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posted by LaminatorX on Thursday May 29 2014, @04:03AM   Printer-friendly
from the Another-one-bites-the-dust dept.

The TrueCrypt website has been changed it now has a big red warning stating "WARNING: Using TrueCrypt is not secure as it may contain unfixed security issues". They recommend using BitLocker for Windows 7/8, FileVault for OS X, or (whatever) for Linux. So, what happened? The TrueCrypt site says:

This page exists only to help migrate existing data encrypted by TrueCrypt. The development of TrueCrypt was ended in 5/2014 after Microsoft terminated support of Windows XP. Windows 8/7/Vista and later offer integrated support for encrypted disks and virtual disk images. Such integrated support is also available on other platforms (click here for more information). You should migrate any data encrypted by TrueCrypt to encrypted disks or virtual disk images supported on your platform.

Did the TrueCrypt devs (or SourceForge?) get a NSL? They are offering a "new" version (7.2), but apparently the signing key has changed and a source code diff seems to indicate a lot of the functionality has been stripped out. What's up?

 
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  • (Score: 5, Interesting) by edIII on Thursday May 29 2014, @08:56AM

    by edIII (791) Subscriber Badge on Thursday May 29 2014, @08:56AM (#48628)

    Brute forcing 256-bit symmetric keys requires energy equivalent to that of an exploding star to do in a reasonable amount of time. Brute forcing a single 128-bit key will still require at least several hundred terawatt-hours of energy, assuming you had perfectly efficient computers capable of doing operations at the von Neumann-Landauer limit, and probably no one has those.

    That's not entirely correct. In fact, it's much worse. You're correct about the physical limitations of classical computing though.

    Bruce Schneier, Applied Cryptography, pp157-8:

    One of the consequences of the second law of thermodynamics is that a certain amount of energy is necessary to represent information. To record a single bit by changing the state of a system requires an amount of energy no less than kT, where T is the absolute temperature of the system and k is the Boltzman constant. (Stick with me; the physics lesson is almost over.)

    Given that k = 1.38×10-16 erg/°Kelvin, and that the ambient temperature of the universe is 3.2°Kelvin, an ideal computer running at 3.2°K would consume 4.4×10-16 ergs every time it set or cleared a bit. To run a computer any colder than the cosmic background radiation would require extra energy to run a heat pump.

    Now, the annual energy output of our sun is about 1.21×1041 ergs. This is enough to power about 2.7×1056 single bit changes on our ideal computer; enough state changes to put a 187-bit counter through all its values. If we built a Dyson sphere around the sun and captured all its energy for 32 years, without any loss, we could power a computer to count up to 2192. Of course, it wouldn't have the energy left over to perform any useful calculations with this counter.

    But that's just one star, and a measly one at that. A typical supernova releases something like 1051 ergs. (About a hundred times as much energy would be released in the form of neutrinos, but let them go for now.) If all of this energy could be channeled into a single orgy of computation, a 219-bit counter could be cycled through all of its states.

    These numbers have nothing to do with the technology of the devices; they are the maximums that thermodynamics will allow. And they strongly imply that brute-force attacks against 256-bit keys will be infeasible until computers are built from something other than matter and occupy something other than space.(emphasis mine)

    This was written nearly 20 years ago. Since then, quantum cryptanalysis has become a lot more feasible. A proof of concept could be less than 10 years away from being public and in the known literature.

    Schneier himself also states that the the whole point of cryptanalysis is to find shortcuts [schneier.com].

    So relying on the brute force strength of 256-bit symmetric key alone is hubris. It's not simply a matter of permutations (which to be pedantic will be 1/2th of an order reduced in practice), but involves probabilities and attack surfaces beyond encrypted data at rest.

    AES 256-bit has already been reduced by 7 orders below it's permutations. New attacks in the known literature go further than that. As the man said, "attacks only get better, not worse". We don't even begin to know what the NSA really has up it's sleeve. They really do employ the world's best cryptographers.

    Cryptanalysis of at-rest ciphertext is only one tool. That usually involves working on the method itself. What about the RNG data being provided? It's almost *never* TRNG. Since, it isn't TRNG, that now allows the CSPRNG to be compromised. Knowing what CSPRNG was used, or likely used, could once again be used to identify valuable shortcuts shaving off the effective keyspace by several orders, or more.

    Regardless of method and CSPRNG, you still have a weakness in key exchange. It matters not that your key was 256-bit. If the probabilities of the key exchange collapse that down to a 40-bit key, you're fucked.

