lib/sign: initial implementation

Added the initial version of signing interface allowing to allowing to
sign and verify commits.
Implemented initial signing modules:
 - dummy -- simple module allowing to sign/verify with ASCII string
 - ed25519 -- module allowing to sign/verify commit with ed25519
   (EdDSA) signature scheme provided by libsodium library.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

src/libostree/ostree-sign-dummy.h

@@ -0,0 +1,63 @@
+/* vim:set et sw=2 cin cino=t0,f0,(0,{s,>2s,n-s,^-s,e2s: */
+
+/*
+ * Copyright © 2019 Collabora Ltd.
+ *
+ * SPDX-License-Identifier: LGPL-2.0+
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Authors:
+ *  - Denis Pynkin (d4s) <denis.pynkin@collabora.com>
+ */
+
+#pragma once
+
+#include "ostree-sign.h"
+
+G_BEGIN_DECLS
+
+#define OSTREE_TYPE_SIGN_DUMMY (ostree_sign_dummy_get_type ())
+
+_OSTREE_PUBLIC
+G_DECLARE_FINAL_TYPE (OstreeSignDummy,
+                      ostree_sign_dummy,
+                      OSTREE,
+                      SIGN_DUMMY,
+                      GObject)
+
+gchar * ostree_sign_dummy_get_name (OstreeSign *self);
+
+gboolean ostree_sign_dummy_data (OstreeSign *self,
+                                 GBytes *data,
+                                 GBytes **signature,
+                                 GCancellable *cancellable,
+                                 GError **error);
+
+gchar * ostree_sign_dummy_metadata_key (OstreeSign *self);
+gchar * ostree_sign_dummy_metadata_format (OstreeSign *self);
+
+gboolean ostree_sign_dummy_metadata_verify (OstreeSign *self,
+                                            GBytes     *data,
+                                            GVariant   *signatures,
+                                            GError     **error);
+
+gboolean ostree_sign_dummy_set_signature (OstreeSign *self, GVariant *key, GError **error);
+
+void ostree_sign_dummy_finalize (GObject *gobject);
+
+G_END_DECLS
+