gboolean lr_gpg_import_key(const char *key_fn, const char *home_dir, GError **err)
gboolean lr_gpg_check_signature_fd(int signature_fd, int data_fd, const char *home_dir, GError **err)
gboolean lr_gpg_check_signature(const char *signature_fn, const char *data_fn, const char *home_dir, GError **err)