Updatable Privacy-Preserving Blueprints
(2025) 30th Annual International Conference on the Theory and Application of Cryptology and Information Security, ASIACRYPT 2024 In Lecture Notes in Computer Science 15484 LNCS. p.105-139- Abstract
Privacy-preserving blueprint schemes (Kohlweiss et al., EUROCRYPT’23) offer a mechanism for safeguarding user’s privacy while allowing for specific legitimate controls by a designated auditor agent. These schemes enable users to create escrows encrypting the result of evaluating a function y=P(t,x), with P being publicly known, t a secret used during the auditor’s key generation, and x the user’s private input. Crucially, escrows only disclose the blueprinting result y=P(t,x) to the designated auditor, even in cases where the auditor is fully compromised. The original definition and construction only support the evaluation of functions P on an input x provided by a single user. We address this limitation by introducing updatable... (More)
Privacy-preserving blueprint schemes (Kohlweiss et al., EUROCRYPT’23) offer a mechanism for safeguarding user’s privacy while allowing for specific legitimate controls by a designated auditor agent. These schemes enable users to create escrows encrypting the result of evaluating a function y=P(t,x), with P being publicly known, t a secret used during the auditor’s key generation, and x the user’s private input. Crucially, escrows only disclose the blueprinting result y=P(t,x) to the designated auditor, even in cases where the auditor is fully compromised. The original definition and construction only support the evaluation of functions P on an input x provided by a single user. We address this limitation by introducing updatable privacy-preserving blueprint schemes (UPPB), which enhance the original notion with the ability for multiple users to non-interactively update the private user input x while blueprinting. Moreover, UPPBs contain a proof that y is the result of a sequence of valid updates, while revealing nothing else about the private inputs {xi} of updates. As in the case of privacy-preserving blueprints, we first observe that UPPBs can be realized via a generic construction for arbitrary predicates P based on FHE and NIZKs. Our main result is uBlu, an efficient instantiation for a specific predicate comparing the values x and t, where x is the cumulative sum of users’ private inputs and t is a fixed private value provided by the auditor in the setup phase. This rather specific setting already finds interesting applications such as privacy-preserving anti-money laundering and location tracking, and can be extended to support more generic predicates. From the technical perspective, we devise a novel technique to keep the escrow size concise, independent of the number of updates, and reasonable for practical applications. We achieve this via a novel characterization of malleability for the algebraic NIZK by Couteau and Hartmann (CRYPTO’20) that allows for an additive update function.
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- author
- David, Bernardo ; Engelmann, Felix LU ; Frederiksen, Tore ; Kohlweiss, Markulf ; Pagnin, Elena and Volkhov, Mikhail
- organization
- publishing date
- 2025
- type
- Chapter in Book/Report/Conference proceeding
- publication status
- published
- subject
- keywords
- Privacy-Preserving Blueprints, Updatable NIZKs
- host publication
- Advances in Cryptology – ASIACRYPT 2024 - 30th International Conference on the Theory and Application of Cryptology and Information Security, Proceedings
- series title
- Lecture Notes in Computer Science
- editor
- Chung, Kai-Min and Sasaki, Yu
- volume
- 15484 LNCS
- pages
- 35 pages
- publisher
- Springer Science and Business Media B.V.
- conference name
- 30th Annual International Conference on the Theory and Application of Cryptology and Information Security, ASIACRYPT 2024
- conference location
- Kolkata, India
- conference dates
- 2024-12-09 - 2024-12-13
- external identifiers
-
- scopus:85213316594
- ISSN
- 0302-9743
- 1611-3349
- ISBN
- 9789819608744
- DOI
- 10.1007/978-981-96-0875-1_4
- language
- English
- LU publication?
- yes
- id
- bc73f80b-02be-476f-9f84-4b96f8cbf6e8
- date added to LUP
- 2026-01-12 08:28:23
- date last changed
- 2026-01-26 09:50:45
@inproceedings{bc73f80b-02be-476f-9f84-4b96f8cbf6e8,
abstract = {{<p>Privacy-preserving blueprint schemes (Kohlweiss et al., EUROCRYPT’23) offer a mechanism for safeguarding user’s privacy while allowing for specific legitimate controls by a designated auditor agent. These schemes enable users to create escrows encrypting the result of evaluating a function y=P(t,x), with P being publicly known, t a secret used during the auditor’s key generation, and x the user’s private input. Crucially, escrows only disclose the blueprinting result y=P(t,x) to the designated auditor, even in cases where the auditor is fully compromised. The original definition and construction only support the evaluation of functions P on an input x provided by a single user. We address this limitation by introducing updatable privacy-preserving blueprint schemes (UPPB), which enhance the original notion with the ability for multiple users to non-interactively update the private user input x while blueprinting. Moreover, UPPBs contain a proof that y is the result of a sequence of valid updates, while revealing nothing else about the private inputs {x<sub>i</sub>} of updates. As in the case of privacy-preserving blueprints, we first observe that UPPBs can be realized via a generic construction for arbitrary predicates P based on FHE and NIZKs. Our main result is uBlu, an efficient instantiation for a specific predicate comparing the values x and t, where x is the cumulative sum of users’ private inputs and t is a fixed private value provided by the auditor in the setup phase. This rather specific setting already finds interesting applications such as privacy-preserving anti-money laundering and location tracking, and can be extended to support more generic predicates. From the technical perspective, we devise a novel technique to keep the escrow size concise, independent of the number of updates, and reasonable for practical applications. We achieve this via a novel characterization of malleability for the algebraic NIZK by Couteau and Hartmann (CRYPTO’20) that allows for an additive update function.</p>}},
author = {{David, Bernardo and Engelmann, Felix and Frederiksen, Tore and Kohlweiss, Markulf and Pagnin, Elena and Volkhov, Mikhail}},
booktitle = {{Advances in Cryptology – ASIACRYPT 2024 - 30th International Conference on the Theory and Application of Cryptology and Information Security, Proceedings}},
editor = {{Chung, Kai-Min and Sasaki, Yu}},
isbn = {{9789819608744}},
issn = {{0302-9743}},
keywords = {{Privacy-Preserving Blueprints; Updatable NIZKs}},
language = {{eng}},
pages = {{105--139}},
publisher = {{Springer Science and Business Media B.V.}},
series = {{Lecture Notes in Computer Science}},
title = {{Updatable Privacy-Preserving Blueprints}},
url = {{http://dx.doi.org/10.1007/978-981-96-0875-1_4}},
doi = {{10.1007/978-981-96-0875-1_4}},
volume = {{15484 LNCS}},
year = {{2025}},
}