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Comment by tptacek | Hacker News Reader

Can you point to an instance where you said anything like that, here or anywhere else, before last week?

It's easy for me to believe that you've internalized "minimize data-dependent branches in crypto code" and thus wouldn't have designed a compressed encrypted transport.

It is very hard for me to believe that you would have spotted this flaw immediately had anyone pointed out to you that TLS supported compression.

There is well-regarded (though not by me) crypto advice recommending that people compress before encrypting, to destroy structure in the plaintext.

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This paper published in 2002 does discuss this attack. http://www.iacr.org/cryptodb/data/paper.php?pubkey=3091

"... both the SSH and TLS protocols support an option for on-the-fly compression. Potential security implications of using compression algorithms are of practical importance to people designing systems that might use both compression and encryption."

Yep. Great paper. Thanks for finding this.

It is very hard for me to believe that you would have spotted this flaw immediately had anyone pointed out to you that TLS supported compression.

I'm not claiming that I'd have noticed this particular attack. I'm saying that having compression in a supposedly secure transport layer was an obviously bad idea even before it was clear how it could be exploited. I don't need to get into a car accident to know that driving at night with my car's headlights turned off is a bad idea.

There is well-regarded (though not by me) crypto advice recommending that people compress before encrypting, to destroy structure in the plaintext.

There's a huge difference between compressing data and compressing an authentication channel. This is why compression should not be included in the secure channel -- it should be left up to the higher-level code to decide if compression is (a) completely pointless or (b) will leak information dangerously.

These are things that are obvious in hindsight. They may have been obvious to you before; or, as I'm claiming, they may just fit snugly into your (probably correct) philosophy about secure channel design.

But compression in TLS is not a relic of the 1990s; it's something that looks to have gained its earliest adoption in SSL/TLS at about the same time as Elliptic Curve.

My issue here isn't that you're wrong; it's that I think this is an extremely clever attack that says something profound about designing cryptosystems, and I wouldn't want to see Thai's and Juliano's (or Pornin's, if he's "wrong" about the prediction) work minimized by a glib comment about TLS.

compression [...] looks to have gained its earliest adoption in SSL/TLS at about the same time as Elliptic Curve

I guess by that point they had thrown in everything but the kitchen sink, and decided they might as well throw in the kitchen sink too.

I wouldn't want to see Thai's and Juliano's (or Pornin's, if he's "wrong" about the prediction) work minimized by a glib comment about TLS.

Oh, of course. I'm just irritated (as usual) by the fact that people continue to use SSL/TLS "because it's the standard" despite the fact that it's a phenomenally broken standard. There's places where you can't avoid it (HTTPS), but where it can be avoided...

Your perspective on HTTPS/TLS is that it has a history of vulnerabilities because it is poorly designed.

My perspective on HTTPS/TLS is that it has a history of vulnerabilities because it is the most carefully studied cryptosystem in human history.

I agree to disagree with you on this.

My perspective is that we know how to design protocols which are provably secure.

Your perspective is... I'm not quite sure, actually. Maybe you just don't believe in mathematical proofs?

As you say, agree to disagree -- but I'm not going to stop pointing and laughing every time a new SSL/TLS vulnerability comes out. :-)

That protocols without security proofs can survive in the real world, and protocols with security proofs still fall to implementation bugs, and that if you were going to bet on incidence of protocol design flaws vs. implementation flaws, the safe bet is on implementation flaws.

If you've got a provably secure protocol, what's the problem with formally verifying the implementation of the protocol?

I work in an area where bugs are very scary, so we use formal verification, and that's on top of having many more testers than developers.

From the perspective of this naive outsider, I'd would have expected FV to be worth it for security sensitive protocols. Is it that the protocols are too complex to be verified, or is it just not considered to be worth the effort?

I'm not making an argument against formal methods. I'm saying that if you replaced TLS with a protocol with a design proof, you could easily end up less secure.

The level of civility in this thread is great, but I would pay money to see a DEF CON panel debate between you two where you each had to take a shot every 8 minutes. We could get Mikko Hypponen to moderate and pour shots!

(a) I would lose the debate, (b) it would be boring, (c) I can drink Colin under the table.

(d) I would probably end up in the hospital.

There's a reason why I don't drink -- type 1 diabetes and large quantities of alcohol don't interoperate well.

Have there been any proposed contenders to TLS/SSL?

SSH and IPv6 come to mind.

For HTTP traffic?

Vulnerabilities don't arise by study, they arise because of vulnerabilities. We have plenty of well-studied crypto that is fine, ranging from SHA to Kerberos.

Colin is right that we know how to prove that cryptographic systems have certain security properties. The academic literature is filled with laments about TLS and proofs of fixed versions of it.

SHA? The Secure Hash Algorithm? The Secure Hash Algorithm with the length extension property? The Secure Hash Algorithm with the length extension property that was specifically forbidden from the SHA-3 contestants because it creates implementation vulnerabilities in the real world? That SHA?

Also, how does one compare a cryptographic hash function core to an entire cryptographic protocol to produce a statement about the fallibility of crypto design?

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