create ServerConfigs with random OBIT value

fixes #356

handshake/server_config.go

@@ -28,6 +28,12 @@ func NewServerConfig(kex crypto.KeyExchange, signer crypto.Signer) (*ServerConfi
 	if _, err = rand.Read(stkSecret); err != nil {
 		return nil, err
 	}
+
+	obit := make([]byte, 8)
+	if _, err = rand.Read(obit); err != nil {
+		return nil, err
+	}
+
 	stkSource, err := crypto.NewStkSource(stkSecret)
 	if err != nil {
 		return nil, err
@@ -35,7 +41,7 @@ func NewServerConfig(kex crypto.KeyExchange, signer crypto.Signer) (*ServerConfi
 
 	return &ServerConfig{
 		ID:        id,
-		obit:      []byte{0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7},
+		obit:      obit,
 		kex:       kex,
 		signer:    signer,
 		stkSource: stkSource,

handshake/server_config_test.go

@@ -12,23 +12,33 @@ import (
 var _ = Describe("ServerConfig", func() {
 	var (
 		kex crypto.KeyExchange
-		scfg *ServerConfig
 	)
 
 	BeforeEach(func() {
 		var err error
 		kex, err = crypto.NewCurve25519KEX()
 		Expect(err).NotTo(HaveOccurred())
-		scfg, err = NewServerConfig(kex, nil)
+	})
-		Expect(err).NotTo(HaveOccurred())
+
+	It("generates a random ID and OBIT", func() {
+		scfg1, err := NewServerConfig(kex, nil)
+		Expect(err).ToNot(HaveOccurred())
+		scfg2, err := NewServerConfig(kex, nil)
+		Expect(err).ToNot(HaveOccurred())
+		Expect(scfg1.ID).ToNot(Equal(scfg2.ID))
+		Expect(scfg1.obit).ToNot(Equal(scfg2.obit))
 	})
 
 	It("gets the proper binary representation", func() {
+		scfg, err := NewServerConfig(kex, nil)
+		Expect(err).NotTo(HaveOccurred())
 		expected := bytes.NewBuffer([]byte{0x53, 0x43, 0x46, 0x47, 0x6, 0x0, 0x0, 0x0, 0x41, 0x45, 0x41, 0x44, 0x4, 0x0, 0x0, 0x0, 0x53, 0x43, 0x49, 0x44, 0x14, 0x0, 0x0, 0x0, 0x50, 0x55, 0x42, 0x53, 0x37, 0x0, 0x0, 0x0, 0x4b, 0x45, 0x58, 0x53, 0x3b, 0x0, 0x0, 0x0, 0x4f, 0x42, 0x49, 0x54, 0x43, 0x0, 0x0, 0x0, 0x45, 0x58, 0x50, 0x59, 0x4b, 0x0, 0x0, 0x0, 0x41, 0x45, 0x53, 0x47})
 		expected.Write(scfg.ID)
 		expected.Write([]byte{0x20, 0x0, 0x0})
 		expected.Write(kex.PublicKey())
-		expected.Write([]byte{0x43, 0x32, 0x35, 0x35, 0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff})
+		expected.Write([]byte{0x43, 0x32, 0x35, 0x35})
+		expected.Write(scfg.obit)
+		expected.Write([]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff})
 		Expect(scfg.Get()).To(Equal(expected.Bytes()))
 	})
 })