Copay peer handshake

gistfile1.txt

Alice             Bob
=================================================
                  .generates Extended PrivKey, PubKey
                  CopayerId=pubkey
                  PeerId=hash(CopayerId)
                  
                  PeerID is provided to the PeerJS/WebRTC
                  P2P facilitator server
          
                  .Connects server with PeerId.
                  .Sends CopayerId to Alice 
                  using an off channel.

.generates Extended 
PrivKey, PubKey
CopayerId=pubkey
PeerId=hash(CopayerId)

.Connects server with PeerId.
BobPeerId = hash(CopayerId)

.Asks for a Bob's p2p channel
to the server using BobPeerId

                  .receives connection request

.sign a "HELLO" 
using HMAC / Bob's
pubkey. See its
pubkey ring.

                  .check sig of HELLO.
                  
                  start signing messages using ECDSA
                  and checking Alice message using her
                  public key.
                  
Only the HELLO message is signed/verified using HMAC. 
Then all messages are signed using ECDSA.

This attemps to remove the need of trust from 
the PeerJS server.

• The initial exchange using HMAC in the HELLO message is only to allow Bob to send an authenticated message
  to Alice, so it is only the pubkey (not extended).
• Once both parties are authenticated, the extended pub keys are shared using PubKeyRing.

Encryption should be easy to implement once we have EC encryption support on bitcore (bitpay/bitcore#287), and using the same pubkeys for signing and encrypting data.