Sensor with signature of data relating to sensor

• US 6,708,049 B1
• Filed: 09/14/2000
• Issued: 03/16/2004
• Est. Priority Date: 09/28/1999
• Status: Expired due to Term

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Fein, Michael E., Mannheimer, Paul D., Porges, Charles E., Olson, Bryan, Schloemer, David, Berson, Thomas A.
• Primary Examiner(s): Hindenburg, Max F.
• Assistant Examiner(s): KREMER, MATTHEW J
• Application Number:
  US09/662,246
• Time in Patent Office: 1,279 Days
• Field of Search: 600/309-310, 600/322-324, 600/331, 356/39-41
• US Class Current: 600/323
• CPC Class Codes: A61B 2562/08 Sensors provided with means for identification, e.g. barcodes or memory chips
• CPC Class Codes: A61B 2562/085 combined with means for recording calibration data
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: G06F 21/6209 to a single file or object, e.g. in a secure envelope, encrypted and accessed using a key, or with access control rules appended to the object itself
• CPC Class Codes: G06F 21/64 Protecting data integrity, e.g. using checksums, certificates or signatures
• CPC Class Codes: G06F 2211/008 Public Key, Asymmetric Key, Asymmetric Encryption
• CPC Class Codes: G06F 2221/2107 File encryption
• CPC Class Codes: H04L 2209/805 Lightweight hardware, e.g. radio-frequency identification [RFID] or sensor
• CPC Class Codes: H04L 2209/88 Medical equipments
• CPC Class Codes: H04L 9/3247 involving digital signatures

Abstract

A sensor has codes useful for a monitor which can be authenticated as accurate. The sensor produces a signal corresponding to a measured physiological characteristic and provides codes which can be assured of being accurate and authentic when used by a monitor. A memory associated with the sensor stores both data relating to the sensor and a digital signature. The digital signature authenticates the quality of the code by ensuring it was generated by an entity having predetermined quality controls, and ensures the code is accurate.

Claims

1. A pulse oximeter apparatus comprising:

a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic;

a memory associated with the sensor and located external to a monitor which receives the sensor signal, said memory containing data relating to said sensor and containing a digital signature,

wherein at least a first portion of said data is contained within said digital signature,

wherein a second portion of said data is outside said digital signature and is masked using a symmetric key contained within the digital signature.

2. The apparatus of claim 1, said memory containing a hash function digest of a portion of said data to be signed, said digest being contained within said digital signature.

3. The apparatus of claim 2, wherein said symmetric key is derivable from said digest.

4. The apparatus of claim 3, wherein a third portion of said data is unmasked and is outside said digital signature, said digest being created from said first, second, and third portions.

6. The apparatus of claim 2 wherein a message digest is contained within the signature for authenticating an accuracy of at least some of the data.

5. A pulse oximeter apparatus comprising:

a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic;

a memory associated with the sensor and located external to a monitor which receives the sensor signal, said memory containing data relating to said sensor and containing a digital signature,

wherein said data includes masked data outside said signature, and a symmetric key for decoding the masked data, the symmetric key being contained within said digital signature.

7. A pulse oximeter apparatus comprising:

a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic;

a memory associated with the sensor and located external to a monitor which receives the sensor signal, said memory containing data relating to said sensor and containing a digital signature,

wherein a field of said data includes a mandatory/optional bit flag, said flag indicating whether knowledge of how to use said field of data by a monitor reading said memory is mandatory for operations of the monitor with said sensor.

8. A pulse oximeter apparatus comprising:

a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic;

a memory associated with the sensor and located external to a monitor which receives the sensor signal, said memory containing data relating to said sensor and containing a digital signature,

wherein said sensor is a pulse oximeter sensor, and at least a portion of said data is contained within said signature, said portion including at least,one of saturation calculation coefficients, sensor OFF thresholds, and thermistor calibration coefficients.

9. The apparatus of claim 8 wherein said data also includes at least one of a date of manufacture, a lot code, a bad sensor flag, manufacturing component test data, LED forward V/I characteristics, LED optical power characteristics, detector efficiency characteristic, maximum safe LED power, sensor data set revision level, write once/write many flag, page size, number of pages, sensor model type, maximum number of recycle events, and adult/neonatal query flag.

