566 research outputs found
Non-malleable Fuzzy Extractors
No full textFuzzy extractors (Dodis et al. EUROCRYPT’04) allow to generate close to uniform randomness using correlated distributions outputting samples that are close over some metric space. The latter requires to produce a helper value (along with the extracted key) that can be used to recover the key using close samples. Robust fuzzy extractors (Dodis et al., CRYPTO’06) further protect the helper string from arbitrary active manipulations, by requiring that the reconstructed key using a modified helper string cannot yield a different extractor output. It is well known that statistical robustness inherently requires large min-entropy (in fact, m>n/2 where n is the bit length of the samples) from the underlying correlated distributions, even assuming trusted setup. Motivated by this limitation, we start the investigation of security properties weaker than robustness, but that can be achieved in the plain model assuming only minimal min-entropy (in fact, m=ω(logn)), while still being useful for applications. We identify one such property and put forward the notion of non-malleable fuzzy extractors. Intuitively, non-malleability relaxes the robustness property by allowing the reconstructed key using a modified helper string to be different from the original extractor output, as long as it is a completely unrelated value. We give a black-box construction of non-malleable fuzzy extractors in the plain model for min-entropy m=ω(logn), against interesting families of manipulations including split-state tampering, small-depth circuits tampering, and space-bounded tampering (in the information-theoretic setting), as well as tampering via partial functions (assuming one-way functions). We leave it as an open problem to establish whether non-malleability is possible for arbitrary manipulations of the helper string. Finally, we show an application of non-malleable fuzzy extractors to protect stateless cryptographic primitives whose secret keys are derived using fuzzy correlated distributions
Multi-key and Multi-input Predicate Encryption (for Conjunctions) from Learning with Errors
No full textWe put forward two natural generalizations of predicate encryption (PE), dubbed multi-key and multi-input PE. More in details, our contributions are threefold. Definitions. We formalize security of multi-key PE and multi-input PE following the standard indistinguishability paradigm, and modeling security both against malicious senders (i.e., corruption of encryption keys) and malicious receivers (i.e., collusions). Constructions. We construct adaptively secure multi-key and multi-input PE supporting the conjunction of poly-many arbitrary single-input predicates, assuming the sub-exponential hardness of the learning with errors (LWE) problem. Applications. We show that multi-key and multi-input PE for expressive enough predicates suffices for interesting cryptographic applications, including non-interactive multi-party computation (NI-MPC) and matchmaking encryption (ME). In particular, plugging in our constructions of multi-key and multi-input PE, under the sub-exponential LWE assumption, we obtain the first ME supporting arbitrary policies with unbounded collusions, as well as robust (resp. non-robust) NI-MPC for so-called all-or-nothing functions satisfying a non-trivial notion of reusability and supporting a constant (resp. polynomial) number of parties. Prior to our work, both of these applications required much heavier tools such as indistinguishability obfuscation or compact functional encryption
Match me if you can: matchmaking encryption and its applications
No full textWe introduce a new form of encryption that we name matchmaking encryption (ME). Using ME, sender S and receiver R (each with its own attributes) can both specify policies the other party must satisfy in order for the message to be revealed. The main security guarantee is that of privacy-preserving policy matching: During decryption nothing is leaked beyond the fact that a match occurred/did not occur. ME opens up new ways of secretly communicating, and enables several new applications where both participants can specify fine-grained access policies to encrypted data. For instance, in social matchmaking, S can encrypt a file containing his/her personal details and specify a policy so that the file can be decrypted only by his/her ideal partner. On the other end, a receiver R will be able to decrypt the file only if S corresponds to his/her ideal partner defined through a policy. On the theoretical side, we define security for ME, as well as provide generic frameworks for constructing ME from functional encryption. These constructions need to face the technical challenge of simultaneously checking the policies chosen by S and R, to avoid any leakage. On the practical side, we construct an efficient identity-based scheme for equality policies, with provable security in the random oracle model under the standard BDH assumption. We implement and evaluate our scheme and provide experimental evidence that our construction is practical. We also apply identity-based ME to a concrete use case, in particular for creating an anonymous bulletin board over a Tor network
Which kind of philosopher was Danilo Pejović?
