Revisiting Shared Data Protection Against Key Exposure

This paper puts a new light on secure data storage inside distributed systems. Specifically, it revisits computational secret sharing in a situation where the encryption key is exposed to an attacker. It comes with several contributions: First, it defines a security model for encryption schemes, where we ask for additional resilience against exposure of the encryption key. Precisely we ask for (1) indistinguishability of plaintexts under full ciphertext knowledge, (2) indistinguishability for an adversary who learns: the encryption key, plus all but one share of the ciphertext. (2) relaxes the "all-or-nothing" property to a more realistic setting, where the ciphertext is transformed into a number of shares, such that the adversary can't access one of them. (1) asks that, unless the user's key is disclosed, noone else than the user can retrieve information about the plaintext. Second, it introduces a new computationally secure encryption-then-sharing scheme, that protects the data in the previously defined attacker model. It consists in data encryption followed by a linear transformation of the ciphertext, then its fragmentation into shares, along with secret sharing of the randomness used for encryption. The computational overhead in addition to data encryption is reduced by half with respect to state of the art. Third, it provides for the first time cryptographic proofs in this context of key exposure. It emphasizes that the security of our scheme relies only on a simple cryptanalysis resilience assumption for blockciphers in public key mode: indistinguishability from random, of the sequence of diferentials of a random value. Fourth, it provides an alternative scheme relying on the more theoretical random permutation model. It consists in encrypting with sponge functions in duplex mode then, as before, secret-sharing the randomness

Ad Hoc Multi-Input Functional Encryption

Consider sources that supply sensitive data to an aggregator. Standard encryption only hides the data from eavesdroppers, but using specialized encryption one can hope to hide the data (to the extent possible) from the aggregator itself. For flexibility and security, we envision schemes that allow sources to supply encrypted data, such that at any point a dynamically-chosen subset of sources can allow an agreed-upon joint function of their data to be computed by the aggregator. A primitive called multi-input functional encryption (MIFE), due to Goldwasser et al. (EUROCRYPT 2014), comes close, but has two main limitations: - it requires trust in a third party, who is able to decrypt all the data, and - it requires function arity to be fixed at setup time and to be equal to the number of parties. To drop these limitations, we introduce a new notion of ad hoc MIFE. In our setting, each source generates its own public key and issues individual, function-specific secret keys to an aggregator. For successful decryption, an aggregator must obtain a separate key from each source whose ciphertext is being computed upon. The aggregator could obtain multiple such secret-keys from a user corresponding to functions of varying arity. For this primitive, we obtain the following results: - We show that standard MIFE for general functions can be bootstrapped to ad hoc MIFE for free, i.e. without making any additional assumption. - We provide a direct construction of ad hoc MIFE for the inner product functionality based on the Learning with Errors (LWE) assumption. This yields the first construction of this natural primitive based on a standard assumption. At a technical level, our results are obtained by combining standard MIFE schemes and two-round secure multiparty computation (MPC) protocols in novel ways highlighting an interesting interplay between MIFE and two-round MPC

KALwEN+: Practical Key Management Schemes for Gossip-Based Wireless Medical Sensor Networks

The constrained resources of sensors restrict the design of a key management scheme for wireless sensor networks (WSNs). In this work, we first formalize the security model of ALwEN, which is a gossip-based wireless medical sensor network (WMSN) for ambient assisted living. Our security model considers the node capture, the gossip-based network and the revocation problems, which should be valuable for ALwEN-like applications. Based on Shamir's secret sharing technique, we then propose two key management schemes for ALwEN, namely the KALwEN+ schemes, which are proven with the security properties defined in the security model. The KALwEN+ schemes not only fit ALwEN, but also can be tailored to other scalable wireless sensor networks based on gossiping

