# US 11,741,242 B2 · Cryptographic pseudonym mapping method, computer system computer program and computer-readable medium

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- Number: US 11,741,242 B2
- Document ID: US11741242B2
- Status: Granted
- Kind: B2
- Application number: 17/901,328
- Filed: 2022-09-01
- Published: 2022-12-29
- Granted: 2023-08-29
- Earliest claimed: 2019-07-15
- Assignees: Xtendr Zrt.
- Applicants: Xtendr Zrt.
- Inventors: Ferenc Vágujhelyi; Gergely Vágujhelyi
- Web page: https://patentgrep.com/patent/US11741242B2

## CPC

- G06F 21/602: {Providing cryptographic facilities or services}
- H04L 9/0866: {involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics}
- G06F 16/211: {Schema design and management}
- H04L 9/0825: {using asymmetric-key encryption or public key infrastructure [PKI], e.g. key signature or public key certificates}
- H04L 9/0861: {Generation of secret information including derivation or calculation of cryptographic keys or passwords}
- H04L 9/0897: {involving additional devices, e.g. trusted platform module [TPM], smartcard or USB}
- H04L 9/302: {involving the integer factorization problem, e.g. RSA or quadratic sieve [QS] schemes}
- H04L 9/3066: {involving algebraic varieties, e.g. elliptic or hyper-elliptic curves}
- H04L 2209/42: Anonymization, e.g. involving pseudonyms
- H04L 2209/76: Proxy, i.e. using intermediary entity to perform cryptographic operations
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

The invention is a cryptographic pseudonym mapping method for an anonymous data sharing system, the method being adapted for generating a pseudonymised database (DB) from data relating to entities and originating from data sources (DSi), wherein the data are identified at the data sources (DSi) by entity identifiers (D) of the respective entities, and wherein the data are identified in the pseudonymised database (DB) by pseudonyms (P) assigned to the respective entity identifiers (D) applying a one-to-one mapping, irrespective of the originating data source. According to the invention, one mapper (M) and one key manager (KM) are applied, and a respective pseudonym (P) is generated by the mapper (M), for each encrypted entity identifier (Ci) encrypted by the data source (DSi), utilizing the mapping cryptographic key (hi) corresponding to the particular data base (DSi).

## Claims

### Claim 1

A cryptographic pseudonym mapping method for an anonymous data sharing system, the method being adapted for generating a pseudonymised database (DB) from data relating to entities and originating from data sources (DSi), wherein the data are identified at the data sources (DSi) by entity identifiers (D) of the respective entities, and wherein the data are identified in the pseudonymised database (DB) by pseudonyms (P),
characterised in that
the pseudonyms (P) are assigned to the respective entity identifiers (D) applying a one-to-one mapping, irrespective of the originating data source, by
applying one mapper (M) and one key manager (KM),
wherein the key manager (KM) is applied for
selecting a secret element (b) from a predetermined algebraic structure constituting a multiplicative or additive cyclic group,
selecting, for each data source (DSi) an element (ei, ai) to be applied as a cryptographic key by the given data source (DSi), from the algebraic structure and sending it to the given data source (DSi) while the element (ei, ai) is kept secret,
calculating an inverse (di) of the element (ei, ai) in the given algebraic structure, and using it, together with the secret element (b), for generating a mapping cryptographic key (hi) of the mapper (M), the mapping cryptographic key (hi) corresponding to the given data source (DSi), and sending the mapping cryptographic key (hi) to the mapper (M) while keeping it secret and assigned to the given data source (DSi),
transforming by the data source (DSi), each entity identifier (D) to be mapped, into a respective encrypted entity identifier (Ci) by using the element (ei, ai) to be applied as a cryptographic key, and
a respective pseudonym (P) is generated by the mapper (M), for each encrypted entity identifier (Ci) encrypted by the data source (DSi), utilizing the mapping cryptographic key (hi) corresponding to the particular data source (DSi).

### Claim 2 (depends on 1)

The method of claim 1, characterised by applying an algebraic structure constituting a multiplicative cyclic group, wherein values selected by the key manager (KM) are represented by residue classes modulo N, for which algebraic structure constants N=p·q, φ(N)=(p−1)·(q−1) are predetermined, wherein p and q are randomly selected prime numbers, the secret element (b) is a randomly selected prime number, and φ(N) is the value of the Euler function obtained for N,
the element (ei) to be applied as the own cryptographic key of the data source (DSi) is randomly selected by the key manager (KM),
the key manager (KM) is applied for computing the inverse (di) of the element (ei) to be applied as a cryptographic key, for which the equation ei·di ≡1 mod φ(N) is satisfied,
then, the mapping cryptographic key hi=di·b is generated by the key manager (KM), and is sent to the mapper (M),
the encrypted entity identifier (Ci) is computed by the data source (DSi) utilizing the formula Ci=Dei mod N, and
the pseudonym (P) P=Cihi mod N is computed by the mapper (M).

### Claim 3 (depends on 2)

The method of claim 2, characterised in that the randomly selected prime numbers p and q can be represented utilizing half the number of bits of a chosen key size.

