1,732 research outputs found
Short undeniable signatures:design, analysis, and applications
Digital signatures are one of the main achievements of public-key cryptography and constitute a fundamental tool to ensure data authentication. Although their universal verifiability has the advantage to facilitate their verification by the recipient, this property may have undesirable consequences when dealing with sensitive and private information. Motivated by such considerations, undeniable signatures, whose verification requires the cooperation of the signer in an interactive way, were invented. This thesis is mainly devoted to the design and analysis of short undeniable signatures. Exploiting their online property, we can achieve signatures with a fully scalable size depending on the security requirements. To this end, we develop a general framework based on the interpolation of group elements by a group homomorphism, leading to the design of a generic undeniable signature scheme. On the one hand, this paradigm allows to consider some previous undeniable signature schemes in a unified setting. On the other hand, by selecting group homomorphisms with a small group range, we obtain very short signatures. After providing theoretical results related to the interpolation of group homomorphisms, we develop some interactive proofs in which the prover convinces a verifier of the interpolation (resp. non-interpolation) of some given points by a group homomorphism which he keeps secret. Based on these protocols, we devise our new undeniable signature scheme and prove its security in a formal way. We theoretically analyze the special class of group characters on Z*n. After studying algorithmic aspects of the homomorphism evaluation, we compare the efficiency of different homomorphisms and show that the Legendre symbol leads to the fastest signature generation. We investigate potential applications based on the specific properties of our signature scheme. Finally, in a topic closely related to undeniable signatures, we revisit the designated confirmer signature of Chaum and formally prove the security of a generalized version
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
A Practical Set-Membership Proof for Privacy-Preserving NFC Mobile Ticketing
To ensure the privacy of users in transport systems, researchers are working
on new protocols providing the best security guarantees while respecting
functional requirements of transport operators. In this paper, we design a
secure NFC m-ticketing protocol for public transport that preserves users'
anonymity and prevents transport operators from tracing their customers' trips.
To this end, we introduce a new practical set-membership proof that does not
require provers nor verifiers (but in a specific scenario for verifiers) to
perform pairing computations. It is therefore particularly suitable for our
(ticketing) setting where provers hold SIM/UICC cards that do not support such
costly computations. We also propose several optimizations of Boneh-Boyen type
signature schemes, which are of independent interest, increasing their
performance and efficiency during NFC transactions. Our m-ticketing protocol
offers greater flexibility compared to previous solutions as it enables the
post-payment and the off-line validation of m-tickets. By implementing a
prototype using a standard NFC SIM card, we show that it fulfils the stringent
functional requirement imposed by transport operators whilst using strong
security parameters. In particular, a validation can be completed in 184.25 ms
when the mobile is switched on, and in 266.52 ms when the mobile is switched
off or its battery is flat
Proxy Signature Scheme with Effective Revocation Using Bilinear Pairings
We present a proxy signature scheme using bilinear pairings that provides
effective proxy revocation. The scheme uses a binding-blinding technique to
avoid secure channel requirements in the key issuance stage. With this
technique, the signer receives a partial private key from a trusted authority
and unblinds it to get his private key, in turn, overcomes the key escrow
problem which is a constraint in most of the pairing-based proxy signature
schemes. The scheme fulfills the necessary security requirements of proxy
signature and resists other possible threats
Keyword-Based Delegable Proofs of Storage
Cloud users (clients) with limited storage capacity at their end can
outsource bulk data to the cloud storage server. A client can later access her
data by downloading the required data files. However, a large fraction of the
data files the client outsources to the server is often archival in nature that
the client uses for backup purposes and accesses less frequently. An untrusted
server can thus delete some of these archival data files in order to save some
space (and allocate the same to other clients) without being detected by the
client (data owner). Proofs of storage enable the client to audit her data
files uploaded to the server in order to ensure the integrity of those files.
In this work, we introduce one type of (selective) proofs of storage that we
call keyword-based delegable proofs of storage, where the client wants to audit
all her data files containing a specific keyword (e.g., "important"). Moreover,
it satisfies the notion of public verifiability where the client can delegate
the auditing task to a third-party auditor who audits the set of files
corresponding to the keyword on behalf of the client. We formally define the
security of a keyword-based delegable proof-of-storage protocol. We construct
such a protocol based on an existing proof-of-storage scheme and analyze the
security of our protocol. We argue that the techniques we use can be applied
atop any existing publicly verifiable proof-of-storage scheme for static data.
Finally, we discuss the efficiency of our construction.Comment: A preliminary version of this work has been published in
International Conference on Information Security Practice and Experience
(ISPEC 2018
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