Sensor secured by physical unclonable function (PUF)
A secure sensor responsive to a physical or environmental phenomenon may include two electrical components connected to a voltage source and may include an analog comparator connected to the two components. The output of the comparator represents one bit of a key. An A/D converter may be connected to an opposing side of one of the components where the A/D converter output is related by a coefficient of the component's characteristic to a physical phenomenon. The components may have the same nominal value. The components and the A/D converter may be encased in a package configured to inhibit inspection and discovery.
1 . A method for generating a secure output comprising the steps of:
providing a plurality of electrical circuits each characterized by electrical components having electrical characteristics based in part on physical properties that are not practically predictable and not practically cloneable wherein each electrical circuit has a first output based in part on said physical properties that are not practically predictable and not practically cloneable and one or more of said electrical circuits has a second output representing a physical phenomenon;
generating a key having a plurality of bits where each bit is based on said first output of a subset of said electrical circuits;
sampling said second output of one or more of said electrical circuits and converting said second output to a digital representation of said physical phenomenon wherein said electrical circuits are used to generate said key and wherein said first output of said one or more electrical circuits and said second output of said one or more of said electrical circuits are dependent on a common component of at least one of said electrical components having electrical characteristics based in part on physical properties that are not practically predictable and not practically cloneable of said subset of electrical circuits; and
using said key to digitally sign said digital representation of said physical phenomenon.
2 . The method for generating a secure output according to claim 1 wherein said secure output is a temperature reading, said electrical circuits include at least one thermistor, and said physical phenomenon is temperature.
3 . The method of generating a secure output according to claim 1 wherein said key is used to generate at least one key of an asymmetric key pair.
4 . The method for generating a secure output according to claim 3 further comprising the steps of:
accumulating a plurality of digitally signed digital representations of said physical phenomenon and storing a time stamp associated with said digitally signed digital representations of said physical phenomenon in a storage device.