# US 11,451,385 B2 · Biometric public key system providing revocable credentials

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- Number: US 11,451,385 B2
- Document ID: US11451385B2
- Status: Granted
- Kind: B2
- Application number: 16/775,711
- Filed: 2020-01-29
- Published: 2020-07-30
- Granted: 2022-09-20
- Earliest claimed: 2019-01-30
- Assignees: Badge Inc.
- Applicants: Badge Inc.
- Inventors: Charles H. Herder, III; Tina P. Srivastava
- Web page: https://patentgrep.com/patent/US11451385B2

## CPC

- H04L 9/0866: {involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics}
- G06V 40/1335: {Combining adjacent partial images (e.g. slices) to create a composite input or reference pattern; Tracking a sweeping finger movement}
- G06V 40/1347: {Preprocessing; Feature extraction}
- G06V 40/1365: {Matching; Classification}
- H04L 9/0825: {using asymmetric-key encryption or public key infrastructure [PKI], e.g. key signature or public key certificates}
- H04L 9/0891: {Revocation or update of secret information, e.g. encryption key update or rekeying}
- H04L 9/0894: {Escrow, recovery or storing of secret information, e.g. secret key escrow or cryptographic key storage}
- H04L 9/3228: {One-time or temporary data, i.e. information which is sent for every authentication or authorization, e.g. one-time-password, one-time-token or one-time-key}
- H04L 9/3231: {Biological data, e.g. fingerprint, voice or retina (network architectures or network communication protocols for supporting authentication of entities using biometrical features in a packet data network H04L63/0861)}
- H04L 9/3239: {involving non-keyed hash functions, e.g. modification detection codes [MDCs], MD5, SHA or RIPEMD}
- H04L 63/0428: {wherein the data content is protected, e.g. by encrypting or encapsulating the payload}
- H04L 63/0861: {using biometrical features, e.g. fingerprint, retina-scan (cryptographic mechanisms or cryptographic arrangements for entity authentication using biological data H04L9/3231)}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G06V: IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING

## Abstract

A device generates a biometric public key for an individual based on both the individual's biometric data and a secret S, in a manner that verifiably characterizes both while tending to prevent recovery of either. The biometric data has a Sparse Representation and is encoded in a manner to include a component of noise, such that it is challenging to identify which locations are actually encoded features. Accordingly, the biometric data are encoded as a vector by choosing marker at locations where features are present and, where features are not present, choosing noisy data. The noisy data may be chaff bit values selected collectively from a group of (a) random values and (b) independent and identically distributed values. The biometric public key may be later used to authenticate a subject purporting to be the individual, using a computing facility that need not rely on a hardware root of trust.

## Claims

### Claim 1

A device for generating a biometric public key for an individual based on biometric data of the individual, without the need for non-transient storage of the biometric data, the device comprising:
a transducer; and
a computing facility, coupled to the transducer, the computing facility including a computing processor and a non-transitory computer readable storage medium encoded with instructions that, when executed by the computing processor, establish computer processes comprising:
receiving by the computing facility, from the transducer, a digital electronic signal that characterizes a biometric of the individual;
extracting by the computing facility, from the digital electronic signal, a set of biometric values of the individual;
identifying, in the set of biometric values, locations where features are present;
encoding the set of biometric values by choosing a marker at locations where features are present and, where features are not present, choosing noisy data;
generating by the computing facility a secret number S;
computing by the computing facility the biometric public key B based on the secret number and the encoded set of biometric values, wherein the biometric public key verifiably characterizes both the biometric data of the individual and the secret number without the need for non-transient storage of either the biometric data of the individual or the secret number; and
storing the biometric public key in a storage facility.

### Claim 2 (depends on 1)

A device according to claim 1, wherein the set of biometric values of the individual has a Sparse Representation.

### Claim 3 (depends on 1)

A device according to claim 1, wherein the encoded set of biometric values is a column vector E having N bits.

### Claim 4 (depends on 1)

A device according to claim 1, wherein the secret number S is a secret column vector of N bits.

### Claim 5 (depends on 1)

A device according to claim 1, wherein generating the secret number S includes computing and storing a hash F(S) of the secret number S in the storage facility.

