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Rather than try to crack the working of the hardware itself, a researcher named Kevin Devine discovered the Thomson algorithm by targeting the setup utility provided on the CD accompanying the device.
He found that a hashed version of the router’s serial number is generated, which then derives both the default SSID and the default encryption key.
Devine gave a high-level overview of the algorithm within the source code of his program stkeys:
Take as example: “CP0615JT109 (53)”
Remove the CC and PP values: CP0615109
Convert the “xxx” values to hexadecimal: CP0615313039
Process with SHA-1: 742da831d2b657fa53d347301ec610e1ebf8a3d0
The last 3 bytes are converted to 6 byte string, and appended to the word “Bigond” which becomes the default SSID: BigPondF8A3D0
The first 5 bytes are converted to a 10 byte string which becomes the default WEP/WPA key: 742DA831D2
It then becomes a matter of effort to brute-force possible serial numbers to find possible passwords for a given default SSID. This is what Devine’s stkeys tool does.
For a unit shipped to hundreds of thousands of homes within the country, the ability to narrow down the number of possible WPA keys to only two with just a matter of time is disturbing and remarkable.
Another security researcher has made tools based on stkeys to speed up the process using a pre-generated table of SSID to keys, meaning the crack becomes merely a lookup rather than a brute-force process. His tool also automatically applies each key to the WiFi network until the valid password is identified.
Although he declined to publish his code it is easy to imagine the possible harm if a fast and completely automated Speedtouch cracking tool were to become available to all and sundry.
Of course, you can still test your own network, just for informational purposes you understand, by using Devine’s stkeys or this dead simple Python script by Stavros aka Poromenos.
What’s the lesson? Never be lulled into a false sense of security when it comes to your home network. Just because a shiny card comes with your box that says “keep this card safe” you absolutely must set your own SSID and WPA key.
