Misunderstanding what was said at the Cryptographers Panel

As usual, the Cryptographers Panel at the RSA Conference was interesting. Unfortunately, some of the remarks made by the panelists seem to have been taken out of context by people who apparently didn’t understand the context to begin with. This has apparently led to some people claiming that cryptography is totally broken and shouldn’t be used to protect sensitive information.

As Dave Barry would say, I’m not making this up.

The remarks that Adi Shamir made about attacks on AES seem to be at the root of this misunderstanding. Let’s look at exactly what Shamir said and see how close it comes to saying that cryptography is totally broken. You can find a recording of the talk here if you missed the RSA Conference last week. Some of the question and answer period has been edited out, and I’m not exactly sure why that happened.

In his opening remarks Shamir notes that progress has been made in the cryptanalysis of AES. Last year, Alex Biryukov and Dmitry Khovratovich found a related-key attack against the full AES-256 algorithm that has both time and memory complexity of 299.5.

This attack is much better than an exhaustive search, but it’s also not even close to being feasible. (If that’s not obvious, do a quick Google search to find out roughly how much information exists in the world today and compare it with the 299.5 memory required by this attack.) If that’s the best that an attacker can do, then you’re still very safe. The fact that the way that standards require you to use AES also eliminates the possibility of actually carrying out a related key attack should make you feel even safer. If you use AES like the standards specify, then this attack can’t be used against you.

Shamir also mentioned an attack on AES-128 that was also found by Biryukov and Khovratovich that runs in 245 time. That’s so fast that it’s practical to do on a typical PC. On the other hand, Shamir also mentions that this attack also assumes that you use AES-128 in a way that is forbidden by the AES standard. In this case, the attack works if you use AES-128, but try to fake AES-256 using the shorter 128-bit key. Again, this isn’t allowed by the AES standard, so it shouldn’t really come as a surprise that it doesn’t work well. Once again, it you use AES like the standards specify, then this attack can’t be used against you.

So I’m not sure exactly how someone heard Shamir’s remarks and interpreted them as saying that encryption is fatally flawed and isn’t suitable for use in protecting sensitive information. It seems to me that a better interpretation is that you really need to follow the standards that specify how encryption is used. If you do that then it provides protection that’s incredibly secure. On the other hand, if you decide to not follow these standards and instead decide to invent new ways to use encryption that haven’t had any sort of independent review, then there’s a possibility that you can do things that dramatically reduce the security that the encryption provides.

There are definitely innovative ways to use encryption safely. These will always come with a peer-reviewed proof that the new technique is secure. If you use one of these, encryption will still provide an essentially unbreakable level of security. But if you use techniques that don’t have such a proof of security then you’re taking a significant risk. Maybe that’s too subtle an interpretation for the opening remarks at the Cryptographers Panel, but it’s certainly more accurate than saying that cryptography is totally broken and shouldn’t be used to protect sensitive information.

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