Add EncryptedEnvelope, update GossipMsg doc.

An EncryptedEnvelope is a special envelope needed for certain phases of
DKG. Update document for the channel field in GossipMessage; note that
we use keccak as the has function, and that pub keys are specifically
StakingPubKeys.

pkg/types/gossip/message.proto

@@ -5,6 +5,8 @@ package gossip;
 
 // Envelope contains a marshalled Message as the payload
 // and a signature over the payload as signature.
+// It also contains the Identities of the sender and receiver.
+// Optionally may contain an encrypted Envelope (in which case the payload will be empty).
 message Envelope {
   // A Marshaled GossipMessage
   bytes payload = 1;
@@ -16,21 +18,32 @@ message Envelope {
   // Signature of the message
   bytes signature = 4;
 
+  EncryptedEnvelope encrypted_envelope = 5;
+
   // TODO: this envelope needs an enum detailing which type of GossipMesssage it is.
 }
 
+// EncryptedEnvelope is a marshalled encrypted message.
+message EncryptedEnvelope {
+  bytes payload = 1;
+  bytes signature = 4;
+}
+
 message Identity {
+  // TODO: consolidate and remove redundant
   bytes public_key = 1;
   bytes bls_id = 2;
+  bytes peer_id = 3;
 }
 
 message GossipMessage {
   // Channel is isomorphic to the group name as well as the pubsub channel
-  // Channel names are HASH(PubKey1 || ... || PubKeyN) of all valid group members.
+  // Channel names are Keccak(StakingPubKey1 || ... || StakingPubKeyN) of
+  // all valid group members.
   bytes channel = 1;
 
   // Proof that the peer that sent this message knows the channel's name.
   bytes channel_MAC = 2;
 
   // TODO: define various messages this GossipMessage can be. Use oneof.
-}
+}