alknet/docs/architecture/crates/vault

status, last_updated

status	last_updated
draft	2026-06-19

alknet-vault

Local key vault: BIP39 mnemonic generation, SLIP-0010 Ed25519 HD key derivation, BIP-0032 secp256k1 derivation (feature-gated), and AES-256-GCM encryption. Holds the master seed — the root of trust for all derived keys and encrypted credentials in the alknet system.

What This Crate Is

alknet-vault is a standalone crate with zero alknet crate dependencies (ADR-018). It provides the cryptographic primitives and runtime API for managing the root of trust. The CLI binary (the alknet crate) is the sole component that talks to the vault directly (ADR-019) — handlers receive derived/decrypted material through capabilities, never through a vault reference.

The vault is not a network service. It has no ALPN, no ProtocolHandler implementation, and no operations registered in the call protocol (ADR-008, ADR-014). The master seed and derived private keys never cross the network.

Documents

Document	Status	Description
mnemonic-derivation.md	draft	BIP39, SLIP-0010, BIP-0032, derivation paths, key types
encryption.md	draft	AES-256-GCM, EncryptedData, key versioning, HD derivation (ADR-020)
service.md	draft	VaultServiceHandle lifecycle, actor dispatch, cache, error model
protocol.md	draft	VaultProtocol irpc messages, DerivedKey redaction, serialization

Applicable ADRs

ADR	Title	Relevance
003	Crate Decomposition	alknet-vault's standalone position
005	irpc as Call Protocol Foundation	VaultProtocol uses irpc directly
008	Vault Integration Point	CLI-embedded, capability source
014	Secret Material Flow and Capability Injection	Capabilities carry vault-derived material
018	Vault as Standalone Crate	Zero alknet crate dependencies
019	Vault Assembly-Layer-Only Access	The assembly layer is the sole caller
020	HD Derivation for Encryption Keys	SLIP-0010 derivation, not PBKDF2; salt unused in v2

Relevant Open Questions

OQ	Title	Status	Relevance
OQ-20	Encryption key derivation	resolved (ADR-020)	HD derivation from seed; salt field unused in v2
OQ-21	Remote vault administration	deferred	Network unlock not supported; needs ADR if ever needed
OQ-22	Key rotation mechanism	open	Key versioning is in place; rotation workflow is not specced

Key Design Principles

1. Standalone: The vault depends on no alknet crate. It defines its own types, errors, and protocol. External crates depend on the vault; the vault depends on nothing in alknet.
2. Assembly-layer only: The vault's API is consumed by the CLI binary, not by handlers. Handlers receive material through capabilities (ADR-014). The vault is not on the wire.
3. Zeroize everything sensitive: The mnemonic, seed, derived private keys, encryption keys, and cached keys all implement Zeroize and ZeroizeOnDrop. Secret material does not linger in freed heap memory.
4. Deterministic derivation: The same mnemonic + passphrase + path always produces the same key. Derivation is reproducible across runs and across nodes.
5. OsRng for nonces: AES-GCM IVs and any cryptographic nonces use OsRng (or equivalent CSPRNG), never rand::random(). IV reuse under the same key is catastrophic for GCM.
6. No unwrap() or expect() outside tests: vault operations propagate errors. A poisoned lock is recovered with unwrap_or_else(|e| e.into_inner()), not unwrap(). A panic in one vault operation must not brick the vault for all other operations.

Security Constraints

These are security-critical implementation requirements, not architectural decisions (the architecture is locked by the ADRs above). They are documented here so implementation agents don't miss them. See service.md → Security Constraints for the full list.

• OsRng for IVs: AES-GCM IVs must use OsRng, not rand::random(). The current source uses rand::random() — this is a known drift from the spec and must be corrected during implementation sync.
• Zeroized drop: Seed, Mnemonic, ExtendedPrivKey, Secp256k1ExtendedPrivKey, EncryptionKey, CachedKey, and DerivedKey all derive Zeroize and ZeroizeOnDrop. The cache must clear on drop, not just on explicit lock().
• No unwrap() outside tests: poisoned lock recovery uses unwrap_or_else(|e| e.into_inner()) or explicit error propagation. The current source uses unwrap() in VaultServiceHandle methods — this is a known drift and must be corrected.
• DerivedKey redaction in JSON: DerivedKey serializes the private_key as "[REDACTED]" in human-readable formats (JSON) and as raw bytes in binary formats (postcard). The redaction is a defense-in- depth measure, not the primary control — the primary control is that DerivedKey never crosses the call protocol wire (ADR-014).

Public API

The vault re-exports its primary types from the crate root:

// Mnemonic and seed
pub use mnemonic::{Language, Mnemonic, Seed};

// Derivation
pub use derivation::{DerivationError, ExtendedPrivKey, PATHS};

// Encryption
pub use encryption::{EncryptedData, EncryptionError};

// Protocol (irpc messages)
pub use protocol::{DerivedKey, KeyType, VaultMessage, VaultProtocol};

// Service (runtime)
pub use service::{VaultService, VaultServiceActor, VaultServiceError, VaultServiceHandle};

// Cache
pub use cache::CacheConfig;

The secp256k1 feature flag gates Ethereum (BIP-0032) derivation:

#[cfg(feature = "secp256k1")]
pub mod ethereum;