418 research outputs found
Anonymous quantum communication
We present the first protocol for the anonymous transmission of a quantum
state that is information-theoretically secure against an active adversary,
without any assumption on the number of corrupt participants. The anonymity of
the sender and receiver is perfectly preserved, and the privacy of the quantum
state is protected except with exponentially small probability. Even though a
single corrupt participant can cause the protocol to abort, the quantum state
can only be destroyed with exponentially small probability: if the protocol
succeeds, the state is transferred to the receiver and otherwise it remains in
the hands of the sender (provided the receiver is honest).Comment: 11 pages, to appear in Proceedings of ASIACRYPT, 200
Making Code Voting Secure against Insider Threats using Unconditionally Secure MIX Schemes and Human PSMT Protocols
Code voting was introduced by Chaum as a solution for using a possibly
infected-by-malware device to cast a vote in an electronic voting application.
Chaum's work on code voting assumed voting codes are physically delivered to
voters using the mail system, implicitly requiring to trust the mail system.
This is not necessarily a valid assumption to make - especially if the mail
system cannot be trusted. When conspiring with the recipient of the cast
ballots, privacy is broken.
It is clear to the public that when it comes to privacy, computers and
"secure" communication over the Internet cannot fully be trusted. This
emphasizes the importance of using: (1) Unconditional security for secure
network communication. (2) Reduce reliance on untrusted computers.
In this paper we explore how to remove the mail system trust assumption in
code voting. We use PSMT protocols (SCN 2012) where with the help of visual
aids, humans can carry out addition correctly with a 99\% degree of
accuracy. We introduce an unconditionally secure MIX based on the combinatorics
of set systems.
Given that end users of our proposed voting scheme construction are humans we
\emph{cannot use} classical Secure Multi Party Computation protocols.
Our solutions are for both single and multi-seat elections achieving:
\begin{enumerate}[i)]
\item An anonymous and perfectly secure communication network secure against
a -bounded passive adversary used to deliver voting,
\item The end step of the protocol can be handled by a human to evade the
threat of malware. \end{enumerate} We do not focus on active adversaries
Universally Convertible Directed Signatures
Many variants of Chaum and van Antwerpen's undeniable signatures have been proposed to achieve specific properties desired in real-world applications of cryptography. Among them, directed signatures were introduced by Lim and Lee in 1993. Directed signatures differ from the well-known confirmer signatures in that the signer has the simultaneous abilities to confirm, deny and individually convert a signature. The universal conversion of these signatures has remained an open problem since their introduction in 1993. This paper provides a positive answer to this quest by showing a very efficient design for universally convertible directed signatures (UCDS) both in terms of computational complexity and signature size. Our construction relies on the so-called xyz-trick applicable to bilinear map groups. We define proper security notions for UCDS schemes and show that our construction is secure, in the random oracle model, under computational assumptions close to the CDH and DDH assumptions. Finally, we introduce and realize traceable universally convertible directed signatures where a master tracing key allows to link signatures to their direction
Rich Counter-Examples for Temporal-Epistemic Logic Model Checking
Model checking verifies that a model of a system satisfies a given property,
and otherwise produces a counter-example explaining the violation. The verified
properties are formally expressed in temporal logics. Some temporal logics,
such as CTL, are branching: they allow to express facts about the whole
computation tree of the model, rather than on each single linear computation.
This branching aspect is even more critical when dealing with multi-modal
logics, i.e. logics expressing facts about systems with several transition
relations. A prominent example is CTLK, a logic that reasons about temporal and
epistemic properties of multi-agent systems. In general, model checkers produce
linear counter-examples for failed properties, composed of a single computation
path of the model. But some branching properties are only poorly and partially
explained by a linear counter-example.
This paper proposes richer counter-example structures called tree-like
annotated counter-examples (TLACEs), for properties in Action-Restricted CTL
(ARCTL), an extension of CTL quantifying paths restricted in terms of actions
labeling transitions of the model. These counter-examples have a branching
structure that supports more complete description of property violations.
Elements of these counter-examples are annotated with parts of the property to
give a better understanding of their structure. Visualization and browsing of
these richer counter-examples become a critical issue, as the number of
branches and states can grow exponentially for deeply-nested properties.
This paper formally defines the structure of TLACEs, characterizes adequate
counter-examples w.r.t. models and failed properties, and gives a generation
algorithm for ARCTL properties. It also illustrates the approach with examples
in CTLK, using a reduction of CTLK to ARCTL. The proposed approach has been
implemented, first by extending the NuSMV model checker to generate and export
branching counter-examples, secondly by providing an interactive graphical
interface to visualize and browse them.Comment: In Proceedings IWIGP 2012, arXiv:1202.422
Anonymous Single-Sign-On for n designated services with traceability
Anonymous Single-Sign-On authentication schemes have been proposed to allow
users to access a service protected by a verifier without revealing their
identity which has become more important due to the introduction of strong
privacy regulations. In this paper we describe a new approach whereby anonymous
authentication to different verifiers is achieved via authorisation tags and
pseudonyms. The particular innovation of our scheme is authentication can only
occur between a user and its designated verifier for a service, and the
verification cannot be performed by any other verifier. The benefit of this
authentication approach is that it prevents information leakage of a user's
service access information, even if the verifiers for these services collude
which each other. Our scheme also supports a trusted third party who is
authorised to de-anonymise the user and reveal her whole services access
information if required. Furthermore, our scheme is lightweight because it does
not rely on attribute or policy-based signature schemes to enable access to
multiple services. The scheme's security model is given together with a
security proof, an implementation and a performance evaluation.Comment: 3
Privacy-Preserving Methods for Sharing Financial Risk Exposures
Unlike other industries in which intellectual property is patentable, the
financial industry relies on trade secrecy to protect its business processes
and methods, which can obscure critical financial risk exposures from
regulators and the public. We develop methods for sharing and aggregating such
risk exposures that protect the privacy of all parties involved and without the
need for a trusted third party. Our approach employs secure multi-party
computation techniques from cryptography in which multiple parties are able to
compute joint functions without revealing their individual inputs. In our
framework, individual financial institutions evaluate a protocol on their
proprietary data which cannot be inverted, leading to secure computations of
real-valued statistics such a concentration indexes, pairwise correlations, and
other single- and multi-point statistics. The proposed protocols are
computationally tractable on realistic sample sizes. Potential financial
applications include: the construction of privacy-preserving real-time indexes
of bank capital and leverage ratios; the monitoring of delegated portfolio
investments; financial audits; and the publication of new indexes of
proprietary trading strategies
E-Voting in an ubicomp world: trust, privacy, and social implications
The advances made in technology have unchained the user from the desktop into interactions where access is anywhere, anytime. In addition, the introduction of ubiquitous computing (ubicomp) will see further changes in how we interact with technology and also socially. Ubicomp evokes a near future in which humans will be surrounded by “always-on,” unobtrusive, interconnected intelligent objects where information is exchanged seamlessly. This seamless exchange of information has vast social implications, in particular the protection and management of personal information. This research project investigates the concepts of trust and privacy issues specifically related to the exchange of e-voting information when using a ubicomp type system
- …