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Wi-Fi Security: Cracking WPA With CPUs, GPUs, And The Cloud

CPU-Based Cracking: Like Watching Paint Dry

Wireless Security Auditor: i5-2500k

If the guy trying to get into your network is only armed with a conventional desktop processor, don't fret about the security of your WPA-protected network. Those 16 388 SHA1 transformation invocations really bog down brute-force attacks. While we were able to crack WinZip archives at 20 million passwords per second in our previous piece, we're only able to manage about 5000 against WPA using an Intel Core i5-2500K.

Total Search Time Search, Assuming 5000 WPA Passwords/SecondPasswords Between 1 and 4 CharactersPasswords Between 1 and 6 CharactersPasswords Between 1 and 8 CharactersPasswords Between 1 and 12 Characters
NumbersInstant4 minutes6.5 hours7.5 years
Lower-case2 minutes18 hours1.5 years662 263 years
Alphanumeric (including Upper-case)52 minutes140 days1481 yearsNext Big Bang
All (Printable) ASCII characters5 hours5 years48 644.66 yearsNext Big Bang

How's this for a sense of futility? There's really no way to brute-force an alphanumeric password longer than six characters using our Core i5 processor. If you're using the entire (printable) ASCII set, a WPA password longer than five characters is reasonably safe.

CoWPAtty: i5-2500k

The calculations above assume you're running WSA in Windows, because the Linux route yields slightly worse CPU performance. Using CoWPAtty and Pyrit, we're down to 3307 passwords per second.

3949.1 PMKs: Pyrit Benchmark on i5-2500k

In the pages to come, we're going to present two numbers from Linux: the result from Pyrit's benchmark command and the figure reported by CoWPAtty using the Pyrit pass-through function. The Pyrit benchmark command is commonly used to highlight GPU performance, but it doesn't figure in the last couple of transformations needed to go from PMK to PTK. There is some overhead there because the PMK-PTK conversion occurs outside of Pyrit.

CoWPAtty and Elcomsoft's Wireless Security Auditor test the speed at which master keys are checked against the PTK information contained within captured packets. As such, those are the real-world numbers you would see in mounting a brute-force attack against a WPA-protected network.