Remote Physical Device Fingerprinting
Here’s the abstract:
We introduce the area of remote physical device fingerprinting, or fingerprinting a physical device, as opposed to an operating system or class of devices, remotely, and without the fingerprinted device’s known cooperation. We accomplish this goal by exploiting small, microscopic deviations in device hardware: clock skews. Our techniques do not require any modification to the fingerprinted devices. Our techniques report consistent measurements when the measurer is thousands of miles, multiple hops, and tens of milliseconds away from the fingerprinted device, and when the fingerprinted device is connected to the Internet from different locations and via different access technologies. Further, one can apply our passive and semi-passive techniques when the fingerprinted device is behind a NAT or firewall, and also when the device’s system time is maintained via NTP or SNTP. One can use our techniques to obtain information about whether two devices on the Internet, possibly shifted in time or IP addresses, are actually the same physical device. Example applications include: computer forensics; tracking, with some probability, a physical device as it connects to the Internet from different public access points; counting the number of devices behind a NAT even when the devices use constant or random IP IDs; remotely probing a block of addresses to determine if the addresses correspond to virtual hosts, e.g., as part of a virtual honeynet; and unanonymizing anonymized network traces.
And an article. Really nice work.
Filias Cupio • March 7, 2005 4:23 PM
I’ve only read the zdnet article, not the paper, but it looks like this technique determines a single number – clock skew. Describing it as a ‘fingerprint’ seems misleading – it is more like knowing the height of someone you’re looking for.
To know how useful this is as an identifier*, we’d need to know:
1) The precision of measurement of clock skew
2) The range of clock skews in the population of computers. (Technically, it is the ratio of (1) to (2) that matters)
3) The stability of the clock skew of a given computer.
Only (3) is (briefly) addressed in the ZDnet article. (And this all assumes no countermeasures are being taken, which may cease to be the case once this method becomes well known.)