Point of sale terminal having pulsed current tamper control sensing

• US 7,551,098 B1
• Filed: 05/28/2005
• Issued: 06/23/2009
• Est. Priority Date: 05/28/2005
• Status: Active Grant

• Current Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Original Assignee: ZiLOG Incorporated (Littelfuse Incorporated)
• Inventors: Chock, Raymond O., Hess, Mark
• Primary Examiner(s): Lee; Benjamin C
• Assistant Examiner(s): NWUGO, OJIAKO K
• Application Number:
  US11/139,418
• Time in Patent Office: 1,487 Days
• Field of Search: 340/660, 340661-663, 340/652, 174/50, 174/520
• US Class Current: 340/660
• CPC Class Codes: G08B 29/08 Signalling of tampering with the line circuit

Abstract

A point of sale terminal includes a microcontroller integrated circuit. In one aspect, a regulator within the IC receives power from a supply voltage terminal and/or a battery terminal. If the regulator does not receive adequate power from either terminal, then energy stored on-chip in a capacitor is used to erase secure memory. In another aspect, pulses of current are made to pulse through conductors of a conductive mesh. A tamper condition is detected if an improper voltage is detected on the IC terminal through which the pulse is conducted. In another aspect, each vendor signs his/her firmware with his own vendor ID. A bootloader uses the vendor ID to lookup a public key that is then used to verify a private key supplied by the firmware to be executed. In another aspect, a magnetic card reader includes a digital peak detector circuit involving programmable positive and negative thresholds.

Claims

1. A point of sale terminal, comprising:

a tamper conductive mesh comprising a plurality of wire pairs; and

an integrated circuit including a processor, a tamper detect circuit and a tamper detect terminal, wherein the tamper conductive mesh is connected to the tamper detect terminal, the tamper detect circuit including a current source and causing a pulse of current to flow through the current source and through the tamper detect terminal and through the tamper conductive mesh, the tamper detect circuit determining whether when the pulse of current is flowing a voltage on the tamper detect terminal is both below a predetermined upper bias voltage and above a predetermined lower bias voltage indicative of tampering by alteration of the conductive mesh pairs.

2. The point of sale terminal of claim 1, wherein the pulse of current flows through the tamper conductive mesh, to the tamper detect terminal, into the integrated circuit and through the current source.

3. The point of sale terminal of claim 1, wherein the pulse of current flows through the current source, to the tamper detect terminal, out of the integrated circuit and through the tamper conductive mesh.

4. The point of sale terminal of claim 1, wherein the tamper detect circuit includes a comparator that compares the voltage on the tamper detect terminal to the predetermined upper bias voltage, wherein the predetermined upper bias voltage is programmable by the processor.

5. The point of sale terminal of claim 1, wherein the pulse of current flows only for a very small proportion of total time.

6. The point of sale terminal of claim 1, wherein the pulse of current starts at a first time, and wherein the integrated circuit samples the voltage on the tamper detect terminal at a second time after the first time, and wherein a time difference between the first time and the second time is programmable by the processor.

7. The point of sale terminal of claim 1, wherein each of the plurality of wire pairs extends in a serpentine fashion in parallel with one another across the top of a microcontroller.

8. The point of sale terminal of claim 1, further comprising:

a resistor coupled to the tamper conductive mesh, wherein the pulse of current flows through the resistor, through the tamper conductive mesh, to the tamper detect terminal, and into the integrated circuit.

9. The point of sale terminal of claim 1, further comprising:

a resistor coupled to the tamper conductive mesh, wherein the pulse of current flows through the current source, to the tamper detect terminal, out of the integrated circuit, through the tamper conductive mesh and through the resistor.

10. A point of sale terminal, comprising:

a tamper conductive mesh comprising a plurality of wire pairs; and

an integrated circuit including a processor, a tamper detect circuit, a first register and a tamper detect terminal, wherein the tamper conductive mesh is connected to the tamper detect terminal, the tamper detect circuit including a current source and causing a pulse of current to flow through the current source and through the tamper detect terminal and through the tamper conductive mesh, wherein the pulse of current starts at a first time, wherein the integrated circuit samples the voltage on the tamper detect terminal at a second time after the first time, wherein a time difference between the first time and the second time is programmable by the processor, wherein the time difference between the first time and the second time is a function of a value stored in the first register, and wherein the tamper detect circuit determines whether a voltage on the tamper detect terminal is in a predetermined acceptable range when the pulse of current is flowing indicative of tampering by alteration of the conductive mesh pairs.

11. The point of sale terminal of claim 10, wherein the pulse of current ends at a third time, and wherein the integrated circuit samples a voltage on the tamper detect terminal at a fourth time after the third time, and wherein a time difference between the third time and the fourth time is programmable by the processor.

