Dual System Groups and its Applications --- Compact HIBE and More

We introduce the notion of *dual system groups*. - We show how to derive compact HIBE by instantiating the dual system framework in Waters (Crypto \u2709) and Lewko and Waters (TCC \u2710) with dual system groups. Our construction provides a unified treatment of the prior compact HIBE schemes from static assumptions. - We show how to instantiate dual system groups under the decisional subgroup assumption in composite-order groups and the decisional linear assumption ($d$-LIN) in prime-order groups. Along the way, we provide new tools for simulating properties of composite-order bilinear groups in prime-order groups. In particular, we present new randomization and parameter-hiding techniques in prime-order groups. Combining the two, we obtain a number of new encryption schemes, notably - a new construction of IBE in prime-order groups with shorter parameters; - a new construction of compact HIBE in prime-order groups whose structure closely mirrors the selectively secure HIBE scheme of Boneh, Boyen and Goh (Eurocrypt \u2705); - a new construction of compact spatial encryption in prime-order groups

Still Wrong Use of Pairings in Cryptography

Several pairing-based cryptographic protocols are recently proposed with a wide variety of new novel applications including the ones in emerging technologies like cloud computing, internet of things (IoT), e-health systems and wearable technologies. There have been however a wide range of incorrect use of these primitives. The paper of Galbraith, Paterson, and Smart (2006) pointed out most of the issues related to the incorrect use of pairing-based cryptography. However, we noticed that some recently proposed applications still do not use these primitives correctly. This leads to unrealizable, insecure or too inefficient designs of pairing-based protocols. We observed that one reason is not being aware of the recent advancements on solving the discrete logarithm problems in some groups. The main purpose of this article is to give an understandable, informative, and the most up-to-date criteria for the correct use of pairing-based cryptography. We thereby deliberately avoid most of the technical details and rather give special emphasis on the importance of the correct use of bilinear maps by realizing secure cryptographic protocols. We list a collection of some recent papers having wrong security assumptions or realizability/efficiency issues. Finally, we give a compact and an up-to-date recipe of the correct use of pairings.Comment: 25 page

Encryption’s Importance to Economic and Infrastructure Security

Det övergripande syftet med den här avhandlingen var att utreda om network coopetition, samarbete mellan konkurrerande aktörer, kan öka värdeskapandet inom hälso- och sjukvården. Inom hälso- och sjukvården är network coopetition ett ämne som fått liten uppmärksamhet i tidigare studier. För att besvara syftet utvecklades en modell för network coopetition inom hälso- och sjukvården. Modellen applicerades sedan på en del av vårdkedjan för patienter i behov av neurokirurgisk vård. Resultaten från avhandlingen visar att: (1) Förutsättningarna för network coopetition i vårdkedjan för patienter i behov av neurokirurgisk vård är uppfyllda. (2) Det finns exempel på horisontell network coopetition i den studerade vårdkedjan. (3) Det existerar en diskrepans mellan hur aktörerna  ser  på  sitt  eget  och  de  andra  aktörernas  värdeskapande. (4)  Värdeskapandet bör utvärderas som ett gemensamt system där hänsyn tas till alla aktörer och utvärderas på process- nivå där hänsyn tas till alla intressenter. Dessa resultat leder fram till den övergripande slutsatsen är att network coopetition bör kunna öka värdeskapandet för högspecialiserade vårdkedjor med en stor andel inomlänspatienter.The overall purpose of this thesis was to investigate whether network coopetition, cooperation between competitive actors, can increase the value creation within the health care system. Within health care, network coopetition is a subject granted little attention in previous research. To fulfil the purpose a model for network coopetition within the health care system was developed. The model was the applied to one part of the chain of care for patients in need of neurosurgery. The results from this thesis show: (1) The conditions for network coopetition in the chain of care for patients in need of neurosurgery are fulfilled. (2) Examples of horizontal network coopetition have been found in the studied chain of care. (3) There is an existing discrepancy between how each actor recognizes its own and the other actors’ value creation. (4) The value creation ought to be evaluated as a common system where all actors are taken into account and at a process level where all stakeholders are considered. These results supports the final conclusion that network coopetition ought to be able to increase the value creation for highly specialized chain of cares with a large share of within-county patients

Attacks on the Search-RLWE problem with small errors

The Ring Learning-With-Errors (RLWE) problem shows great promise for post-quantum cryptography and homomorphic encryption. We describe a new attack on the non-dual search RLWE problem with small error widths, using ring homomorphisms to finite fields and the chi-squared statistical test. In particular, we identify a "subfield vulnerability" (Section 5.2) and give a new attack which finds this vulnerability by mapping to a finite field extension and detecting non-uniformity with respect to the number of elements in the subfield. We use this attack to give examples of vulnerable RLWE instances in Galois number fields. We also extend the well-known search-to-decision reduction result to Galois fields with any unramified prime modulus q, regardless of the residue degree f of q, and we use this in our attacks. The time complexity of our attack is O(nq2f), where n is the degree of K and f is the residue degree of q in K. We also show an attack on the non-dual (resp. dual) RLWE problem with narrow error distributions in prime cyclotomic rings when the modulus is a ramified prime (resp. any integer). We demonstrate the attacks in practice by finding many vulnerable instances and successfully attacking them. We include the code for all attacks

A Survey on Homomorphic Encryption Schemes: Theory and Implementation

Legacy encryption systems depend on sharing a key (public or private) among the peers involved in exchanging an encrypted message. However, this approach poses privacy concerns. Especially with popular cloud services, the control over the privacy of the sensitive data is lost. Even when the keys are not shared, the encrypted material is shared with a third party that does not necessarily need to access the content. Moreover, untrusted servers, providers, and cloud operators can keep identifying elements of users long after users end the relationship with the services. Indeed, Homomorphic Encryption (HE), a special kind of encryption scheme, can address these concerns as it allows any third party to operate on the encrypted data without decrypting it in advance. Although this extremely useful feature of the HE scheme has been known for over 30 years, the first plausible and achievable Fully Homomorphic Encryption (FHE) scheme, which allows any computable function to perform on the encrypted data, was introduced by Craig Gentry in 2009. Even though this was a major achievement, different implementations so far demonstrated that FHE still needs to be improved significantly to be practical on every platform. First, we present the basics of HE and the details of the well-known Partially Homomorphic Encryption (PHE) and Somewhat Homomorphic Encryption (SWHE), which are important pillars of achieving FHE. Then, the main FHE families, which have become the base for the other follow-up FHE schemes are presented. Furthermore, the implementations and recent improvements in Gentry-type FHE schemes are also surveyed. Finally, further research directions are discussed. This survey is intended to give a clear knowledge and foundation to researchers and practitioners interested in knowing, applying, as well as extending the state of the art HE, PHE, SWHE, and FHE systems.Comment: - Updated. (October 6, 2017) - This paper is an early draft of the survey that is being submitted to ACM CSUR and has been uploaded to arXiv for feedback from stakeholder