I study two privacy-preserving social network graphs to dis- close the types of relationships of connecting edges and provide flexible multigrained access control. To create such graphs, my schemes employ the concept of secretaries and types of relationships. It is significantly more efficient than those that using expensive cryptographic primitives. I also show how these schemes can be used for multigrained access control with various options. In addition, I describe how much these schemes are resilient to infer the types of connecting edges.
Frikken and Srinivas @cite_2 suggested a key management scheme in social networks without a trusted third party. With the derived keys, it protects user's content as well as enhances access control to a social network. A key for each user is derived based on the proximity of relationship between users. Suppose Alice, a friend of Bob, can access Bob's social network with her friendship of Bob's key and Carol, a friend of friend of Bob, can access Bob's social network with her friend of friend of Bob's key. Access can be controlled based on the those relationship keys that have different access policy of Bob's. This access control is done asynchronously, which means it does not require multiple users to be online simultaneously for the access control to allow access other users. For the social network graph protection, they encrypts destination nodes as well as edges in between. One drawback as the authors mentioned is that malicious users could access to the content of other unauthorized users by publishing other users' keys.
@cite_2
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In this paper we introduce a novel scheme for key management in social networks that is a first step towards the creation of a private social network. A social network graph (i.e., the graph of friendship relationships) is private and social networks are often used to share content, which may be private, amongst its users. In the status quo, the social networking server has access to both this graph and to all of the content, effectively requiring that it is a trusted third party. The goal of this paper is to produce a mechanism through which users can control how their content is shared with other users, without relying on a trusted third party to manage the social network graph and the users' data. The specific access control model considered here is that users will specify access policies based on distance in the social network; for example some content is visible to friends only, while other content is visible to friends of friends, etc. This access control is enforced via key management. That is for each user, there is a key that only friends should be able to derive, there is a key that both friends of the user and friends of friends can derive, etc. The proposed scheme enjoys the following properties: i) the scheme is asynchronous in that it does not require users to be online at the same time, ii) the scheme provides key indistinguishability (that is if a user is not allowed to derive a key according to the access policy, then that key is indistinguishable from a random value), iii) the scheme is efficient in terms of server storage and key derivation time, and iv) the scheme is collusion resistant. The semantics of online authentication in the web are rather straightforward: if Alice has a certificate binding Bob's name to a public key, and if a remote entity can prove knowledge of Bob's private key, then (barring key compromise) that remote entity must be Bob. However, in reality, many websites' and the majority of the most popular ones-are hosted at least in part by third parties such as Content Delivery Networks (CDNs) or web hosting providers. Put simply: administrators of websites who deal with (extremely) sensitive user data are giving their private keys to third parties. Importantly, this sharing of keys is undetectable by most users, and widely unknown even among researchers. In this paper, we perform a large-scale measurement study of key sharing in today's web. We analyze the prevalence with which websites trust third-party hosting providers with their secret keys, as well as the impact that this trust has on responsible key management practices, such as revocation. Our results reveal that key sharing is extremely common, with a small handful of hosting providers having keys from the majority of the most popular websites. We also find that hosting providers often manage their customers' keys, and that they tend to react more slowly yet more thoroughly to compromised or potentially compromised keys. Conventional mobile social services such as Loopt and Google Latitude rely on two classes of trusted relationships: participants trust a centralized server to manage their location information and trust between users is based on existing social relationships. Unfortunately, these assumptions are not secure or general enough for many mobile social scenarios: centralized servers cannot always be relied upon to preserve data confidentiality, and users may want to use mobile social services to establish new relationships. To address these shortcomings, this paper describes SMILE, a privacy-preserving "missed-connections" service in which the service provider is untrusted and users are not assumed to have pre-established social relationships with each other. At a high-level, SMILE uses short-range wireless communication and standard cryptographic primitives to mimic the behavior of users in existing missed-connections services such as Craigslist: trust is founded solely on anonymous users' ability to prove to each other that they shared an encounter in the past. We have evaluated SMILE using protocol analysis, an informal study of Craigslist usage, and experiments with a prototype implementation and found it to be both privacy-preserving and feasible. In a public key setting, Alice encrypts an email with the public key of Bob, so that only Bob will be able to learn the contents of the email. Consider a scenario where the computer of Alice is infected and unbeknown to Alice it also embeds a malware into the message. Bob's company, Carol, cannot scan his email for malicious content as it is encrypted so the burden is on Bob to do the scan. This is not efficient. We construct a mechanism that enables Bob to provide trapdoors to Carol such that Carol, given an encrypted data and a malware signature, is able to check whether the encrypted data contains the malware signature, without decrypting it. We refer to this mechanism as public-key encryption with delegated search (PKEDS). We formalize PKEDS and give a construction based on ElGamal public-key encryption (PKE). The proposed scheme has ciphertexts which are both searchable and decryptable. This property of the scheme is crucial since an entity can search the entire content of the message, in contrast to existing searchable public-key encryption schemes where the search is done only in the metadata part. We prove in the standard model that the scheme is ciphertext indistinguishable and trapdoor indistinguishable under the Symmetric External Diffie-Hellman (SXDH) assumption. We prove also the ciphertext one-wayness of the scheme under the modified Computational Diffie-Hellman (mCDH) assumption. We show that our PKEDS scheme can be used in different applications such as detecting encrypted malware and forwarding encrypted email.