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Comment by Mithrandir | Hacker News Reader

They just enabled forward secrecy today: https://twitter.com/duckduckgo/status/349948709418696706

This link has a nice rundown of why RC4 is no longer recommended for SSL/TLS: http://blog.cryptographyengineering.com/2013/03/attack-of-we...

Basically:

"According to AlFardan, Bernstein, Paterson, Poettering and Schuldt (a team from Royal Holloway, Eindhoven and UIC) the RC4 ciphersuite used in SSL/TLS is broken. If you choose to use it -- as do a ridiculous number of major sites, including Google -- then it may be possible for a dedicated attacker to recover your authentication cookies. The current attack is just on the edge of feasibility, and could probably be improved for specific applications."

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A frustrating problem with ssllabs.com and RC4 is that it appears there is no way to achieve a 100% score. Sites are penalized for supporting RC4 if RC4 is placed above AES-CBC, and penalized as being vulnerable to BEAST if AES-CBC is placed above RC4. If CBC and RC4 are both disabled then no major browser can successfully negotiate a cipher.

The BEAST penalty applies even if the preferred AES-CBC ciphers are defined by TLSv1.2 and thus shouldn't be vulnerable to BEAST.

https://www.ssllabs.com/ssltest/analyze.html?d=john-millikin...

It is actually possible to achieve 100%, but you have to run only TLS 1.2, IIRC. But that would also make your web site inaccessible to most users.

But don't blame us, that's just the current situation with SSL/TLS. We're only reporting it. BTW, we used to show scores in the result, but too many people were trying to game the system (rather than be reasonable). As a result, we're showing only the grades now. In the future, the numerical scoring will be probably removed completely (switching to rule-based scoring).

As for BEAST, our test tests SSL 3.0 and TLS 1.0 specifically, but not TLS 1.1+. So, the way to go with BEAST is to force RC4 with TLS 1.0 and earlier, some CBC suite with TLS 1.1, and GCM suites with TLS 1.2.

  > So, the way to go with BEAST is to force RC4 with TLS
  > 1.0 and earlier, some CBC suite with TLS 1.1, and GCM
  > suites with TLS 1.2.

Since most browsers now include mitigations for BEAST, don't you think that the proven insecurity of RC4 is more dangerous to users than BEAST?

Both (BEAST and RC4) are proven to be real. The only question is which is worse, and if the attacks are practical. In my view, both are equally unlikely to be a threat for an average web site.

I'd love to get rid of the BEAST penalty, but there are no good (high-volume) stats on what percentage of "all" users is vulnerable to the BEAST attack. Because Apple is not yet deploying 1/n-1 in their browsers, the vulnerable BEAST percentage is still quite high. On SSL Labs, about 15%.

Given that attacks against RC4 are not very practical (yet), one possible direction is to focus on supporting TLS 1.2 (without RC4, obviously), at which point both RC4 and BEAST attacks will become irrelevant.

> I'd love to get rid of the BEAST penalty

Please don't. The more attention is paid to it, the more ammo I have in pressuring the manufacturers of certain embedded systems I'm stuck dealing with to upgrade their ancient browser codebases.

What's wrong with IE6?

Believe it or not, IE6 would actually be a major @#!%ing improvement in one or two cases. At least we'd already know how to work around much of its braindamage.

"So, the way to go with BEAST is to force RC4 with TLS 1.0 and earlier, some CBC suite with TLS 1.1, and GCM suites with TLS 1.2."

Is it possible to configure nginx like this? From what I can tell, there is no way to select a cipher based on the protocol.

Yes, it's possible. OpenSSL does not allow for per-protocol tuning, but there are some tricks you can use to achieve the same effect. In particular, GCM suites and SHA256/SHA384 suites work only in TLS 1.2, so if you put those first you are effectively prioritizing them on per protocol-basis.

Try this:

AESGCM:SHA384:SHA256:RC4:AES !aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!kEDH:!PSK:!SRP:!kECDH

This is from an example that's not related to PFS, so some tuning may be needed. The example is from my (free) OpenSSL Cookbook, which you can get from here:

https://www.feistyduck.com/books/bulletproof-ssl-tls-and-pki...

You are required to register in order to get the book (because the book is not just the PDF). If you don't want to receive any email from me, after you log in, go to the Settings section and unsubscribe from the marketing list.

Thanks, this is helpful. Which CBC suites work in TLS 1.1, but not 1.0?

These are my test results: https://www.ssllabs.com/ssltest/analyze.html?d=forkly.com

In general, I don't think the protocol specifications call for some suites to be allowed with certain protocol and some not to. (There are some exceptions, when weak suites need to be deprecated.) In practice, it comes down to how library developers have implemented them. For example, in OpenSSL, you have SSL v2 suites, TLS 1.2 suites, and >= SSL v3 suites. I don't think there are any TLS 1.1-only suites.

Okay, then my current config is probably as good as it gets for now.

Thanks for the help :)

> But that would also make your web site inaccessible to most users.

I call this a feature and part of the sad state of the web. In other words i think that is a point they would like to illustrate. I dont think a 100% score should be possible if it isnt technically correct. Poor compatibility on the browser end isnt really their problem and certinly shouldn't limit scoring.

It's hard to believe that anyone could play with that attack (Bernstein/Paterson is a refinement of an older variant) and come away being OK with using RC4.

Adam Langley suggested on HN a few months ago that he was more comfortable with RC4 than with AES-CBC, which TLS unfortunately (due to its '90s heritage) specified in a MAC-then-encrypt construction that leaks timing, but the RC4 attack is scarily simple. Both attacks are extremely noisy, though; with what we understand about the flaws now, you'd surely notice if either attack was being directed at you.

Did Paypal notice when Duong and Rizzo demoed BEAST against them?

I don't know what is or isn't public about the BEAST demo, but stand by my original point regarding the (unrelated) Lucky 13 and RC4 attacks. The RC4 attack takes, like, a day to run.

Right. Beast has been demonstrated live on stage. It's on Youtube. Paypal couldn't block it in time even though they probably heard it was coming.

RC4 is broken and the bias attack is very bad, but the attack requires a lot more connections.

Or you could just watch this video to see what's wrong with RC4! https://class.coursera.org/crypto-007/lecture/7

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