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21:17 [Pub][ePrint] Structural Evaluation of AES and Chosen-Key Distinguisher of 9-round AES-128, by Pierre-Alain Fouque and Jérémy Jean and Thomas Peyrin

  While the symmetric-key cryptography community has now a good

experience on how to build a secure and efficient fixed permutation,

it remains an open problem how to design a key-schedule for block

ciphers, as shown by the numerous candidates broken in the related-key

model or in a hash function setting. Provable security against

differential and linear cryptanalysis in the related-key scenario is

an important step towards a better understanding of its construction.

Using a structural analysis, we show that the full AES-128 cannot be

proven secure unless the exact coefficients of the MDS matrix and the

S-Box differential properties are taken into account since its

structure is vulnerable to a related-key differential attack. We then

exhibit a chosen-key distinguisher for AES-128 reduced to 9 rounds,

which solves an open problem of the symmetric community. We obtain

these results by revisiting algorithmic theory and graph-based ideas

to compute all the best differential characteristics in SPN ciphers,

with a special focus on AES-like ciphers subject to related-keys. We

use a variant of Dijkstra\'s algorithm to efficiently find the most

efficient related-key attacks on SPN ciphers with an algorithm linear

in the number of rounds.

21:17 [Pub][ePrint] On the Security of TLS-DH and TLS-RSA in the Standard Model, by Florian Kohlar and Sven Schäge and Jörg Schwenk

  TLS is the most important cryptographic protocol in the Internet. At CRYPTO 2012, Jager et al. presented the first proof of the unmodified TLS with ephemeral Diffie-Hellman key exchange (TLS-DHE) for mutual authentication. Since TLS cannot be proven secure under the classical definition of authenticated key exchange (AKE), they introduce a new security model called authenticated and confidential channel establishment (ACCE) that captures the security properties expected from TLS in practice. We extend this result in two ways. First we show that the cryptographic cores of the remaining ciphersuites, RSA encrypted key transport (TLS-RSA) and static Diffie-Hellman (TLS-DH), can be proven secure for mutual authentication in an extended ACCE model that also allows the adversary to register new public keys. In our security analysis we show that if TLS-RSA is instantiated with a CCA secure public key cryptosystem and TLS-DH is used in scenarios where a) the knowledge of secret key assumption holds or b) the adversary may not register new public keys at all, both ciphersuites can be proven secure in the standard model under standard security assumptions. Next, we present new and strong definitions of ACCE (and AKE) for server-only authentication which fit well into the general framework of Bellare-Rogaway-style models. We show that all three ciphersuites families do remain secure in this server-only setting. Our work identifies which primitives need to be exchanged in the TLS handshake to obtain strong security results under standard security assumptions (in the standard model) and may so help to guide future revisions of the TLS standard and make improvements to TLS\'s extensibility pay off.

21:17 [Pub][ePrint] Security in $O(2^n)$ for the Xor of Two Random Permutations\\\\ -- Proof with the standard $H$ technique--, by Jacques Patarin

  Xoring two permutations is a very simple way to construct pseudorandom functions from pseudorandom permutations. In~\\cite{P08a}, it is proved that we have security against CPA-2 attacks when $m \\ll O(2^n)$, where $m$ is the number of queries and $n$ is the number of bits of the inputs

and outputs of the bijections. In this paper, we will obtain similar (but slightly different) results by using the

``standard H technique\'\' instead of the ``$H_{\\sigma}$ technique\'\'. It will be interesting to

compare the two techniques, their similarities and the differences between the proofs and the


20:44 [PhD][New] Martin M. Lauridsen: Lightweight Cryptography

  Name: Martin M. Lauridsen
Topic: Lightweight Cryptography
Category: secret-key cryptography

20:43 [PhD][New] Hao Chen

  Name: Hao Chen

20:42 [PhD][New] Christian Rechberger

  Name: Christian Rechberger

18:55 [Job][New] 1 post-doc and 2 PhD posotions , University of Luxembourg

  PhD and Post-doc Positions in Computer Security

The University of Luxembourg in collaboration with the Luxembourg Government (CTIE) will start a new research project “Supporting e-Democracy” for which we have two PhD candidates and one Research Associate (post-doc) positions available. The positions are within the APSIA (Applied Security and Information Assurance) ( research group led by Prof. Dr. P.Y. Ryan.

The successful candidates will be working in an exciting, international and multicultural environment in the heart of Europe.

Project Description

The successful candidates will be working within the research project “Supporting e-Democracy”, collaboration between the University of Luxembourg and the Luxembourg Government (CTIE).

The research will focus on (a) design and security analysis of accurate and robust communication systems in specific electoral systems (b) design of reliable and secure computer assisted counting of paper ballots, (c) design and analysis of verifiable, computer assisted voting systems and a broader e-democracy platform.

