300 Billion Passwords in One Second

The Register reports more advances in brute force password cracking. Swiss security firm Objectif Sécurité used Solid State Drives (SSD) to store rainbow tables and consequently speed up each brute force attack. The read speed from an SSD is typically quicker than that from a traditional drive, which is why there is an overall performance increase.

Objectif Sécurité claims a throughput of 300 billion passwords per second when attacking a Windows XP MD4 password hash.

My own testing using Objectif Sécurité’s online proof of concept easily cracked the passwords from my test XP machine including the complex x%fF*Z3$. It couldn’t crack my 29 character pass phrase from Size Does Matter, but this is because Windows XP stores passwords longer than 14 characters in a different way.

Of course the default LMHash used with MD4 to store Windows XP passwords is weak and has largely been replaced in modern operating systems. However the speed improvement can be applied to accelerate brute force attacks on other algorithms.

What does this mean in real terms? It was already true that if someone could get physical access to your XP PC, they could extract your data. Now it is trivial to steal your passwords as well, which of course opens up all sorts of identity theft related crime possibilities. This makes disk encryption, and not reusing passwords more important that ever.

For info, I “harvested” the passwords on my XP machine by booting from my favourite Linux Live CD, Backtrack. I then used Bkhive to extract the key used to encrypted the SAM file where the LMHashes are stored. Finally I used Samdump2 to extract the hashes themselves.

WPA Cracker

The was an interesting article on the Register this morning about a new cloud based service that allows you to brute force crack wireless WPA passwords. The service, run by Moxie Marlinspike of null byte prefix fame, claims it can compare your key against a 135 million word dictionary, optimised for WPA passwords, in around 20 minutes. It can achieve such speed by spreading the load over a 400 CPU cloud cluster.

Although the figures are impressive, the service falls way short of guaranteeing being able to crack your WPA password (Note, it doesn’t claim that it can). For an 8 letter key that uses upper and lower case and numbers, there are 2.18 x e¹⁴ possible combinations. This rises to 4.77 x e²⁸ for a 16 letter password. Hence the chance of the service successfully finding your password depends on how closely it resembles a dictionary word.

Of course in reality, your WPA key almost certainly does resemble a dictionary word. If you want to make it safer but still keep it possible to remember, then increase its length as discussed here.

If you want to test the strength of you WPA password, you need to capture the WPA handshake using something like Aircrack-ng, then submit it to the site and hand over $17.

Practical Password Management

I did a quick count today of the passwords that I use at least once per month and was surprised to find that I have 41. I appreciate that this is higher than the average but suspect that anyone who uses a PC for work and does a bit of online shopping or banking is at least in double figures. It’s all very well security specialists (like me) telling us to use different complex passwords for each account and to change them regularly but how the hell can you remember 41 passwords? What I imagine most people do is to use the same password for all accounts and change them as infrequently as possible. This is obviously far from ideal so a compromise needs to be found.

The most important password is the one for your email. Nearly every other password you have will rely on it in some form for resetting it in the event that it is forgotten. Hence a unique strong password here is vital. Afterwards it is a case of assessing the importance of the data held with each account. If it limited personal information you can get away with your generic password, although it should still be difficult to guess.

Another option is to use password management tools. The idea is that you have a secure encrypted database of all your passwords, protected by a strong pass phrase, which means you only need to remember one password. I use Ubuntu Linux which comes with just such a program called Seahorse. It can also be used to managed PGP keys and certificates. More recent versions of Windows come with something called Credentials Manager which is fine in a Windows centric world but isn’t much use for storing passwords where the authentication is built into the end application. An open source utility that I use for password management on Windows but which also works on Linux and possibly MacOS is Password Safe. There are many programs of this type available for free but this one is particularly easy to use and so far has never let me down.

Another thing to do, at least for your systems is to change the default username. A recent study from Microsoft showed that brute force attacks target usernames such as administrator or administrateur.

Size Does Matter

There was an interesting article today in the Register about brute force password cracking using Amazon’s EC2 cloud architecture. The main focus was on how much it would cost to crack passwords of different lengths and complexity. One of the conclusions which is almost counter instinctive is that a long lower case only password is much harder to crack than a shorter complex one consisting of lower and upper case characters as well as numbers. I did my own calculations to verify the findings and came up with the same results.

Take for example an 8 character complex password containing upper case and lower case characters, numbers and also a choice of 20 non standard characters such as % . When considering brute force cracking, the 8 character complex password is easier to break than a 9 character one containing upper and lower case characters and also easier than an 11 character password containing only lower case characters.

Hence, next time that nasty Systems Administrator tells you that your password should resemble something like x%fF*Z3$ you can tell them that this is less secure than a password like HelloFred or even mycarisblue. Note that at various times in my working career, I have been one of those administrators so I know where they are coming from.

No doubt the Systems Admin would respond that in reality a brute force attack would not be random in the words and phrases it attempts and subsequently would crack a long non-complex password quicker than a short complex one. This is probably true when length diferences are small but difficult to quantify accurately. Coming back to the real world, nearly nobody can remember a password such as x%fF*Z3$ but it’s not so hard to recall a semi abstract phrase such as MyDogisfrenchThanksforthefish. This non complex password is approximately 2.8 x e³⁴ more difficult to crack than the complex one when considering only a brute force approach. Even when factoring in dictionary approaches it’s probably still a lot safer as well as being easier to recall. Hence when next choosing a password, remember, size really does matter.