Slashdot Mirror
Cheap GPUs Rendering Strong Passwords Useless
StrongGlad writes with a story at ZDNet describing how it's getting easier to use GPU processing against passwords once considered quite strong.
"Take a cheap GPU (like the Radeon HD 5770) and the free GPU-powered password busting tool called 'ighashgpu' and you have yourself a lean, mean password busting machine. How lean and mean? Working against NTLM login passwords, a password of 'fjR8n' can be broken on the CPU in 24 seconds, at a rate of 9.8 million password guesses per second. On the GPU, it takes less than a second at a rate of 3.3 billion passwords per second. Increase the password to 6 characters (pYDbL6), and the CPU takes 1 hour 30 minutes versus only four seconds on the GPU. Go further to 7 characters (fh0GH5h), and the CPU would grind along for 4 days, versus a frankly worrying 17 minutes 30 seconds for the GPU."
And any system worth its salt (crypto-hashing joke) won't allow that many attempts against any external or internal authenticator and will NEVER expose its password hashes.
Seriously, if someone has your password hash, it's game over anyway and it doesn't matter if it takes 2 weeks or 2 months to guess the passwords. And if they don't, then you shouldn't be letting them try several BILLION attempts at guessing a password anyway.
Go further to 7 characters (fh0GH5h), and the CPU would grind along for 4 days, versus a frankly worrying 17 minutes 30 seconds for the GPU."
OK, so go to 15 characters. Using a password generator I can go as far as I like. Using some sort of password bank program, I can store passwords / phrases of any complexity and use copy and paste, thus having only one strong password to remember.
So, what am I missing? (And lets keep it on topic, folks).
Faster! Faster! Faster would be better!
It is well known that if someone gets your hashed password, it is as good as cracked. 17 minutes vs 4 minutes is irrelevant.
On a live system, it is quite another story. You can't just remotely try 3.3 Billion passwords per second.. You'll be locked out after 10 attempts or so.
This is about offline hash cracking, not bruteforcing passwords over a network connection.
Emotions! In your brain!
Hooray, you can crack an NTLM password in like five seconds! Too bad Windows has preferentially used Kerberos since Win2K, which means that pretty much any in-practice Windows network you'd like to hack in to is using a real security scheme.
I mean, really. This article isn't about how much faster a GPU is than a CPU for hash cracking (after all, four days to reverse a hash is still unacceptable, and that's brute forcing it and not using one of the widely available NTLM rainbow tables), it's about how much NTLM sucks and Microsoft should have never contravened the first rule of cryptography and tried to roll their own.
This is really a Windows problem. Windows uses a simple, fast hashing function (I think some version of HMAC). This means that an attacker can churn through many passwords very quickly (apparently billions per second per the article). You should really use a slow hashing function that takes around 0.1 to 1 seconds to calculate one hash on the server. Even a GPU will then take very long! Plus don't forget salt (different per user) against rainbow table attacks, plus key strengthening. Something like bcrypt is pretty good, but scrypt is probably even better as it does not only require a lot of CPU time but also significant memory (making dedicated hardware crackers much more expensive).
A 6-7 letter password only using letters and numbers is NOT strong.
It would be trivial to cover it with rainbow tables and have near realtime cracking even without GPUs.
_Not weak_ would be 10 letter+, with a salt. Would make brute forcing not really that easy anymore...
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
You are misunderstanding it. Salting only protects from precomputed tables containing (password, hash) entries (rainbow tables) when using a unique salt. I didn't read TFA, but I assume this is a simple brute-force attack. The attacker would just add the salt to each guess, which does not make it any more difficult.
8-character passwords were strong enough for Unix thirty years ago, but that was a long time ago in Moore's Law cycles; I've got wristwatches faster than that PDP-11. It's annoying how many systems still seem to use them.
For systems that do passwords interactively, you're not going to get the same brute force speed, but you're still exposed to automated attacks - using a CAPTCHA in addition to the password can help prevent them.
Bill Stewart
New Fast-Compression-only CPR http://preview.tinyurl.com/dy575ks
3m are going to introduce a larger post-it-note
The title of the article is extremely misleading.
I don't really care that someone can break short passwords generated via MD4. MD4 is very broken. NTLM is essentially 1992-era technology that was later picked up by Microsoft, who now deprecates its use.
When a GPU can break 15-character AES256 keys, then I'll start to worry about the security of my 24-character key.
Am I part of the core demographic for Swedish Fish?
Even for Slashdot, this is a little pathetic: the link is to a ZDNet article, which regurgitates a PCPro article, which in turn regurgitates a blog post by the guy who actually ran the tests, Vijay Devakumar. And here's Ivan Golubev, who wrote the cracking tool.
Still, ZDNet's advertisers thank you for the hits!
Solution: Make a stronger password.
Your shameless plug is correct, but for one problem:
When you use a fingerprint sensor, the traditional attack methods (brute forcing, social engineering, etc) still work. But you also add a new attack method, by generating a fake fingerprint from that coffee cup you threw into the trash that morning.
Needless to say, increasing the possible attack vectors decreases security, rather than increasing it.
"City hall" in German is "Rathaus" Kinda explains a few things......
It doesn't work like you think it does.
Basically, most modern password protection techniques work like this: they take a password, say "my nice password" and transform it into a hash, say :"uq10ajg901a0##". Now only the hash is stored on the system. There is no way to go from the hash to the password. Classical hash functions are MD4, MD5 and SHA1. NTLM users MD4. Linux mostly uses MD5. There are added niceties likes salt, etc. You can look these up if you want.