Full text linkU ovom kratkom prilogu autorica pokušava opisati narav Danila Pejovića kao filozofa. Njegovo bitno obilježje bila je filozofijska i svetovna suverenost.In this short contribution the author tries to describe the nature of Danilo Pejović as a philosopher. His main characteristic was a philosophical and secular sovereignity
Public immunization against complete subversion without random oracles
No full textWe seek constructions of general-purpose immunizers that take arbitrary cryptographic primitives, and transform them into ones that withstand a powerful “malicious but proud” adversary, who attempts to break security by possibly subverting the implementation of all algorithms (including the immunizer itself!), while trying not to be detected. This question is motivated by the recent evidence of cryptographic schemes being intentionally weakened, or designed together with hidden backdoors, e.g., with the scope of mass surveillance. Our main result is a subversion-secure immunizer in the plain model (assuming collision-resistant hashing), that works for a fairly large class of deterministic primitives, i.e., cryptoschemes where a secret (but tamperable) random source is used to generate the keys and the public parameters, whereas all other algorithms are deterministic. The immunizer relies on an additional independent source of public randomness, which is used to sample a public seed. While the public source is untamperable, the subversion of all other algorithms is allowed to depend on it. Previous work in the area only obtained subversion-secure immunization for very restricted classes of primitives, often in weaker models of subversion and relying on random oracles, or by leveraging a higher number of independent random sources
O realismo de Danilo Zolo
Full text linkThe article aims to make an analysis of the main aspects of the thought of Danilo Zolo, who turned 80 in January 2016. Initially, we examine the epistemological foundations of the legal realism proposed by Zolo. Then we deal with the significance of this realism for a possible theory of democracy. Finally, we analyze the contributions of that author to the philosophy of international law, which made him one of the leading thinkers in this area in recent decades.Keywords: philosophy of law, political philosophy, legal realism.O artigo se propõe a fazer uma análise de aspectos centrais do pensamento do jusfilósofo Danilo Zolo, que completou 80 anos em janeiro de 2016. Inicialmente, examina os fundamentos epistemológicos do realismo jurídico proposto por Zolo. Em seguida, aborda a significância desse realismo para uma possível teoria da democracia. Por fim, analisa as contribuições do referido autor para a filosofia do direito internacional, as quais o colocam como um dos mais destacados pensadores desta área nas últimas décadas.Palavras-chave: filosofia do direito, filosofia política, realismo jurídico
La prospettiva pluralistica e multiculturale in Danilo Zolo
No full textThis essay takes into consideration the pluralistic perspective in Danilo
Zolo’s thought, dealing with the way in which the multiculturalist theme is situated
in the legal-philosophical reflection of the author. In this regard, the article underlines
a pioneering attention to multiculturalism as a theoretical approach inextricably
linked to the political and legal dimension. The analysis will focus on the connection
between the multiculturalist instance and Zolo’s substantive approach on citizenship,
in the context of a discourse on the concept of national belonging. Finally, within a
brief dialogue with Danilo Zolo starting from the Canadian experience, the paper aims
to highlight the difference between an analytical and interpretative horizon focused
on the crisis of the monistic Nation-State and a radical disarticulation of national
citizenship
Pisanie Ojca. „Gen schulzowski” w prozie Danilo Kiša
Full text linkDanilo Kiš claimed that his favorite works of other writers not only contributed to his own books as their “ancestors,” but also became parts of his spiritual DNA. The author makes an attempt at finding the “Schulzean gene” in The Family Circus and reveal the invisible presence of Schulz in other works by Kiš. Schulz has not been mentioned there, but he remains “present through his absence,” just like Kiš’s father, the protagonist of Hourglass, called “a novel about absence.
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