11,716 research outputs found
Making Existential-Unforgeable Signatures Strongly Unforgeable in the Quantum Random-Oracle Model
Strongly unforgeable signature schemes provide a more stringent security
guarantee than the standard existential unforgeability. It requires that not
only forging a signature on a new message is hard, it is infeasible as well to
produce a new signature on a message for which the adversary has seen valid
signatures before. Strongly unforgeable signatures are useful both in practice
and as a building block in many cryptographic constructions.
This work investigates a generic transformation that compiles any
existential-unforgeable scheme into a strongly unforgeable one, which was
proposed by Teranishi et al. and was proven in the classical random-oracle
model. Our main contribution is showing that the transformation also works
against quantum adversaries in the quantum random-oracle model. We develop
proof techniques such as adaptively programming a quantum random-oracle in a
new setting, which could be of independent interest. Applying the
transformation to an existential-unforgeable signature scheme due to Cash et
al., which can be shown to be quantum-secure assuming certain lattice problems
are hard for quantum computers, we get an efficient quantum-secure strongly
unforgeable signature scheme in the quantum random-oracle model.Comment: 15 pages, to appear in Proceedings TQC 201
Well-Founded Semantics for Extended Datalog and Ontological Reasoning
The Datalog± family of expressive extensions of Datalog has recently been introduced as a new paradigm for query answering over ontologies, which captures and extends several common description logics. It extends plain Datalog by features such as existentially quantified rule heads and, at the same time, restricts the rule syntax so as to achieve decidability and tractability. In this paper, we continue the research on Datalog±. More precisely, we generalize the well-founded semantics (WFS), as the standard semantics for nonmonotonic normal programs in the database context, to Datalog± programs with negation under the unique name assumption (UNA). We prove that for guarded Datalog± with negation under the standard WFS, answering normal Boolean conjunctive queries is decidable, and we provide precise complexity results for this problem, namely, in particular, completeness for PTIME (resp., 2-EXPTIME) in the data (resp., combined) complexity
When Can We Answer Queries Using Result-Bounded Data Interfaces?
We consider answering queries on data available through access methods, that
provide lookup access to the tuples matching a given binding. Such interfaces
are common on the Web; further, they often have bounds on how many results they
can return, e.g., because of pagination or rate limits. We thus study
result-bounded methods, which may return only a limited number of tuples. We
study how to decide if a query is answerable using result-bounded methods,
i.e., how to compute a plan that returns all answers to the query using the
methods, assuming that the underlying data satisfies some integrity
constraints. We first show how to reduce answerability to a query containment
problem with constraints. Second, we show "schema simplification" theorems
describing when and how result bounded services can be used. Finally, we use
these theorems to give decidability and complexity results about answerability
for common constraint classes.Comment: 65 pages; journal version of the PODS'18 paper arXiv:1706.0793
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