Candidates Profile

The candidates are expected to have:

• A previous degree in computer science or related subject;

• A proven (theoretical and practical) interest in security;

• Knowledge of Network and System security;

• Fluent written and oral English skills;


The candidates must apply online at the following addresses:

PhD positions (open until July 31st, 2013):

Research Associate position (open until June 20th, 2013):

For further inquiries, please contact Prof. Dr. Peter Y. A. Ryan

15:17 [Pub][ePrint] Ideal-Cipher (Ir)reducibility for Blockcipher-Based Hash Functions, by Paul Baecher and Pooya Farshim and Marc Fischlin and Martijn Stam

  Preneel et al.~(Crypto 1993) assessed 64 possible ways to construct a compression function out of a blockcipher. They conjectured that 12 out of these 64 so-called PGV constructions achieve optimal security bounds for collision resistance and preimage resistance. This was proven by Black et al.~(Journal of Cryptology, 2010), if one assumes that the blockcipher is ideal. This result, however, does not apply to ``non-ideal\'\' blockciphers such as AES. To alleviate this problem, we revisit the PGV constructions in light of the recently proposed idea of random-oracle reducibility (Baecher and Fischlin, Crypto 2011). We say that the blockcipher in one of the 12 secure PGV constructions reduces to the one in another construction, if \\emph{any} secure instantiation of the cipher, ideal or not, for one construction also makes the other secure. This notion allows us to relate the underlying assumptions on blockciphers in different constructions, and show that the requirements on the blockcipher for one case are not more demanding than those for the other. It turns out that this approach divides the 12 secure constructions into two groups of equal size, where within each group a blockcipher making one construction secure also makes all others secure. Across the groups this is provably not the case, showing that the sets of ``good\'\' blockciphers for each group are qualitatively distinct. We also relate the ideal ciphers in the PGV constructions with those in double-block-length hash functions such as Tandem-DM, Abreast-DM, and Hirose-DM. Here, our results show that, besides achieving better bounds, the double-block-length hash functions rely on weaker assumptions on the blockciphers to achieve collision and everywhere preimage resistance.

15:17 [Pub][ePrint] Time-Optimal Interactive Proofs for Circuit Evaluation, by Justin Thaler

  Several research teams have recently been working toward the development of practical general-purpose protocols for verifiable computation. These protocols enable a computationally weak verifier to offload computations to a powerful but untrusted prover, while providing the verifier with a guarantee that the prover performed the requested computations correctly. Despite substantial progress, existing implementations require further improvements before they become practical for most settings. The main bottleneck is typically the extra effort required by the prover to return an answer with a guarantee of correctness, compared to returning an answer with no guarantee.

We describe a refinement of a powerful interactive proof protocol due to Goldwasser, Kalai, and Rothblum. Cormode, Mitzenmacher, and Thaler show how to implement the prover in this protocol in time $O(S \\log S)$, where $S$ is the size of an arithmetic circuit computing the function of interest. Our refinements apply to circuits with sufficiently ``regular\'\' wiring patterns; for these circuits, we bring the runtime of the prover down to $O(S)$. That is, our prover can evaluate the circuit with a guarantee of correctness, with only a constant-factor blowup in work compared to evaluating the circuit with no guarantee.

We argue that our refinements capture a large class of circuits, and we complement our theoretical results with experiments on problems such as matrix multiplication and determining the number of distinct elements in a data stream. Experimentally, our refinements yield a 200x speedup for the prover over the implementation of Cormode et al., and our prover is less than 10x slower than a C++ program that simply evaluates the circuit. Along the way, we describe a special-purpose protocol for matrix multiplication that is of interest in its own right.

Our final contribution is the design of an interactive proof protocol targeted at general data parallel computation. Compared to prior work, this protocol can more efficiently verify complicated computations as long as that computation is applied independently to many different pieces of data.

15:17 [Pub][ePrint] Constrained Pseudorandom Functions and Their Applications, by Dan Boneh and Brent Waters

  We put forward a new notion of pseudorandom functions (PRFs) we call

constrained PRFs. In a standard PRF there is a master key k that enables one to evaluate the function at all points in the domain of the

function. In a constrained PRF it is possible to derive constrained keys kS from the master key k. A constrained key kS enables the

evaluation of the PRF at a certain subset S of the domain and

nowhere else. We present a formal framework for this concept and show

that constrained PRFs can be used to construct powerful primitives such as identity-based key exchange and an optimal private broadcast

encryption system. We then construct constrained PRFs for several natural set systems needed for these applications. We conclude with several open problems relating to this new concept.

15:17 [Pub][ePrint] Profiling DPA: Efficacy and efficiency trade-offs, by Carolyn Whitnall and Elisabeth Oswald

  Linear regression-based methods have been proposed as efficient means of characterising device leakage in the training phases of profiled side-channel attacks. Empirical comparisons between these and the `classical\' approach to template building have confirmed the reduction in profiling complexity to achieve the same attack-phase success, but have focused on a narrow range of leakage scenarios which are especially favourable to simple (i.e.\\ efficiently estimated) model specifications. In this contribution we evaluate---from a theoretic perspective as much as possible---the performance of linear regression-based templating in a variety of realistic leakage scenarios as the complexity of the model specification varies. We are particularly interested in complexity trade-offs between the number of training samples needed for profiling and the number of attack samples needed for successful DPA: over-simplified models will be cheaper to estimate but DPA using such a degraded model will require more data to recover the key. However, they can still offer substantial improvements over non-profiling strategies relying on the Hamming weight power model, and so represent a meaningful middle-ground between `no\' prior information and `full\' prior information.