### Claim 6 (depends on 1)

A device according to claim 1, wherein the biometric public key B is computed using a matrix A having M rows and N columns of bits, and matrix A is stored in the storage facility.

### Claim 7 (depends on 6)

A device according to claim 6, wherein the biometric public key B is computed by multiplying the secret number S and the matrix A, and adding a column vector E of the encoded set of biometric values.

### Claim 8 (depends on 1)

A device according to claim 1, wherein the marker is a constant value.

### Claim 9 (depends on 8)

A device according to claim 8, wherein the marker is “0”.

### Claim 10 (depends on 1)

A device according to claim 1, wherein the noisy data is a set of chaff bit values selected collectively from a group of (a) random values and (b) independent and identically distributed values.

### Claim 11

A device for using biometric data to authenticate a subject as an individual whose biometric data has been previously obtained using a first transducer, without the need for non-transient storage of the biometric data, the device comprising:
a second transducer; and
a computing facility that is coupled to the second transducer, the computing facility including a computing processor and a non-transitory computer readable storage medium encoded with instructions that, when executed by the computing processor, establish computer processes comprising:
receiving by the computing facility, from the second transducer, a digital electronic signal that characterizes a biometric of the subject;
extracting by the computing facility, from the digital electronic signal, (a) a set of biometric values of the subject and (b), for each member of the set of biometric values of the subject, a confidence value indicating a degree of confidence that the corresponding biometric value is stable between characterizations;
encoding the set of biometric values of the subject;
using the confidence values to select, by the computing facility, a confident subset of the encoded set of biometric values of the subject, the confident subset being a reliable discriminant of the identity of the subject based on the biometric;
receiving, by the computing facility, from a storage facility, (i) a hash F(S) of a secret number S and (ii) a biometric public key B that was computed based on the secret number S and the biometric data of the individual that has been previously obtained using the first transducer, wherein the biometric data of the individual had been encoded to have a marker at locations where features are present and, where features are not present, to have noisy data;
computing, by the computing facility, a candidate value S′ for the secret number S using the biometric public key and the confident subset; and
performing an authentication process by determining whether the candidate value S′ is deemed equivalent to the secret number S.

### Claim 12 (depends on 11)

A device according to claim 11, wherein the biometric data of the individual has a Sparse Representation.

### Claim 13 (depends on 11)

A device according to claim 11, wherein the encoded set of biometric values of the subject is a column vector E′ having M bits.

### Claim 14 (depends on 11)

A device according to claim 11, wherein the encoded biometric data of the individual is a column vector E having N bits.

### Claim 15 (depends on 11)

A device according to claim 11, wherein (a) the secret number S is a first secret column vector of N bits and (b) the candidate value for the secret number S′ is a second column vector of N bits.

### Claim 16 (depends on 11)

A device according to claim 11, wherein the computer processes further comprise:
receiving, by the computing facility, from the storage facility, a matrix A having M rows and N columns of bits, wherein the biometric public key B was computed based on the matrix A.

### Claim 17 (depends on 16)

A device according to claim 16, wherein the candidate value for the secret number S′ is computed by (a) multiplying the inverse of the matrix A with (b) the difference between the biometric public key and the confident subset of column vector E′ of the encoded set of biometric values of the subject.

### Claim 18 (depends on 11)

A device according to claim 11, wherein the computer processes further comprise:
computing a hash F(S′) of the candidate value for the secret number S′; and
performing the authentication process by determining whether (a) the hash F(S′) of the candidate value for the secret number S′ is deemed equivalent to (b) the hash F(S) of the secret number S.

### Claim 19 (depends on 11)

A device according to claim 11, wherein the set of biometric values of the subject is encoded to have the marker at locations where features are present and, where features are not present, to have noisy data.

### Claim 20 (depends on 11)

A device according to claim 11, wherein the marker is a constant value.

### Claim 21 (depends on 20)

A device according to claim 20, wherein the marker is “0”.

### Claim 22 (depends on 11)

A device according to claim 11, wherein the noisy data is a set of chaff bit values selected collectively from a group of (a) random values and (b) independent and identically distributed values.