10. A method for creating a digital signature in a pulse oximeter apparatus including a memory associated with a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic, said method comprising:

signing at least a portion of data relating to said sensor to create a digital signature;

storing said digital signature in said memory;

storing data relating to said sensor in said memory; and

a program for verifying and authenticating the signature by reading a message derived from the memory digital data, creating a first digest from the message, and comparing for identity the first digest with a second digest contained within the digital signature.

11. A method for creating a digital signature in a pulse oximeter apparatus including a memory associated with a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic, said method comprising:

signing at least a portion of data relating to said sensor to create a digital signature;

storing said digital signature in said memory;

storing data relating to said sensor in said memory; and

wherein a second portion of said data is outside said digital signature and is masked using a symmetric key.

12. The method of claim 11, further comprising creating a hash function digest of a portion of said data to be signed, said digest being contained within said digital signature.

13. The method of claim 11, wherein said symmetric key is derivable from said digest.

14. The method of claim 13, wherein a third portion of said data is unmasked and is outside said digital signature, said digest being created from said first, second, and third data portions.

15. A method for operating a sensor, comprising:

storing at least one field of data in a memory associated with said sensor;

storing a mandatory/optional flag within said field of data;

reading said flag with a sensor reader;

if said sensor reader does not recognize said field of data and said flag indicates the field is optional, ignoring said field of data; and

if said sensor reader does not recognize said field of data and said flag indicates the field is mandatory, producing an error signal indicating inability to use said sensor.

16. The method of claim 15 further comprising:

storing a field length associated with said field;

reading said field length; and

skipping said field by using said field length if said sensor reader does not recognize said field and said flag indicates the field is optional.

17. An apparatus comprising:

a sensor having an output for providing a signal corresponding to a measured physiological characteristic;

a memory associated with the sensor and located external to a monitor which receives the sensor signal, said memory containing data relating to said sensor and containing a digital signature;

wherein at least a first portion of said data is contained within said digital signature; and

wherein a second portion of said data is outside said digital signature and is masked using a symmetric key contained within the digital signature.

18. A method for creating a digital signature in an apparatus including a memory associated with a sensor having an output for providing a signal corresponding to a measured physiological characteristic, said method comprising:

signing at least a portion of said data relating to said sensor to create a digital signature;

storing said digital signature in said memory;

storing data relating to said sensor in said memory;

wherein a portion of said data is outside said digital signature and is masked using a symmetric key.

19. A sensor reader comprising:

a housing;

a sensor input for receiving a signal from a sensor corresponding to a measured physiological characteristic;

a sensor processing circuit coupled to said sensor input;

a memory input for receiving digital data stored in a memory associated with said sensor, said digital data including a digital signature;

a first sensor reader memory coupled to said memory input for storing said digital data;

a second sensor reader memory storing a signature verification key;

a third sensor reader memory storing a program for verifying the digital signature of said digital data using said signature verification key and for unmasking a portion of data outside said digital signature using a symmetric key contained within the digital signature; and

a transfer circuit for providing at least a portion of said digital data to said sensor processing circuit.

20. A system comprising:

(a) a sensor apparatus including

a sensor, said sensor having an output for providing a signal corresponding to a measured physiological characteristic, and

a sensor memory associated with said sensor, said sensor memory having digital data relating to said sensor and having a digital signature, said digital signature being a signature of at least a portion of said data, wherein a second portion of said data is outside said digital signature and is masked using a symmetric key contained within the digital signature; and

(b) a sensor reader including

a sensor reader housing;

a sensor input for receiving said signal from said sensor corresponding to a measured physiological characteristic;

a sensor processing circuit coupled to said sensor input;

a memory input for receiving said digital data from said sensor memory;

a first sensor reader memory coupled to said memory input for storing said digital data;

a second sensor reader memory storing a signature verification key; and

a third sensor reader memory storing a program for verifying said digital signature using said signature verification key and for unmasking a portion of data outside said digital signature using a symmetric key contained within the digital signature.

21. A pulse oximeter apparatus comprising:

a pulse oximeter sensor having an output for providing a signal corresponding to a measured physiological characteristic;

a memory associated with the sensor and located external to a monitor which receives the sensor signal, said memory containing data relating to said sensor and containing a digital signature;

wherein said data includes a sensor OFF threshold, for indicating if the sensor is off a patient.