Deep Dives

In-depth technical explorations of specific design decisions in Arx Runa — covering cryptographic primitive choices, key recovery trade-offs, and padding strategies. Each document surveys alternatives, evaluates them against the zero-knowledge threat model, and records the rationale for what was chosen.

• Cryptographic Primitive Rationale — Justification and alternative analysis for every cryptographic primitive in the design: XChaCha20-Poly1305, HKDF-SHA256, Argon2id, per-file key wrapping, BLAKE3 checksums, and ZeroizeOnDrop + Secret<T> memory protection.
• File Sharing Cryptography — Cryptographic decisions for Phase 5 file sharing: HPKE (RFC 9180) over ad-hoc ECIES, X25519 curve confirmation, CTX-ChaCha20-Poly1305 as the committing AEAD, and simplification of the share package envelope.
• Password and Key Recovery — Feasibility survey of every known vault recovery mechanism (recovery phrases, Shamir's SSS, SLIP-39 shares, trusted-contact key wrapping, platform biometrics, cloud escrow) evaluated against the zero-knowledge threat model.
• Reducing Padding Overhead — Survey of all known techniques for reducing per-file padding waste: Padmé padding, tiered chunk sizes, smaller uniform chunk size, content-defined chunking (rejected — fingerprinting attacks), and epoch-based deferred batching.