Restricted use of IMP DDT (RFC0521)
Original Publication Date: 1973-May-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
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
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