In this paper we present reclaimID: An architecture that allows users to reclaim their digital identities by securely sharing identity attributes without the need for a centralised service provider. We propose a design where user attributes are stored in and shared over a name system under user-owned namespaces. Attributes are encrypted using attribute-based encryption (ABE), allowing the user to selectively authorize and revoke access of requesting parties to subsets of his attributes. We present an implementation based on the decentralised GNU Name System (GNS) in combination with ciphertext-policy ABE using type-1 pairings. To show the practicality of our implementation, we carried out experimental evaluations of selected implementation aspects including attribute resolution performance. Finally, we show that our design can be used as a standard OpenID Connect Identity Provider allowing our implementation to be integrated into standard-compliant services.
DP5 @cite_3 is a privacy-friendly presence notification service that through the use of asymmetric pairing functions and pseudo-random functions provides a secure and private personal information retrieval (PIR). While DP5 addresses the most relevant privacy and security issues, it does not address availability as does with a redundant DHT. A powerful attacker might coerce a DP5 service provider to discontinue its services without having to deal with any of the users trying to share information. Participants in are not individually protected against such an attack, but the lack of central service instances mitigates the collapse of the whole system.
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2242794960 2154473393 2620403523 2157855380
Users of social applications like to be notified when their friends are online. Typically, this is done by a central server keeping track of who is online and offline, as well as of all of the users' "buddy lists", which contain sensi- tive information. We present DP5, a cryptographic service that implements online presence indication in a privacy-friendly way. DP5 allows clients to register their online presence and query the presence of their list of friends while keeping this list secret. Besides presence, high-integrity status updates are supported, to facilitate key update and rendezvous protocols. While infrastructure services are required for DP5 to operate, they are designed to not require any long-term secrets and pro- vide perfect forward secrecy in case of compromise. We pro- vide security arguments for the indistinguishability properties of the protocol, as well as an evaluation of its scalability and performance. Privacy leaks are an unfortunate and an integral part of the current Internet domain name resolution. Each DNS query generated by a user reveals -- to one or more DNS servers -- the origin and the target of that query. Over time, users' communication (e.g., browsing) patterns might become exposed to entities with little or no trust. Current DNS privacy leaks stem from fundamental features of DNS and are not easily fixable by simple patches. Moreover, privacy issues have been overlooked by DNS security efforts (such as DNSSEC) and are thus likely to propagate into future versions of DNS. In order to mitigate privacy issues in DNS, this paper proposes a Privacy-Preserving DNS (PPDNS), that offers privacy during domain name resolution. PPDNS is based on distributed hash tables (DHTs), an alternative naming infrastructure, and computational private information retrieval (cPIR), an advanced cryptographic construct. PPDNS takes advantage of the DHT index structure to provide name resolution query privacy, while leveraging cPIR to reduce communication overhead for bandwidth-sensitive clients. Our analysis shows that PPDNS is a viable approach for obtaining a reasonably high level of privacy for name resolution queries. PPDNS also serves as a demonstration of blending advanced systems techniques with their cryptographic counterparts. We propose a multi-user Symmetric Searchable Encryption (SSE) scheme based on the single-user Oblivious Cross Tags (OXT) protocol (, CRYPTO 2013). The scheme allows any user to perform a search query by interacting with the server and any ( -1 ) ‘helping’ users, and preserves the privacy of database content against the server even assuming leakage of up to ( -1 ) users’ keys to the server (for a threshold parameter ( )), while hiding the query from the ( -1 ) ‘helping users’. To achieve the latter query privacy property, we design a new distributed key-homomorphic pseudorandom function (PRF) that hides the PRF input (search keyword) from the ‘helping’ key share holders. By distributing the utilized keys among the users, the need of constant online presence of the data owner to provide services to the users is eliminated, while providing resilience against user key exposure. Mobile devices equipped with positioning capabilities (e.g., GPS) can ask location-dependent queries to Location Based Services (LBS). To protect privacy, the user location must not be disclosed. Existing solutions utilize a trusted anonymizer between the users and the LBS. This approach has several drawbacks: (i) All users must trust the third party anonymizer, which is a single point of attack. (ii) A large number of cooperating, trustworthy users is needed. (iii) Privacy is guaranteed only for a single snapshot of user locations; users are not protected against correlation attacks (e.g., history of user movement). We propose a novel framework to support private location-dependent queries, based on the theoretical work on Private Information Retrieval (PIR). Our framework does not require a trusted third party, since privacy is achieved via cryptographic techniques. Compared to existing work, our approach achieves stronger privacy for snapshots of user locations; moreover, it is the first to provide provable privacy guarantees against correlation attacks. We use our framework to implement approximate and exact algorithms for nearest-neighbor search. We optimize query execution by employing data mining techniques, which identify redundant computations. Contrary to common belief, the experimental results suggest that PIR approaches incur reasonable overhead and are applicable in practice.