Implement curve X25519 (Golang 1.8) (#1376)

* Implement curve X25519

* caddytls: Added a default curves list

* caddytls: Improve tests

caddytls/config.go

@@ -311,6 +311,11 @@ func MakeTLSConfig(configs []*Config) (*tls.Config, error) {
 		config.CipherSuites = append([]uint16{tls.TLS_FALLBACK_SCSV}, config.CipherSuites...)
 	}
 
+	// Default curves
+	if len(config.CurvePreferences) == 0 {
+		config.CurvePreferences = defaultCurves
+	}
+
 	// Set up client authentication if enabled
 	if config.ClientAuth != tls.NoClientCert {
 		pool := x509.NewCertPool()
@@ -367,6 +372,11 @@ func SetDefaultTLSParams(config *Config) {
 	// (prepend since having it at end breaks http2 due to non-h2-approved suites before it)
 	config.Ciphers = append([]uint16{tls.TLS_FALLBACK_SCSV}, config.Ciphers...)
 
+	// If no curves provided, use default list
+	if len(config.CurvePreferences) == 0 {
+		config.CurvePreferences = defaultCurves
+	}
+
 	// Set default protocol min and max versions - must balance compatibility and security
 	if config.ProtocolMinVersion == 0 {
 		config.ProtocolMinVersion = tls.VersionTLS11
@@ -438,9 +448,20 @@ var defaultCiphers = []uint16{
 // Map of supported curves
 // https://golang.org/pkg/crypto/tls/#CurveID
 var supportedCurvesMap = map[string]tls.CurveID{
-	"P256": tls.CurveP256,
-	"P384": tls.CurveP384,
-	"P521": tls.CurveP521,
+	"X25519": tls.X25519,
+	"P256":   tls.CurveP256,
+	"P384":   tls.CurveP384,
+	"P521":   tls.CurveP521,
+}
+
+// List of all the curves we want to use by default
+//
+// This list should only include curves which are fast by design (e.g. X25519)
+// and those for which an optimized assembly implementation exists (e.g. P256).
+// The latter ones can be found here: https://github.com/golang/go/tree/master/src/crypto/elliptic
+var defaultCurves = []tls.CurveID{
+	tls.X25519,
+	tls.CurveP256,
 }
 
 const (

caddytls/setup_test.go

@@ -88,6 +88,18 @@ func TestSetupParseBasic(t *testing.T) {
 	if !cfg.PreferServerCipherSuites {
 		t.Error("Expected PreferServerCipherSuites = true, but was false")
 	}
+
+	// Ensure curve count is correct
+	if len(cfg.CurvePreferences) != len(defaultCurves) {
+		t.Errorf("Expected %v Curves, got %v", len(defaultCurves), len(cfg.CurvePreferences))
+	}
+
+	// Ensure curve ordering is correct
+	for i, actual := range cfg.CurvePreferences {
+		if actual != defaultCurves[i] {
+			t.Errorf("Expected curve in position %d to be %0x, got %0x", i, defaultCurves[i], actual)
+		}
+	}
 }
 
 func TestSetupParseIncompleteParams(t *testing.T) {
@@ -288,7 +300,7 @@ func TestSetupParseWithKeyType(t *testing.T) {
 
 func TestSetupParseWithCurves(t *testing.T) {
 	params := `tls {
-            curves p256 p384 p521
+            curves x25519 p256 p384 p521
         }`
 	cfg := new(Config)
 	RegisterConfigGetter("", func(c *caddy.Controller) *Config { return cfg })
@@ -299,11 +311,11 @@ func TestSetupParseWithCurves(t *testing.T) {
 		t.Errorf("Expected no errors, got: %v", err)
 	}
 
-	if len(cfg.CurvePreferences) != 3 {
-		t.Errorf("Expected 3 curves, got %v", len(cfg.CurvePreferences))
+	if len(cfg.CurvePreferences) != 4 {
+		t.Errorf("Expected 4 curves, got %v", len(cfg.CurvePreferences))
 	}
 
-	expectedCurves := []tls.CurveID{tls.CurveP256, tls.CurveP384, tls.CurveP521}
+	expectedCurves := []tls.CurveID{tls.X25519, tls.CurveP256, tls.CurveP384, tls.CurveP521}
 
 	// Ensure ordering is correct
 	for i, actual := range cfg.CurvePreferences {