nonce(records: &[MkbRecord]) -> Option<[u8; 16]> {
+    let r = records.iter().find(|r| r.rec_type == 0x83)?;
+    if r.body.len() < 16 {
+        return None;
+    }
+    let mut out = [0u8; 16];
+    out.copy_from_slice(&r.body[..16]);
+    Some(out)
+}
+
+/// Body of the Variant Key Data record. Returns the first `0x82` body
+/// that is a non-empty multiple of 16 bytes.
+pub fn variant_key_data(records: &[MkbRecord]) -> Option<&[u8]> {
+    records
+        .iter()
+        .find(|r| r.rec_type == 0x82 && !r.body.is_empty() && r.body.len() % 16 == 0)
+        .map(|r| r.body.as_slice())
+}
+
+// ── AES-G ────────────────────────────────────────────────────────────────
+
+/// AES-G(x1, x2) = AES-128D(x1, x2) XOR x2.
+///
+/// The Media Key Variant chain uses AES-G to derive both the variant
+/// number (`Kvn = AES-G(Kp, Nonce)`) and the Volume Unique Key
+/// (`Kvu = AES-G(Km, VID)`). See [`super::keys::derive_vuk`] for the
+/// classical VUK form — the math is identical, this exposes it as a
+/// neutral primitive for the variant chain.
+fn aes_g(x1: &[u8; 16], x2: &[u8; 16]) -> [u8; 16] {
+    let mut out = aes_ecb_decrypt(x1, x2);
+    for i in 0..16 {
+        out[i] ^= x2[i];
+    }
+    out
+}
+
+// ── Subset-difference walk that exposes (Kp, uv) ──────────────────────────
+
+/// AES-G3 seed register initial value.
+const AESG3_SEED: [u8; 16] = [
+    0x7B, 0x10, 0x3C, 0x5D, 0xCB, 0x08, 0xC4, 0xE5, 0x1A, 0x27, 0xB0, 0x17, 0x99, 0x05, 0x3B, 0xD9,
+];
+
+/// AES-G3 single step: AES-G against the seed register at offset `inc`.
+fn aesg3_step(key: &[u8; 16], inc: u8) -> [u8; 16] {
+    let mut seed = AESG3_SEED;
+    seed[15] = seed[15].wrapping_add(inc);
+    aes_g(key, &seed)
+}
+
+fn calc_v_mask(uv: u32) -> u32 {
+    let mut v_mask: u32 = 0xFFFF_FFFF;
+    while (uv & !v_mask) == 0 && v_mask != 0 {
+        v_mask <<= 1;
+    }
+    v_mask
+}
+
+fn calc_pk_from_dk(dk: &[u8; 16], uv: u32, v_mask: u32, dev_key_v_mask: u32) -> [u8; 16] {
+    let mut left_child = aesg3_step(dk, 0);
+    let mut pk = aesg3_step(dk, 1);
+    let mut right_child = aesg3_step(dk, 2);
+    let mut current_v_mask = dev_key_v_mask;
+
+    while current_v_mask != v_mask {
+        let mut bit_pos: i32 = -1;
+        for i in (0..32).rev() {
+            if (current_v_mask & (1u32 << i)) == 0 {
+                bit_pos = i;
+                break;
+            }
+        }
+
+        let curr_key = if bit_pos < 0 || (uv & (1u32 << bit_pos as u32)) == 0 {
+            left_child
+        } else {
+            right_child
+        };
+
+        left_child = aesg3_step(&curr_key, 0);
+        pk = aesg3_step(&curr_key, 1);
+        right_child = aesg3_step(&curr_key, 2);
+
+        current_v_mask = ((current_v_mask as i32) >> 1) as u32;
+    }
+
+    pk
+}
+
+/// Outcome of a subset-difference walk against an MKB. Carries the
+/// processing key and the matching `uv` slot — both needed as inputs
+/// to the variant chain.
+#[derive(Debug, Clone, Copy)]
+pub struct ProcessingKeyMatch {
+    /// Processing Key.
+    pub kp: [u8; 16],
+    /// Subset-difference node number that matched.
+    pub uv: u32,
+    /// 16-byte cvalue that the matched uv selected.
+    pub cvalue: [u8; 16],
+    /// Index of the matching cvalue within the cvalues record.
+    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()
+        .find(|r| (r.rec_type == 0x81 || r.rec_type == 0x86) && r.body.len() >= 16)?;
+    let mut out = [0u8; 16];
+    out.copy_from_slice(&r.body[..16]);
+    Some(out)
+}
+
+/// Walk an MKB and return the first `(Kp, uv, cvalue)` that
+/// `device_keys` covers. Returns `None` if no DK walks any uv.
+pub fn walk_processing_key(
+    records: &[MkbRecord],
+    device_keys: &[DeviceKey],
+) -> Option<ProcessingKeyMatch> {
+    let mk_dv = mkb_find_mk_dv(records)?;
+    let uvs = mkb_find_body(records, 0x04)?;
+    let cvalues = mkb_find_body(records, 0x07).or_else(|| mkb_find_body(records, 0x05))?;
+
+    let num_uvs = uvs
+        .chunks(5)
+        .take_while(|c| c.len() == 5 && (c[0] & 0xC0) == 0)
+        .count();
+
+    for dk in device_keys {
+        let device_number = dk.node as u32;
+
+        for uvs_idx in 0..num_uvs {
+            let p_uv = &uvs[1 + 5 * uvs_idx..];
+            let u_mask_shift = uvs[5 * uvs_idx];
+
+            if u_mask_shift & 0xC0 != 0 {
+                break;
+            }
+
+            let uv = u32::from_be_bytes([p_uv[0], p_uv[1], p_uv[2], p_uv[3]]);
+            if uv == 0 {
+                continue;
+            }
+
+            let u_mask: u32 = 0xFFFF_FFFFu32.wrapping_shl(u_mask_shift as u32);
+            let v_mask = calc_v_mask(uv);
+
+            if ((device_number & u_mask) == (uv & u_mask))
+                && ((device_number & v_mask) != (uv & v_mask))
+            {
+                let dev_key_v_mask = calc_v_mask(dk.uv);
+                let dev_key_u_mask: u32 = 0xFFFF_FFFFu32.wrapping_shl(dk.u_mask_shift as u32);
+
+                if u_mask == dev_key_u_mask && (uv & dev_key_v_mask) == (dk.uv & dev_key_v_mask) {
+                    let pk = calc_pk_from_dk(&dk.key, uv, v_mask, dev_key_v_mask);
+
+                    if uvs_idx >= cvalues.len() / 16 {
+                        continue;
+                    }
+                    let mut cv = [0u8; 16];
+                    cv.copy_from_slice(&cvalues[uvs_idx * 16..(uvs_idx + 1) * 16]);
+
+                    // Validate: AES-D(Kp, cv), XOR uv into low 4 bytes,
+                    // then AES-D(.., mk_dv) must reveal the verify magic.
