Another thought. Even if everyone else doesn't encrypt, are their opportunities to "crypto load" some services with useless, though encrypted information? Of course, the loading can't make the service useless or even notceably degrade, or it won't be available in the long run. For instance, it seems to me that for some P2P services, it might be very useful to constantly encypt and then "share" biggish files, even if no one can actually de-encrypt the file. If the bandwidth of such encrypted files is reasonable (though not a degrading % of the network's bandwidth), then that service becomes a useful channel for transmitting information that's actually encrypted, otherwise the one PGP-encrypted file that gets sent through Kazaa or whatever is like a red cow standing in a sea of black-and-whites. It's arguably less secure than not encrypting (ie, they -might- not be able to read the text, but they damn sure know that this sender/receiver is very interesting). Actually, this may notbe too hard to acheive through something like Kazaa. All that would be needed is N "bots" that "share" a steady stream of encrypted files with each other. Of course, it's far better if they do some kind of identity-hopping somehow, or perhaps sit behind a wall of anonymity. But this doesn't require encouraging everyone to encrypt. In other words, if you've got a needle you want to hide it's far better to plop some bigass haystack on it. -TD

From: Eugen Leitl <eugen@leitl.org> To: cypherpunks@jfet.org Subject: [Victor.Duchovni@MorganStanley.com: Re: Status of opportunistic encryption] Date: Mon, 29 May 2006 18:53:20 +0200

----- Forwarded message from Victor Duchovni <Victor.Duchovni@MorganStanley.com> -----

From: Victor Duchovni <Victor.Duchovni@MorganStanley.com> Date: Mon, 29 May 2006 12:03:05 -0400 To: cryptography@metzdowd.com Subject: Re: Status of opportunistic encryption Reply-To: cryptography@metzdowd.com User-Agent: Mutt/1.4.1i

On Mon, May 29, 2006 at 07:21:29AM +0200, Florian Weimer wrote:

...

* Sandy Harris:

...

Recent news stories seem to me to make it obvious that anyone with privacy concerns (i.e. more-or-less everyone) should be encrypting as much of their communication as possible. Implementing opportunistic encryption is the best way I know of to do that for the Internet.

I'm somewhat out of touch, though, so I do not know to what extent people are using it now. That is my question here.

It seems to me opportunistic encryption has moved to the application layer, at least as far as Internet mail is concerned. Many MTAs use TLS automatically with whatever certificates they can get. Of course, this only guards against active attacks, but it seems to me that this is a reasonable threat model.

It only guards against *passive* eavesdropping. Active attacks can forge DNS MX records, inject BGP routes, ... Actual MITM resistant peer authentication with SMTP+TLS is extremely rare. I know it happens sometimes because I have it running for a small number of destinations, otherwise I would suspect that nobody is doing it.

http://www.postfix.org/TLS_README.html#client_tls_harden

Once the new 2.3 TLS code is folded into the production Postfix 2.3 snapshots (at which point the new documentation will be published), see

http://www.postfix.org/TLS_README.html#client_tls_levels http://www.postfix.org/TLS_README.html#client_tls_policy

Preview:

It is regrettably the case, that TLS secure-channels (fully authenticated and immune to man-in-the-middle attacks) impose constraints on the sending and receiving sites that preclude ubiquitous deployment. One needs to manually configure this type of security for each destination domain, and in many cases implement non-default TLS policy table entries for additional domains hosted at a common secured destination. With Postfix 2.3, we make secure-channel configurations substantially easier to configure, but they will never be the norm. For the generic domain with which you have made no specific security arrangements, this security level is not a good fit.

Historical note: while the documentation of these issues and many of the related features are new with Postfix 2.3, the issue was well understood before Postfix 1.0, when Lutz Jaenicke was designing the first unofficial Postfix TLS patch. See, his original post http://thread.gmane.org/gmane.ietf.apps-tls/304/focus=304 and the first response http://thread.gmane.org/gmane.ietf.apps-tls/304/focus=305. The problem is not even unique to SMTP or even TLS, similar issues exist for secure connections via aliases for HTTPS and Kerberos. SMTP merely uses indirect naming (via MX records) more frequently.

I should also note that once one abandons the (still) unrealistic assumption of a secure DNS, it is not just SMTP + TLS that runs into trouble.

For example, many Kerberos client libraries do a forward lookup (to alias- expand CNAMEs) and some perversely a reverse lookup (often the owner of the IP address is the worst source of the machine's name), and then give you a mutually authenticated channel to whatever principal they construct from now rather questionable data. This carries over to SASL GSSAPI, where GSSAPI abstraction makes working around this (in practice nobody tries even with native Kerberos) even harder.

Consequently, also SSH with GSS KEX, is not MITM resistant when the attacker can tamper with DNS responses.

Ultimately, to close similar security issues in many other protocols, we need a secure DNS, but I am somewhat pessimistic about the likelihood of this happening soon.

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