4d1f07f253bca792febcd008d742db98c28b3adf
3
Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 jaap-jan
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7016ce36f1 |
Key the local cache to the identity, not to the door it was opened through
Groundwork for a device key, and a spec change rather than a feature. ADR 0007 records the decision it clears the way for: a Windows Hello gesture guarding a protected blob, with the passphrase kept as a permanent fallback. The reason that decision needed this first is that a device key cannot open a session on its own. SessionOpener derived two things from the passphrase master key — the bundle, and the local cache key — and a device wrap is SealTo(device_x25519_pk), which yields the bundle and never computes a master key at all. A device unlock could therefore have opened the identity and still not read the cache it had itself written. So LocalCacheKey now derives from the bundle: dsh1/localcache/v1 → v2, specified in crypto.md §3.2. Every wrap that opens a vault ends up holding the bundle, so every door reaches the same cache. Extract-and-expand, not expand alone. Everything derived from the master key uses HKDF-Expand directly, which is sound because an Argon2id output is uniformly random over its whole length. The bundle's encoding is not — it opens with a fixed 14-byte label and carries a version, a generation and a timestamp before reaching any key material — so it needs the extract step to become a pseudorandom key first. Two consequences fell out, both improvements and neither the point: - A passphrase change no longer discards the local cache. The bundle is unchanged by a re-wrap, so the cache key is too. Under v1 changing a passphrase silently orphaned every cached row and the next launch re-pulled the whole vault. - Recovery-code unlock is fixed before it ships. It derives a different master key from a different secret and a different salt, so under v1 it would have had the same defect as the device path, and nobody would have noticed until it landed. The cache becomes unreadable exactly when the identity is rotated, which is the correct moment to discard it. Existing caches are discarded and re-pulled on upgrade — already the specified behaviour for a stale cache, and the reason the label is versioned rather than reused: a v1 cache must fail to open rather than decrypt to nonsense. One stated guarantee got weaker and now says so. crypto.md §10 claimed locking meant "nothing on disk can be read again without the passphrase." Where a device wrap exists that is no longer true, and it would have been untrue under either candidate design — the alternative was storing a copy of the cache key in the device blob, which is the same door with an extra key lying next to it. The wording now points at ADR 0007, because what guards the device key is a platform decision and not a property of this specification. A golden vector was quietly lying, which is the part worth reading twice. The "local-cache" entry pinned HKDF-SHA512-Expand over a fixed PRK — a construction the cache key no longer uses. Regenerating it would have produced a green suite describing a derivation this code does not perform. It is replaced by a vector over a bundle whose every byte is pinned: the label, version 1, generation 1, a fixed timestamp and two recognisable key scalars, all visible in the fixture so a second implementation can check itself against it. UserSecretBundle.TryDecode is internal for this, because Create draws fresh randomness and so can never produce a reproducible input. Mutation tested, and this one earns its keep: dropping the extract step now fails CommittedVectors_MatchCurrentImplementation. The vector it replaced could not have caught that, because it never touched the bundle at all. One test became false and says so. ARecordSealedUnderAnotherPassphrase is now ARecordSealedByAnotherIdentity: a different passphrase deliberately no longer changes the cache key, and TheLocalCacheKey_SurvivesAPassphraseChange pins that. What must still be unreadable is another user's cache. CacheHarness therefore generates an identity rather than deriving from a passphrase, and has no passphrase parameter left — the cache key is not a question about passphrases any more. SyncHarness's two simulated machines now derive the same cache key, which is what keying on the bundle means: they are the same user holding the same identity. They still have separate cache databases, so nothing is shared between them but the key that would open either. Both harnesses lost a MasterKey field that existed only to make a protector. 858 tests green. Zero warnings, dotnet format clean. Not done: the device key itself. Three pieces remain, and the middle one was a discovery rather than a plan — EnrollmentService.AddDevice runs only during enrollment, so every already-enrolled account, which is all of them, needs an endpoint to add a device wrap while unlocked. The client proves possession by producing the wrap, so that shape falls out of the crypto. After that: the protector seam with the wrap cached locally for offline unlock, then the Hello implementation and the unlock-screen UI, which is where the Windows TFM lands and where automated testing stops. |
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|
