e.
However, since the protocol requires that Alice send out location data, once she starts using it she reveals her physical location to Eve, Mallory, and anyone ese who can see the packets. Since the nature of the protocol is that Alice's location does not change frequently (and needs to transmitted via a trusted channel to Bob when it does), after the first usage Mallory *knows* the physical location he is trying to simulate, and can use this information for future spoofing.
The upshot of this is that Denning's scheme not only provides no security against spoofing, and leaks potentially sensitive data about locations.
If Sadaam Huissain (sp?) had used this scheme during the Gulf War, we'd have been able to send a cruise missile directly to his keyboard.
This could be prevented by encrypting the data packets, but that would introduce more delay into the protocol, and make it easier to spoof distant locations.
[These flaws in the protocol seem so obvious that I can't help but wonder if we're missing something - Dorothy isn't *that* stupid.]
Isn't she about the age where Alzheimer's starts kicking in? Jonathan Wienke