When users enter their password, they are hashed again, and the *hash* are compared, not the passwords. If you enter the right password, no matter whether this is a nice word or sentence or jumbled letters, the system lets you in.
Crackers simply assume that the *hash* is available. It is in fact very easy to get it if you have access to the console, both for Linux or Windows. They then generate any and all combination of letters, signs, symbols and so on as input as potential password, they compute their hash, and they compare it to the hashes they know. If there is a match, bingo, they have found the password.
So the upshot is it doesn't really matter what the input password look like as long as the crackers can generate it and compute their hash. If the crackers know that you have used only letters, however, they can cut down dramatically on the numbers passwords they have to generate and save time.
So in some sense you are right but not for the reason you mention.
Hope this helps.
It is well known that if someone gets your hashed password, it is as good as cracked. 17 minutes vs 4 minutes is irrelevant.
Bullshit. It is well known by people who don't know what they're talking about, which includes TFA.
Do you seriously think that in the age of bitcoin we can't make a hash function that is arbitrarily difficult?
Use an adaptive cryptographic hash function: bcrypt, PBKDF2 or scrypt. The key feature is a tunable stretch factor that basically sets the number of rounds of hashing. Set that factor (by means of a simple timing loop) to require 1 second of CPU time (or GPU time or whatever) to hash.
Now the simplest 8 character A-Z password will take an expected 3,311 years to break. You'll obviously want a safety margin, and will expect them to have more computing power a few years down the road. But you can tune the stretch factor to ensure that a reasonably strong password is perfectly good against offline attacks.
This article spells it out:
http://www.baekdal.com/tips/password-security-usability
Too bad most sites are too stupid to allow a long enough password. I'll take a 16-character pass-phrase with all lower case + whitespace over a hard to remember 8 character one anyday.
Same shit with all the scare on rainbow tables. I remember the hype of "It can crack any password in seconds!" Then I found out it meant any LM password, which has some real limitations on it (14 characters total max, as two 7 character hashes, no upper and lower case). Ahh, not so impressive then.
Same shit with NTLM. Worlds better than LM, but not current. Wake me when it is a threat vs NTLMv2, which is what Vista and 7 use exclusively unless you manually change security policy (and XP and 2000 support it).
Then there's the fact that they are talking about short passwords. Security comes in length and it goes up drastically with each character. They are crowing on about how easy 7 character passwords are. Ok, fine, try 14 then. It isn't like if 7 takes 18 minutes 14 takes 38 minutes. It is more like if 7 takes 18 minutes 14 takes years.
Also to make a long, secure, password doesn't have to be that hard. Just take a phrase and modify it a bit. Say you decide the phrase "There can only be one," should be your password. Do something like "Th3r3 can only be #1!" Fairly easy to remember, yet you have to exhaust a massive space for a brute force attack.
Finally, all this is an attack against the hashes. While we want hashes to be strong, let's face it they are a last line of defense. This is a situation where someone has already gotten in, gotten high privileges, and stolen that list. This has no relevance to dealing with breaking in to a random system remotely.
Pretty much this is just fear mongering. Yes, you need to use longer passwords these days. So do so. However a short password really isn't as bad as they make it seem. The risk they are talking about here is only if someone happens to get the hash file from a system with NTLM passwords stored that you use a short password on. Given that the only system that qualifies for that for most people is their home desktop, if they get it the hacker has owned your system already (you have to have admin to get the SAM file) so it doesn't matter.
Doesn't matter how strong a password is, xkcd have it covered.
I've got a fever and the only prescription is more COBOL.
It's not that simple. Cryptography is an asymmetric game: you always have to assume the attacker has orders of magnitude more computing resources than the target. Cryptography works because we can (usually) find problems that get exponentially harder and harder to crack. For instance, let's say you just want to encrypt something. A block cipher with a 64-bit key is just on the edge of being brute-forcible today. But, as a general rule, you could use a block cipher with a 128-bit key and it should only be half as fast as the 64-bit cipher (note I said this is a general rule, there are number of factors that influence speed). A 128-bit block cipher is 2^64 times more difficult to crack than a 64-bit block cipher. So, the target can make something 2^64 times more difficult to crack by just doing twice the work.
Your proposed solution just grows linearly, not exponentially. If you iterate SHA-1 10,000 times instead of just 5,000 you're also doing twice the work, but this time you've only made your password twice as difficult to crack. If you can suddenly start doing twice the work you did before, you have to assume the attackers can as well.
Yes, iterating hash functions buys us more time, but this is a game that targets can't win. Plus, you're ignoring all of the problems associated with moving to higher iteration counts. Probably first and foremost is interoperability. There's a massive application base out there that just uses MD5 or SHA1 with little to no iteration. It's not easy for software like Windows to change. I think it wasn't until Vista that Microsoft stopped storing a LAN Manager hash of users' passwords, which made then trivial to break. That's been known to be bad for a long, long time. Plus, in most web-based applications its not the client that does the hash operation, its the server. While your new Core i5 processor could probably easily handle bumping up the iteration count by an order of magnitude or so, Google's Gmail servers probably can't.
Longer, more complicated passwords would be more effective than increasing iteration counts, but people are bad at generating and remembering long passwords. So, the only long term solution seems to be moving to stronger forms of authentication, like smart cards or using devices like smart phones as one-time password devices.
Bottom line: Want a strong password that you can type anywhere? Make it 12 mixed case letters, numbers and at least one punctuation mark. Based on the times claimed in the article, that should take 35,000 current GPU-cracker-years.