+                    let mut km_candidate = aes_ecb_decrypt(&pk, &cv);
+                    let uv_bytes = uv.to_be_bytes();
+                    for i in 0..4 {
+                        km_candidate[12 + i] ^= uv_bytes[i];
+                    }
+                    let dec_vd = aes_ecb_decrypt(&km_candidate, &mk_dv);
+                    const VERIFY_MAGIC: [u8; 8] = [0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF];
+                    // On a classical (non-variant) MKB this magic must
+                    // match. On a variant MKB it won't — `km_candidate`
+                    // is really Kmp and the magic check is moot. We
+                    // still gate the walk on cvalue indexing being
+                    // sane; the chain itself enforces the variant
+                    // semantics downstream.
+                    let classical_ok = dec_vd[..8] == VERIFY_MAGIC;
+                    let variant_present = is_variant_mkb(records);
+                    if !(classical_ok || variant_present) {
+                        continue;
+                    }
+
+                    return Some(ProcessingKeyMatch {
+                        kp: pk,
+                        uv,
+                        cvalue: cv,
+                        cvalue_index: uvs_idx,
+                    });
+                }
+            }
+        }
+    }
+    None
+}
+
+// ── Error reporting ───────────────────────────────────────────────────────
+
+/// Outcome of [`derive_media_key_variant`] when the chain cannot
+/// produce a Media Key. Every variant is a classification only — no
+/// strings, no Display impl beyond the error code.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum MediaKeyVariantError {
+    /// MKB carries no Variant records. Caller should fall back to the
+    /// classical single-stage derivation.
+    NotVariantMkb,
+    /// MKB is missing a required record (mk_dv, subset-difference,
+    /// cvalues, variant data, or variant nonce).
+    MkbIncomplete,
+    /// `device_keys` did not cover any uv slot in this MKB.
+    ProcessingKeyUnavailable,
+    /// `Kmp[15]` carries bit `0x02`: the soft-correction path applies
+    /// for this Precursor. Out of scope for the hardcoded-KCD chain.
+    SoftCorrectionRequired,
+    /// `Kmp[15]` carries bit `0x04`: the online-challenge path applies
+    /// for this Precursor. Out of scope for the hardcoded-KCD chain.
+    OnlineChallengeRequired,
+    /// Supplied KCD equals [`KEY_CORRECTION_DATA_PLACEHOLDER`]. The
+    /// derivation refuses to run with the all-zero placeholder.
+    KcdNotProvided,
+    /// `VARIANTS[uv]` lookup for the matched uv is not implemented.
+    VariantsTableUnavailable,
+    /// VKD index resolved out of the supplied `vkd_table`.
+    VkdIndexOutOfRange,
+}
+
+impl std::fmt::Display for MediaKeyVariantError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let code: u16 = match self {
+            MediaKeyVariantError::NotVariantMkb => 7100,
+            MediaKeyVariantError::MkbIncomplete => 7101,
+            MediaKeyVariantError::ProcessingKeyUnavailable => 7102,
+            MediaKeyVariantError::SoftCorrectionRequired => 7103,
+            MediaKeyVariantError::OnlineChallengeRequired => 7104,
+            MediaKeyVariantError::KcdNotProvided => 7105,
+            MediaKeyVariantError::VariantsTableUnavailable => 7106,
+            MediaKeyVariantError::VkdIndexOutOfRange => 7107,
+        };
+        write!(f, "E{code}")
+    }
+}
+
+impl std::error::Error for MediaKeyVariantError {}
+
+// ── Chain ─────────────────────────────────────────────────────────────────
+
+/// Look up `VARIANTS[uv]` for the matched uv. The byte layout of the
+/// per-uv slot in the Variant Number record is undocumented and is
+/// disc-specific; this helper returns `None` until a Variant disc is
+/// available to fix the layout against.
+fn variants_for_uv(_records: &[MkbRecord], _uv_index: usize) -> Option<u16> {
+    None
+}
+
+/// Run the Media Key Variant chain on an MKB.
+///
+/// Inputs:
+///
+/// - `mkb_records`  : MKB pre-walked via [`walk_mkb`].
+/// - `device_keys`  : pool of device keys; the chain runs against the
+///   first uv slot any DK covers.
+/// - `kcd`          : integrator-supplied Key Correction Data. Must not
+///   equal [`KEY_CORRECTION_DATA_PLACEHOLDER`].
+/// - `vid`          : 16-byte Volume ID for the disc. Used to derive
+///   the final VUK alongside the Media Key.
+///
+/// Returns `(Km, Kvu)` on success.
+pub fn derive_media_key_variant(
+    mkb_records: &[MkbRecord],
+    device_keys: &[DeviceKey],
+    kcd: &[u8; 16],
+    vid: &[u8; 16],
+) -> Result<([u8; 16], [u8; 16]), MediaKeyVariantError> {
+    if !is_variant_mkb(mkb_records) {
+        return Err(MediaKeyVariantError::NotVariantMkb);
+    }
+
+    let pkm = walk_processing_key(mkb_records, device_keys)
+        .ok_or(MediaKeyVariantError::ProcessingKeyUnavailable)?;
+
+    let nonce = variant_nonce(mkb_records).ok_or(MediaKeyVariantError::MkbIncomplete)?;
+    let vkd_table = variant_key_data(mkb_records).ok_or(MediaKeyVariantError::MkbIncomplete)?;
+    let c_value = variant_data_record(mkb_records).ok_or(MediaKeyVariantError::MkbIncomplete)?;
+    if c_value.len() < 16 {
+        return Err(MediaKeyVariantError::MkbIncomplete);
+    }
+    let mut c_block = [0u8; 16];
+    c_block.copy_from_slice(&c_value[..16]);
+
+    // Step: Kmp = AES-128D(Kp, C) XOR uv  (uv into low 4 bytes).
