At 12:28 AM 10/13/2003, Ian Grigg wrote:
Problem is, it's also wrong.  The end systems
are not secure, and the comms in the middle is
actually remarkably safe.

I think this is an interesting, insightful analysis, but I also think it's drawing a stronger contrast between the real world and the Internet threat model than is warranted.

It's true that a large number of machines are compromised, but they were generally compromised by malicious communications that came over the network. If correctly implemented systems had protected these machines from untrustworthy Internet data, they wouldn't have been compromised.

Similarly, the statement is true at large (many systems are compromised), but not necessarily true in the small (I'm fairly confident that my SSL endpoints are not compromised). This means that the threat model is valid for individuals who take care to make sure that they comply with its assumptions, even if it may be less valid for the Internet at large.

And it's true that we define the threat model to be as large as the problem we know how to solve: we protect against the things we know how to protect against, and don't address problems at this level that we don't know how to protect against at this level. This is no more incorrect than my buying clothes which will protect me from rain, but failing to consider shopping for clothes which will do a good job of protecting me from a nuclear blast: we don't know how to make such clothes, so we don't bother thinking about that risk in that environment. Similarly, we have no idea how to design a networking protocol to protect us from the endpoints having already been compromised, so we don't worry about that part of the problem in that space. Perhaps we worry about it in another space (firewalls, better OS coding, TCPA, passing laws).

So, I disagree: I don't think that the SSL model is wrong: it's the right model for the component of the full problem it looks to address. And I don't think that the Internet threat model has failed to address the problem of host compromise: the fact is that these host compromises resulted, in part, from the failure of operating systems and other software to adequately protect against threats described in the Internet threat model: namely, that data coming in over the network cannot be trusted.

That doesn't change the fact that we should worry about the risk in practice that those assumptions of endpoint security will not hold.

- Tim

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