### Claim 4 (depends on 2)

The method of claim 2, characterised by sending to an authorised entity (A)
by the key manager (KM), the inverse (di) of the element (ei) to be applied as a cryptographic key,
by the mapper (M), the encrypted entity identifier (Ci).

### Claim 5 (depends on 1)

The method of claim 1, characterised by applying an algebraic structure constituting an additive cyclic group, wherein values are represented by points of elliptic curves defined over a number field of residue classes modulo p, where p is a prime number, for which algebraic structure the following constants are predetermined: the parameters A, B of the formula y2=x3+Ax+B mod p defining the points of an elliptic curve defined over the residue classes of the prime number p, and a point G of the curve that has an order q that is greater than the number of entity identifiers (D), a secret element (b) having a value chosen arbitrarily from among residue classes mod q,
the key manager (KM) is applied for randomly selecting, from among residue classes mod q, an element (ai) to be applied as a cryptographic key by the data source (DSi),
then, a mapping cryptographic key hi=ai+b is generated by the key manager (KM), and is sent to the mapper (M),
the encrypted entity identifier (Ci) is computed by the data source (DSi) utilizing the formula Ci=M⊕aiG, where operator ⊕ is the sum of the points of the elliptic curve, and
and the pseudonym (P) P=Ci ⊖hiG is calculated by the mapper (M), where A⊖B=A⊕(−B).

### Claim 6 (depends on 5)

The method of claim 5, characterised by passing on to an authorised entity (A)
by the key manager (KM), the inverse (di) of the element (ai) to be applied as a cryptographic key, and
by the mapper (M), the encrypted entity identifier (Ci).

### Claim 7

A computer system for cryptographic pseudonymisation, the system comprising:
data sources (DSi) comprising data by the entity identifiers (D) of the entities,
a pseudonymised database (DB), in which the data are identified by pseudonyms (P),
characterised in that
the pseudonyms (P) are assigned to the respective entity identifiers (D) applying a one-to-one mapping, irrespective of the originating data source, and
the system further comprises
a mapper (M) and a key manager (KM),
a module adapted for selecting, applying the key manager (KM), a secret element (b) from a predetermined algebraic structure constituting a multiplicative or an additive cyclic group,
a module adapted for selecting from the algebraic structure, applying the key manager (KM), for each data source (DSi), an element (ei, ai) to be applied as a cryptographic key by the given data source (DSi), and for sending it to the given data source (DSi) while the element (ei, ai) is kept secret,
a module adapted for computing, applying the key manager (KM), an inverse (di) of the element (ei, ai) in the given algebraic structure, for generating, by using said inverse (di), together with the secret element (b), a mapping cryptographic key (hi) of the mapper (M) corresponding to the given data source (DSi), and for sending said mapping cryptographic key (hi) to the mapper (M) while keeping it secret and assigned to the given data source (DSi),
a module adapted for transforming, applying the data source (DSi), each entity identifier (D) to be mapped into a respective encrypted entity identifier (Ci) utilizing the element (ei, ai) to be applied as a cryptographic key, and
a module adapted for mapping, applying the mapper (M), each encrypted entity identifier (Ci) encrypted by the data source (DSi) utilizing the mapping cryptographic key (hi) corresponding to the particular data source (DSi) into a respective pseudonym (P).

### Claim 8 (depends on 7)

The computer system of claim 7, characterised in that it comprises modules adapted for performing a cryptographic pseudonym mapping method for an anonymous data sharing system, the method being adapted for generating a pseudonymised database (DB) from data relating to entities and originating from data sources (DSi), wherein the data are identified at the data sources (DSi) by entity identifiers (D) of the respective entities, and wherein the data are identified in the pseudonymised database (DB) by pseudonyms (P),
characterised in that
the pseudonyms (P) are assigned to the respective entity identifiers (D) applying a one-to-one mapping, irrespective of the originating data source, by
applying one mapper (M) and one key manager (KM),
wherein the key manager (KM) is applied for
selecting a secret element (b) from a predetermined algebraic structure constituting a multiplicative or additive cyclic group,
selecting, for each data source (DSi) an element (ei, ai) to be applied as a cryptographic key by the given data source (DSi), from the algebraic structure and sending it to the given data source (DSi) while the element (ei, ai) is kept secret,
calculating an inverse (di) of the element (ei, ai) in the given algebraic structure, and using it, together with the secret element (b), for generating a mapping cryptographic key (hi) of the mapper (M), the mapping cryptographic key (hi) corresponding to the given data source (DSi), and sending the mapping cryptographic key (hi) to the mapper (M) while keeping it secret and assigned to the given data source (DSi),
transforming by the data source (DSi), each entity identifier (D) to be mapped, into a respective encrypted entity identifier (Ci) by using the element (ei, ai) to be applied as a cryptographic key, and
a respective pseudonym (P) is generated by the mapper (M), for each encrypted entity identifier (Ci) encrypted by the data source (DSi), utilizing the mapping cryptographic key (hi) corresponding to the particular data source (DSi).

### Claim 9 (depends on 1)

A computer program comprising instructions which, when the program is executed by a computer, cause the computer to perform the steps of the method of claim 1.

### Claim 10 (depends on 9)

A computer-readable medium storing the computer program of claim 9.