+    let mut kmp = aes_ecb_decrypt(&pkm.kp, &c_block);
+    let uv_bytes = pkm.uv.to_be_bytes();
+    for i in 0..4 {
+        kmp[12 + i] ^= uv_bytes[i];
+    }
+
+    // Condition bits on Kmp[15] route off the hardcoded-KCD path.
+    if kmp[15] & 0b0000_0010 != 0 {
+        return Err(MediaKeyVariantError::SoftCorrectionRequired);
+    }
+    if kmp[15] & 0b0000_0100 != 0 {
+        return Err(MediaKeyVariantError::OnlineChallengeRequired);
+    }
+    if kcd == &KEY_CORRECTION_DATA_PLACEHOLDER {
+        return Err(MediaKeyVariantError::KcdNotProvided);
+    }
+
+    // Step: Kpnew = Kmp XOR KCD.
+    let mut kpnew = [0u8; 16];
+    for i in 0..16 {
+        kpnew[i] = kmp[i] ^ kcd[i];
+    }
+
+    // Step: Kvn = AES-G(Kp, Nonce) & 0xFFFF  (low 16 bits, BE).
+    let kvn_block = aes_g(&pkm.kp, &nonce);
+    let kvn = u16::from_be_bytes([kvn_block[14], kvn_block[15]]);
+
+    // Step: VKD_idx = Kvn XOR VARIANTS[uv].
+    let v_for_uv = variants_for_uv(mkb_records, pkm.cvalue_index)
+        .ok_or(MediaKeyVariantError::VariantsTableUnavailable)?;
+    let vkd_idx = kvn ^ v_for_uv;
+
+    // Step: VKD = vkd_table[VKD_idx * 16 .. +16].
+    let off = (vkd_idx as usize) * 16;
+    if off + 16 > vkd_table.len() {
+        return Err(MediaKeyVariantError::VkdIndexOutOfRange);
+    }
+    let mut vkd = [0u8; 16];
+    vkd.copy_from_slice(&vkd_table[off..off + 16]);
+
+    // Step: Km = AES-128D(Kpnew, VKD) XOR uv.
+    let mut km = aes_ecb_decrypt(&kpnew, &vkd);
+    for i in 0..4 {
+        km[12 + i] ^= uv_bytes[i];
+    }
+
+    // Step: Kvu = AES-G(Km, VID).
+    let kvu = aes_g(&km, vid);
+
+    Ok((km, kvu))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ── Helpers ──
+
+    fn synthetic_mkb_classical() -> Vec<u8> {
+        // Minimal MKB: type/version record + cvalues + mk_dv. No variant
+        // records.
+        let mut mkb = vec![
+            0x10, 0x00, 0x00, 0x0C, 0x48, 0x14, 0x10, 0x03, 0x00, 0x00, 0x00, 0x4D,
+        ];
+        mkb.extend_from_slice(&[0x07, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0xAB; 16]);
+        mkb.extend_from_slice(&[0x86, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0xCD; 16]);
+        mkb
+    }
+
+    fn synthetic_mkb_with_variant() -> Vec<u8> {
+        let mut mkb = synthetic_mkb_classical();
+        // 0x82 — 16-byte body (Variant data / VKD slot).
+        mkb.extend_from_slice(&[0x82, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0xEE; 16]);
+        // 0x83 — 16-byte body (Variant Nonce).
+        mkb.extend_from_slice(&[0x83, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0x55; 16]);
+        mkb
+    }
+
+    // ── Walker / record detection ──
+
+    #[test]
+    fn walker_parses_synthetic_mkb() {
+        let mkb = synthetic_mkb_classical();
+        let recs = walk_mkb(&mkb);
+        assert_eq!(recs.len(), 3);
+        assert_eq!(recs[0].rec_type, 0x10);
+        assert_eq!(recs[1].rec_type, 0x07);
+        assert_eq!(recs[2].rec_type, 0x86);
+    }
+
+    #[test]
+    fn variant_detection_negative_on_classical() {
+        let recs = walk_mkb(&synthetic_mkb_classical());
+        assert!(!is_variant_mkb(&recs));
+        assert!(variant_nonce(&recs).is_none());
+        assert!(variant_key_data(&recs).is_none());
+        assert!(variant_data_record(&recs).is_none());
+    }
+
+    #[test]
+    fn variant_detection_positive_on_variant() {
+        let recs = walk_mkb(&synthetic_mkb_with_variant());
+        assert!(is_variant_mkb(&recs));
+        assert_eq!(variant_nonce(&recs), Some([0x55; 16]));
+        assert_eq!(variant_key_data(&recs), Some(&[0xEE; 16][..]));
+        assert_eq!(variant_data_record(&recs), Some(&[0xEE; 16][..]));
+    }
+
+    // ── Chain entry-point classification ──
+
+    #[test]
+    fn chain_rejects_non_variant_mkb() {
+        let recs = walk_mkb(&synthetic_mkb_classical());
+        let err = derive_media_key_variant(&recs, &[], &[0xAA; 16], &[0u8; 16])
+            .expect_err("classical MKB must be rejected");
+        assert_eq!(err, MediaKeyVariantError::NotVariantMkb);
+    }
+
+    #[test]
+    fn chain_rejects_placeholder_kcd() {
+        // To reach the KCD check we need a complete variant MKB AND a
+        // DK that walks it. We construct both via the synthetic
+        // fixture below.
+        let (recs, dk, _kp, _expected_kmp) = synthetic_variant_setup(/*kmp15*/ 0x00);
+        let err =
+            derive_media_key_variant(&recs, &[dk], &KEY_CORRECTION_DATA_PLACEHOLDER, &[0u8; 16])
+                .expect_err("placeholder KCD must be rejected");
+        assert_eq!(err, MediaKeyVariantError::KcdNotProvided);
+    }
+
+    #[test]
+    fn chain_detects_soft_correction_bit() {
+        let (recs, dk, _, _) = synthetic_variant_setup(/*kmp15*/ 0x02);
+        let err = derive_media_key_variant(&recs, &[dk], &[0xAA; 16], &[0u8; 16])
+            .expect_err("bit 0x02 must surface SoftCorrectionRequired");
+        assert_eq!(err, MediaKeyVariantError::SoftCorrectionRequired);
+    }
+
+    #[test]
+    fn chain_detects_online_challenge_bit() {
+        let (recs, dk, _, _) = synthetic_variant_setup(/*kmp15*/ 0x04);
+        let err = derive_media_key_variant(&recs, &[dk], &[0xAA; 16], &[0u8; 16])
+            .expect_err("bit 0x04 must surface OnlineChallengeRequired");
+        assert_eq!(err, MediaKeyVariantError::OnlineChallengeRequired);
+    }
+
+    #[test]
+    fn chain_surfaces_variants_table_gap_on_clean_kmp() {
+        // With both condition bits clear and a non-placeholder KCD, the
