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25-GPU cluster cracks every standard Windows password in less than 6 hours

arstechnica.com

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Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#21

Post by [deleted] »

ramidarigaz wrote: post #18
cynwoody wrote: post #10

Impressive as the numbers are, it's worth remembering that this is an "offline crack", going against a stolen list of encrypted passwords. If they can steal your database of encrypted passwords, you've got a problem no matter how strong the passwords are. How many guesses per second do you get in a typical online crack? E.g., a script kiddie trying to guess your cloud server's SSH password?

On my webserver, you get 3 chances and then a 24 hour ip ban. I think that comes out to 0.00003 passwords per second :) The particularly persistent IPs get a special iptables rule.

[deleted]

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#23

Post by cgag »

ramidarigaz wrote: post #18
cynwoody wrote: post #10

Impressive as the numbers are, it's worth remembering that this is an "offline crack", going against a stolen list of encrypted passwords. If they can steal your database of encrypted passwords, you've got a problem no matter how strong the passwords are. How many guesses per second do you get in a typical online crack? E.g., a script kiddie trying to guess your cloud server's SSH password?

On my webserver, you get 3 chances and then a 24 hour ip ban. I think that comes out to 0.00003 passwords per second :) The particularly persistent IPs get a special iptables rule.

I suppose it's a bit different from a user facing login, but does anyone know why these limits tend to be set so low? I've locked myself out of plenty of things, and so have plenty of people I know. It seems like setting the limit to 20 would be just as effective in blocking brute force attacks without being user unfriendly.

Is it that with user facing services the common user/passwords are so common it's reasonable to just try just the top x most common passwords?

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#24

Post by mitchi »

cynwoody wrote: post #10

Impressive as the numbers are, it's worth remembering that this is an "offline crack", going against a stolen list of encrypted passwords. If they can steal your database of encrypted passwords, you've got a problem no matter how strong the passwords are. How many guesses per second do you get in a typical online crack? E.g., a script kiddie trying to guess your cloud server's SSH password?

These hash functions are made to be fast to hash :P Check out the NIST competition, they picked the fastest hash that can be calculated with special hardware :) People who want real offline password security should use slow hash functions (and passphrases of course).

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#25

Post by plaguuuuuu »

cynwoody wrote: post #10

Impressive as the numbers are, it's worth remembering that this is an "offline crack", going against a stolen list of encrypted passwords. If they can steal your database of encrypted passwords, you've got a problem no matter how strong the passwords are. How many guesses per second do you get in a typical online crack? E.g., a script kiddie trying to guess your cloud server's SSH password?

it's my understanding that NTLM hashes are sent over the wire...? therefore any machine on the local network could intercept this hash via network-level attacks such as ARP poisoning, WiFi attacks, etc. Then the cracking box would quite happily and easily brute force the entire 8 char keyspace and reveal the pass.

it's a different threat model to hash+email retrieval via sql injection which can lead to all sorts of nastiness involving hijacking email and then other accts

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#26

Post by plaguuuuuu »

patrickgzill wrote: post #16
bradleyland wrote: post #7

Earlier quoted context omitted.

Put your tin foil hats away. This doesn't "crack" NTLM, it brute forces at a very high rate. The NSA has more money to spend, but are similarly limited by the hardware available at any given point.

The NSA has access to their own chip fabrication facilities. I do not know if they own their own plant, or just have secure fab space at some other company's plant. So they could have easily fabbed something like this, or a tuned architecture specifically designed for the purpose.

It's very probable that they have and if so, it's almost certain that it would involve specialized hardware implementations (ASIC, FPGA, whatever) rather than commodity graphics hardware which is burdened with expensive and useless stuff like onboard memory and would be power inefficient

considering that the entire purpose of NSA in the first place is to provide SIGINT and encrypt or decrypt signals, it's almost a given that they're trying to the best of their ability to crack stuff.

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#27

Post by ramidarigaz »

cgag wrote: post #23
ramidarigaz wrote: post #18

Earlier quoted context omitted.

On my webserver, you get 3 chances and then a 24 hour ip ban. I think that comes out to 0.00003 passwords per second :) The particularly persistent IPs get a special iptables rule.

I suppose it's a bit different from a user facing login, but does anyone know why these limits tend to be set so low? I've locked myself out of plenty of things, and so have plenty of people I know. It seems like setting the limit to 20 would be just as effective in blocking brute force attacks without being user unfriendly. Is it that with user facing services the common user/passwords are so common it's reasonable…

So far it hasn't been a problem (fingers crossed). I have a couple ways into the server in case I get myself banned. Also, it's my personal server, so the only user that would complain is me :)

For other sites, I'm honestly not sure how they go about choosing a limit. 20 does seem to be more reasonable, while still being perfectly safe.

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#29

Post by Caerus »

hayksaakian wrote: post #14
apawloski wrote: post #11

Earlier quoted context omitted.

I know for practical purposes this doesn't seem like that big of a deal, but you have to understand that 8 chars of mixed case, numbers, and symbols is still a gigantic key space. That this can be done so quickly on commodity hardware is pretty impressive.

Individual char variance is less significant compared to additional chars. Look at the xkcd password entropy comic

From what I remember of the comic, the point was not the length of the password. The entropy was calculated based on 4 possible words.

Assuming ~2000 common English words, the number of possible passwords in that format is 2000^4 ~= 2^44. If the calculation is based on a completely random string of letters it is far stronger at 26^30 ~= 2^141 but it's safe to assume people aren't going to memorize a 30 character random password.

It's worth noting that the fairly common 8 character upper/lower case, numbers, and symbols they cracked in 6 hours is more secure than "correcthorsebatterystaple" at 72^8 ~= 2^49.

Re: 25-GPU cluster cracks every standard Windows password in less than 6 hours

#30

Post by trb »

cgag wrote: post #23
ramidarigaz wrote: post #18

Earlier quoted context omitted.

On my webserver, you get 3 chances and then a 24 hour ip ban. I think that comes out to 0.00003 passwords per second :) The particularly persistent IPs get a special iptables rule.

I suppose it's a bit different from a user facing login, but does anyone know why these limits tend to be set so low? I've locked myself out of plenty of things, and so have plenty of people I know. It seems like setting the limit to 20 would be just as effective in blocking brute force attacks without being user unfriendly. Is it that with user facing services the common user/passwords are so common it's reasonable…

Intuition, most of the time. Here are some quite common ones:

http://www.splashdata.com/press/PR121023.htm

There's no reason why you would have a three attempts limit, or five, or ten, and so on. If I get three per account, I'll just use the top three and try again different accounts. If I get three attempts per IP, I'll use many different IPs and do the same.

To remain user friendly, delays are the way to go. E.g. you could have three different delays that add to each other: Account-level, IP-level and global. Increase each with every failed attempt up to 30 seconds of wait time, and add them together. This will slow down brute force attempts to the point where they're useless, while still allowing legitimate users to login (just with a little inconvenience).

As a result, if I failed three attempts with one account, and three one next, etc., my IP-level limit will prohibit me from moving on to other accounts. If I try a lot of passwords on one account, the account-level and IP-level ones will slow me down. And if there's a distributed attack with many IPs, the global delay will reduce the damage the attack can do. All the while legitimate users can still use the service.

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