*19:17* [Pub][ePrint]
Secure Signatures and Chosen Ciphertext Security in a Post-Quantum World, by Dan Boneh and Mark Zhandry
We initiate the study of quantum-secure digital signatures and quantum chosen ciphertext security. In the case of signatures, we enhance the standard chosen message query model by allowing the adversary to issue quantum chosen message queries: given a superposition of messages, the adversary receives a superposition of signatures on those messages. Similarly, for encryption, we allow the adversary to issue quantum chosen ciphertext queries: given a superposition of ciphertexts, the adversary receives a superposition of their decryptions. These adversaries model a natural post-quantum environment where end-users sign messages and decrypt ciphertexts on a personal quantum computer.We construct classical systems that remain secure when exposed to such quantum queries. For signatures we construct two compilers that convert classically secure signatures into signatures secure in the quantum setting and apply these compilers to existing post-quantum signatures. We also show that standard constructions such as Lamport one-time signatures and Merkle signatures remain secure under quantum chosen message attacks, thus giving signatures whose quantum security is based on generic assumptions. For encryption, we define security under quantum chosen ciphertext attacks and present both public-key and symmetric-key constructions.

*19:17* [Pub][ePrint]
Functional Encryption Supporting Recursive Languages, by Somindu C. Ramanna and Palash Sarkar
We provide a construction for functional encryption over the set of recursive languages. In this scheme, a secret key $\\sk_{\\mathcal{M}}$ encodes a halting double-stack deterministic pushdown

automaton (2DPDA) $\\mathcal{M}$ that accepts by final state. Encryption algorithm takes a message $m$

and a string $w$ as input and outputs a ciphertext $\\cipher$. A user possessing $\\sk_{\\mathcal{M}}$ can

decrypt $\\cipher$ only if $\\mathcal{M}$ accepts $w$. Halting 2DPDAs can simulate halting deterministic

Turing machines and hence our construction essentially covers all

recursive languages.

The construction is built upon Waters\' bilinear pairing-based functional encryption scheme

over regular languages. The main technical novelty is in handling stack contents and

$\\lambda$-transitions (i.e., transitions that do not advance the input pointer)

of the automata. This is reflected both in the construction and the security arguments.

The scheme is shown to be selectively secure based on the decision $\\ell$-expanded bilinear

Diffie-Hellman exponent assumption introduced by Waters.

*19:17* [Pub][ePrint]
On the security of a certificateless aggregate signature scheme, by Lin Cheng and Qiaoyan Wen and Zhengping Jin and Hua Zhang and Liming Zhou
Aggregate signature can combinensignatures on nmessages fromnusers into a single short signature, and the resulting signature can convince the verifier that thenusers indeed signedthe 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.

*19:17* [Pub][ePrint]
On-the-Fly Multiparty Computation on the Cloud via Multikey Fully Homomorphic Encryption, by Adriana Lopez-Alt and Eran Tromer and Vinod Vaikuntanathan
We propose a new notion of secure multiparty computation aided by a computationally-powerful but untrusted \"cloud\" server. In this notion that we callon-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.

*18:44* [Job][New]
Canada Excellence Research Chair in Security & Privacy, *University of Waterloo, Canada*
We invite expressions of interest for the position of Canada Excellence Research Chair (CERC) in Security and Privacy for the New Digital Economy, to be held at the tenured full or associate professor level in the David R. Cheriton School of Computer Science at the University of Waterloo.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

*13:17* [Pub][ePrint]
Towards Provably Secure Software Attestation, by Frederik Armknecht and Ahmad-Reza Sadeghi and Steffen Schulz and Christian Wachsmann
Software attestation has become a popular and challenging research topic at many established security conferences. It aims for verifying the software integrity of (typically) resource-constrained embedded devices. However, for practical reasons, software attestation cannot rely on stored cryptographic secrets or dedicated trusted hardware. Instead, it exploits side-channel information, such as the time that the underlying device needs for a specific computation. Unfortunately, traditional cryptographic solutions and arguments are not applicable in this setting, making new approaches for the design and analysis necessary. This is certainly one of the main reasons why the security properties and assumptions of software attestation have been only vaguely discussed and have never been formally treated, as it is common sense in modern cryptography. Thus, despite its popularity and its expected impact for practice, a sound approach for designing secure software attestation schemes is still an important open problem.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.

*13:17* [Pub][ePrint]
Security of Quantum-Readout PUFs against quadrature based challenge estimation attacks, by Boris Skoric and Allard P. Mosk and Pepijn W.H. Pinkse
The concept of quantum-secure readout of Physical Unclonable Functions (PUFs) has recently been realized experimentally in an optical PUF system. We analyze the security of this system under the strongest type of classical attack: the challenge estimation attack.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.

*13:17* [Pub][ePrint]
Between a Rock and a Hard Place: Interpolating Between MPC and FHE, by Ashish Choudhury and Jake Loftus and Emmanuela Orsini and Arpita Patra and Nigel P. Smart
We present a computationally secure MPC protocol for thresholdadversaries 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.