Wouter Lueks's research while affiliated with Helmholtz Center for Information Security and other places
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Publications (38)
Humanitarian organizations provide aid to people in need. To use their limited budget efficiently, their distribution processes must ensure that legitimate recipients cannot receive more aid than they are entitled to. Thus, it is essential that recipients can register at most once per aid program. Taking the International Committee of the Red Cross...
We introduce Private Collection Matching (PCM) problems, in which a client aims to determine whether a collection of sets owned by a server matches their interests. Existing privacy-preserving cryptographic primitives cannot solve PCM problems efficiently without harming privacy. We propose a modular framework that enables designers to build privac...
Humanitarian aid-distribution programs help bring physical goods (e.g., food, blankets) to people in need. Traditional paper-based solutions to support aid distribution do not scale to large populations and are hard to secure. Existing digital solutions solve these issues, at the cost of collecting large amount of personal information. Failing to p...
We introduce Private Set Matching (PSM) problems, in which a client aims to determine whether a collection of sets owned by a server matches her interest. Existing privacy-preserving cryptographic primitives cannot solve PSM problems efficiently without harming privacy. We propose a new modular framework that enables designers to build privacy-frie...
There is growing evidence that SARS-CoV-2 can be transmitted beyond close proximity contacts, in particular in closed and crowded environments with insufficient ventilation. To help mitigation efforts, contact tracers need a way to notify those who were present in such environments at the same time as infected individuals. Neither traditional human...
Digital proximity tracing (DPT) for Sars-CoV-2 pandemic mitigation is a complex intervention with the primary goal to notify app users about possible risk exposures to infected persons. DPT not only relies on the technical functioning of the proximity tracing application and its backend server, but also on seamless integration of health system proc...
In this document, we analyse the potential harms a large-scale deployment of the Luca system might cause to individuals, venues, and communities. The Luca system is a digital presence tracing system designed to provide health departments with the contact information necessary to alert individuals who have visited a location at the same time as a SA...
Digital proximity tracing (DPT) for Sars-CoV-2 pandemic mitigation is a complex intervention with the primary goal to notify app users about possible risk exposures to infected persons. Policymakers and DPT operators need to know whether their system works as expected in terms of speed or yield (performance) and whether DPT is making an effective c...
In the wake of the pandemic of coronavirus disease 2019 (COVID-19), contact tracing has become a key element of strategies to control the spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Given the rapid and intense spread of SARS-CoV-2, digital contact tracing has emerged as a potential complementary tool to support containme...
In the wake of the pandemic of coronavirus disease 2019 (COVID-19), contact tracing has become a key element of strategies to control the spread of severe acute respiratory syndrome coronavirus 2019 (SARS-CoV-2). Given the rapid and intense spread of SARS-CoV-2, digital contact tracing has emerged as a potential complementary tool to support contai...
Users’ devices, e.g., smartphones or laptops, are typically incapable of securely storing and processing cryptographic keys.We present Tandem, a novel set of protocols for securing cryptographic keys with support from a central server. Tandem uses one-time-use key-share tokens to preserve users’ privacy with respect to a malicious central server. A...
Investigative journalists collect large numbers of digital documents during their investigations. These documents could greatly benefit other journalists' work. However, many of these documents contain sensitive information and their possession of such documents can endanger reporters, their stories, and their sources. Thus, many documents are only...
This document describes and analyzes a system for secure and privacy-preserving proximity tracing at large scale. This system, referred to as DP3T, provides a technological foundation to help slow the spread of SARS-CoV-2 by simplifying and accelerating the process of notifying people who might have been exposed to the virus so that they can take a...
The strongest threat model for voting systems considers coercion resistance: protection against coercers that force voters to modify their votes, or to abstain. Existing remote voting systems either do not provide this property; require an expensive tallying phase; or burden users with the need to store cryptographic key material and with the respo...
Zero-knowledge proofs are an essential building block in many privacy-preserving systems. However, implementing these proofs is tedious and error-prone. In this paper, we present zksk, a well-documented Python library for defining and computing sigma protocols: the most popular class of zero-knowledge proofs. In zksk, proofs compose: programmers ca...
