Privacy-preserving user certificates
A method, system, and computer program product are disclosed. The method includes separating a user certificate into a private component and a non-private component. The method further includes storing the non-private component in a database and providing a pointer to the non-private component stored in the database.
1. A method, comprising:
issuing a digitally-signed assertion, the issuing comprising:
receiving user data;
separating the user data into a private component and a non-private component, wherein the separating comprises:
determining, based on a size of an area, an amount of the user data that can be encoded in the area; and
selecting, from the user data, data for the private component based on the determined amount and a categorization of the user data;
encoding the private component and a nonce in the area as a barcode;
separately from the barcode, storing the non-private component and a digital signature in a database; and
generating a user certificate comprising the barcode and a pointer to the non-private component in the database.
2. The method of claim 1 , wherein the issuing further comprises deriving the pointer deterministically from the private component.
3. The method of claim 2 , wherein the pointer is derived by means of a cryptographic hash of the private component.
4. The method of claim 1 , wherein the barcode is a 2-dimensional barcode.
5. The method of claim 1 , wherein the database is embodied as a centralized storage or a decentralized storage.
6. The method of claim 1 , wherein the private component comprises data selected from the group consisting of personally identifiable information and demographics data.
7. The method of claim 1 , wherein the non-private component comprises data selected from the group consisting of an issuer identity, and non-personally identifiable information.
8. The method of claim 1 , the issuing further comprising augmenting the non-private component with verification data of a proof system, wherein the proof system is configured to enable a verifier of the user certificate to prove knowledge of at least a subset of the private component corresponding to the pointer.
9. The method of claim 1 , wherein the pointer can be derived from the private component by a verification device, and wherein the verification device can submit the pointer to an access software that, in response, provides the non-private component.
10. The method of claim 9 , wherein the access software provides the non-private component only upon verification of a proof demonstrating knowledge of at least a subset of the private component.
11. The method of claim 10 , wherein the proof comprises a zero-knowledge proof.
12. The method of claim 1 , wherein the categorization of the user data is based on whether or not the data is personal identifying information.
13. The method of claim 1 , wherein the issuing further comprises:
estimating a minimum entropy of the data selected for the private component; and
determining a size of a nonce field for the nonce in the private component based on the minimum entropy.
14. The method of claim 1 , wherein the issuing further comprises computing the digital signature based on the user data and the nonce.
15. A system, comprising:
a memory; and
a processor communicatively coupled to the memory, wherein the processor is configured to perform a method of issuing a digitally-signed assertion, the method comprising:
receiving user data;
computing a digital signature on the user data and a nonce;
separating the user data into a private component and a non-private component, wherein the separating comprises:
determining, based on a size of an area, an amount of the user data that can be encoded in the area; and
selecting, from the user data, data for the private component based on the determined amount and a categorization of the user data;
encoding the private component and the nonce in the area as a barcode;
separately from the barcode, storing the non-private component and the digital signature in a database; and
generating a user certificate comprising, the barcode and a pointer to the non-private component in the database.
16. The system of claim 15 , wherein the storing further comprises augmenting the non-private component with verification data of a proof system, and wherein the proof system is configured to enable a verifier of the user certificate to prove knowledge of at least a subset of the private component corresponding to the pointer.
17. The system of claim 15 , wherein the pointer can be derived from the private component by a verification device, and wherein the verification device can submit the pointer to an access software of the database that, in response, provides the non-private component.
18. The system of claim 17 , wherein the access software provides the non-private component only upon verification of a proof demonstrating knowledge of at least a subset of the private component.
19. A computer program product, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause a device to perform a method of issuing a digitally-signed assertion, the method comprising:
receiving user data;
computing a digital signature on the user data and a nonce;
separating the user data into a private component and a non-private component, wherein the separating comprises:
determining, based on a size of an area, an amount of the user data that can be encoded in the area; and
selecting, from the user data, data for the private component based on the determined amount and a categorization of the data;
encoding the private component and the nonce in the area as a barcode;
separately storing the non-private component and the digital signature in a database; and
generating a user certificate comprising the barcode and a pointer to the non-private component in the database.
20. The computer program product of claim 19 , wherein the issuing further comprises generating the pointer by hashing the private component or a subset of the private component.