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    Saturday, September 27, 2008

    Silicon Biometrics : The OCV Authentication Solution

    I never thought I'd say this ever: There's finally a reason to appreciate OCV and we can all thank Verayo for it. In one of my earlier posts, I wrote about the growing problem of counterfeit ASICs (Will The Real ASIC Please Stand Up?)The variation of on-die device and metal parameters that is the bane of designers all over the globe has turned out to be useful in the most unique way. OCV, it seems, is the silicon equivalent of a fingerprint. Let us review the salient points about OCV:

    • On-die variations are always present in all devices
    • Although on-die variations obey statistics, individual variations are essentially random
    • The OCV solution space is huge. Assume that a single transitor can be one of a types and a single net can be any one of b types. If you have x transistors and n nets, a single ASIC can be any one of a *b * c *d possibilities.
    • The probability of two ASICs having the exact same characteristics is so small, it is essentially zero.
    The existence of OCV is half the solution. It sort of like saying I can uniquely identify a grain of sand by the fact that each of its trillion odd molecules is differently positioned when compared to any other grain of sand. For the solution to be complete, there has to be a feasible way of measuring OCV for a given device or its effects. Hmm, Why do I worry about OCV? what's the worst that can happen? I'm guessing the phrase "timing violations" are flashing in six foot neon letters in your head right about now.

    By creating a circuit with lots of reconvergent logic with very low (or zero margins) margin setup and hold paths, you can observe the effects of OCV. The values captured at the output will not only change with each device but also change with the input stimulus. Depending on the stimulus, the path taken through the reconvergent cone may or may not suffer from a timing violation. By observing the outputs for a set of random stimuli, each device can be uniquely identified.

    If you want to know more about this technology, it's official name is "Physically Unclonable Functions(PUF)" . For the academically oriented, the home page of Professor Srini Devadas (MIT/ Verayo Co-founder) has download links for all his published PUF papers.

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