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.
This is about offline hash cracking, not bruteforcing passwords over a network connection.
Emotions! In your brain!
Exponential growth. Get the point?
Using the same scaling as the summary, you can crack 8 characters with about 64 GPU hours, which is about $50 on AWS.
By the time you get to 10 characters, you are talking $700k. 12 characters is into the billions. Of course, I doubt that AWS will scale their fleet to billions of servers just so you can rent it for one hour, so you're going to have to pay to build your own data centers and, for that matter, chip factories.
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!
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......
That's amazing. I've got the same combination on my luggage.
"The Sun would burn out first."
Especially if it's an old Ultra 5.
http://www.rootstrikers.org/
What you're missing is that the percentage of the general population that can consistently (a) remember a long password and (b) type it without a failure at least 50% of the time, is in the single digits. Remember, general population, not geeks.
I've expressed the opinion for several years now that password authentication is broken, and that we need to move to two-factor authentication schemes ASAP.
--Paul
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.
Screw the general population. I'm a geek and a 120+ WPM @ 98% accuracy typist to boot and I can't even enter our administrative password more than 50% of the time at work.
Let's look at some alternative alternative math: that 3.3 billion passwords/sec were at http://www.golubev.com/files/ighashgpu/readme.htm. Note that this is the speed for cracking MD5 passwords, which were deemed "almost ready to crack" a few years ago. Modern Linux systems all support sha256 and sha512 hashing; given that this tool is 1/3 slower for sha1 (aka "sha160"), one can guess that current sha2 (sha256/sha512) algorithms will be slower. It's also worth nothing that the algorithms supported by the tool mentioned in the article are *all* not supposed to be used as of 2009: http://csrc.nist.gov/groups/ST/hash/policy.html; the tool doesn't currently even support the sha2 algorithms. The common algorithms which are currently supported (ie, md5) have been breakable in fractions of a second through rainbow tables for years anyway - which was NIST's point, IIRC.
I suppose I'll also note that the Ubuntu 11.04 system I'm typing this upon right now is configured out of the box to use sha512 hashing in /etc/shadow (check /etc/login.defs on most Linux systems, look for password strings which start with $6$). Assuming the use of PAM for anything important and passwords stored either in root-only shadow file or in an LDAP directory which does compare-only access or server-side hashing, and a secure transport such as current TLS, then this is a non-issue on a Unix system which hasn't already been compromised. It'd be easier and probably more effective, as usual, to socially engineer a password (or otherwise gain access through the human interface weak point) than to get password hashes and break them.
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.