udp: Rotate connection ID generation IVs every hour

udp/connection.go

@@ -5,31 +5,37 @@
 package udp
 
 import (
+	"bytes"
 	"crypto/aes"
 	"crypto/cipher"
 	"crypto/rand"
 )
 
-var connectionKey, connectionIV []byte
+type ConnectionIDGenerator struct {
+	iv, iv2 []byte
+	block   cipher.Block
+}
 
-func InitConnectionIDEncryption() error {
-	connectionKey = make([]byte, 16)
-	_, err := rand.Read(connectionKey)
+func (g *ConnectionIDGenerator) Init() error {
+	key := make([]byte, 16)
+	_, err := rand.Read(key)
 	if err != nil {
 		return err
 	}
 
-	connectionIV = make([]byte, 16)
-	_, err = rand.Read(connectionIV)
-	return err
-}
-
-func GenerateConnectionID(ip []byte) []byte {
-	block, err := aes.NewCipher(connectionKey)
+	g.block, err = aes.NewCipher(key)
 	if err != nil {
-		panic(err)
+		return err
 	}
 
+	return g.NewIV()
+}
+
+func (g *ConnectionIDGenerator) Generate(ip []byte) []byte {
+	return g.generate(ip, g.iv)
+}
+
+func (g *ConnectionIDGenerator) generate(ip []byte, iv []byte) []byte {
 	if len(ip) > 16 {
 		panic("IP larger than 16 bytes")
 	}
@@ -39,7 +45,7 @@ func GenerateConnectionID(ip []byte) []byte {
 	}
 
 	ct := make([]byte, 16)
-	stream := cipher.NewCFBDecrypter(block, connectionIV)
+	stream := cipher.NewCFBDecrypter(g.block, iv)
 	stream.XORKeyStream(ct, ip)
 
 	for i := len(ip) - 1; i >= 8; i-- {
@@ -49,6 +55,28 @@ func GenerateConnectionID(ip []byte) []byte {
 	return ct[:8]
 }
 
-func init() {
-	InitConnectionIDEncryption()
+func (g *ConnectionIDGenerator) Matches(id []byte, ip []byte) bool {
+	if expected := g.generate(ip, g.iv); bytes.Equal(id, expected) {
+		return true
+	}
+
+	if iv2 := g.iv2; iv2 != nil {
+		if expected := g.generate(ip, iv2); bytes.Equal(id, expected) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (g *ConnectionIDGenerator) NewIV() error {
+	newiv := make([]byte, 16)
+	if _, err := rand.Read(newiv); err != nil {
+		return err
+	}
+
+	g.iv2 = g.iv
+	g.iv = newiv
+
+	return nil
 }