more efficient signing

[calvinmetcalf]

rsa can be a bit slow especially if you have to do it a lot, it might be faster to just come up with a shared secret (ecdh is pretty cheap) and use hmacs to verify it incrementing the key each time (https://github.com/calvinmetcalf/hmac-stream does it for a binary stream or since it's already an object stream you could just do it manually).

[mafintosh]

Rsa is actually just used for the initial two messages. After that it uses webrtcs dtls stack. I wanna make this more generic though so we can support multiple schemes :)