How it works
Like most flash drives, the primary components of this flash drive consist of a USB controller and the flash memory itself. In this case the USB controller is internally designed by SanDisk to fit the need for this Cruzer Profile Flash Drive and the memory used is a Multi Level Cell, or MLC, NAND flash memory type, also designed by SanDisk. This flash drive has something added on top of what the regular flash drives have in terms components; it's the biometric security or fingerprint scanning. That part of this flash drive is licensed from a company named UPEK. Here is what I found on their website on the Cruzer Profile and fingerprint scanning. "SanDisk’s Cruzer® Profile USB flash drive incorporates UPEK’s TouchStrip™ Fingerprint Authentication Solution to protect user data and enables portable access to password-protected applications and websites with the swipe of a finger..." "...UPEK’s TouchStrip Fingerprint Authentication Solution enables the SanDisk Cruzer Profile to ensure that authorized users gain access and unauthorized users are denied access by leveraging the accurate sensing capability of UPEK’s patented active capacitive sensing technology. UPEK’s embedded chipset also enables the security of on-drive authentication by performing storage and matching at the hardware level and eliminating the vulnerability of data transfer to the host PC."
As you can see the security processing is done by an embedded chipset, which should explain why there the drive is quick to scan your fingerprints. It also means that fingerprint ID truly locks and unlocks the drive and doesn't encrypt data on the fly.
The site contains more information on how active capacitive sensing works. Look at the following exurbs to see what it does. The picture shows a sensor cell or pixel extremely enlarged.
"Each sensor cell (pixel) contains an active capacitive feedback circuit whose effective feedback capacitance is modulated by the presence of live skin close to the surface of the sensor. This active sensing approach provides much higher immunity to parasitic effects...."  "...The surface of each pixel is composed of two adjacent metal plates, which are separated from the skin and the environment by an ultra-hard protective coating. These sensor plates create a fringing capacitance between them whose field lines extend beyond the surface of the silicon. When live skin is brought in close proximity to the sensor plates, the skin interferes with field lines between the two plates and reduces the effective capacitance between them. When the skin is on the sensor surface (fingerprint ridge) the feedback capacitance is minimized, while when the skin is far from the sensor surface (fingerprint valley) the feedback capacitance is maximized..."
So by placing your finger on the sensor you effectively change the value of the capacitor that makes up the sensor and because your fingerprint has ridges and valleys, those values change a lot. This in turn means that you get a lot of data from a fingerprint and that data can then be used as a unique image or fingerprint scan. It's not like opening or closing an electric circuit because those values could only be 'open' or 'closed' and the protective coating prevents that, it's actually sensing depth in ridges and valleys and that makes it so much more accurate.
If you would like to read about USB drives in general or about the components themselves you can use the links I have used to research this information. Check out the links below to find the information.
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