The vault uses SLIP-0010 HD derivation from the BIP39 seed for the
AES-256-GCM encryption key, not PBKDF2. This replaces the TypeScript
predecessor's (@alkdev/storage/src/graphs/crypto.ts) PBKDF2-based
approach.
Key decisions:
- HD derivation at m/74'/2'/0'/0' produces the encryption key
- PBKDF2 is not implemented in the vault; no password-based derivation
- salt field is unused in v2 (wire-format compat only)
- key_version=1 reserved for TS PBKDF2 data; key_version=2 for vault HD
- TS-encrypted data requires one-time migration to v2
- CURRENT_KEY_VERSION changes from 1 to 2 (source drift flagged)
OQ-20 resolved: the encryption key derivation method is locked. OQ-22
(key rotation workflow) remains open but does not block implementation.
Spec the vault crate from its existing implementation. The vault is
stable (implementation exists); this spec documents what IS so the
implementation-sync agent can reconcile source drift.
New spec documents (crates/vault/):
- README.md — crate index, security constraints, public API
- mnemonic-derivation.md — BIP39, SLIP-0010, BIP-0032, derivation paths
- encryption.md — AES-256-GCM, EncryptedData, key versioning, salt
- service.md — VaultServiceHandle lifecycle, actor dispatch, cache
- protocol.md — VaultProtocol irpc messages, DerivedKey redaction
New ADRs:
- ADR-018: Vault as standalone crate (zero alknet deps; own types/errors)
- ADR-019: Vault assembly-layer-only access (CLI is sole caller)
New open questions:
- OQ-20: Salt/KDF Phase B (open, low priority — salt field reserved)
- OQ-21: Remote vault administration (deferred — needs ADR if ever needed)
- OQ-22: Key rotation mechanism (open, low priority — workflow not specced)
Spec-vs-source drift explicitly flagged (for the sync agent):
- rand::random() used for IVs instead of OsRng (security-critical)
- unwrap() on every RwLock acquisition (must use unwrap_or_else)
- ADR-038 / OQ-SVC-03 references in source comments are stale (old numbering)
- VaultServiceActor::spawn returns a non-functional second actor (source bug)
- KeyVersionMismatch error variant is defined but unused in v1