Zero-knowledge proofs are an essential building block in many privacy-preserving systems. However, implementing these proofs is tedious and error-prone. In this paper, we present zksk, a well-documented Python library for defining and computing sigma protocols: the most popular class of zero-knowledge proofs. In zksk proofs compose: programmers can...
Most encrypted data formats leak metadata via their plaintext headers, such as format version, encryption schemes used, number of recipients who can decrypt the data, and even the recipients’ identities. This leakage can pose security and privacy risks to users, e.g., by revealing the full membership of a group of collaborators from a single encryp...
The social demand for email end-to-end encryption is barely supported by mainstream service providers. Autocrypt is a new community-driven open specification for e-mail encryption that attempts to respond to this demand. In Autocrypt the encryption keys are attached directly to messages, and thus the encryption can be implemented by email clients w...
Users' devices, e.g., smartphones or laptops, are typically incapable of securely storing and processing cryptographic keys. We present Tandem, a novel set of protocols for securing cryptographic keys with support from a central server. Tandem uses one-time-use key-share tokens to, unlike traditional threshold-cryptographic solutions, preserve user...
Attribute-based credentials allow a user to prove properties about herself anonymously. Revoking such credentials, which requires singling them out, is hard because it is at odds with anonymity. All revocation schemes proposed to date either sacrifice anonymity altogether, require the parties to be online, or put high load on the user or the verifi...
Service providers are often reluctant to support anonymous access, because this makes it hard to deal with misbehaving users. Anonymous blacklisting and reputation systems can help prevent misbehaving users from causing more damage. However, by the time the user is blocked or has lost reputation, most of the damage has already been done. To help th...
Security and privacy often seem to be at odds with one another. In this paper, we revisit the design principle of revocable privacy which guides the creation of systems that offer anonymity for people who do not violate a predefined rule, but can still have consequences for people who do violate the rule. We first improve the definition of revocabl...
Self-blindable credential schemes allow users to anonymously prove ownership of credentials. This is achieved by randomizing the credential before each showing in such a way that it still remains valid. As a result, each time a different version of the same credential is presented. A number of such schemes have been proposed, but unfortunately many...
Attribute-based credentials allow a user to prove properties about herself anonymously. Revoking such credentials, which requires singling them out, is hard because it is at odds with anonymity. All revocation schemes proposed to date either sacrifice anonymity altogether, require the parties to be online, or put high load on the user or the verifi...
Private information retrieval (PIR) allows clients to retrieve records from online database servers without revealing to the servers any information about what records are being retrieved. To achieve this, the servers must typically do a computation involving the entire database for each query. Previous work by Ishai et al. has suggested using batc...
Distributed encryption is a cryptographic primitive that implements revocable privacy. The primitive allows a recipient of a message to decrypt it only if enough senders encrypted that same message. We present a new distributed encryption scheme that is simpler than the previous solution by Hoepman and Galindo–in particular it does not rely on pair...
Recent research has shown that using public-key cryptography in order to meet privacy requirements for RFID tags is not only necessary, but also now practically feasible. This has led to the development of new protocols like the Randomized Schnorr [6] identification protocol. This protocol ensures that the identity of a tag only becomes known to au...
The growing number of dimensionality reduction methods available for data visualization has recently inspired the development of formal measures to evaluate the resulting low-dimensional representation independently from the methods' inherent criteria. Many evaluation measures can be summarized based on the co-ranking matrix. In this work, we analy...
Based on an approach for the temporal change of abstraction in molecular visualization we describe how to achieve a spatially ex-plicit control of abstraction. This allows us to depict different ab-straction stages of a single molecule in a single still-image visual-ization. This approach works best for long, linear molecules with repeating substru...
The growing number of dimensionality reduction methods available for data
visualization has recently inspired the development of quality assessment
measures, in order to evaluate the resulting low-dimensional representation
independently from a methods' inherent criteria. Several (existing) quality
measures can be (re)formulated based on the so-cal...
Molecular systems may be visualized with various degrees of structural abstraction, support of spatial perception, and 'illustrativeness.' In this work we propose and realize methods to create seamless transformations that allow us to affect and change each of these three parameters individually. The resulting transitions give viewers a dedicated c...
Nonparametric dimensionality reduction (DR) techniques such as locally linear embedding or t-distributed stochastic neighbor (t-SNE) embedding constitute standard tools to visualize high dimensional and complex data in the Euclidean plane. With increasing data volumes and streaming applications, it is often no longer possible to project all data po...
