This paper firstly reports a security flaw and a way to fix it detected in a multi-coupon system presented by Liu et al. in a paper published in 2017. That proposal provides selectively-revocable anonymity in the sense that the anonymity of customers is guaranteed unless they act dishonestly by redeeming a multi-coupon more times than allowed. Nevertheless, that system lacks two important security properties of multi-coupons: unlinkability and unsplittability. After that, we propose a novel multi-coupon construction which takes Brands off-line e-coin system as a building block. In this way, the multi-coupon system inherits the selective-revocability property of the mentioned e-coin system without the need to develop new ad-hoc cryptography. Furthermore, the proposed system is also proven to be unlinkable and strongly unsplittable. Its design makes use of a novel extension of the RSA blind signature protocol which endows it with conditional secret recovery.

Abstract Priced oblivious transfer (POT) is a cryptographic protocol in which a merchant provides a set of items for sale and a customer acquires one of them. The protocol guarantees that the customer receives the item if and only if they have paid its price, while the merchant remains oblivious to the acquired item. Obviously, the merchant cannot not know what price the client has paid, as such price could be unique. A recent paper proposes a POT protocol that is built from two blocks: an e-coin system and an asymmetric secure computation protocol. In this paper, we present a quantum-resistant proposal for the latter building block. As a result, we are able to construct a quantum-resistant POT protocol implemented from the newly proposed asymmetric secure computation protocol and a post-quantum implementation of the mentioned e-coin system. To our knowledge, no quantum-resistant POT protocol has been proposed so far.

Abstract A ‘1-out-of-n’ oblivious transfer (OT) protocol involves two participants: a sender, who provides a set of items as input, and a receiver. The protocol guarantees that the receiver gets exactly one of the items of the input set, while the sender is unable to determine which. Priced OT (POT) protocols further allow each item of the input set to be assigned a price in such a way that, after a proper execution of the protocol, the receiver gets the requested item if and only if the corresponding sum of money has been paid. In this paper, we present a construction which takes a ‘1-out-of-n’ OT protocol and transform it into a POT one. Moreover, the resulting system is unlinkable in the sense that the sender is unable to determine whether two executions of the protocol were run by the same receiver or not. When compared to existing unlinkable POT protocols, our construction offers a lower conceptual complexity as it does not involve the use of zero-knowledge proofs.

Some social networks, such as LinkedIn and ResearchGate, allow user endorsements for specific skills. In this way, for each skill we get a directed graph where the nodes correspond to users’ profiles and the arcs represent endorsement relations. From the number and quality of the endorsements received, an authority score can be assigned to each profile. In this paper we propose an authority score computation method that takes into account the relations existing among different skills. Our method is based on enriching the information contained in the digraph of endorsements corresponding to a specific skill, and then applying a ranking method admitting weighted digraphs, such as PageRank. We describe the method, and test it on a synthetic network of 1493 nodes, fitted with endorsements.

Vehicular ad hoc networks (VANETs) allow vehicle-to-vehicle communication and, in particular, vehicle-generated announcements. Vehicles can use such announcements to warn nearby vehicles about road conditions (traffic jams, accidents). Thus, they can greatly increase the safety of driving. However, their trustworthiness must be guaranteed. A new system for vehicle-generated announcements is presented that is secure against external and internal attackers attempting to send fake messages. Internal attacks are thwarted by using an endorsement mechanism based on multisignatures. Besides, this scheme ensures that vehicles volunteering to generate and/or endorse trustworthy announcements do not have to sacrifice their privacy.

Checking data possession in networked information systems such as those related to critical infrastructures (power facilities, airports, data vaults, defense systems, etc.) is a matter of crucial importance. Remote data possession checking protocols permit to check that a remote server can access an uncorrupted file in such a way that the verifier does not need to know beforehand the entire file that is being verified. Unfortunately, current protocols only allow a limited number of successive verifications or are impractical from the computational point of view. In this paper, we present a new remote data possession checking protocol such that: i) it allows an unlimited number of file integrity verifications; ii) its maximum running time can be chosen at set-up time and traded off against storage at the verifier.

Data mining aims at extracting knowledge from data. Sometimes this requires the data owner to make data available to the data analyst. Unless the analyst is trusted by the data owner, the latter may wish to have his intellectual property rights protected. Watermarking is a way to provide some protection, not only for multimedia data, but also for numerical data. It consists of imperceptibly embedding a secret mark into the data to be protected. The mark can later be used to resolve any subsequent disputes on data ownership. This paper presents a watermarking method that embeds a watermark into each attribute of a multivariate continuous numerical dataset. This watermarking method is shown to be robust against random noise addition attacks. Data quality is assured to the extent that the watermarked data nearly preserve the attribute means and the covariance matrix from the original dataset. Our proposal is the first known watermarking system for multivariate numerical datasets with such robustness and quality properties.

Intellectual property protection of multimedia content is essential to the successful deployment of Internet content delivery platforms. There are two general approaches to multimedia copy protection: copy prevention and copy detection. Past experience shows that only copy detection based on mark embedding techniques looks promising. Multimedia fingerprinting means embedding a different buyer-identifying mark in each copy of the multimedia content being sold. Fingerprinting is subject to collusion attacks: a coalition of buyers collude and follow some strategy to mix their copies with the aim of obtaining a mixture from which none of their identifying marks can be retrieved; if their strategy is successful, the colluders can redistribute the mixture with impunity. A construction is presented in this paper to obtain fingerprinting codes for copyright protection which survive any collusion strategy involving up to three buyers (3-security). It is shown that the proposed scheme achieves 3-security with a codeword length dramatically shorter than the one required by the general Boneh-Shaw construction. Thus the proposed fingerprints require much less embedding capacity. Due to their own clandestine nature, collusions tend to involve a small number of buyers, so that there is plenty of use for codes providing cost-effective protection against collusions of size up to three.