6. Messages and Attachments

Work in progress — not audited

This chapter is part of an initial draft specification. Enkrypted Chat has not been independently audited. Content may change.

6.1 Application message path

1. User plaintext composed in UI.
2. Serialized to an application envelope (JSON-based in current implementation).
3. Encrypted through the cascade (Chapter 4).
4. Sent over WebRTC data channel via MLSProvider / PeerJS.

6.2 Wire format

Normative PDU catalog and schemas: P4. PDU catalog.

Cascade envelope: P5. Cascade wire encoding.

Processing rules (encrypt/decrypt): P6. Processing rules.

Encoding: JSON UTF-8 on WebRTC data channels; every PDU has a type string. Profile: EnkryptedChat-Profile-v0 (single implementation; not an interoperability standard yet).

Peers MUST reject messages that fail decryption at any cascade layer (P6).

6.3 Text messages

Text messages use the full cascade when enableCascadingCipher is true in the product shell.

6.4 File transfer

Two paths exist:

6.4.1 Standard path (cascade + chunking)

• Files are split into chunks sized for data channel limits.
• Chunks are encrypted with the same cascade as messages.
• Reassembly occurs on the receiver.

Suitable when full application E2EE is required.

6.4.2 Fast file transfer (optional)

When enableFastFileTransfer is enabled:

• A optimized WebRTC data channel path may transfer file data with reduced or bypassed cascade overhead for performance.
• User toggles this in settings (persisted in localStorage).

Security tradeoff: Fast path prioritizes throughput over full cascade protection. The specification requires this behavior to be documented in UI and user-controlled.

6.5 Local files, OPFS, and editor

Enkrypted Chat stores files in OPFS (Origin Private File System) by default, with optional folder mount. Features include in-browser preview and document editing.

6.6 Encryption at rest (work in progress)

At-rest encryption is in active development. Intended design:

Element	Behavior
Data encryption key (DEK)	Cryptographically random, encrypts local vault
DEK wrapping	User unlock via passkey, passcode, or password
Recovery password	Generated at setup; user prompted to back up

Until shipped, local data MAY be stored without at-rest encryption depending on build flags — treat as high risk on shared devices.

6.7 Calendar and plan data

Calendar events are managed locally in the browser for the Plan feature. They inherit the same at-rest posture as other local app data.

6.8 Multimedia in chat

Images, video, and animations sent as chat attachments follow the file/message paths above. Large media SHOULD prefer chunked standard path unless user enables fast transfer.