Refactor - now wireguard based. (#7)

peer/multicast/packet.go

@@ -0,0 +1,54 @@
+package multicast
+
+import (
+	"encoding/binary"
+	"net/netip"
+
+	"golang.org/x/crypto/nacl/sign"
+)
+
+const (
+	BufferSize       = packetSize + SignedPacketSize
+	SignedPacketSize = packetSize + signSize
+	packetSize       = 43
+	signSize         = 64
+)
+
+// Layout:
+//
+// [0]      final octet of the sender's VPN IP
+// [1:33]   WG public key
+// [33:35]  WG listen port (big-endian uint16)
+// [35:43]  send time, Unix seconds (big-endian int64) — freshness/replay gate
+type Packet struct {
+	PeerIP    byte       // Final octet of the sender's VPN IP.
+	WGPubKey  [32]byte   // WG public key.
+	WGPort    uint16     // WG listen port.
+	Timestamp int64      // Unix timestamp.
+	Src       netip.Addr // Source of packet.
+	Signed    []byte     // Raw signed message for verification (incoming packet).
+}
+
+// Marshal the packet into a buffer with prefixed signature.
+func (p Packet) Marshal(buf []byte, signKey *[64]byte) []byte {
+	buf[0] = p.PeerIP
+	copy(buf[1:33], p.WGPubKey[:])
+	binary.BigEndian.PutUint16(buf[33:35], p.WGPort)
+	binary.BigEndian.PutUint64(buf[35:43], uint64(p.Timestamp))
+	return sign.Sign(buf[packetSize:packetSize], buf[:packetSize], signKey)
+}
+
+func (p Packet) Verify(buf []byte, pubKey *[32]byte) bool {
+	_, ok := sign.Open(buf, p.Signed, pubKey)
+	return ok
+}
+
+func Unmarshal(signed []byte) (p Packet) {
+	buf := signed[signSize:]
+	p.PeerIP = buf[0]
+	copy(p.WGPubKey[:], buf[1:33])
+	p.WGPort = binary.BigEndian.Uint16(buf[33:35])
+	p.Timestamp = int64(binary.BigEndian.Uint64(buf[35:43]))
+	p.Signed = signed
+	return
+}