Citations
... Thereby, the authorities can detect people who may have had close contact with the infected one and notify them promptly to break the infection chain of diseases. However, to handle the privacy issues, the Decentralized Privacy-Preserving Proximity Tracing (DP-3T) protocol [60] is developed to facilitate privacy-preserving digital contact tracing of infected cases. This protocol ensures that the central server does not access contact records. ...
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... Furthermore, Apple and Google jointly developed an API for exposure notification, which can be used across borders. It is mainly based on the DP3T protocol [18], a decentralized protocol. Exposure notification APIs have been applied by applications in many countries, such as COVID Tracker in Ireland and My Trace in Malaysia [19]. ...
... Via Bluetooth, the smartphone will exchange encrypted random identifiers with other devices. These identifiers, provide information solely about duration and distance of an encounter and allow a user to inform anonymously its contacts that used the app in case of a COVID-19 diagnosis [8][9][10][11]. ...
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... To reduce time and cost intensive resources required by contact tracing solely performed by humans, numerous digital contact tracing (DCT) protocols and smartphone apps have been developed [2]. These protocols commonly utilize native smartphone features, such as Bluetooth, WiFi (e.g., WiFiTrace [3]), GPS (e.g., SafePaths [4]), acoustic signals (e.g., ATurf [5] and NOVID [6]), or QR code scanning (e.g., CrowdNotifier [7]) to provide the underlying mechanisms for smartphone apps to determine encounters with other individuals and ultimately notify of potential exposure to positive diagnosed users. ...
... The coronavirus disease 2019 (COVID- 19) pandemic has been the first in which digital contact tracing (DCT) tools have been widely deployed as part of several national responses, including in Australia, 1,2 China, 3,4 several states of the USA, 5,6 and multiple European countries including France, 7 Germany, 8 Ireland, 9 Italy, 10 the Netherlands, 11 Switzerland, 12 and the UK. 13 The ability to rapidly contact trace can assist in timely case identification, allowing for better case management and disease spread control by notifying individuals that they may be infected at an earlier stage. 14 The magnitude of outbreak peaks can also be reduced if, following such alerts, infected individuals modify their behaviour to reduce social interactions or to isolate themselves either before they become infectious or at an earlier stage of their infectious period. ...
... Contact tracing mobile apps were one of the useful measures for combating the spread of SARS-CoV-2 during the phases of the pandemic when vaccines were not yet available (Salathé et al., 2020). Comparable with other recommended protective behaviors during the pandemic such as social distancing and mask wearing, the effectiveness of contact tracing apps increases with the number of people actually using them (Wymant et al., 2021). ...
... During the COVID-19 pandemic, we have seen a revolution of the contact tracing technology, which helped track and contain the epidemic (Braithwaite et al. 2020;Kretzschmar et al. 2020). Some contact tracing programs were conducted by governmental/ health agencies , while others relied on decentralized approaches (Troncoso et al. 2020). Most contact tracing approaches work by notifying people who could have received the infection from known infectious patients, i.e., they trace "forward" in time. ...
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... In Sec. IV, we empirically evaluate these algorithms using two real-world datasets to compare the security they provide to recently published algorithms for similar goals, for both per-object padding and per-request padding [17], [58]. Our evaluation shows that in terms of both information gain for the adversary and the adversary's practical ability to detect object retrievals as being in classes of interest, our per-request padding algorithm provided better security than the per-request padding contender, and similarly, our per-object padding algorithm dominated its contenders. ...
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... These signatures bind the key of the identity holder to the disclosed data and usually allow derivation of a new signature that is also valid for the same data (which is claimed to make this data unlinkable, though fingerprinting makes users completely linkable as we have previously discussed). Examples of these systems are IRMA [4], Jolocom and uPort [26], ClaimChain [31], HyperLedger Indy and Sovrin [45]. ...
Reference: A Truly Self-Sovereign Identity System
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... Subsequently, the ability to hold users accountable for their actions insures that the integrity of shared intelligence can be maintained. Like trust, accountability is also dependent on being able to reveal a producers real identity given that they have made a malicious contribution [33] [34]. ...
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