Encrypt clipboard text and file bytes at the engine with ChaCha20-Poly1305
(nonce‖ciphertext; clipboard base64'd into the text field) using a key derived
from the shared account secret. Sealing happens BEFORE any transport, so LAN,
the SSE relay, and RTC all carry only ciphertext — the server is reduced to pure
signaling (presence/SDP/ICE), never content. RTC stays doubly protected under
DTLS. Receive decrypts in the message + file sinks; undecryptable payloads (wrong
key) are dropped. Plaintext passthrough when signed out (account="").
Honest caveat (in crypto.rs): the key is sha256(account) and the account is an
email — low entropy, so this stops passive eavesdroppers but not someone who
knows the account. The real fix is a high-entropy secret (Sign in with Apple
`sub` / passphrase) → same from_secret() API.
Verified by examples/e2e_demo.rs: B decrypts A's clipboard over LAN; a relayed
send carries ciphertext only (plaintext never on the bus).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Patrick Ecord
33d0fb7f7e
