backport candidate:

Refuse to start with certain directory authority keys, and 
encourage people using them to stop.


svn:r11171

ChangeLog

@@ -28,6 +28,8 @@ Changes in version 0.2.0.5-alpha - 2007-08-19
 
   o Minor features (security):
     - Warn about unsafe ControlPort configurations.
+    - Refuse to start with certain directory authority keys, and
+      encourage people using them to stop.
 
   o Minor features (controller):
     - Add a PROTOCOLINFO controller command. Like AUTHENTICATE, it

src/or/config.c

@@ -3823,6 +3823,13 @@ parse_dir_server_line(const char *line, int validate_only)
              (int)strlen(fingerprint));
     goto err;
   }
+  if (!strcmp(fingerprint, "E623F7625FBE0C87820F11EC5F6D5377ED816294")) {
+    /* a known bad fingerprint. refuse to use it. */
+    log_warn(LD_CONFIG, "Dangerous dirserver line. To correct, erase your "
+             "torrc file (%s), or reinstall Tor and use the default torrc.",
+             get_torrc_fname());
+    goto err;
+  }
   if (base16_decode(digest, DIGEST_LEN, fingerprint, HEX_DIGEST_LEN)<0) {
     log_warn(LD_CONFIG, "Unable to decode DirServer key digest.");
     goto err;