    I respect that you have implemented and coded the encryption algorithms and have experience, but I don't think it's anything but hubris to say that a 256-bit symmetric key encrypted ciphertext requires more energy than several stars to brute force. Seems reckless really.

    In order to do that, you also need to show me a really impressive CSPRNG, or a massively insanely fast TRNG, *and* a truly solid and novel key exchange.

    If you really wanted to impress me with bullet proof encryption you would either perfect OTP (which is not), or make quantum encryption possible. Most importantly, make it possible to have quantum encrypted data at rest and not just "cycling" in an active system. I'm betting that perfect cryptography will be solved by using quantum to provide the missing links in OTP myself.

    We've been through all this before many times. People saying that a method was bullet proof, only to find a surprising and novel attack that somehow reduced the effort required by 99%. The most notable of them all *is* OTP, which is *mathematically* perfect. Except, that they found in order to be perfect in practice, you could never reuse the pad data. Damn... back to the drawing board...

    --
    Technically, lunchtime is at any moment. It's just a wave function.
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  • (Score: 5, Interesting) by stormwyrm on Thursday May 29 2014, @09:45AM

    by stormwyrm (717) on Thursday May 29 2014, @09:45AM (#48649) Journal

    We are discussing here the brute forcing of the key to a TrueCrypt volume. So everything else you've written about CPRNGs and key exchange isn't really germane to the discussion, as that isn't what I'm talking about. If you can find shortcuts, well, you aren't doing brute force any more right? You might as well have just spoken about the infamous $5 wrench [xkcd.com] to extract the key, and that qualifies as "brute force" only to the facetious. Quantum cryptanalysis changes Schneier's argument about brute force only a little. Apparently there's been analysis that shows that quantum mechanics can do no more than halve the effective keyspace, so a 256-bit keyspace becomes effectively 128-bit. Not a lot of help when you can do triple encryption, and you wind up at 768 bits, or effectively a 384-bit keyspace to a quantum computer.

    Why do you think the NSA seems to be beefing up its ability to use exploits and put in back doors wherever they can? They cannot beat the mathematics, so they get around it by attacking the implementation rather than the mathematics. TrueCrypt may well have been on its way to becoming the sort of software that they couldn't touch in that way, and they couldn't have that.

    --
    Numquam ponenda est pluralitas sine necessitate.
    • (Score: 2) by edIII on Thursday May 29 2014, @10:27AM

      by edIII (791) Subscriber Badge on Thursday May 29 2014, @10:27AM (#48658)

      We are discussing here the brute forcing of the key to a TrueCrypt volume. So everything else you've written about CPRNGs and key exchange isn't really germane to the discussion, as that isn't what I'm talking about. If you can find shortcuts, well, you aren't doing brute force any more right?

      No, we are talking about the same thing, even with the shortcuts. Brute forcing does not simply mean "trying all the keys that are possible". Brute force means that you don't possess a key, and you don't possess some mathematical insight that allows to you perform the reverse process with the same amount of effort regardless of key possession. Sufficient mathematical insight can allow you to break encryption without even finding the key. See frequency analysis among others IIRC. Whatever shortcuts are used, they only reduce effective keyspace. In the end, you are still brute forcing effective keyspaces. They just became much smaller.

      CSPRNG is quite relevant to the discussion. Admittedly, key exchange is less important for TrueCrypt if we are going to strictly limit the discussion to it alone.

      The CSPRNG is relevant because all encryption methods, including the ones employed by TrueCrypt, are used to provide random numbers that greatly influence key generation and routine encryption operations that generate ciphertext. If a CSPRNG is compromised this means you understand, and are able to better predict, the numbers that were used. A compromised CSPRNG is invaluable to ciphertext-only attacks, which is exactly the situation you present in TrueCrypt data at-rest. To say otherwise explicitly means you did NOT use a CSPRNG during ciphertext generation.

      You are, in fact, talking about generating random numbers, following a method of encryption, and then generating ciphertext. How a CSPRNG is not critical in that undertaking is not something I can understand, or reasonably believe. The NSA *did* compromise a CSPRNG and paid very well (by their standards) to have it added to at least two different national standards for that very reason.

      As for the quantum mechanics only reducing the effective keyspace by half, I cannot say anything about that but [citation needed]. I'm greatly interested in any papers that show any kind of effective limit for quantum mechanics. I don't know that is true, and by all other accounts it could allow one to slice through crypto like butter precisely because it bypasses brute force entirely in some cases.

