Disc::decrypt_with now takes Device / Processing / Media / Volume keys in
addition to Unit. A caller hands in whatever level it resolved and the
library derives down the AACS chain to the per-CPS-unit keys, then
decrypts:
Device -> MKB walk -> media key -> VUK -> per-CPS unit keys
Processing -> MKB -> media key -> VUK -> per-CPS unit keys
Media -> Volume ID -> VUK -> per-CPS unit keys
Volume -> Unit_Key_RO.inf, one unit key per CPS unit
Unit -> used directly (terminal)
Derivation stays centralized in the version-dispatched resolver
(1.0 / 2.0 / 2.1), fed by a single-key provider built from the supplied
key — no new crypto. Volume notably does NOT stop at the volume key: it
decrypts every CPS unit's key.
Scan stashes the AACS inputs (Unit_Key_RO.inf and MKB) on AacsState so an
out-of-band decrypt_with can derive without re-reading the disc.
Non-breaking: Key is #[non_exhaustive] and the existing Unit path is
unchanged. New tests cover the Volume -> per-CPS derive-down, the
missing-inputs error, and the no-units rejection.
keydb stores Media Keys per-disc, but an MK is MKB-scoped (shared across a
pressing/MKB-family). A disc whose own hash/VID isn't keyed can still resolve
if any stored MK verifies against its MKB. New path 2.5 (between PK and the
VID lookup) collects the distinct MK pool from the providers, km_verifies each
against the disc MKB, and on a UNIQUE pass derives VUK (with the disc VID) then
the UK — matching the online resolver's behavior so local keydb mode resolves
the same discs (e.g. an MK present in keydb under a sibling pressing).
km_verifies is one AES-D + magic check per candidate (cheap). Adds
KeyProvider::media_keys() + a path-2.5 unit test.
The ScanOptions.unit_key path is a generic primitive — a caller-supplied Unit
Key that bypasses keydb lookup. Doc comments + a tracing log named a specific
external source; reworded to neutral 'out-of-band / external key service' so
the library makes no assumptions about where the key came from.
Two coherent additions to the AACS resolver:
KeyProvider abstraction (provider.rs) — key material comes from pluggable
backends; KeyDb implements it (device/processing keys, host certs,
disc-by-hash / disc-by-vid lookup) plus orphan-DK parsing. ResolveContext
takes a provider array. Adds the SD-tree PK walker
(derive_media_key_from_pk_walked) and a `probe` module (km_verifies MK
oracle, mkb_* record parsers) used for offline key verification. Cvalue
record selection prefers 0x05, falls back to 0x07.
External-UK key source — the second, mutually-exclusive key source for the
keyserver path. ScanOptions/InputOptions gain `unit_key`; when set,
resolve_encryption_static skips keydb entirely and uses the caller-supplied
Unit Key directly (KeySource::ExternalUk). Disc::read_aacs_inputs exposes a
disc's Unit_Key_RO.inf + MKB so a caller can fetch the UK out-of-band; the
library makes no network call itself.
CHANGELOG: redact test-disc title in historical notes.
MattJackson