multicast cleanup

peer/on_multicast.go

@@ -1,57 +1,46 @@
 package peer
 
 import (
-	"encoding/binary"
 	"net/netip"
 
-	"golang.org/x/crypto/nacl/sign"
 	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+
+	"vppn/peer/multicast"
 )
 
-func (a *App) onMulticastDiscovery(e MulticastEvent) {
+func (a *App) onMulticastDiscovery(pkt multicast.Packet) {
 	if a.isPublic {
 		return
 	}
 
-	// Peek at the VPN IP byte to find the sender peer before verifying.
-	// nacl/sign prepends a 64-byte signature, so payload starts at offset sign.Overhead.
-	if len(e.signed) != mcSignedBeaconLen {
-		return
-	}
-	netAddr := a.vpnNet.Addr().As4()
-	octets := netAddr
-	octets[3] = e.signed[sign.Overhead]
+	// Locate the sender peer by its VPN IP (final octet carried in the beacon).
+	octets := a.vpnNet.Addr().As4()
+	octets[3] = pkt.PeerIP
 	vpnIP := netip.AddrFrom4(octets)
 
 	peer, ok := a.peersByIP[vpnIP]
-	if !ok {
+	if !ok || peer.IsPublic || peer.State == StateDirect {
 		return
 	}
 
-	if peer.IsPublic || peer.State == StateDirect {
+	// Authenticate the beacon against the peer's known sign key.
+	if !pkt.Verify(a.mcVerifyBuf, &peer.SignPubKey) {
 		return
 	}
 
-	payload, ok := sign.Open(nil, e.signed, &peer.SignPubKey)
-	if !ok {
+	// The beacon is authentic but must also advertise the WG key the hub gave
+	// us for this peer; otherwise it's inconsistent — drop it.
+	if wgtypes.Key(pkt.WGPubKey) != peer.PubKey() {
 		return
 	}
 
-	// payload: [1 VPN IP byte][32 WG pubkey][2 WG port][8 timestamp]
-	// (timestamp freshness is gated in the reader before this point).
-	wgPubKey, err := wgtypes.NewKey(payload[1:33])
-	if err != nil || wgPubKey != peer.PubKey() {
-		return
-	}
-
-	wgPort := binary.BigEndian.Uint16(payload[33:35])
-	endpoint := netip.AddrPortFrom(e.src, wgPort)
+	endpoint := netip.AddrPortFrom(pkt.Src, pkt.WGPort)
 	if !endpoint.IsValid() {
 		return
 	}
 
 	var v4, v6 netip.AddrPort
-	if e.src.Is4() {
+	if pkt.Src.Is4() {
 		v4 = endpoint
 	} else {
 		v6 = endpoint