1 files changed, 115 insertions, 0 deletions
diff --git a/doc/rfc/rfc521.txt b/doc/rfc/rfc521.txt
new file mode 100644
index 0000000..030d4cc
--- /dev/null
+++ b/doc/rfc/rfc521.txt
@@ -0,0 +1,115 @@
+
+
+
+
+
+
+Network Working Group                                        A. McKenzie
+RFC #521                                                     BBN-NET
+NIC #16855                                                   30 May 1973
+
+
+                       Restricted Use of IMP DDT
+
+
+    At the recent workshop on "Automated Resource Sharing on the
+ARPANET", considerable interest was expressed on the topic of network
+security.  In particular, representatives of several sites felt that
+uncontrolled use of IMP DDT made access control mechanisms quite
+vulnerable to interception or tampering.* Individuals at the workshop
+seemed to be in general agreement that use of DDT should be much more
+controlled than at present.  In addition, as the network continues to
+take on a more and more operational character, and NCC use of DDT (which
+must be coordinated with other DDT usage) increases** we begin to see
+other reasons for controlling access to the DDT mechanism.
+
+    Currently, and for the foreseeable future, it is important that the
+NCC be able to use DDT at any IMP at any time.  It is also sometimes
+necessary for site personnel to be able to operate a stand alone DDT
+after an IMP crash.  Sometimes the NCC needs to ask site personnel to
+operate the IMP DDT for the NCC if the network is partitioned.  We have
+protected all DDT commands that can affect the running IMP program by
+requiring that sense switch 4 be turned on at the site, or a software
+override flag be enabled.  Only the BBN IMP Teletype, the BBN TIP
+Teletype, and the PDP-1 can enable override.  The NCC monitors these
+flags and reports any change in status.
+
+    In line with this approach, we will soon modify the IMP system so
+that any access to IMP DDT will require the same enabling actions (sense
+switch four turned on or override enabled from BBN) now required for
+core modification.  This will still allow the NCC the same ability to
+operate DDT which it now has, and will permit site personnel to operate
+DDT at the request of the NCC.  As is currently true, the NCC will
+
+
+----------------
+*Examples are easy to construct, but are intentionally omitted from this
+document.
+
+**DDT is currently used by the NCC operators for core verification, for
+interface debugging, for loading TIP and VDH code, etc.  There is
+discussion of using DDT in conjunction with an "auto-dialer" to examine
+a TIP's "view" of a modem port at the same time that the auto-dialer is
+examining the outside world's "view" of the port, of running "automatic"
+core verification, of loading Satellite IMP code, etc.
+
+
+
+McKenzie                                                        [Page 1]
+
+RFC 521                Restricted Use of IMP DDT                May 1973
+
+
+monitor the setting of sense switch four and take appropriate action if
+unauthorized use is observed.  We feel that this change will be
+sufficient to discourage "hackers", although it is obviously
+insufficient to protect a node against a determined and malicious
+attack.
+
+    It should be noted that it is not our current intent to prohibit
+occasional use of DDT for communication between sites via "DDT"
+messages.  Currently, there are two DDT commands, C and L, which set the
+single-character message and multi-character message headers
+respectively.  We will continue this facility, either by always
+permitting the use of these DDT commands, or by implementing some new
+code outside DDT for this purpose.
+
+
+
+
+
+
+
+
+
+
+       [ This RFC was put into machine readable form for entry ]
+       [ into the online RFC archives by Alex McKenzie with    ]
+       [ support from GTE, formerly BBN Corp.            10/99 ]
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+McKenzie                                                        [Page 2]
+