793 research outputs found
Attribute-Based Signatures for Circuits from Bilinear Map
In attribute-based signatures, each signer receives a signing key from the authority,
which is associated with the signer\u27s attribute,
and using the signing key, the signer can issue a signature on any message under a predicate,
if his attribute satisfies the predicate.
One of the ultimate goals in this area
is to support a wide class of predicates,
such as the class of \emph{arbitrary circuits},
with \emph{practical efficiency} from \emph{a simple assumption},
since these three aspects determine the usefulness of the scheme.
We present an attribute-based signature scheme
which allows us to use an arbitrary circuit as the predicate
with practical efficiency from the symmetric external Diffie-Hellman assumption.
We achieve this by combining the efficiency of Groth-Sahai proofs,
which allow us to prove algebraic equations efficiently,
and the expressiveness of Groth-Ostrovsky-Sahai proofs,
which allow us to prove any NP relation via circuit satisfiability
Private Outsourcing of Polynomial Evaluation and Matrix Multiplication using Multilinear Maps
{\em Verifiable computation} (VC) allows a computationally weak client to
outsource the evaluation of a function on many inputs to a powerful but
untrusted server. The client invests a large amount of off-line computation and
gives an encoding of its function to the server. The server returns both an
evaluation of the function on the client's input and a proof such that the
client can verify the evaluation using substantially less effort than doing the
evaluation on its own. We consider how to privately outsource computations
using {\em privacy preserving} VC schemes whose executions reveal no
information on the client's input or function to the server. We construct VC
schemes with {\em input privacy} for univariate polynomial evaluation and
matrix multiplication and then extend them such that the {\em function privacy}
is also achieved. Our tool is the recently developed {mutilinear maps}. The
proposed VC schemes can be used in outsourcing {private information retrieval
(PIR)}.Comment: 23 pages, A preliminary version appears in the 12th International
Conference on Cryptology and Network Security (CANS 2013
素因数分解に基づく暗号における新たな手法
学位の種別: 課程博士審査委員会委員 : (主査)東京大学准教授 國廣 昇, 東京大学教授 山本 博資, 東京大学教授 津田 宏治, 東京大学講師 佐藤 一誠, 東京工業大学教授 田中 圭介University of Tokyo(東京大学
Advances in Functional Encryption
Functional encryption is a novel paradigm for public-key encryption that enables both fine-grained access control and selective computation on encrypted data, as is necessary to protect big, complex data in the cloud. In this thesis, I provide a brief introduction to functional encryption, and an overview of my contributions to the area
Attribute-Based Signatures for Unbounded Languages from Standard Assumptions
Attribute-based signature (ABS) schemes are advanced signature schemes
that simultaneously provide fine-grained authentication while protecting
privacy of the signer. Previously known expressive ABS schemes support
either the class of deterministic finite automata and circuits from
standard assumptions or Turing machines from the existence of
indistinguishability obfuscations.
In this paper, we propose the first ABS scheme for a very general policy
class, all deterministic Turin machines, from
a standard assumption, namely, the Symmetric External Diffie-Hellman (SXDH)
assumption. We also propose the first ABS scheme that allows
nondeterministic finite automata (NFA) to be used as policies.
Although the expressiveness of NFAs are more restricted than Turing
machines, this is the first scheme that supports nondeterministic
computations as policies.
Our main idea lies in abstracting ABS constructions
and presenting the concept of history of computations; this allows
a signer to prove possession of a policy that accepts the string associated
to a message in zero-knowledge while also hiding the policy, regardless of
the computational model being used. With this abstraction in hand, we are
able to construct ABS for Turing machines and NFAs using a surprisingly weak
NIZK proof system. Essentially we only require a NIZK proof system for proving that a (normal) signature is valid. Such a NIZK proof system together with a base signature scheme are, in turn, possible from bilinear groups under the SXDH assumption, and hence so are our ABS schemes
Multilinear Maps in Cryptography
Multilineare Abbildungen spielen in der modernen Kryptographie eine immer bedeutendere Rolle. In dieser Arbeit wird auf die Konstruktion, Anwendung und Verbesserung von multilinearen Abbildungen eingegangen
ADSNARK: Nearly practical and privacy-preserving proofs on authenticated data
We study the problem of privacy-preserving proofs on authenticated data, where a party receives data from a trusted source and is requested to prove computations over the data to third parties in a correct and private way, i.e., the third party learns no information on the data but is still assured that the claimed proof is valid. Our work particularly focuses on the challenging requirement that the third party should be able to verify the validity with respect to the specific data authenticated by the source — even without having access to that source. This problem is motivated by various scenarios emerging from several application areas such as wearable computing, smart metering, or general business-to-business interactions. Furthermore, these applications also demand any meaningful solution to satisfy additional properties related to usability and scalability. In this paper, we formalize the above three-party model, discuss concrete application scenarios, and then we design, build, and evaluate ADSNARK, a nearly practical system for proving arbitrary computations over authenticated data in a privacy-preserving manner. ADSNARK improves significantly over state-of-the-art solutions for this model. For instance, compared to corresponding solutions based on Pinocchio (Oakland’13), ADSNARK achieves up to 25× improvement in proof-computation time and a 20× reduction in prover storage space
Efficient Attribute-Based Signatures for Unbounded Arithmetic Branching Programs
This paper presents the first attribute-based signature (ABS) scheme in which the correspondence between
signers and signatures is captured in an arithmetic model of computation. Specifically, we design a fully
secure, i.e., adaptively unforgeable and perfectly signer-private ABS scheme for signing policies realizable
by arithmetic branching programs (ABP), which are a quite expressive model of arithmetic computations.
On a more positive note, the proposed scheme places no bound on the size and input length of the
supported signing policy ABP’s, and at the same time, supports the use of an input attribute for an
arbitrary number of times inside a signing policy ABP, i.e., the so called unbounded multi-use of attributes.
The size of our public parameters is constant with respect to the sizes of the signing attribute vectors
and signing policies available in the system. The construction is built in (asymmetric) bilinear groups
of prime order, and its unforgeability is derived in the standard model under (asymmetric version of)
the well-studied decisional linear (DLIN) assumption coupled with the existence of standard collision
resistant hash functions. Due to the use of the arithmetic model as opposed to the boolean one, our ABS
scheme not only excels significantly over the existing state-of-the-art constructions in terms of concrete
efficiency, but also achieves improved applicability in various practical scenarios. Our principal technical
contributions are (a) extending the techniques of Okamoto and Takashima [PKC 2011, PKC 2013], which
were originally developed in the context of boolean span programs, to the arithmetic setting; and (b)
innovating new ideas to allow unbounded multi-use of attributes inside ABP’s, which themselves are of
unbounded size and input length
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