p2p/discover: add some more code comments

p2p/discover/v5_encoding.go

@@ -321,10 +321,16 @@ func (c *wireCodec) encodeEncrypted(toID enode.ID, toAddr string, packet packetV
 // encodeAuthHeader creates the auth header on a call packet following WHOAREYOU.
 func (c *wireCodec) makeAuthHeader(nonce []byte, challenge *whoareyouV5) (*authHeaderList, *handshakeSecrets, error) {
 	resp := &authResponse{Version: 5}
+
+	// Add our record to response if it's newer than what remote
+	// side has.
 	ln := c.localnode.Node()
 	if challenge.RecordSeq < ln.Seq() {
 		resp.Record = ln.Record()
 	}
+
+	// Create the ephemeral key. This needs to be first because the
+	// key is part of the ID nonce signature.
 	var remotePubkey = new(ecdsa.PublicKey)
 	if err := challenge.node.Load((*enode.Secp256k1)(remotePubkey)); err != nil {
 		return nil, nil, fmt.Errorf("can't find secp256k1 key for recipient")
@@ -334,17 +340,21 @@ func (c *wireCodec) makeAuthHeader(nonce []byte, challenge *whoareyouV5) (*authH
 		return nil, nil, fmt.Errorf("can't generate ephemeral key")
 	}
 	ephpubkey := encodePubkey(&ephkey.PublicKey)
+
+	// Add ID nonce signature to response.
 	idsig, err := c.signIDNonce(challenge.IDNonce[:], ephpubkey[:])
 	if err != nil {
 		return nil, nil, fmt.Errorf("can't sign: %v", err)
 	}
 	resp.Signature = idsig
 
-	// Encrypt the authentication response.
+	// Create session keys.
 	sec := c.deriveKeys(c.localnode.ID(), challenge.node.ID(), ephkey, remotePubkey, challenge)
 	if sec == nil {
 		return nil, nil, fmt.Errorf("key derivation failed")
 	}
+
+	// Encrypt the authentication response and assemble the auth header.
 	respRLP, err := rlp.EncodeToBytes(resp)
 	if err != nil {
 		return nil, nil, fmt.Errorf("can't encode auth response: %v", err)
@@ -492,7 +502,7 @@ func (c *wireCodec) decodeAuth(fromID enode.ID, fromAddr string, head *authHeade
 
 // decodeAuthResp decodes and verifies an authentication response.
 func (c *wireCodec) decodeAuthResp(fromID enode.ID, fromAddr string, head *authHeaderList, challenge *whoareyouV5) (*handshakeSecrets, *enode.Node, error) {
-	// Decrypt / decode.
+	// Decrypt / decode the response.
 	if head.Scheme != authSchemeName {
 		return nil, nil, errUnknownAuthScheme
 	}

p2p/discover/v5_udp.go

@@ -529,8 +529,12 @@ func (t *UDPv5) sendNextCall(id enode.ID) {
 // This performs a handshake if needed.
 func (t *UDPv5) sendCall(c *callV5) {
 	if len(c.authTag) > 0 {
+		// The call already has an authTag from a previous handshake attempt. Remove the
+		// entry for the authTag because we're about to generate a new authTag for this
+		// call.
 		delete(t.activeCallByAuth, string(c.authTag))
 	}
+
 	addr := &net.UDPAddr{IP: c.node.IP(), Port: c.node.UDP()}
 	newTag, _ := t.send(c.node.ID(), addr, c.packet, c.challenge)
 	c.authTag = newTag