+        // chain advances to the per-uv VARIANTS[uv] lookup, which is
+        // not yet wired. That returns VariantsTableUnavailable —
+        // proving the bit checks and KCD check all passed.
+        let (recs, dk, _, _) = synthetic_variant_setup(/*kmp15*/ 0x00);
+        let err = derive_media_key_variant(&recs, &[dk], &[0xAA; 16], &[0u8; 16])
+            .expect_err("expected VariantsTableUnavailable at the per-uv lookup");
+        assert_eq!(err, MediaKeyVariantError::VariantsTableUnavailable);
+    }
+
+    #[test]
+    fn error_display_is_code_only() {
+        // No English in Display — every variant emits "E7xxx" and
+        // nothing else.
+        let cases = [
+            MediaKeyVariantError::NotVariantMkb,
+            MediaKeyVariantError::MkbIncomplete,
+            MediaKeyVariantError::ProcessingKeyUnavailable,
+            MediaKeyVariantError::SoftCorrectionRequired,
+            MediaKeyVariantError::OnlineChallengeRequired,
+            MediaKeyVariantError::KcdNotProvided,
+            MediaKeyVariantError::VariantsTableUnavailable,
+            MediaKeyVariantError::VkdIndexOutOfRange,
+        ];
+        for e in cases {
+            let s = e.to_string();
+            assert!(
+                s.starts_with('E') && s.len() == 5,
+                "error display must be E#### only, got {s:?}"
+            );
+            assert!(
+                s.chars().skip(1).all(|c| c.is_ascii_digit()),
+                "error display must be E + digits, got {s:?}"
+            );
+        }
+    }
+
+    // ── Fixture construction ──
+
+    /// Build a synthetic variant MKB plus a DK that walks the single
+    /// subset-difference slot it carries. `kmp15` is the value of the
+    /// low byte of `Kmp[15]` that the chain will land on — pick `0x02`
+    /// to exercise the SoftCorrection bit, `0x04` to exercise
+    /// OnlineChallenge, `0x00` otherwise.
+    ///
+    /// The fixture pins:
+    /// - MKB subset-difference: `u_mask_shift=3, uv=2`. With these
+    ///   masks the discriminator bit (u_mask=1, v_mask=0) is bit 2.
+    /// - one DK at `node=4, uv=2, u_mask_shift=3`. node 4 has bit 2 set
+    ///   (differs from uv=2 on bit 2 → disagrees on v_mask) while
+    ///   agreeing with uv on bits 3+ (the u_mask=1 region). dk.uv ==
+    ///   MKB.uv and dk.u_mask_shift == MKB.u_mask_shift make
+    ///   `dev_key_v_mask == v_mask`, so `calc_pk_from_dk` loops zero
+    ///   times — Kp = aesg3_step(dk, 1).
+    /// - one cvalue in record 0x07 chosen so AES-D(Kp, C) ⊕ uv produces a
+    ///   Kmp whose byte-15 is exactly `kmp15`.
+    /// - record 0x82 with a 16-byte body (acts as both Variant Data
+    ///   and Variant Key Data; satisfies the parser heuristics).
+    /// - record 0x83 with a 16-byte Nonce.
+    ///
+    /// Returns (records, dk, planted_kp, planted_kmp).
+    fn synthetic_variant_setup(kmp15: u8) -> (Vec<MkbRecord>, DeviceKey, [u8; 16], [u8; 16]) {
+        use crate::aacs::decrypt::aes_ecb_encrypt;
+
+        // Build header.
+        let mut mkb = vec![
+            0x10, 0x00, 0x00, 0x0C, 0x48, 0x14, 0x10, 0x03, 0x00, 0x00, 0x00, 0x4D,
+        ];
+
+        // Subset-difference (0x04): u_mask_shift=3, uv=00 00 00 02.
+        mkb.extend_from_slice(&[0x04, 0x00, 0x00, 0x09]);
+        mkb.extend_from_slice(&[0x03, 0x00, 0x00, 0x00, 0x02]);
+
+        // Pick a known DK; with dk.uv == MKB.uv (==2) and
+        // dk.u_mask_shift == MKB.u_mask_shift (==1), dev_key_v_mask
+        // equals the MKB's v_mask and the calc_pk_from_dk loop is a
+        // no-op — Kp = aesg3_step(dk, 1).
+        let dk_bytes: [u8; 16] = [
+            0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE,
+            0xFF, 0x00,
+        ];
+        let kp = aesg3_step(&dk_bytes, 1);
+
+        // Plant Kmp with chosen byte-15, then compute C such that
+        // AES-D(Kp, C) ⊕ uv == Kmp. uv=2 → low-4 bytes XOR is 00 00 00 02.
+        let mut kmp = [0x42u8; 16];
+        kmp[15] = kmp15;
+        let mut aes_d_result = kmp;
+        aes_d_result[15] ^= 0x02;
+        let c_block = aes_ecb_encrypt(&kp, &aes_d_result);
+
+        // cvalues record (0x07): one 16-byte cvalue. The walker
+        // indexes it for the magic-check step; on a variant MKB the
+        // magic check fails but `variant_present` is true so the
+        // walker still returns the match. Content is don't-care.
+        mkb.extend_from_slice(&[0x07, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0xAB; 16]);
+
+        // Verify Media Key (0x86): body content is don't-care.
+        mkb.extend_from_slice(&[0x86, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0xCD; 16]);
+
+        // 0x82 record: holds C (Encrypted Media Key Variant Data) AND
+        // doubles as the VKD table (single 16-byte entry → VKDidx must
+        // resolve to 0 for `chain_surfaces_variants_table_gap` test —
+        // but the test never reaches the VKD lookup since the
+        // VARIANTS[uv] helper is not yet wired).
+        mkb.extend_from_slice(&[0x82, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&c_block);
+
+        // 0x83 record: 16-byte Nonce.
+        mkb.extend_from_slice(&[0x83, 0x00, 0x00, 0x14]);
+        mkb.extend_from_slice(&[0x77; 16]);
+
+        let recs = walk_mkb(&mkb);
+
+        let dk = DeviceKey {
+            key: dk_bytes,
+            node: 4,
+            uv: 2,
+            u_mask_shift: 3,
+        };
+        (recs, dk, kp, kmp)
+    }
+}

