Privately Connecting Mobility to Infectious Diseases via Applied Cryptography

Human mobility is undisputedly one of the critical factors in infectious disease dynamics. Until a few years ago, researchers had to rely on static data to model human mobility, which was then combined with a transmission model of a particular disease resulting in an epidemiological model. Recent works have consistently been showing that substituting the static mobility data with mobile phone data leads to significantly more accurate models. While prior studies have exclusively relied on a mobile network operator's subscribers' aggregated data, it may be preferable to contemplate aggregated mobility data of infected individuals only. Clearly, naively linking mobile phone data with infected individuals would massively intrude privacy. This research aims to develop a solution that reports the aggregated mobile phone location data of infected individuals while still maintaining compliance with privacy expectations. To achieve privacy, we use homomorphic encryption, zero-knowledge proof techniques, and differential privacy. Our protocol's open-source implementation can process eight million subscribers in one and a half hours. Additionally, we provide a legal analysis of our solution with regards to the EU General Data Protection Regulation.Comment: Added differentlial privacy experiments and new benchmark

Multi-Party Computation in the GDPR

The EU GDPR has two main goals: Protecting individuals from personal data abuse and simplifying the free movement of personal data. Privacy-enhancing technologies promise to fulfill both goals simultaneously. A particularly effective and versatile technology solution is multi-party computation (MPC). It allows protecting data during a computation involving multiple parties. This paper aims for a better understanding of the role of MPC in the GDPR. Although MPC is relatively mature, little research was dedicated to its GDPR compliance. First, we try to give an understanding of MPC for legal scholars and policymakers. Then, we examine the GDPR relevant provisions regarding MPC with a technical audience in mind. Finally, we devise a test that can assess the impact of a given MPC solution with regard to the GDPR. The test consists of several questions, which a controller can answer without the help of a technical or legal expert. Going through the questions will classify the MPC solution as (1) a means of avoiding the GDPR, (2) Data Protection by Design, or (3) having no legal benefits. Two concrete case studies should provide a blueprint on how to apply the test. We hope that this work also contributes to an interdisciplinary discussion of MPC certification and standardization

Multi-Party Revocation in Sovrin: Performance through Distributed Trust

Accumulators provide compact representations of large sets and compact membership witnesses. Besides constant-size witnesses, public-key accumulators provide efficient updates of both the accumulator itself and the witness. However, bilinear group based accumulators come with drawbacks: they require a trusted setup and their performance is not practical for real-world applications with large sets. In this paper, we introduce multi-party public-key accumulators dubbed dynamic (threshold) secret-shared accumulators. We present an instantiation using bilinear groups having access to more efficient witness generation and update algorithms that utilize the shares of the secret trapdoors sampled by the parties generating the public parameters. Specifically, for the q-SDH-based accumulators, we provide a maliciously-secure variant sped up by a secure multi-party computation (MPC) protocol (IMACC\u2719) built on top of SPDZ and a maliciously secure threshold variant built with Shamir secret sharing. For these schemes, a performant proof-of-concept implementation is provided, which substantiates the practicability of public-key accumulators in this setting. We explore applications of dynamic (threshold) secret-shared accumulators to revocation schemes of group signatures and credentials system. In particular, we consider it as part of Sovrin\u27s system for anonymous credentials where credentials are issued by the foundation of trusted nodes

Pasta: A Case for Hybrid Homomorphic Encryption

The idea of hybrid homomorphic encryption (HHE) is to drastically reduce bandwidth requirements when using homomorphic encryption (HE) at the cost of more expensive computations in the encrypted domain. To this end, various dedicated schemes for symmetric encryption have already been proposed. However, it is still unclear if those ideas are already practically useful, because (1) no cost-benefit analysis was done for use cases and (2) very few implementations are publicly available. We address this situation in several ways. We build an open-source benchmarking framework involving several use cases covering three popular libraries. Using this framework, we explore properties of the respective HHE proposals. It turns out that even medium-sized use cases are infeasible, especially when involving integer arithmetic. Next, we propose Pasta, a cipher thoroughly optimized for integer HHE use cases. Pasta is designed to minimize the multiplicative depth, while also leveraging the structure of two state-of-the-art integer HE schemes (BFV and BGV) to minimize the homomorphic evaluation latency. Using our new benchmarking environment, we extensively evaluate Pasta in SEAL and HElib and compare its properties to 8 existing ciphers in two use cases. Our evaluations show that Pasta outperforms its competitors for HHE both in terms of homomorphic evaluation time and noise consumption, showing its efficiency for applications in real-world HE use cases. Concretely, Pasta outperforms Agrasta by a factor of up to 82, Masta by a factor of up to 6 and Hera up to a factor of 11 when applied to the two use cases

Pasta: A Case for Hybrid Homomorphic Encryption

The idea of hybrid homomorphic encryption (HHE) is to drastically reduce bandwidth requirements when using homomorphic encryption (HE) at the cost of more expensive computations in the encrypted domain. To this end, various dedicated schemes for symmetric encryption have already been proposed. However, it is still unclear if those ideas are already practically useful, because (1) no cost-benefit analysis was done for use cases and (2) very few implementations are publicly available. We address this situation in several ways. We build an open-source benchmarking r framework, we explore properties of the respective HHE proposals. It turns out that even medium-sized use cases are infeasible, especially when involving integer arithmetic. Next, we propose Pasta, a cipher thoroughly optimized for integer HHE use cases. Pasta is designed to minimize the multiplicative depth, while also leveraging the structure of two state-of-the-art integer HE schemes (BFV and BGV) to minimize the homomorphic evaluation latency. Using our new benchmarking environment, we extensively evaluate Pasta in SEAL and HElib and compare its properties to 8 existing ciphers in two use cases. Our evaluations show that Pasta outperforms its competitors for HHE both in terms of homomorphic evaluation time and noise consumption, showing its efficiency for applications in real-world HE use cases. Concretely, Pasta outperforms Agrasta by a factor of up to 82, Masta by a factor of up to 6 and Hera up to a factor of 11 when applied to the two use cases

Phenology and morphology of the invasive legume Lupinus polyphyllus along a latitudinal gradient in Europe

Plant phenology, i. e. the timing of life cycle events, is related to individual fitness and species distributionranges. Temperature is one of the most important drivers of plant phenology together with day length.The adaptation of their phenology may be important for the success of invasive plant species. The presentstudy aims at understanding how the performance and the phenology of the invasive legume Lupinuspolyphyllus vary with latitude. We sampled data across a >2000 km latitudinal gradient from Centralto Northern Europe. We quantified variation in phenology of flowering and fruiting of L. polyphyllususing >1600 digital photos of inflorescences from 220 individual plants observed weekly at 22 sites. Theday of the year at which different phenological phases were reached, increased 1.3–1.8 days per degreelatitude, whereas the growing degree days (gdd) required for these phenological phases decreased 5–16 gddper degree latitude. However, this difference disappeared, when the day length of each day included inthe calculation of gdd was considered. The day of the year of the earliest and the latest climatic zone toreach any of the three studied phenological phases differed by 23–30 days and temperature requirementsto reach these stages differed between 62 and 236 gdd. Probably, the invasion of this species will furtherincrease in the northern part of Europe over the next decades due to climate warming. For invasive speciescontrol, our results suggest that in countries with a large latitudinal extent, the mowing date should shiftby ca. one week per 500 km at sites with similar elevations