12. The point of sale terminal of claim 11, wherein the integrated circuit includes a second register, wherein the time difference between the third time and the fourth time is a function of a value stored in the second register.

13. A point of sale terminal, comprising:

a tamper conductive mesh comprising a plurality of wire pairs; and

an integrated circuit including a processor, a tamper detect circuit and a tamper detect terminal, wherein the tamper conductive mesh is connected to the tamper detect terminal, the tamper detect circuit including a current source and causing a pulse of current to flow through the current source and through the tamper detect terminal and through the tamper conductive mesh, the tamper detect circuit determining whether a voltage on the tamper detect terminal is in a predetermined acceptable range when the pulse of current is flowing, and wherein said determining involves comparing the voltage on the tamper detect terminal to a first programmable bias voltage and also involves comparing the voltage on the tamper detect terminal to a second programmable bias voltage indicative of tampering by alteration of the conductive mesh pairs.

14. A point of sale terminal, comprising:

a tamper conductive mesh comprising a plurality of wire pairs; and

an integrated circuit including a processor, a tamper detect circuit and a tamper detect terminal, wherein the tamper conductive mesh is connected to the tamper detect terminal, the tamper detect circuit including a current source and causing a pulse of current to flow through the current source and through the tamper detect terminal and through the tamper conductive mesh, wherein the tamper detect circuit determines whether a voltage on the tamper detect terminal is in a predetermined acceptable range when the pulse of current is flowing, and wherein the tamper detect circuit also determines whether a voltage on the tamper detect terminal is in a second predetermined acceptable range when the pulse of current is not flowing indicative of tampering by alteration of the conductive mesh pairs.

15. A method comprising:

(a) storing a first value and a second value in an integrated circuit;

(b) starting to draw a pulse of current through a tamper detect terminal and into the integrated circuit, the pulse starting at a first time, the tamper detect terminal connected to a tamper conductive mesh responsive to a tampering event;

(c) at a second time, after the first time and while the pulse is being drawn, sampling a voltage on the tamper detect terminal and determining whether the voltage is in a first acceptable voltage range, wherein a time difference between the first time and the second time is at least in part determined by the first value;

(d) stopping the pulse of current at a third time;

(e) at a fourth time after the third time sampling a voltage on the tamper detect terminal and determining whether the voltage is in a second acceptable voltage range, wherein a time difference between the third time and the fourth time is at least in part determined by the second value; and

(f) detecting the tampering event based on (c) and (e).

16. The method of claim 15, wherein the integrated circuit includes a processor and a tamper detect circuit, wherein the first and second values are stored in the tamper detect circuit, and wherein the processor can change the first and second values that are stored in the tamper detect circuit.

17. The method of claim 15, wherein the voltage is determined in (c) to be in the first acceptable range by comparing the voltage to a first bias voltage and by comparing the voltage to a second bias voltage, and the voltage is determined in (e) to be in the second acceptable range by comparing the voltage to a third bias voltage and by comparing the voltage to a fourth bias voltage.

18. The method of claim 17, wherein the integrated circuit includes a processor, and wherein the first, second, third and fourth bias voltages are programmable by the processor.

19. The method of claim 15, wherein the integrated circuit includes a processor, wherein the time difference between the first time and the second time is programmable by the processor, and wherein the time difference between the third time and the fourth time is programmable by the processor.

20. The method of claim 15, wherein the tamper detect terminal is coupled to a comparator, wherein the comparator compares the voltage on the tamper detect terminal to a bias voltage, and wherein the voltage on the tamper detect terminal is determined to be in the first acceptable voltage range by comparing the bias voltage to the voltage on the tamper detect terminal.

21. The method of claim 15, wherein a current source draws the pulse of current by sinking a magnitude of current, wherein after the pulse of current starts at the first time, the voltage on the tamper detect terminal falls exponentially based on the magnitude of current sunk by the current source.

22. A point of sale terminal, comprising:

a tamper conductive mesh comprising a plurality of wire parts; and

an integrated circuit including a processor, a tamper detect circuit and a tamper detect terminal, wherein the tamper detect terminal is coupled to an inverting input lead of a first comparator and to a non-inverting input lead of a second comparator, wherein the tamper conductive mesh is connected to the tamper detect terminal, the tamper detect circuit including a current source and causing a pulse of current to flow through the current source and through the tamper detect terminal and through the tamper conductive mesh, the tamper detect circuit determining whether a voltage on the tamper detect terminal is in a predetermined acceptable range when the pulse of current is flowing indicative of tampering by alteration of the conductive mesh pairs.

23. The point of sale terminal of claim 22, wherein the tamper detect terminal is coupled to the current source.