A Survey on Interdependent Privacy <s> Cryptography <s> In this paper we show how to divide data D into n pieces in such a way that D is easily reconstructable from any k pieces, but even complete knowledge of k - 1 pieces reveals absolutely no information about D . This technique enables the construction of robust key management schemes for cryptographic systems that can function securely and reliably even when misfortunes destroy half the pieces and security breaches expose all but one of the remaining pieces. <s> BIB001 </s> A Survey on Interdependent Privacy <s> Cryptography <s> From the Publisher: ::: A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols; more than 200 tables and figures; more than 1,000 numbered definitions, facts, examples, notes, and remarks; and over 1,250 significant references, including brief comments on each paper. <s> BIB002 </s> A Survey on Interdependent Privacy <s> Cryptography <s> This paper investigates a novel computational problem, namely the Composite Residuosity Class Problem, and its applications to public-key cryptography. We propose a new trapdoor mechanism and derive from this technique three encryption schemes : a trapdoor permutation and two homomorphic probabilistic encryption schemes computationally comparable to RSA. Our cryptosystems, based on usual modular arithmetics, are provably secure under appropriate assumptions in the standard model. <s> BIB003 </s> A Survey on Interdependent Privacy <s> Cryptography <s> As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE). <s> BIB004 </s> A Survey on Interdependent Privacy <s> Cryptography <s> Online social networks' (OSNs) epic popularity has accustomed users to the ease of sharing information. At the same time, OSNs have been a focus of privacy concerns with respect to the information shared. Therefore, it is important that users have some assurance when sharing on OSNs: popular OSNs provide users with mechanisms, to protect shared information access rights. However, these mechanisms do not allow collaboration when defining access rights for joint content related to more than one user (e.g, party pictures in which different users are being tagged). In fact, the access rights list for such content is represented by the union of the access list defined by each related user, which could result in unwanted leakage. We propose a collaborative access control scheme, based on secret sharing, in which sharing of content on OSNs is decided collaboratively by a number of related users. We demonstrate that such mechanism is feasible and benefits users' privacy. <s> BIB005 </s> A Survey on Interdependent Privacy <s> Cryptography <s> The capabilities of modern devices, coupled with the almost ubiquitous availability of Internet connectivity, have resulted in photos being shared online at an unprecedented scale. This is further amplified by the popularity of social networks and the immediacy they offer in content sharing. Existing access control mechanisms are too coarse-grained to handle cases of conflicting interests between the users associated with a photo; stories of embarrassing or inappropriate photos being widely accessible have become quite common. In this paper, we propose to rethink access control when applied to photos, in a way that allows us to effectively prevent unwanted individuals from recognizing users in a photo. The core concept behind our approach is to change the granularity of access control from the level of the photo to that of a user's personally identifiable information (PII). In this work, we consider the face as the PII. When another user attempts to access a photo, the system determines which faces the user does not have the permission to view, and presents the photo with the restricted faces blurred out. Our system takes advantage of the existing face recognition functionality of social networks, and can interoperate with the current photo-level access control mechanisms. We implement a proof-of-concept application for Facebook, and demonstrate that the performance overhead of our approach is minimal. We also conduct a user study to evaluate the privacy offered by our approach, and find that it effectively prevents users from identifying their contacts in 87.35% of the restricted photos. Finally, our study reveals the misconceptions about the privacy offered by existing mechanisms, and demonstrates that users are positive towards the adoption of an intuitive, straightforward access control mechanism that allows them to manage the visibility of their face in published photos. <s> BIB006 </s> A Survey on Interdependent Privacy <s> Cryptography <s> Online social network (OSN) users are exhibiting an increased privacy-protective behaviour especially since multimedia sharing has emerged as a popular activity over most OSN sites. Popular OSN applications could reveal much of the users’ personal information or let it easily derived, hence favouring different types of misbehaviour. In this article