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PRivacy preserving pOst-quantuM systEms from advanced crypTograpHic mEchanisms Using latticeS

Periodic Reporting for period 2 - PROMETHEUS (PRivacy preserving pOst-quantuM systEms from advanced crypTograpHic mEchanisms Using latticeS)

Reporting period: 2019-07-01 to 2021-06-30

Privacy-preserving cryptographic protocols allow users to take common daily life actions online (e.g purchases, reservations or voting) without leaking sensitive personal information. They typically combine various tools such as digital signatures, homomorphic encryption or zero-knowledge proofs. While practical solutions exist under RSA or discrete logarithm assumptions, they are all completely vulnerable to quantum attacks, so that working quantum computers would immediately make them obsolete.
To address this threat, the PROMETHEUS project will enable users’ privacy in the post-quantum world by providing a complete toolbox of innovative, efficient and quantum-secure cryptographic techniques adapted to modern services. It will provide new building blocks in relation with international competitions and standardisation processes, as well as advanced properties dedicated to the design of sophisticated protocols. To this end, PROMETHEUS will focus on lattice-based cryptography. It will first conduct an in-depth study of the hardness of lattice problems in the quantum world, which will drive the development of better basic tools for lattice-based cryptography. PROMETHEUS will then design and implement basic cryptographic building blocks such as signatures and encryption, and will provide concrete realisations of advanced privacy-preserving protocols.
As a concrete outcome, PROMETHEUS will highlight the feasibility of post-quantum privacy via demonstrators for several real-life use-cases, including electronic payments, e-voting and cyberthreat intelligence.
During this second period, until the Month 42 of the project, the PROMETHEUS Consortium performed all the milestones scheduled for this second period, which were:
- first cryptographic specifications;
- intermediate results of cryptographic fondations; and
- cryptographic APIs and first prototype.

Three workpackages presented their intermediate results in specific deliverables:
- Intermediate results on computational problems, cryptanalysis and basic tools;
- Intermediate results on building blocks for practical advanced protocols; and
- Intermediate results on privacy-preserving cryptographic protocols.

Two other deliverables submitted focused on the implementation of the results:
- Implementation of building blocks for practical advanced protocols; and
- Implementation of privacy-preserving cryptographic protocols.

During this second period, the PROMETHEUS project proposed written deliverables in order to specify the four use cases:
- e-voting use case specifications ;
- e-consumer use case specifications ;
- Anonymous credential use case specifications; and
- Cyber threat intelligence use case specifications.

Besides, the website is available at this address: and the members communicate about their activities with the twitter account h2020prometheus.
Since the beginning of the project, we have built a more precise and complete study of the foundations of lattice-based cryptography. We have published several tens of articles related to lattice-based assumptions, new cryptanalysis and dedicated side-channel attacks and countermeasures. We have also provided new innovative lattice-based cryptographic primitives some of them are now quite close to standardization through the NIST competition, and some others are pushed in other standardization bodies such as ISO, IETF and ETSI. Regarding lattice-based advanced protocols, we have provided to the community many new major results on e.g. blind signatures, attribute-based encryption and zero-knowledge proofs of knowledge. We have finally designed advanced cryptographic protocols and specified that will become, before the end of the project, the very first prototypes of post-quantum anonymous credential system, e-cash system and e-voting system.

As the PROMETHEUS project is working on the future of cryptography, secure in a quantum world, it has impacts in many kinds of ICT services that are today deployed in Europe. With our results in advanced cryptographic protocols, the outcomes of our project also impacts the way services will protect the fundamental rights of privacy and data protection in the future. Eventually, the impact of PROMETHEUS for the research community is major as we have quite passed the hundred publications in topmost conferences."