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On Wed, Jun 25, 2008 at 9:24 PM, Sebastian Wiesner <basti.wiesner@×××.net> |
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wrote: |
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> Chris Walters <cjw2004d@×××××××.net> at Wednesday 25 June 2008, 22:25:18 |
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> > Are you a cryptology expert? |
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> |
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> Are you then? |
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I doubt that either of you are cryptology experts. I've known a few, and I |
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am a crypto-expert, who has worked for the government of the US. |
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|
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> |
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> > The only thing that cryptography attempts to do is reduce the |
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> > **probability** of cracking the key and gaining access to the data as low |
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> > as possible. |
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> |
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> No news. That's, why cryptology defines "security" not as "being |
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> impossible |
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> to crack", but as "being sufficiently improbable to crack". The only |
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> cipher, that can't be "brute-forced", is the OTP, which is |
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> considered "perfectly secure". |
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There is no such thing as perfectly secure, but a cipher algorithm that |
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would take *all* the computers on Earth a year or more to crack is pretty |
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secure. |
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|
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> |
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> > As for brute forcing a passphrase: Since most implementations of AES |
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> > (Rijndael) use a hash of the passphrase to form the key, it amounts to |
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> > the same thing, in practice, as cracking the key. |
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> |
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> First of all, you can perform hard disk encryption _without_ a passphrase. |
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> You can store keyfiles on smart cards, usb sticks, etc. In this case, you |
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> can generate a _truely random_ key. |
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> |
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> Using a passphrase is the most insecure approach, but still, with a |
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> sufficiently random passphrase, you can gain a level of security, that even |
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> the NSA will find difficult to come around. |
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> |
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> The randomness of a 30-char passphrase does of course by far not match the |
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> randomness of a 256-bit key, so there is a real chance, that it can be |
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> guessed by brute force. Still it will take much cpu time, which is not |
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> endless, even to the NSA. |
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I don't think I can really comment on this, except to say that smart cards |
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and usb thumb drives are the way to go for security. As long as you can keep |
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control of the device. |
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|
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> |
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> In such a case, the question is, if the data, you ciphered, is really worth |
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> the effort of putting a super computer into work for a long time to try any |
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> possible passphrase. |
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Mr. Walters' claim is not that they would put a single super-computer to |
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decrypting it, but a "network of supercomputers". I truly don't think you |
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have to worry about that occurring, unless you are deemed a danger to US |
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National Security. Even then, AES is very hard to crack. The major weakness |
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is the person who encrypts the data. Under questioning, most will give up |
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their keys. |
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|
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> |
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> > Cryptology is, at least partly about finding the weakest link, because |
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> > that is what is likely to be attacked in any cryptosystem. |
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> |
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> Of course, absolutely true. Hard disk encryption is by far not perfect, |
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> just look at the cold boot attacks that gained public interest in the last |
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> time. But you didn't talk of _cryptosystems_ in your previous posts, you |
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> did talk about _algorithms_. |
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By themselves algorithms are relatively useless. It is only the application |
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of those algorithms that make them useful. In this case, Mr. Walters pointed |
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out how *NOT* to apply cipher algorithms. Some of the ways, anyway. |
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|
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> |
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> Summarizing, the modern ciphers themselves are secure, as there is mostly |
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> no |
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> way to crack them save a brute-force attack on the key. On the other hand, |
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> cryptosystems built around these algorithms can of course contain |
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> weaknesses and holes, like weak passphrases, unsecure key storage, etc. |
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> |
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> > The US Government only keeps classified information on non-networked |
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> > computers in secure environments, so the cipher used does not matter as |
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> > much as the other security measures taken to ensure that the data does |
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> > not fall into the wrong hands. |
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> |
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> May be. I do not know, which restrictions apply to US classified data, I |
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> only know about official statements, the US government made towards the |
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> security of AES. |
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I can neither confirm nor deny Mr. Walters' statement. I will state that the |
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United States Government does, in fact, use ciphers to communicate with |
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Embassies, Military Camps and Bases abroad, and Naval vessels. That hardly |
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fits Mr. Walters' statement. |
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|
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> |
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> > A final thought: It is a fact that both the US Navy and the NSA are |
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> > *very* interested in cryptology and data security. The NSA also does |
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> > have large networks of supercomputers that, using parallel, distributed |
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> > or concurrent computing principles can crack keys more quickly than you |
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> > may think. |
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> |
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> You can use simple mathematics to find out, that even the largest super |
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> computers, having one peta flop, needs millions of years to perform an |
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> exhaustive search through AES key space. |
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> |
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> Anyway, you may believe, what you want to believe, I'm just reflecting, |
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> what |
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> real experts like Bruce Schneier have been telling for years: It's wrong |
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> to trust into simple ciphers, but it's equally wrong, to believe, that |
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> anything can be broken. |
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It is equally wrong to believe that any cipher is immune to attack, but it |
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is not nearly as easy as Mr. Walters would have you believe. |
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> |
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> |
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> my 2 cents |
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> |
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My nickel... Jase |