the authors deal with these privacy concerns by applying fine-grained access control and co-ownership management over the shared data. This proposal defines access policy as any linear boolean formula that is collectively determined by all users being exposed in that data collection namely the co-owners. All co-owners are empowered to take part in the process of data sharing by expressing (secretly) their privacy preferences and, as a result, jointly agreeing on the access policy. Access policies are built upon the concept of secret sharing systems. A number of predicates such as gender, affiliation or postal code can define a particular privacy setting. User attributes are then used as predicate values. In addition, by the deployment of privacy-enhanced attribute-based credential technologies, users satisfying the access policy will gain access without disclosing their real identities. The authors have implemented this system as a Facebook application demonstrating its viability, and procuring reasonable performance costs. <s> BIB007 </s> A Survey on Interdependent Privacy <s> Cryptography <s> Individuals share increasing amounts of personal data online. This data often involves–or at least has privacy implications for–data subjects other than the individuals who shares it (e.g., photos, genomic data) and the data is shared without their consent. A sadly popular example, with dramatic consequences, is revenge pornography. In this paper, we propose ConsenShare, a system for sharing, in a consensual (wrt the data subjects) and privacy-preserving (wrt both service providers and other individuals) way, data involving subjects other than the uploader. We describe a complete design and implementation of ConsenShare for photos, which relies on image processing and cryptographic techniques, as well as on a two-tier architecture (one entity for detecting the data subjects and contacting them; one entity for hosting the data and for collecting consent). We benchmark the performance (CPU and bandwidth) of ConsenShare by using a dataset of 20k photos from Flickr. We also conduct a survey targeted at Facebook users (N = 321). Our results are quite encouraging: The experimental results demonstrate the feasibility of our approach (i.e., acceptable overheads) and the survey results demonstrate a potential interest from the users. <s> BIB008
Cryptography refers to the process of transforming intelligible information (plaintext) into unintelligible one (ciphertext) BIB002 ]. Modern cryptography can be split into two main fields: symmetric and asymmetric cryptography. Symmetric-key cryptography (e.g., AES) refers to the case where both the sender and the receiver share the same key, while asymmetric cryptography (e.g., RSA) relies on two different keys, a public key that can be accessed by anyone, and a private key, that should be known only to its owner. Secret sharing is a cryptographic scheme that enables a group of users to protect a secret. It can be used to protect a symmetric key among n users for instance. Each user receives a share in such a way that any subset of t or more users can reconstruct the secret, but no information can be learned from less than t shares. One of the most popular secret sharing scheme was proposed by Shamir; it is based on interpolation of a polynomial of degree t − 1 BIB001 ]. Attribute-based encryption is a public-key crypto-system that allows for a fine-grained sharing of encrypted data BIB004  . In such a crypto-system, the ciphertext and/or the user's secret key are labeled with a set of descriptive attributes, and decryption of the ciphertext is possible only by users who hold a set of attributes that match the rules included upon encryption. Homomorphic encryption is a class of cryptographic methods that allows computations directly on the ciphertexts and for which only the results of the computations can be returned in the plaintext domain. This approach can be especially useful in the context where a central entity (e.g., service operator) is not trusted. Notable examples of (partially) homomorphic encryption schemes are the Paillier BIB003 ] and ElGamal  ] crypto-systems. Application to interdependent privacy. In general, cryptography can be helpful in the case of interdependent privacy (mostly for co-owned data as cryptographic techniques are data agnostic, and therefore cannot address data correlation issues per se), to hide information to certain adversarial parties. For instance, to share content online or decide on the visibility of some shared content without the service providers and unauthorized users having access to it BIB005 BIB008 BIB007 ] (see Section 5.2 and more specifically Table 4 on page 32). In the case of co-owned data and multi-party privacy conflicts, cryptography can be used to ensure that some content can only be accessed with the consent of the co-owners. For this purpose, cryptographic secret-sharing techniques (used by BIB006 ) are particularly well suited.