src/css/mod.rs

@@ -16,6 +16,7 @@ pub mod lfsr;
 pub(crate) mod tables;
 
 use crate::disc::Extent;
+use crate::drive::Drive;
 use crate::sector::SectorSource;
 
 /// CSS decryption state for a DVD title.
@@ -25,6 +26,50 @@ pub struct CssState {
     pub title_key: [u8; 5],
 }
 
+/// Inputs for CSS key acquisition.
+///
+/// The acquisition path depends on which inputs the caller supplies:
+///
+/// - With `drive` + `auth_lba` set, [`resolve`] runs the full SCSI bus
+///   auth + title-key path (live BU40N / DVD drive).
+/// - With `reader` + `extents` set, [`resolve`] falls back to the
+///   crack path (Stevenson known-plaintext attack on encrypted PES
+///   headers; works on disc images and on drives whose CSS auth path
+///   is unavailable).
+///
+/// `live_drive` always wins when both modes are populated.
+pub struct CssContext<'a> {
+    /// Live SCSI drive — when present, [`resolve`] tries the auth path.
+    pub drive: Option<&'a mut Drive>,
+    /// LBA of a known-scrambled sector for the auth path's title-key
+    /// query. Required when `drive` is set.
+    pub auth_lba: Option<u32>,
+    /// Sector source for the crack path.
+    pub reader: Option<&'a mut dyn SectorSource>,
+    /// Extents to scan for the crack path. Required when `reader` is
+    /// set.
+    pub extents: Option<&'a [Extent]>,
+}
+
+/// Acquire a CSS title key using whichever inputs the context provides.
+///
+/// Order of attempts:
+///   1. SCSI auth path (when `drive` and `auth_lba` are set).
+///   2. Crack path (when `reader` and `extents` are set).
+///
+/// Returns `None` if neither path is configured or both fail.
+pub fn resolve(ctx: &mut CssContext<'_>) -> Option<CssState> {
+    if let (Some(drive), Some(lba)) = (ctx.drive.as_deref_mut(), ctx.auth_lba) {
+        if let Ok(title_key) = auth::authenticate_and_read_title_key(drive, lba) {
+            return Some(CssState { title_key });
+        }
+    }
+    if let (Some(reader), Some(extents)) = (ctx.reader.as_deref_mut(), ctx.extents) {
+        return crack_key(reader, extents);
+    }
+    None
+}
+
 /// Crack the CSS title key by reading encrypted sectors and applying
 /// a known-plaintext attack on MPEG-2 headers.
 ///

src/disc/encrypt.rs

@@ -13,64 +13,31 @@ pub(super) struct HandshakeResult {
     pub read_data_key: Option<[u8; 16]>,
 }
 
-/// Retrieve VID via the libredrive alternate read path. The drive's
-/// runtime firmware has cleared bus encryption AND no longer requires
-/// a cert-based AGID for protected-area queries — standard
-/// READ_DISC_STRUCTURE format 0x80 with AGID = 0 returns the raw VID.
-///
-/// Layout matches the spec response (4-byte header + 16-byte VID +
-/// 16-byte MAC), but MAC is meaningless without a bus key derivation;
-/// libredrive mode delivers `[0u8; 16]` (or stale bytes) in the MAC
-/// field. We extract the VID bytes only and skip MAC validation
-/// entirely — this is the documented behavior gap when bus encryption
-/// is off.
-fn read_volume_id_libredrive(session: &mut crate::drive::Drive) -> Result<[u8; 16]> {
-    // CDB: READ_DISC_STRUCTURE (0xAD), media=Blu-ray (0x01), AGID=0,
-    // format=0x80 (AACS Volume ID), allocation_length=36 (4-byte
-    // header + 16-byte VID + 16-byte MAC).
-    let mut cdb = [0u8; 12];
-    cdb[0] = crate::scsi::SCSI_READ_DISC_STRUCTURE;
-    cdb[1] = 0x01; // Blu-ray media type
-    cdb[7] = 0x80; // format = Volume ID
-    cdb[8] = 0x00;
-    cdb[9] = 36;
-    cdb[10] = 0; // AGID = 0 (no auth session)
-
-    let mut buf = [0u8; 36];
-    let result = session.scsi_execute(
-        &cdb,
-        crate::scsi::DataDirection::FromDevice,
-        &mut buf,
-        5_000,
-    )?;
-    if result.bytes_transferred < 20 {
-        return Err(Error::AacsVidRead);
-    }
-    let mut vid = [0u8; 16];
-    vid.copy_from_slice(&buf[4..20]);
-    Ok(vid)
-}
-
 impl Disc {
-    /// SCSI handshake — retrieve VID (and bus keys when applicable).
+    /// SCSI handshake — AACS mutual auth via host certs from the keydb,
+    /// returning VID (and bus keys when applicable) on success.
     ///
-    /// Branches on `Drive::is_libredrive_active()`:
+    /// `Drive::is_libredrive_active()` is logged for diagnostics but no
-    ///   * libredrive raw-read mode active → skip cert auth, read VID
+    /// longer alters the auth path. v0.25.11 introduced a "raw-read VID"
-    ///     directly via the alternate path (bus encryption is already
+    /// shortcut that issued `READ_DISC_STRUCTURE` format 0x80 with
-    ///     off; the drive accepts standard READ_DISC_STRUCTURE format
+    /// AGID=0 on libredrive-active drives, on the hypothesis that the
-    ///     0x80 without an AGID).
+    /// firmware-uploaded drive would serve VID without cert auth. The
-    ///   * libredrive inactive → traditional AACS mutual auth using
+    /// BU40N returned 0x05/0x6F/0x02 (`KEY NOT ESTABLISHED`) to that
-    ///     host certs from the keydb. Caps attempts at 3 with a 1 s
+    /// CDB — the AACS spec requires an AGID established via successful
-    ///     backoff to avoid the firmware-wedge hammering we hit in
+    /// `REPORT_KEY` / `SEND_KEY` before format 0x80 will return VID,
-    ///     v0.25.7.
+    /// regardless of firmware-upload state. The shortcut was deleted
+    /// in v0.25.13. Firmware upload still helps — it removes bus
+    /// encryption and (per memory) may allow HRL-burned certs through
+    /// the cert handshake — but it doesn't bypass the AGID requirement.
     ///
     /// Returns `(handshake, error)`:
     ///   * `(Some(_), None)`  — VID acquired
-    ///   * `(None, Some(_))`  — specific failure mode (see new
+    ///   * `(None, Some(_))`  — specific failure mode (see
     ///     `AacsHostCertRejected` / `AacsLibredriveUnsupported` /
     ///     `AacsVidUnavailable` variants in `error.rs`)
     ///   * `(None, None)`     — handshake not attempted (no keydb;
-    ///     resolution will proceed with built-in keys and VID=zero)
+    ///     resolution will proceed with VID=zero and rely on path 1
+    ///     disc-hash → VUK lookup)
     pub(super) fn do_handshake(
         session: &mut crate::drive::Drive,
         opts: &ScanOptions,
@@ -82,51 +49,11 @@ impl Disc {
             "do_handshake entered"
         );
 
-        // Libredrive mode: skip cert auth entirely. The drive returns
-        // VID via READ_DISC_STRUCTURE format 0x80 with no AGID and no
-        // bus encryption applied. This is what MakeMKV does on the
-        // same drive + disc combination where libfreemkv used to fail
-        // with E7000 — empirically confirmed 2026-05-21 on rip1
-        // (BU40N + Barbie UHD, MKB v77, libaacs leaked cert revoked
-        // by HRL but disc rips cleanly via libredrive).
-        if session.is_libredrive_active() {
-            return match read_volume_id_libredrive(session) {
-                Ok(vid) => {
-                    tracing::debug!(
-                        target: "freemkv::disc",
-                        phase = "handshake_libredrive_ok",
-                        "libredrive VID acquired without cert auth"
-                    );
-                    (
-                        Some(HandshakeResult {
-                            volume_id: vid,
-                            // No bus key in libredrive mode -> no
-                            // encrypted-read-data-key to decrypt.
-                            // AACS 2.0 bus-encrypted sectors are
-                            // already plaintext when libredrive is
-                            // active, so consumers don't need RDK.
-                            read_data_key: None,
-                        }),
-                        None,
-                    )
-                }
-                Err(e) => {
-                    tracing::warn!(
-                        target: "freemkv::disc",
-                        phase = "handshake_libredrive_vid_failed",
-                        error_code = e.code(),
-                        "libredrive VID read failed"
-                    );
-                    (None, Some(Error::AacsVidUnavailable))
-                }
-            };
-        }
-
         Self::do_handshake_cert(session, opts)
     }
 
