3,772 research outputs found
Predictable arguments of knowledge
We initiate a formal investigation on the power of predictability for argument of knowledge systems for NP. Specifically, we consider private-coin argument systems where the answer of the prover can be predicted, given the private randomness of the verifier; we call such protocols Predictable Arguments of Knowledge (PAoK).
Our study encompasses a full characterization of PAoK, showing that such arguments can be made extremely laconic, with the prover sending a single bit, and assumed to have only one round (i.e., two messages) of communication without loss of generality.
We additionally explore PAoK satisfying additional properties (including zero-knowledge and the possibility of re-using the same challenge across multiple executions with the prover), present several constructions of PAoK relying on different cryptographic tools, and discuss applications to cryptography
Finding Structured and Unstructured Features to Improve the Search Result of Complex Question
-Recently, search engine got challenge deal with such a natural language questions.
Sometimes, these questions are complex questions. A complex question is a question that
consists several clauses, several intentions or need long answer.
In this work we proposed that finding structured features and unstructured features of
questions and using structured data and unstructured data could improve the search result
of complex questions. According to those, we will use two approaches, IR approach and
structured retrieval, QA template.
Our framework consists of three parts. Question analysis, Resource Discovery and
Analysis The Relevant Answer. In Question Analysis we used a few assumptions, and
tried to find structured and unstructured features of the questions. Structured feature
refers to Structured data and unstructured feature refers to unstructured data. In the
resource discovery we integrated structured data (relational database) and unstructured
data (webpage) to take the advantaged of two kinds of data to improve and reach the
relevant answer. We will find the best top fragments from context of the webpage In the
Relevant Answer part, we made a score matching between the result from structured data
and unstructured data, then finally used QA template to reformulate the question.
In the experiment result, it shows that using structured feature and unstructured
feature and using both structured and unstructured data, using approach IR and QA
template could improve the search result of complex questions
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A New Lightweight Symmetric Searchable Encryption Scheme for String Identification
In this paper, we provide an efficient and easy-to-implement symmetric searchable encryption scheme (SSE) for string search, which takes one round of communication, O(n) times of computations over n documents. Unlike previous schemes, we use hash-chaining instead of chain of encryption operations for index generation, which makes it suitable for lightweight applications. Unlike the previous SSE schemes for string search, with our scheme, server learns nothing about the frequency and the relative positions of the words being searched except what it can learn from the history. We are the first to propose probabilistic trapdoors in SSE for string search. We provide concrete proof of non-adaptive security of our scheme against honest-but-curious server based on the definitions of [12]. We also introduce a new notion of search pattern privacy, which gives a measure of security against the leakage from trapdoor. We have shown that our scheme is secure under search pattern indistinguishability definition. We show why SSE scheme for string search cannot attain adaptive indistinguishability criteria as mentioned in [12]. We also propose modifications of our scheme so that the scheme can be used against active adversaries at the cost of more rounds of communications and memory space. We validate our scheme against two different commercial datasets (see [1],[2])
Non-malleable secret sharing against joint tampering attacks
Since thousands of years ago, the goal of cryptography has been to hide messages from prying eyes. In recent times, cryptography two important changes: first, cryptography itself evolved from just being about encryption to a broader class of situations coming from the digital era; second, the way of studying cryptography evolved from creating ``seemingly hard'' cryptographic schemes to constructing schemes which are provably secure.
However, once the mathematical abstraction of cryptographic primitives started to be too hard to break, attackers found another way to defeat security. Side channel attacks have been proved to be very effective in this task, breaking the security of otherwise provably secure schemes. Because of this, recent trends in cryptography aim to capture this situation and construct schemes that are secure even against such powerful attacks.
In this setting, this thesis specializes in the study of secret sharing, an important cryptographic primitive that allows to balance privacy and integrity of data and also has applications to multi-party protocols. Namely, continuing the trend which aims to protect against side channel attacks, this thesis brings some contributions to the state of the art of the so-called leakage-resilient and non-malleable secret sharing schemes, which have stronger guarantees against attackers that are able to learn information from possibly all the shares and even tamper with the shares and see the effects of the tampering.
The main contributions of this thesis are twofold. First, we construct secret sharing schemes that are secure against a very powerful class of attacks which, informally, allows the attacker to jointly leak some information and tamper with the shares in a continuous fashion. Second, we study the capacity of continuously non-malleable secret sharing schemes, that is, the maximum achievable information rate. Roughly speaking, we find some lower bounds to the size that the shares must have in order to achieve some forms of non-malleability
Automating quantitative information flow
PhDUnprecedented quantities of personal and business data are collected, stored,
shared, and processed by countless institutions all over the world. Prominent
examples include sharing personal data on social networking sites, storing
credit card details in every store, tracking customer preferences of supermarket
chains, and storing key personal data on biometric passports.
Confidentiality issues naturally arise from this global data growth. There
are continously reports about how private data is leaked from confidential
sources where the implications of the leaks range from embarrassment to serious
personal privacy and business damages.
This dissertation addresses the problem of automatically quantifying the
amount of leaked information in programs. It presents multiple program analysis
techniques of different degrees of automation and scalability.
The contributions of this thesis are two fold: a theoretical result and two
different methods for inferring and checking quantitative information flows are
presented.
The theoretical result relates the amount of possible leakage under any
probability distribution back to the order relation in Landauer and Redmond’s
lattice of partitions [35]. The practical results are split in two analyses: a first
analysis precisely infers the information leakage using SAT solving and model
counting; a second analysis defines quantitative policies which are reduced to
checking a k-safety problem. A novel feature allows reasoning independent of
the secret space.
The presented tools are applied to real, existing leakage vulnerabilities in
operating system code. This has to be understood and weighted within the
context of the information flow literature which suffers under an apparent lack
of practical examples and applications. This thesis studies such “real leaks”
which could influence future strategies for finding information leaks
Forward and Backward Private Searchable Encryption from Constrained Cryptographic Primitives
Using dynamic Searchable Symmetric Encryption, a user with limited storage resources can securely outsource a database to an untrusted server, in such a way that the database can still be searched and updated efficiently. For these schemes, it would be desirable that updates do not reveal any information a priori about the modifications they carry out, and that deleted results remain inaccessible to the server a posteriori. If the first property, called forward privacy, has been the main motivation of recent works, the second one, backward privacy, has been overlooked.
In this paper, we study for the first time the notion of backward privacy for searchable encryption. After giving formal definitions for different flavors of backward privacy, we present several schemes achieving both forward and backward privacy, with various efficiency trade-offs.
Our constructions crucially rely on primitives such as constrained pseudo-random functions and puncturable encryption schemes. Using these advanced cryptographic primitives allows for a fine-grained control of the power of the adversary, preventing her from evaluating functions on selected inputs, or decrypting specific ciphertexts. In turn, this high degree of control allows our SSE constructions to achieve the stronger forms of privacy outlined above. As an example, we present a framework to construct forward-private schemes from range-constrained pseudo-random functions.
Finally, we provide experimental results for implementations of our schemes, and study their practical efficiency
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