A practical and secure multi-keyword search method over encrypted cloud data

Cloud computing technologies become more and more popular every year, as many organizations tend to outsource their data utilizing robust and fast services of clouds while lowering the cost of hardware ownership. Although its benefits are welcomed, privacy is still a remaining concern that needs to be addressed. We propose an efficient privacy-preserving search method over encrypted cloud data that utilizes minhash functions. Most of the work in literature can only support a single feature search in queries which reduces the effectiveness. One of the main advantages of our proposed method is the capability of multi-keyword search in a single query. The proposed method is proved to satisfy adaptive semantic security definition. We also combine an effective ranking capability that is based on term frequency-inverse document frequency (tf-idf) values of keyword document pairs. Our analysis demonstrates that the proposed scheme is proved to be privacy-preserving, efficient and effective

POPE: Partial Order Preserving Encoding

Recently there has been much interest in performing search queries over encrypted data to enable functionality while protecting sensitive data. One particularly efficient mechanism for executing such queries is order-preserving encryption/encoding (OPE) which results in ciphertexts that preserve the relative order of the underlying plaintexts thus allowing range and comparison queries to be performed directly on ciphertexts. In this paper, we propose an alternative approach to range queries over encrypted data that is optimized to support insert-heavy workloads as are common in "big data" applications while still maintaining search functionality and achieving stronger security. Specifically, we propose a new primitive called partial order preserving encoding (POPE) that achieves ideal OPE security with frequency hiding and also leaves a sizable fraction of the data pairwise incomparable. Using only O(1) persistent and $O(n^\epsilon)$ non-persistent client storage for $0<\epsilon<1$, our POPE scheme provides extremely fast batch insertion consisting of a single round, and efficient search with O(1) amortized cost for up to $O(n^{1-\epsilon})$ search queries. This improved security and performance makes our scheme better suited for today's insert-heavy databases.Comment: Appears in ACM CCS 2016 Proceeding

SPAE un schéma opératoire pour l'AES sur du matériel bas-coût.

We propose SPAE, a single pass, patent free, authenticated encryption with associated data (AEAD) for AES. The algorithm has been developped to address the needs of a growing trend in IoT systems: storing code and data on a low cost flash memory external to the main SOC. Existing AEAD algorithms such as OCB, GCM, CCM, EAX , SIV, provide the required functionality however in practice each of them suffer from various drawbacks for this particular use case. Academic contributions such as ASCON and AEGIS-128 are suitable and efficient however they require the development of new hardware accelerators and they use primitives which are not 'approved' by governemental institutions such as NIST, BSI, ANSSI. From a silicon manufacturer point of view, an efficient AEAD which use existing AES hardware is much more enticing: the AES is required already by most industry standards invovling symmetric encryption (GSMA, EMVco, FIDO, Bluetooth, ZigBee to name few). This paper expose the properties of an ideal AEAD for external memory encryption, present the SPAE algorithm and analyze various security aspects. Performances of SPAE on actual hardware are better than OCB, GCM and CCM.Nous présentons SPAE, un schéma en une passe, libre de droit, d'encryption authentifiée avec données associées (AEAD) appliqué à l'AES. Cet algorithme a été développé afin de répondre à une tendance grandissante dans l'internet des objets: stocker du code et des données sur une mémoire flash à bas coût externe au système sur puce (SOC). Des algorithmes AEAD existent déjà tels que OCB, GCM, CCM, EAX, SIV, ils répondent à l'usage demandé cependant en pratique chacun de ces algorithmes présente des désavantages pour cet usage particulier. Les contributions académique telles que ASCON et AEGIS-128 sont appropriés et efficaces cependant ils nécessitent le développement de nouveaux accélérateurs matériels et ils utilisent des primitives qui ne sont pas approuvés par les instituions gouvernementales telles que le NIST, BSI ANSSI. Du point de vue du fabricant de silicone, un AEAD efficace qui utilise du matériel AES existant est beaucoup plus attirant: l'AES est déjà requis par la plupart des standards industriels utilisant de l’encryption symétrique (GSMA, EMVco, FIDO, Bluetooth, ZigBee par exemple). Cet article montre les propriétés d'un AEAD idéal pour de la mémoire encryptée externe, présente l'algorithme SPAE et analyse plusieurs aspects de sécurité. Les performances de SPAE sur du matériel actuel sont meilleures que sur OCB, GCM, et CCM