Author here. Started with a simple problem: sync data between two phones with no backend.
WebRTC signaling SDPs are ~2.5KB. Too large for practical QR scanning. When you control both endpoints, most of that is unnecessary ceremony.
Key insights: derive ICE credentials from DTLS fingerprint via HKDF, use binary encoding (IP as 4 bytes not ASCII), skip compression (DEFLATE increases size on high-entropy data), skip base64 (QR supports raw binary).
obiefernandez•2w ago
Love the creativity and that you took the time to explain every step of the discovery.
martinprins•2w ago
Thanks! The write-up took longer than the actual protocol design.
martinprins•2w ago
WebRTC signaling SDPs are ~2.5KB. Too large for practical QR scanning. When you control both endpoints, most of that is unnecessary ceremony.
Key insights: derive ICE credentials from DTLS fingerprint via HKDF, use binary encoding (IP as 4 bytes not ASCII), skip compression (DEFLATE increases size on high-entropy data), skip base64 (QR supports raw binary).