-    /// Cert-based AACS handshake. Only called when libredrive mode is
+    /// Cert-based AACS handshake. The only auth path post-v0.25.13;
-    /// NOT active — see `do_handshake` for the dispatch.
+    /// `do_handshake` is now a thin diagnostic wrapper.
     fn do_handshake_cert(
         session: &mut crate::drive::Drive,
         opts: &ScanOptions,
@@ -173,8 +100,8 @@ impl Disc {
         );
 
         if host_cert_count == 0 {
-            // Drive isn't in libredrive mode AND keydb has no host
+            // No host certs in keydb -> cert auth cannot proceed.
-            // certs -> cert auth cannot proceed. Surface as
+            // Surface as
             // LibredriveUnsupported so the caller knows neither path
             // is available on this configuration.
             return (None, Some(Error::AacsLibredriveUnsupported));
@@ -282,6 +209,7 @@ impl Disc {
         handshake: Option<&HandshakeResult>,
     ) -> Result<AacsState> {
         use crate::aacs::{self, KeyDb};
+        use crate::drm::{DrmContext, DrmProbe, DrmScheme, ResolvedScheme};
 
         let keydb = KeyDb::load(keydb_path).map_err(|_| Error::KeydbLoad {
             path: keydb_path.display().to_string(),
@@ -362,17 +290,45 @@ impl Disc {
         } else {
             Error::AacsVukNotInKeydb
         };
-        let resolved = aacs::resolve_keys(
+
-            &uk_ro_data,
+        // Build a probe + context and let the dispatcher pick V10 / V20
-            cc_data.as_deref(),
+        // / V21. CSS is impossible here (this function is only called
-            &volume_id,
+        // when /AACS exists), so we don't populate the DVD probe sector
-            &keydb,
+        // or a CSS context.
-            mkb_data.as_deref(),
+        let probe = DrmProbe {
-        )
+            dvd_sample_sector: None,
-        .ok_or(miss_error)?;
+            content_cert: cc_data.as_deref(),
+            mkb: mkb_data.as_deref(),
+        };
+        let scheme = match DrmScheme::detect(&probe) {
+            Some(s) => s,
+            None => return Err(miss_error),
+        };
+        let aacs_ctx = aacs::ResolveContext {
+            unit_key_ro: &uk_ro_data,
+            content_cert: cc_data.as_deref(),
+            volume_id: &volume_id,
+            keydb: &keydb,
+            mkb: mkb_data.as_deref(),
+        };
+        let mut ctx = DrmContext {
+            aacs: Some(aacs_ctx),
+            css: None,
+        };
+        let resolved = match scheme.load(&mut ctx) {
+            Some(ResolvedScheme::Aacs(r)) => r,
+            // Resolution against /AACS inputs can only produce AACS
+            // keys. Either the dispatcher returned None (load failed)
+            // or — structurally impossible here — a CSS state. Both
+            // surface as the upstream miss-error.
+            _ => return Err(miss_error),
+        };
 
         Ok(AacsState {
-            version: if resolved.aacs2 { 2 } else { 1 },
+            version: match resolved.version {
+                aacs::AacsVersion::V10 => 1,
+                aacs::AacsVersion::V20 | aacs::AacsVersion::V21 => 2,
+            },
             bus_encryption: resolved.bus_encryption,
             mkb_version: mkb_ver,
             disc_hash: aacs::disc_hash_hex(&resolved.disc_hash),

src/disc/mod.rs

@@ -1043,10 +1043,9 @@ impl Disc {
     /// The session must be open and unlocked (Drive::open handles this).
     /// All disc reads use standard READ(10) via UDF -- no vendor SCSI commands.
     pub fn scan(session: &mut Drive, opts: &ScanOptions) -> Result<Self> {
-        // AACS handshake (Blu-ray/UHD). Branches internally on
+        // AACS handshake (Blu-ray/UHD). Cert-based mutual auth; logs
-        // libredrive raw-read mode: when active the drive serves VID
+        // is_libredrive_active() as a diagnostic but the auth path no
-        // without cert auth and no bus encryption is in play. When
+        // longer branches on it.
-        // inactive we fall back to the cert-based mutual auth.
         let (handshake, handshake_error) = Self::do_handshake(session, opts);
 
         // Request max read speed — removes riplock on DVD
@@ -1073,27 +1072,45 @@ impl Disc {
 
         // CSS key extraction for DVDs (bus auth → disc key → title key).
         // Must be a single auth session — can't call authenticate() separately.
+        // Route through the DRM dispatcher: probe a title sector, detect
+        // CSS if scrambled, then load via the SCSI auth path.
         if disc.css.is_none()
             && disc.content_format == ContentFormat::MpegPs
             && !disc.titles.is_empty()
         {
-            let lba = disc.titles[0].extents.iter().find_map(|ext| {
+            let mut probe_buf = vec![0u8; 2048];
-                let mut buf = vec![0u8; 2048];
+            let auth_lba = disc.titles[0].extents.iter().find_map(|ext| {
                 if session
-                    .read_sectors(ext.start_lba, 1, &mut buf, true)
+                    .read_sectors(ext.start_lba, 1, &mut probe_buf, true)
                     .is_ok()
-                    && crate::css::is_scrambled(&buf)
                 {
-                    return Some(ext.start_lba);
+                    let probe = crate::drm::DrmProbe {
+                        dvd_sample_sector: Some(&probe_buf),
+                        content_cert: None,
+                        mkb: None,
+                    };
+                    if crate::drm::DrmScheme::detect(&probe) == Some(crate::drm::DrmScheme::Css) {
+                        return Some(ext.start_lba);
+                    }
                 }
                 None
             });
 
-            if let Some(lba) = lba {
+            if let Some(lba) = auth_lba {
-                if let Ok(title_key) =
+                let css_ctx = crate::css::CssContext {
-                    crate::css::auth::authenticate_and_read_title_key(session, lba)
+                    drive: Some(session),
+                    auth_lba: Some(lba),
+                    reader: None,
+                    extents: None,
+                };
+                let mut ctx = crate::drm::DrmContext {
+                    aacs: None,
+                    css: Some(css_ctx),
+                };
+                if let Some(crate::drm::ResolvedScheme::Css(state)) =
+                    crate::drm::DrmScheme::Css.load(&mut ctx)
                 {
-                    disc.css = Some(crate::css::CssState { title_key });
+                    disc.css = Some(state);
                     disc.encrypted = true;
                 }
             }
@@ -1218,9 +1235,27 @@ impl Disc {
         let layers = if capacity > 24_000_000 { 2 } else { 1 };
         let region = DiscRegion::Free;
 
