error if bit size specified with ed25519 keys

init.go

@@ -200,6 +200,9 @@ func CreateIdentity(out io.Writer, opts []options.KeyGenerateOption) (Identity,
 		sk = priv
 		pk = pub
 	case "ed25519":
+		if settings.Size != -1 {
+			return ident, fmt.Errorf("number of key bits does not apply when using ed25519 keys")
+		}
 		fmt.Fprintf(out, "generating ED25519 keypair...")
 		priv, pub, err := ci.GenerateEd25519Key(rand.Reader)
 		if err != nil {

init_test.go

@@ -34,3 +34,16 @@ func TestCreateIdentity(t *testing.T) {
 		t.Fatal("unexpected type:", pk.Type())
 	}
 }
+
+func TestCreateIdentityOptions(t *testing.T) {
+	var w bytes.Buffer
+
+	// ed25519 keys with bit size must fail.
+	_, err := CreateIdentity(&w, []options.KeyGenerateOption{
+		options.Key.Type(options.Ed25519Key),
+		options.Key.Size(2048),
+	})
+	if err == nil {
+		t.Errorf("ed25519 keys cannot have a custom bit size")
+	}
+}