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the ncorresponding messages. This feature makes aggregate signature very useful especially in environments with low bandwidth communication, low storage and low computability since it
greatly reduces the total signature length and verification cost. Recently, Xiong et al. presented an efficient certificateless aggregate signature scheme. They proved that their scheme is secure in a strengthened security model, where the \"malicious-but-passive\" KGC attack was considered. In this paper, we show that Xiong et al.\'s certificateless aggregate signature scheme is not secure
even in a weaker security model called \"honest-but-curious\" KGC attack model.
on-the-fly multiparty computation (MPC), the cloud can non-interactively perform arbitrary, dynamically chosen computations on data belonging to arbitrary sets of users chosen on-the-fly. All user\'s input data and intermediate results are protected from snooping by the cloud as well as other users.
This extends the standard notion of fully homomorphic encryption (FHE), where users can only enlist the cloud\'s help in evaluating functions on their own encrypted data.
In on-the-fly MPC, each user is involved only when initially uploading his (encrypted) data to the cloud, and in a final output decryption phase when outputs are revealed; the complexity of both is independent of the function being computed and the total number of users in the system. When users upload their data, they need not decide in advance which function will be computed, nor who they will compute with; they need only retroactively approve the eventually-chosen functions and on whose data the functions were evaluated.
This notion is qualitatively the best possible in minimizing interaction, since the users\' interaction in the decryption stage is inevitable: we show that removing it would imply generic program obfuscation and is thus impossible.
Our contributions are two-fold:
1. We show how on-the-fly MPC can be achieved using a new type of encryption scheme that we call multikey FHE, which is capable of operating on inputs encrypted under multiple, unrelated keys. A ciphertext resulting from a multikey evaluation can be jointly decrypted using the secret keys of all the users involved in the computation.
2. We construct a multikey FHE scheme based on NTRU, a very efficient public-key encryption scheme proposed in the 1990s. It was previously not known how to make NTRU fully homomorphic even for a single party. We view the construction of (multikey) FHE from NTRU encryption as a main contribution of independent interest. Although the transformation to a fully homomorphic system deteriorates the efficiency of NTRU somewhat, we believe that this system is a leading candidate for a practical FHE scheme.
The CERC program awards world-class researchers up to $10 million over seven years to establish ambitious research programs at Canadian universities. Further details are offered at www.cerc.gc.ca. An overall package worth more than twice this amount will fund the CERC, additional faculty and staff, and their required infrastructure.
The applicant will be an outstanding researcher, well-recognized as exceptional within the subfield of security and privacy. It will also be essential for the candidate to demonstrate remarkable promise in leadership and in the mobilization of talents to deliver successful outcomes. In particular, we are looking for an individual who is expert in security solutions for networked and mobile environments with a critical appreciation for linking privacy to the required solutions. To promote the adoption of novel technological solutions, the CERC must also have an aptitude in working well with public policy experts.
To apply, send a cover letter and a curriculum vitae by e-mail at deanmath (at) uwaterloo.ca or by regular mail.
Applications received by May 30, 2013 will receive full consideration. Selection of the candidate is subject to final oversight by the government\\\'s CERC Selection Committee.
The University of Waterloo encourages applications from all qualified individuals, including women, members of visible minorities, native people and persons with disabilities. We are proud to offer organizations for Women in Computer Science (cs.uwaterloo.ca/~wics) and Women in Mathematics (women.math.uwaterloo.ca) as well as an AccessAbility Services Office for persons with disabiliti
We introduce the first formal security framework for software attestation and formalize various system and design parameters. Moreover, we present a generic software attestation scheme that captures most existing schemes in the literature. Finally, we analyze its security within our framework, yielding sufficient conditions for provably secure software attestation schemes. We regard these results as a first step towards putting software attestation on a solid ground and as a starting point for further research.
The adversary performs a measurement on the challenge quantum state in order to learn as much about it as he can. Using this knowledge he then tries to reconstruct the challenge and to emulate the PUF.
We consider quadrature measurements, which are the most informative practical measurements known to us.
We prove that even under this attack the expected number of photons
detected in the verification mechanism is approximately a factor $S+1$ too low; here $S$ is the Quantum Security Parameter, defined as the number of modes in the optical system divided by the number of photons in the challenge. The photon count allows for a reliable distinction between an authentic PUF and a challenge estimation attack.
adversaries which is parametrized by a value L. When L=2 we obtain a classical form of MPC protocol in which interaction is required for multiplications, as L increases interaction is reduced in that one requires interaction only after computing a higher degree function. When L approaches infinity one obtains the FHE based protocol of Gentry, which requires no interaction. Thus one can trade communication for computation in a simple way.
Our protocol is based on an interactive protocol for ``bootstrapping\'\' a somewhat homomorphic encryption scheme. The key contribution is that our presented protocol is highly communication efficient enabling us to obtain reduced communication when compared to traditional MPC protocols for relatively small values of L.
three-share hardware implementation require a number of traces that scales in the third power of the algorithmic noise variance. Finally, we apply and test our model on Keccak in a keyed mode.