arbiter/IMPLEMENTATION.md

Implementation Details

This document covers concrete technology choices and dependencies. For the architectural design, see ARCHITECTURE.md.

---

Cryptography

Authentication

• Signature scheme: ed25519

Encryption at Rest

• Scheme: Symmetric AEAD — currently XChaCha20-Poly1305
• Version tracking: Each aead_encrypted database entry carries a scheme field denoting the version, enabling transparent migration on unseal

Server Identity

• Transport: TLS with a self-signed certificate
• Key type: Generated on first run; long-term (no rotation mechanism yet)

---

Communication

• Protocol: gRPC with Protocol Buffers
• Server identity distribution: ServerInfo protobuf struct containing the TLS public key fingerprint
• Future consideration: grpc-web lacks bidirectional stream support, so a browser-based wallet may require protojson over WebSocket

---

Memory Protection

The unsealed root key must be held in a hardened memory cell resistant to dumps, page swaps, and hibernation.

• Current: Using the memsafe crate as an interim solution
• Planned: Custom implementation based on mlock (Unix) and VirtualProtect (Windows)