jaap-jan
|
d2a2ed8a29 |
Specify the key statement encoding and key log chain (crypto.md 7.1, 7.2)
Section 7 always required "a canonical, length-prefixed encoding" for signatures without ever specifying one. That gap had to be closed before enrollment could exist: the client hashes the key statement and uses the result as an OIDC nonce, so the provider signs over those exact bytes. Two implementations disagreeing by one byte produce two nonces and an enrollment nobody can verify -- and it only shows up against a real provider, never in a local test. JSON cannot be the hashed form. Property order, number formatting, Unicode escaping and whitespace all vary between serialisers. So the statement is transmitted as JSON and hashed as a fixed binary encoding, and the two are independent by construction. Three details are load-bearing rather than stylistic: - The presence byte before each string is what makes the encoding injective. Without it an absent email and an empty one encode identically, and two different statements share a binding. - Timestamps truncate to milliseconds. PostgreSQL stores microseconds, so a statement that has been through the database must still hash to what the client hashed. The same applies to the key log, where an entry that cannot reproduce its own hash after being read back makes the chain unverifiable. - The key log entry hash deliberately excludes the database sequence. It is unknown until the insert runs, and order already follows the hash links -- so a renumbered or gapped sequence column cannot silently reorder history. KeyStatementFields is separate from Contracts.KeyStatement on purpose: one may gain JSON fields freely, the other cannot change without invalidating every stored binding, and Crypto must not depend on the contract assembly. KeyStatementDriftTests makes a field added to one and not the other a build failure, because a wire field outside the binding is unauthenticated data the server can change undetected. 54 new tests and two new golden vector sections. The vectors pin the absent-versus-empty email case and confirm that an offset-bearing sub-millisecond timestamp encodes identically to its truncated UTC form. Only additions to vectors.json; nothing existing moved. |
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jaap-jan
|
b15af836a3 |
Freeze DSH1 crypto specification and implement the core (M1)
docs/crypto.md is now the normative, frozen specification. This had to land before anything else in M1: the server holds ciphertext and no keys, so it can never re-encrypt, and a format change after users hold data is a coordinated client rewrite with no rollback. Specification: - DSH1 envelope layout, canonical 64-byte AAD encoding, SealTo construction, key hierarchy, Argon2id profiles, fingerprints, and the change rules for each version field. - AAD encoding is fixed-width binary rather than delimited string concatenation, so no field value can forge a field boundary. This supersedes the illustrative form sketched in ADR 0001, which now points here. - UUIDs are RFC 4122 big-endian. Guid.ToByteArray() emits the first three groups little-endian and would have made our ciphertext unreadable by any other implementation of this spec, failing only at a cross-implementation boundary. Verified rather than assumed: - PrimitiveAvailabilityTests proves X25519, Ed25519, XChaCha20-Poly1305, Argon2id and HKDF-SHA512 all function on net10.0. NSec 26.4.0 targets net9.0 and is consumed by forward compatibility; this closes one of the two package questions the plan flagged. - Argon2Profile exists because NSec's MemorySize is in KIBIBYTES, not bytes. Passing bytes gives either a 256 GiB allocation or a 256 KiB KDF that cracks instantly. The type takes mebibytes so the unit cannot be got wrong at a call site. Found by benchmarking: the first measurements were ~1000x too slow, which turned out to be 19 GiB of work. - Parameters measured, not guessed: 256 MiB/t=4 is 323 ms on this machine; the table of candidates is in the spec. Implementation and tests (83 total, up from 17): - AadDescriptor, DshEnvelope, DshCrypto (Seal/Open/SealTo/OpenSealed/fingerprints). - Decryption returns null rather than throwing: ciphertext comes from a server that is explicitly not trusted, so a failed tag is an expected outcome. - Envelope readers reject unknown algorithms and any non-zero flag bit, so an envelope that is not fully understood fails closed. - Executable form of the spec's substitution claims: a server cannot move ciphertext between resources, roll back a key generation or item version, repurpose a payload as metadata, or confuse the two constructions. - Golden vectors in tests/fixtures/crypto/vectors.json guard the format. Mutation-checked: a one-byte schema version change trips four tests including the guard. Two build-infrastructure bugs found and fixed along the way: - .editorconfig forced camelCase on const and static readonly fields. PascalCase is the .NET convention for both; the config was wrong, not the code. - The golden fixture was resolved with [CallerFilePath], which ContinuousIntegrationBuild rewrites to /_/... under deterministic source paths. It passed locally and would have failed only in CI. Now copied to the output directory and read from there. |