Ranting about NTLM, I am also shocked at how many people are unaware of the pass-the-hash vulnerability enabled by the mere possession of hashes, without having to brute-force them: http://www.youtube.com/watch?v=DkbBCR_vfRQ (disclaimer: I made this video and was a developer for Metasploit/Nexpose).

That's just depressing, considering how long this has been a problem.

Advice has been, for many years, to avoid using passwords 14 chars or less to force use of NTLMv2.

Here's a Microsoft document from 2004: (http://www.windowsecurity.com/articles/Protect-Weak-Authenti...)

> You would be surprised at the number of IT people who have no clue [...]

No, you're right. It's widespread lack of knowledge, and letting people know that some stuff is not secure, and other stuff is more secure if you have a complex passphrase, is important.

Admittedly LinkedIn isn't a critical application calling for people's most secure passwords - but it's evident that only 5-10% of users use passwords that take more than 1 month to crack when hashed with SHA-1.

[1] http://securitynirvana.blogspot.co.uk/2012/06/final-word-on-...

People re-use passwords. Often it's not access to the LinkedIn account that's the problem, but that that same password will give you access to their email account, after that, you have everything.

Depending on how widespread this behaviour is, while 90-95% of linkedin passwords were easily cracked, that might not generalise to all sites.

According to current theory of physics, every computation needs at least a certain amount of energy. So if you want to do many computations today, you will have to use a certain amount of energy today. Now lets say, you have a machine that turns any matter into energy without any loss. You put in m mass and you get out e=mc^2 energy. Problem is: You cannot get more matter into that machine today then is around you in a radius of 24 light hours.

So that would be a hard limit.

But quantum computers have proven to break that limit. One theory is that using a quantum computer means using computers in an unlimited number of parallel universes. So there is no limit to the number of calculations you can do. (See David Deutsch and his theories about parallel universes)

I think there are theories about the limits of what a quantum computer can calculate. But I dont know them. Would be interesting to read about it if there is something published.

Then again, what might look like a "hard limit" today will probably not do so tomorrow. Some time ago the "lower limit on energy per calculation" sounded like a hard limit. Then quantum computers came along and blasted through it.

This is not, strictly speaking, true. You are talking, I believe, about Lanadauer's principle [1]. This states that it is the destruction of entropy that costs energy. There are computational methods that can theoretically avoid these energy losses [2]. In fact, Lanadaer theorized about reversible computing in his original paper [3].

Bremmerman's limit, mentioned below, is more applicable.

1. http://en.wikipedia.org/wiki/Landauer%27s_principle 2. http://en.wikipedia.org/wiki/Reversible_computing 3. http://www.cc.gatech.edu/computing/nano/documents/Bennett%20...

Apparently it takes a minimum amount of energy to flip one bit in a conventional (non quantum) computer.

In order to brute force a 128 bit key, you'd need some sort of 128 bit register. Multiply the amount of energy needed per bit flip and the result implies there are never likley to be enough power plants on Earth to iterate through all the combinations (let alone perform the computations required to test the candidate key).

Hope this helps, perhaps this is enough for you to find the original reference.

Edit: perhaps it was http://en.wikipedia.org/wiki/Landauer%27s_principle as mentioned below.

The cost/time trade-off for such cracking makes this rig pointless for such cracking, unless you absolutely must have it in 6 minutes.

I don't see any other major use for this; it's simply not powerful enough to attack anything new (Edit: even with 128, rather than 25, GPU's).