On 5/10/2004 3:02 AM, RL 'Bob' Morgan wrote:
So a "secure ports only" policy has very little to do with security and
very much to do with organizational power relationships, and making
your computing environment dysfunctional.
Somebody check my math on this please, but it seems to me that the whole
STARTTLS approach is succeptible to a specific attack which the secure
socket model is not.
Specifically, a man-in-the-middle can "blank out" the STARTTLS feature
advertisement, and thus make the client believe that TLS is not available.
For example:
server-A MitM client-C
| 250-DSN | 250-DSN
+--> 250-AUTH +-> 250-AUTH
250-STARTTLS 250 ok [...pad...]
250 ok
The client, seeing that TLS is not available, dumbs down to cleartext.
Most clients would probably do that invisibly without even barking at the
user, or not doing so in a way that most of them would appreciate.
Using an encrypted port just means an attack can only produce failure,
rather than inducing fallback.
Unless that's wrong for some reason, I'd say that a "secure ports policy"
actually is more secure.
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