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Security: CRTYPUBG/Linkora

Security

docs/SECURITY.md

Linkora Security, Cryptography & Trust Model

1. Cryptographic Architecture

Transport Layer

  • Media Streams (WebRTC): Standard DTLS 1.2/1.3 with SRTP (AES-128-GCM or AES-256-GCM) ensures transport-level encryption between peers and any intervening TURN relay.
  • Signaling Channel: WSS (WebSocket over TLS 1.3).

Application Layer (E2EE)

  • Key Derivation: 256-bit AES key derived from a shared secret passphrase and unique room salt (linkora-salt-{roomCode}) using PBKDF2 with 100,000 iterations of SHA-256.
  • Cipher: AES-GCM-256 with 128-bit authentication tags.
  • IV Construction: 12-byte IV consisting of a 4-byte static protocol prefix (LK\x01) and an 8-byte big-endian monotonic transmission counter (sendCounter).
  • Sliding-Window Replay Protection: RFC 6479-inspired sliding-window mechanism (window size: 1024 frames) tracking received frame counters per sender hash. This allows legitimate out-of-order UDP packet delivery without dropping packets, while strictly rejecting duplicate/replayed frames and frames outside the window.

2. Safety Fingerprints (Short Authentication Strings)

  • To prevent man-in-the-middle attacks and signaling server impersonation, Linkora calculates an out-of-band Safety Fingerprint: $$\text{Fingerprint} = \text{Hex}(\text{SHA-256}(K_{\text{derived}}))[0..16]$$ formatted into chunks: XXXX-XXXX-XXXX-XXXX.
  • Participants compare this string out-of-band (e.g. over voice or secondary channel).

3. Honest Status of WebRTC Encoded Transform in WebView2

  • Standard WebRTC (DTLS-SRTP) is 100% functional and verified across Windows WebView2.
  • While the Linkora cryptographic package (@linkora/crypto) provides fully tested AES-GCM-256 frame payload encryption and sliding-window replay protection, native Chromium RTCRtpScriptTransform / WebRTC Insertable Streams have variable experimental availability depending on the host's installed Microsoft Edge WebView2 runtime version.
  • Honest Security Distinction: DTLS-SRTP ensures that the signaling server never sees media content. Only a designated TURN relay can forward encrypted UDP packets (unable to decrypt them without DTLS keys). Application-level frame encryption can be layered whenever WebView2 runtime flags enable encoded transform workers.

4. Metadata Visibility

  • Visible to Signaling Server:
    • Peer display names.
    • Room identifiers.
    • Connection timestamps.
    • Client IP addresses (for WebSocket connections).
  • Hidden from Signaling Server:
    • Audio content.
    • Video and screen-sharing contents.
    • E2EE passphrase and derived cryptographic keys.

There aren't any published security advisories