crypto

ryu-crypto

The encryption-at-rest primitive for Ryu — one crypto path every local store hangs off (docs/encryption-at-rest.md).

Role in the decomposition

An extracted Core capability crate (L0), compiled into Core by default and consumed as a NON-optional path dependency: the session/chat loop and long-term memory encrypt every row unconditionally, so there is no off build. ZERO dependency on apps/core.

Key API

• FieldCipher — ChaCha20-Poly1305 AEAD with a self-describing field envelope enc:v1:<base64(nonce||ciphertext)>. seal/open for string columns, encrypt/decrypt for blobs. open transparently passes through legacy plaintext (anything without the enc:v1: prefix), so already-stored rows keep working and upgrade to ciphertext on the next write. is_sealed tests a value.
• global_cipher() — the process-wide cipher backed by the swappable master key, resolved in priority order: RYU_MASTER_KEY (env) → OS keychain (default) → ~/.ryu file fallback, with legacy in-memory-key migration. The key lives outside the data it protects, so a copy of ~/.ryu alone cannot decrypt. Headless-safe: no interactive prompts.

Kernel seam (CryptoHost)

The two things the crate needs from the kernel — the profile-scoped keychain account suffix and the ~/.ryu data dir — invert through the narrow CryptoHost trait. Core implements it once (crate::crypto_host::CoreCryptoHost) and installs it at boot via set_global_host before the first store opens.

Swap seam

Key-custody policy (env/keychain/file, legacy migration) stays in-crate; the internal Keychain port is the swap seam for a future local-key → KMS backend. The per-platform keychain backend (Windows Credential Manager / macOS Keychain / Linux Secret Service) is selected by cfg(target_os).

Placement

At-rest encryption of local orchestration data is what runs → Core. The Gateway's firewall/DLP governs what is allowed/shared on egress — a separate layer.