-        // 6. CSS detection for DVDs
+        // 6. CSS detection for DVDs — route through the DRM dispatcher.
+        //    Detection from a single probe sector would miss
+        //    DVDs whose first sector is unscrambled, so we go straight
+        //    to `DrmScheme::Css.load` with the crack-path context; the
+        //    crack path scans extents internally and bottoms out at
+        //    None on unencrypted media.
         let css = if content_format == ContentFormat::MpegPs && !titles.is_empty() {
-            crate::css::crack_key(reader, &titles[0].extents)
+            let css_ctx = crate::css::CssContext {
+                drive: None,
+                auth_lba: None,
+                reader: Some(reader),
+                extents: Some(&titles[0].extents),
+            };
+            let mut ctx = crate::drm::DrmContext {
+                aacs: None,
+                css: Some(css_ctx),
+            };
+            match crate::drm::DrmScheme::Css.load(&mut ctx) {
+                Some(crate::drm::ResolvedScheme::Css(s)) => Some(s),
+                _ => None,
+            }
         } else {
             None
         };

src/drm/mod.rs

@@ -0,0 +1,287 @@
+//! Top-level DRM scheme dispatch.
+//!
+//! Four content-protection schemes ride through a single
+//! detect-then-load pipeline:
+//!
+//! | Scheme              | Discriminator                                  |
+//! |---------------------|------------------------------------------------|
+//! | [`DrmScheme::Css`]  | DVD probe sector flagged scrambled             |
+//! | [`DrmScheme::Aacs10`] | Content cert type byte `0x00`                |
+//! | [`DrmScheme::Aacs20`] | Content cert type byte `!= 0x00`, no Variant |
+//! | [`DrmScheme::Aacs21`] | Content cert + MKB records `0x82` / `0x83`   |
+//!
+//! Detection happens from a [`DrmProbe`] (raw inputs the caller has
+//! already extracted from the disc); resolution runs through a
+//! [`DrmContext`] (the full set of inputs the loaders need).
+//!
+//! The AACS 2.1 arm is wired but disabled. The dispatcher leaves
+//! [`crate::aacs::resolve_keys_v21`] reachable as a library entry point
+//! for fixture-driven validation, but production consumers go through
+//! [`DrmScheme::load`], which short-circuits V21 to `None` until the
+//! Variant chain has a real Variant-scheme disc to validate against.
+
+use crate::aacs;
+use crate::css;
+
+/// Which content-protection scheme governs a disc.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DrmScheme {
+    /// DVD Content Scramble System.
+    Css,
+    /// AACS 1.0 — original BD-ROM.
+    Aacs10,
+    /// AACS 2.0 — UHD-BD, classical Media Key chain.
+    Aacs20,
+    /// AACS 2.1 — UHD-BD with Media Key Variant chain.
+    Aacs21,
+}
+
+/// Inputs to [`DrmScheme::detect`]. All borrows — caller retains
+/// ownership.
+pub struct DrmProbe<'a> {
+    /// 2048-byte sample sector from inside a DVD title's extents. Used
+    /// only for CSS scramble-flag detection. `None` for non-DVD discs.
+    pub dvd_sample_sector: Option<&'a [u8]>,
+    /// Content Certificate file bytes (typically `/AACS/Content000.cer`).
+    /// `None` when the disc has no AACS directory.
+    pub content_cert: Option<&'a [u8]>,
+    /// MKB file bytes (typically `/AACS/MKB_RW.inf`). Required to
+    /// distinguish AACS 2.0 from AACS 2.1.
+    pub mkb: Option<&'a [u8]>,
+}
+
+/// Inputs to [`DrmScheme::load`]. Carries everything needed by either
+/// the AACS or CSS loader.
+pub struct DrmContext<'a> {
+    /// AACS resolver inputs — required when the scheme is any AACS
+    /// variant.
+    pub aacs: Option<aacs::ResolveContext<'a>>,
+    /// CSS resolver inputs — required when the scheme is [`DrmScheme::Css`].
+    pub css: Option<css::CssContext<'a>>,
+}
+
+/// Resolved key material, tagged by scheme.
+#[derive(Debug)]
+pub enum ResolvedScheme {
+    Css(css::CssState),
+    Aacs(aacs::ResolvedKeys),
+}
+
+impl DrmScheme {
+    /// Detect which DRM scheme protects the disc described by `probe`.
+    ///
+    /// Returns `None` for unencrypted media. The order is intentional:
+    /// CSS is checked first (DVD-format probe), then AACS (Blu-ray
+    /// format).
+    pub fn detect(probe: &DrmProbe<'_>) -> Option<DrmScheme> {
+        // CSS — DVD probe sector carries the scramble flag.
+        if let Some(sector) = probe.dvd_sample_sector {
+            if css::is_scrambled(sector) {
+                return Some(DrmScheme::Css);
+            }
+        }
+
+        // AACS — content cert type byte distinguishes V10 from V20+.
+        // V21 promotion requires MKB Variant records.
+        let cc = probe.content_cert.and_then(aacs::parse_content_cert)?;
+        match cc.version {
+            aacs::AacsVersion::V10 => Some(DrmScheme::Aacs10),
+            aacs::AacsVersion::V20 | aacs::AacsVersion::V21 => {
+                if let Some(mkb) = probe.mkb {
+                    let recs = aacs::variants::walk_mkb(mkb);
+                    if aacs::variants::is_variant_mkb(&recs) {
+                        return Some(DrmScheme::Aacs21);
+                    }
+                }
+                Some(DrmScheme::Aacs20)
+            }
+        }
+    }
+
+    /// Run key resolution for this scheme against `ctx`.
+    ///
+    /// Returns `None` when the scheme's resolver could not produce keys
+    /// (missing context, KEYDB miss, failed crypto walk, etc.) or when
+    /// the scheme itself is gated off (see the inline comment on the
+    /// `Aacs21` arm).
+    pub fn load(self, ctx: &mut DrmContext<'_>) -> Option<ResolvedScheme> {
+        match self {
+            DrmScheme::Css => ctx
+                .css
+                .as_mut()
+                .and_then(css::resolve)
+                .map(ResolvedScheme::Css),
+            DrmScheme::Aacs10 => ctx
+                .aacs
+                .as_ref()
+                .and_then(aacs::resolve_keys_v1)
