> Actually, encryption can do some good, even in the absence of authentication.
> 
> Even if the remote end is totally unauthenticated, you have at least 
> guaranteed
> that nobody is doing any passive sniffing of the content in transit.  You've
> at least forced an attacker to mount an active MitM attack, which is both more
> challenging and has a higher risk of detection....

I concede.  In the vast majority of communications situations, MitM is
only a little more difficult than passive sniffing, but in some it does
make a difference.  In particular, some broadcast mediums make MitM very
difficult without detection (radio broadcast, for instance).

In addition, if you can guarantee perfect forward secrecy without
authentication, at least the attacker must use a MitM attack right then.
Offline analysis won't reveal the encrypted content.

thanks,
tim.

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