Implement KeyCache in cache.rs with CachedKey (Zeroize-protected),
CacheConfig (TTL + max_entries), and lazy eviction. Wire cache into
SecretServiceInner: derive_* methods check cache before re-deriving,
Lock clears and zeroizes all cache entries, encrypt/decrypt use
cached encryption key. Per ADR-038 and OQ-SVC-04.
Implements deterministic password derivation using SLIP-0010 at the
given path. derive_password returns raw truncated key bytes;
derive_password_string returns Base64url-encoded (no padding) string.
Both require unlocked state (ServiceLocked if locked). Includes unit
tests for determinism, different paths, length truncation, locked
error, and Base64url encoding.
Per ADR-038, DerivedKey.private_key now derives Zeroize with #[zeroize(drop)]
ensuring sensitive key material is zeroized before deallocation. DerivedKey
is now move-only (no Clone), and JSON/debug output redacts private_key as
"[REDACTED]". Deserialization still works for postcard/irpc wire format.
Also fixes clippy needless_borrows_for_generic_args in encryption.rs and
applies cargo fmt to existing code.
Add module-level documentation explaining that the salt field is reserved
for Phase B KDF-based key rotation. Add doc comment on the salt field
clarifying it is not used in v1 key derivation. Add TODO(Phase B) comment
on salt generation in encrypt().
Create the alknet-secret crate with BIP39 mnemonic generation, SLIP-0010
Ed25519 HD key derivation, AES-256-GCM encryption, and SecretProtocol
irpc service definition. This is Phase 3.1 from the integration plan.
Architecture changes:
- Promote secret-service.md to reviewed status with full spec format
(crate structure, public API, security model, phase progression,
ADR/OQ cross-references, wire format compatibility section)
- Add ADR-038 (seed lifecycle and memory security): zeroize for v1,
mlock deferred to Phase B
- Add OQ-SEC-01 (mlock/VirtualLock for seed RAM) to open-questions.md
- Update README.md with ADR-038 and secret-service status
Crate structure:
- src/mnemonic.rs: BIP39 phrase generation, validation, seed derivation
- src/derivation.rs: SLIP-0010 HD key derivation, path constants (74')
- src/encryption.rs: AES-256-GCM encrypt/decrypt, EncryptedData type
- src/protocol.rs: SecretProtocol irpc enum, DerivedKey, KeyType
- src/service.rs: SecretServiceHandle with Unlock/Lock lifecycle
- 40 passing tests (unit + integration + doc)
