scd: Add the "undefined" stub application.

* scd/app.c (select_application): Implement the "undefined"
application.

2 files changed, 21 insertions, 0 deletions

diff --git a/doc/scdaemon.texi b/doc/scdaemon.texi
index 9184ce202..200fed890 100644
--- a/doc/scdaemon.texi
+++ b/doc/scdaemon.texi
@@ -181,6 +181,8 @@ write hashed data to files named @code{dbgmd-000*}
 trace Assuan protocol.  See also option @option{--debug-assuan-log-cats}.
 @item 11 (2048)
 trace APDU I/O to the card.  This may reveal sensitive data.
+@item 12 (4096)
+trace some card reader related function calls.
 @end table
 
 @item --debug-all
@@ -327,6 +329,7 @@ stripping off the two leading dashes.
 * DINSIG Card::           The DINSIG card application
 * PKCS#15 Card::          The PKCS#15 card application
 * Geldkarte Card::        The Geldkarte application
+* Undefined Card::        The Undefined stub application
 @end menu
 
 @node OpenPGP Card
@@ -367,6 +370,14 @@ This is a simple application to display information of a German
 Geldkarte.  The Geldkarte is a small amount debit card application which
 comes with almost all German banking cards.
 
+@node Undefined Card
+@subsection The Undefined card application ``undefined''
+
+This is a stub application to allow the use of the APDU command even
+if no supported application is found on the card.  This application is
+not used automatically but must be explicitly requested using the
+SERIALNO command.
+
 
 @c *******************************************
 @c ***************            ****************
diff --git a/scd/app.c b/scd/app.c
index 6f0d7560b..63ef4fa65 100644
--- a/scd/app.c
+++ b/scd/app.c
@@ -387,6 +387,14 @@ select_application (ctrl_t ctrl, int slot, const char *name, app_t *r_app)
   if (err && is_app_allowed ("geldkarte")
       && (!name || !strcmp (name, "geldkarte")))
     err = app_select_geldkarte (app);
+  if (err && is_app_allowed ("undefined")
+      && (name && !strcmp (name, "undefined")))
+    {
+      /* We switch to the "undefined" application only if explicitly
+         requested.  */
+      app->apptype = "UNDEFINED";
+      err = 0;
+    }
   if (err && name)
     err = gpg_error (GPG_ERR_NOT_SUPPORTED);
 
@@ -422,6 +430,8 @@ get_supported_applications (void)
     "p15",
     "dinsig",
     "geldkarte",
+    /* Note: "undefined" is not listed here because it needs special
+       treatment by the client.  */
     NULL
   };
   int idx;