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My weekend of attempting to recover an old WinZip password left me slightly surprised. We live in a world where secure data isn't so secure (*cough* Sony's PSN *cough*), so it's hard not to be afraid of what general purpose computing means for the future as our graphics processors become even more powerful.
In the past, there was no way you could expect to bring down an ASCII password with a length of 10 characters in any reasonable period. This was only possible with custom hardware. That's what the Electronic Frontier Foundation did in 1998 with its Deep Crack. At a final cost of nearly $250 000, a group of security experts built a machine that could scan about 90 billion passwords per second, thanks to more than 1800 AWT-4500s working in tandem.
I can’t manage that level of performance with my office workstation, but two GeForce GTX 570s in SLI achieve about 1.5 billion passwords per second against Zip 2.0 encryption. That’s 1/60th of the performance at less than 1/100th of the cost. Obviously, I'm comparing apples against oranges. After all, Zip 2.0 encryption is old. But it's clear that massively parallel graphics architectures will continue enabling increased performance density at more commodity-like prices, so at some point we will be able to get 90 billion passwords per second from a desktop-sized box.
So, what have we learned? First off, steer clear of Zip 2.0. It’s an older encryption scheme supported for legacy purposes, and even WinZip suggests that you use AES to ward off brute-force attacks.
Targeted attempts are another story. Most people use passwords that include words, and as such, those passwords are vulnerable to dictionary-based attacks no matter what encryption scheme you use. The number of words in the English language is less than 1 million. However, a GeForce GTX 460 can manage at least 150 000 passwords per second against AES encryption. Even if you add a few variations, you really only need to spend a day crunching passwords to break the proverbial lock. Why? Because an entire word is functionally the same as a single letter, like "a."
Ideally you should avoid the following if you are trying to make your files more secure:
An encryption scheme is only as good as the password that protects it. That's the weakness in a symmetric password, where the encryption key is the same as the decryption key. If you are stubbornly paranoid, the ultimate in security probably lies in PGP or certificate-based encryption. On an everyday basis, this isn't a practical option unless you and your company are willing to migrate to PKZIP. That's why password length should be your primary concern.
Fortunately, math is our friend (seriously, it is). If you use the full ASCII character set, then your password strength is 94(password length), because every additional character makes a password 94 times more secure. By adding a few extra characters to your password, you're making it "computationally infeasible" for hackers to attempt a brute-force attack. If 7 298 831 534 994 528 possible combinations (in a one- to nine-character password) isn’t enough to make you comfortable, use a 10-character password, and give any hacker 699 823 827 359 474 784 combinations to try.
Based on our testing, you probably could hit a little over 3 million passwords per second against AES encryption using a pair of Radeon HD 6990s. That means it'd take 7397 years to perform a search of passwords from one to 10 characters long using AMD's Stream acceleration. Even if you could double your speed from there, it wouldn't be much help. To get under one year, you'd have to scale your efforts to 7397 machines working full-time.
In the future, it might be possible for the average user to access that class of parallel compute power. Distributed computing is the next step, and Parallel Password Recovery is already working on a way to enable GPU-accelerated processing across multiple clients.
For the time being, this shouldn't keep you up at night. As the old adage goes, "if there is a will, there is a way." Ever since there were locks, there were lock picks. If you want to keep something secure, you need to understand how easy (or difficult) it is to pick the lock. That's what password recovery tools do. Surprisingly, WinZip agrees with us on this. As Tom Vaughan, VP at WinZip states, "I view the makers of password recovery tools as white hats, not black hats. It’s the software that you don’t know about that should scare you (software developed by black hats that is faster or more capable of cracking security than you could have predicted)."
It might sound like we're selling up some bogeyman or disseminating information that shouldn't be "out there," but we hope you come away from this story with a reminder that you can’t buy the truly impressive software. Custom cryptography stuff always advances faster than what’s commercially available. So if you are bent out of shape on security, your password should follow these basic guidelines.
These rules will give you a fighting chance against password hackers. Hackers have an unlimited number of attempts to crack a password. So breaking encryption is really only a matter of time. That's why the security experts understand that the real goal is to deter access to relevant data. If it takes you 50 years to break into a WinZip archive that contains information about my stock trades last week, that information is no longer relevant. Create longer random passwords, and you can also enjoy that level of security and peace of mind.