Cracking Passwords With Amazon EC2 GPU Instances

suraj.sun writes "As of Nov. 15, 2010, Amazon EC2 is providing what they call 'Cluster GPU Instances': An instance in the Amazon cloud that provides you with the power of two NVIDIA Tesla 'Fermi' M2050 GPUs... Using the CUDA-Multiforce, I was able to crack all hashes from this file with a password length from 1-6 in only 49 Minutes (1 hour costs $2.10 by the way.). This is just another demonstration of the weakness of SHA1 — you really don't want to use it anymore."

Comments

Dictionnary attack doesn't show any weakness

[kiwix]

This just shows one more time that SHA1 is deprecated — You really don't want to use it anymore.

No it doesn't show anything. Your "attack" would only have been marginally slower with SHA-2, because SHA-2 is a bit slower of SHA-1. You didn't exploit any weakness of SHA-1 in this brute-force attack.

Re:Dictionnary attack doesn't show any weakness

[Anonymous Coward]

No it doesn't show anything. Your "attack" would only have been marginally slower with SHA-2, because SHA-2 is a bit slower of SHA-1. You didn't exploit any weakness of SHA-1 in this brute-force attack.

He exploited the "is fast to calculate" weakness.

Clearly, we need hash functions which take long amounts of time to compute.

large cloud, small brain

[epine]

I agree the story could have been framed better. There is in any case some story here. For certain computational tasks, the linear performance scaling that vanished in a puff of Prescott has returned from the grave.

And not only that, instead of spending $20,000 to buy a Fermi class workstation and getting your result in a year, you can throw the same $20,000 at the cloud and have 10,000 machines deliver your result in an hour, for large instances of cloud.

This applies to a class of computational tasks denominated in CPU cycles where you can cut a wide swath.

Moore's law still exists, it's just not evenly distributed.

proper use of hashing algorithms

[MyDixieWrecked]

So this also proves that, ultimately, this list of passwords was not properly hashed.

People jump up and down and scream that SHA1 and MD5 are broken, but if properly used, they still offer significant password security. One trick is to use salts when storing passwords in the database.

password: 'foo'
salt: '2010-11-16T08:39:05Z - some_random_string$#@!'
password-hash (md5): 14e80778512f578a5fe263abe4b58e9c

that increased the amount of time required to brute-force the password significantly. Also, the use of a database of hashes is largely worthless since each password in the list would have a completely unique hash. for the sake of brute-forcing the data, short passwords don't matter (on the other hand, brute-forcing login to the application is not affected). Having a different salt for each password makes the time spent on each other password completely worthless once the cracker gets to the next item in the list.

to improve that, we can say... hash the result 1000 times in a row. For someone trying to brute force the hash, they would spend 1000x the CPU resources creating the hash. It's mostly not a big deal to run that hash 1000 times when creating the information for the database or authenticating the user.

of course, SHA1 and MD5 are still broken when it comes to file integrity checking (when it comes to tampering) since there are documented collisions. For this case, cryptographic signatures are where it's at. You can guarantee that not only was the file not tampered with, but also that the person who supplied the signature was who they say they were. Gotta love public key encryption.

Re:Yes, SHA1 security is questionable..

[jandrese]

It's impossible for a hash algorithm not to have collisions. You're mapping an arbitrarily large problem space down into just a handful of bits. There are infinitely more possible inputs to the algorithm than there are outputs. That said, it's supposed to be computationally prohibitive to find those collisions, and that's where MD5 and SHA1 are failing.