card: New command 'authenticate'.

* tools/card-tool-misc.c (hex_to_buffer): New.
* tools/gpg-card-tool.c (get_data_from_file): Change to allow returning
a string.
(cmd_authenticate): New.
(cmds): Add command "authenticate".

Signed-off-by: Werner Koch <wk@gnupg.org>

tools/card-tool-misc.c

@@ -42,3 +42,38 @@ find_kinfo (card_info_t info, const char *keyref)
       return kinfo;
   return NULL;
 }
+
+
+/* Convert STRING into a newly allocated buffer while translating the
+ * hex numbers.  Blanks and colons are allowed to separate pairs of
+ * hex digits.  Returns NULL on error or a newly malloced buffer and
+ * its length in LENGTH.  */
+void *
+hex_to_buffer (const char *string, size_t *r_length)
+{
+  unsigned char *buffer;
+  const char *s;
+  size_t n;
+
+  buffer = xtrymalloc (strlen (string)+1);
+  if (!buffer)
+    return NULL;
+  for (s=string, n=0; *s; s++)
+    {
+      if (ascii_isspace (*s) || *s == ':')
+        continue;
+      if (hexdigitp (s) && hexdigitp (s+1))
+        {
+          buffer[n++] = xtoi_2 (s);
+          s++;
+        }
+      else
+        {
+          xfree (buffer);
+          gpg_err_set_errno (EINVAL);
+          return NULL;
+        }
+    }
+  *r_length = n;
+  return buffer;
+}