+                .map(ResolvedScheme::Aacs),
+            DrmScheme::Aacs20 => ctx
+                .aacs
+                .as_ref()
+                .and_then(aacs::resolve_keys_v2)
+                .map(ResolvedScheme::Aacs),
+            // AACS 2.1 derivation is wired but disabled. KCD validation
+            // against a Variant-scheme disc is pending. To enable,
+            // uncomment the line below.
+            // DrmScheme::Aacs21 => ctx
+            //     .aacs
+            //     .as_ref()
+            //     .and_then(aacs::resolve_keys_v21)
+            //     .map(ResolvedScheme::Aacs),
+            DrmScheme::Aacs21 => None,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Build a minimal cert: type byte + bus-encryption byte + 6 zero
+    // cc_id bytes.
+    fn cert(type_byte: u8) -> Vec<u8> {
+        let mut v = vec![0u8; 8];
+        v[0] = type_byte;
+        v
+    }
+
+    // Synthetic AACS 2.x MKB with no Variant records.
+    fn mkb_classical() -> Vec<u8> {
+        vec![
+            0x10, 0x00, 0x00, 0x0C, 0x48, 0x14, 0x10, 0x03, 0x00, 0x00, 0x00, 0x4D,
+        ]
+    }
+
+    // Synthetic AACS 2.x MKB with a 0x82 + 0x83 record pair.
+    fn mkb_with_variant() -> Vec<u8> {
+        let mut m = mkb_classical();
+        m.extend_from_slice(&[0x82, 0x00, 0x00, 0x14]);
+        m.extend_from_slice(&[0xEE; 16]);
+        m.extend_from_slice(&[0x83, 0x00, 0x00, 0x14]);
+        m.extend_from_slice(&[0x55; 16]);
+        m
+    }
+
+    // Synthetic scrambled DVD sector — byte 0x14 carries the CSS
+    // scramble flag in bits 4-5.
+    fn scrambled_dvd_sector() -> Vec<u8> {
+        let mut s = vec![0u8; 2048];
+        s[0x14] = 0x30;
+        s
+    }
+
+    #[test]
+    fn detect_returns_none_for_unencrypted() {
+        let probe = DrmProbe {
+            dvd_sample_sector: None,
+            content_cert: None,
+            mkb: None,
+        };
+        assert_eq!(DrmScheme::detect(&probe), None);
+    }
+
+    #[test]
+    fn detect_returns_css_for_scrambled_dvd() {
+        let sector = scrambled_dvd_sector();
+        let probe = DrmProbe {
+            dvd_sample_sector: Some(&sector),
+            content_cert: None,
+            mkb: None,
+        };
+        assert_eq!(DrmScheme::detect(&probe), Some(DrmScheme::Css));
+    }
+
+    #[test]
+    fn detect_returns_aacs10_for_type0_cert() {
+        let c = cert(0x00);
+        let probe = DrmProbe {
+            dvd_sample_sector: None,
+            content_cert: Some(&c),
+            mkb: None,
+        };
+        assert_eq!(DrmScheme::detect(&probe), Some(DrmScheme::Aacs10));
+    }
+
+    #[test]
+    fn detect_returns_aacs20_for_type1_cert_no_variant() {
+        let c = cert(0x01);
+        let mkb = mkb_classical();
+        let probe = DrmProbe {
+            dvd_sample_sector: None,
+            content_cert: Some(&c),
+            mkb: Some(&mkb),
+        };
+        assert_eq!(DrmScheme::detect(&probe), Some(DrmScheme::Aacs20));
+    }
+
+    #[test]
+    fn detect_returns_aacs21_for_type1_cert_with_variant() {
+        let c = cert(0x01);
+        let mkb = mkb_with_variant();
+        let probe = DrmProbe {
+            dvd_sample_sector: None,
+            content_cert: Some(&c),
+            mkb: Some(&mkb),
+        };
+        assert_eq!(DrmScheme::detect(&probe), Some(DrmScheme::Aacs21));
+    }
+
+    #[test]
+    fn detect_returns_aacs20_when_mkb_absent() {
+        // Type-1 cert but no MKB to upgrade with -> Aacs20.
+        let c = cert(0x01);
+        let probe = DrmProbe {
+            dvd_sample_sector: None,
+            content_cert: Some(&c),
+            mkb: None,
+        };
+        assert_eq!(DrmScheme::detect(&probe), Some(DrmScheme::Aacs20));
+    }
+
+    #[test]
+    fn load_aacs21_returns_none() {
+        // The Aacs21 dispatch arm is commented out; load() must
+        // return None until KCD validation lands.
+        let uk_ro = vec![0u8; 256];
+        let vid = [0u8; 16];
+        let keydb = aacs::KeyDb::empty();
+        let ctx_aacs = aacs::ResolveContext {
+            unit_key_ro: &uk_ro,
+            content_cert: None,
+            volume_id: &vid,
+            keydb: &keydb,
+            mkb: None,
+        };
+        let mut ctx = DrmContext {
+            aacs: Some(ctx_aacs),
+            css: None,
+        };
+        assert!(DrmScheme::Aacs21.load(&mut ctx).is_none());
+    }
+
+    /// Exercises the V21 helper directly. Gated `#[ignore]` because
+    /// the chain reaches `MediaKeyVariantError::VariantsTableUnavailable`
+    /// without a real Variant-scheme disc to fix the per-uv table
+    /// layout against — running it here would assert only the
+    /// not-yet-wired error code. Kept as a wiring smoke-test for
+    /// future enablement.
+    #[test]
+    #[ignore]
+    fn resolve_keys_v21_helper_exists() {
+        let uk_ro = vec![0u8; 256];
+        let vid = [0xAAu8; 16];
+        let keydb = aacs::KeyDb::empty();
+        let mkb = mkb_with_variant();
+        let ctx = aacs::ResolveContext {
+            unit_key_ro: &uk_ro,
+            content_cert: None,
+            volume_id: &vid,
+            keydb: &keydb,
+            mkb: Some(&mkb),
+        };
+        // Just confirm the symbol is callable; we don't assert on the
+        // result.
+        let _ = aacs::resolve_keys_v21(&ctx);
+    }
+}

src/lib.rs

@@ -77,6 +77,7 @@ pub mod css;
 pub mod decrypt;
 pub mod disc;
 pub mod drive;
+pub mod drm;
 pub mod error;
 pub mod event;
 pub mod halt;

tests/crypto_tests.rs

@@ -724,7 +724,7 @@ fn aacs_parse_unit_key_ro_minimal() {
         data[key_pos + i] = (0xA0 + i) as u8;
     }
 
-    let result = aacs::parse_unit_key_ro(&data, false);
+    let result = aacs::parse_unit_key_ro(&data, aacs::AacsVersion::V10);
     assert!(
         result.is_some(),
         "parse_unit_key_ro should succeed on valid data"