      At a very high level of abstraction, encryption is merely a simple mixing process by which it's vastly more expensive to perform de-mixing without some critical kind of knowledge. You're only arguing that a brute force defense against de-mixing without key possession is physically precluded in a very limited use case where the brute force is strictly limited to the keyspace provided by permutations alone. That's an oversimplification, and ignores whole hosts of ciphertext-only attacks, and the methods by which the keyspace for brute forcing, is reduced. Many of which focus on the random numbers used by the method, and not the method itself.

      It's almost always about reducing effective keyspaces to be brute forced. That typically involves every step of the process, which by definition, includes random number generation and key exchange (where appropriate).

      --
      Technically, lunchtime is at any moment. It's just a wave function.
      • (Score: 4, Interesting) by stormwyrm on Thursday May 29 2014, @01:15PM

        by stormwyrm (717) on Thursday May 29 2014, @01:15PM (#48714) Journal

        Just had to make a few simplifying assumptions. Cryptosystems are complicated beasts, as you evidently understand as well as I do, and any vulnerability in any one area can and probably will eventually be discovered and exploited if someone cares to do so. The OP I replied to was talking about brute force attacks, and was saying how those would all eventually become feasible given advances in computing power, and speculated that that could be one reason why TrueCrypt was abandoned, just when an auditing project has gone underway that is intended to ensure that the code is solid. I didn't buy it, and considered the OP's other two speculations to be far more likely, because a simple brute force attack on the underlying block ciphers is infeasible with our current knowledge of mathematics and physics. That was all I was trying to argue, and you had to go and muddy the waters with all this talk about other components of cryptosystems that might be the source of vulnerability. :) I was not trying to argue the about the security or lack thereof of TrueCrypt as a whole.

        Note that I never disputed the assertion that there might be vulnerabilities in TrueCrypt that result in its being insecure. This is actually highly probable, as the codebase is complicated and has not been fully audited as of this writing, and the true authors are anonymous. But the fact that these vulnerabilities probably exist doesn't sound to me like a reason for the maintainers of TrueCrypt to completely abandon their work the way they have, which is the real topic of the discussion. Something smells very fishy here, and what's happened to their site makes something like an NSL or its equivalent a more likely explanation.

        And you were asking for a citation for why I say quantum mechanics can probably only cut the key search space in half. Here it is: Bennett C.H., Bernstein E., Brassard G., Vazirani U., The strengths and weaknesses of quantum computation. [arxiv.org] SIAM Journal on Computing 26(5): 1510-1523 (1997).

        --
        Numquam ponenda est pluralitas sine necessitate.
        • (Score: 2) by edIII on Thursday May 29 2014, @06:47PM

          by edIII (791) Subscriber Badge on Thursday May 29 2014, @06:47PM (#48872)

          I didn't buy it, and considered the OP's other two speculations to be far more likely, because a simple brute force attack on the underlying block ciphers is infeasible with our current knowledge of mathematics and physics. That was all I was trying to argue, and you had to go and muddy the waters with all this talk about other components of cryptosystems that might be the source of vulnerability. :)

          Well, I do agree that right now attempting the entire keyspace without any shortcuts is highly likely precluded by physics. That's what has provided all the momentum to work against the other components.

          I just to tend to disagree with the assertions that we should rest on our laurels so to speak and concentrate all of our efforts on shoring up implementations. To be completely honest, it just smells fishy and full of hubris. I'm suspicious and skeptical by nature and any time somebody seems to be saying something is near perfect and astronomical I tend to immediately wonder why it's being said, not that it was said. I have to muddy things up :)

          Something smells very fishy here, and what's happened to their site makes something like an NSL or its equivalent a more likely explanation.

          Now on that, we agree completely. It's far more likely IMO, that government got involved at a low level to attack implementation or other components and backdoor it, as we are talking about spying, logistics, and human behavior, not mathematics.

          Thank you very much for the citation. I got some reading to do...

          --
          Technically, lunchtime is at any moment. It's just a wave function.
    • (Score: 1) by Fry on Thursday May 29 2014, @09:13PM

      by Fry (642) on Thursday May 29 2014, @09:13PM (#48921)

      quantum mechanics can do no more than halve the effective keyspace, so a 256-bit keyspace becomes effectively 128-bit.

      2**128 != 2...

      • (Score: 1) by fnj on Thursday May 29 2014, @10:10PM

        by fnj (1654) on Thursday May 29 2014, @10:10PM (#48935)

        Unless, you measure keyspace in number of bits needed to represent all possible keys, rather than the number of all possible keys.