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2015-06-15
09:17 [Pub][ePrint] Improved All-Subkeys Recovery Attacks on FOX, KATAN and SHACAL-2 Block Ciphers, by Takanori Isobe and Kyoji Shibutani

  The all-subkeys recovery (ASR) attack is an extension of the meet-in-the-middle

attack, which allows evaluating the security of a block cipher without analyzing its key

scheduling function. Combining the ASR attack with some advanced techniques such as the

function reduction and the repetitive ASR attack, we show the improved ASR attacks on the

7-round reduced FOX64 and FOX128. Moreover, the improved ASR attacks on the 119-, 105-

and 99-round reduced KATAN32, KATAN48 and KATAN64, and the 42-round reduced SHACAL-2

are also presented, respectively. As far as we know, all of those attacks are the best single-key

attacks with respect to the number of attacked rounds in literature.





2015-06-14
21:17 [Pub][ePrint] An Improved BKW Algorithm for LWE with Applications to Cryptography and Lattices, by Paul Kirchner and Pierre-Alain Fouque

  In this paper, we study the Learning With Errors problem and its binary variant, where

secrets and errors are binary or taken in a small interval. We introduce a new variant of the Blum,

Kalai and Wasserman algorithm, relying on a quantization step that generalizes and fine-tunes modulus

switching. In general this new technique yields a significant gain in the constant in front of the exponent

in the overall complexity. We illustrate this by solving

p within half a day a LWE instance with dimension

n = 128, modulus q = n^2 , Gaussian noise alpha = 1/(sqrt(n/pi)log^2 n) and binary secret, using 2^28 samples,

while the previous best result based on BKW claims a time complexity of 2^74 with 2^60 samples for the

same parameters.

We then introduce variants of BDD, GapSVP and UniqueSVP, where the target point is required to lie

in the fundamental parallelepiped, and show how the previous algorithm is able to solve these variants

in subexponential time. Moreover, we also show how the previous algorithm can be used to solve the

BinaryLWE problem with n samples in subexponential time 2^((ln 2/2+o(1))n/log log n) . This analysis does

not require any heuristic assumption, contrary to other algebraic approaches; instead, it uses a variant

of an idea by Lyubashevsky to generate many samples from a small number of samples. This makes

it possible to asymptotically and heuristically break the NTRU cryptosystem in subexponential time

(without contradicting its security assumption). We are also able to solve subset sum problems in

subexponential time for density o(1), which is of independent interest: for such density, the previous

best algorithm requires exponential time. As a direct application, we can solve in subexponential time

the parameters of a cryptosystem based on this problem proposed at TCC 2010.



21:17 [Pub][ePrint] Round-Optimal Black-Box Two-Party Computation, by Rafail Ostrovsky and Silas Richelson and Alessandra Scafuro

  In [Eurocrypt 2004] Katz and Ostrovsky establish the exact round complexity of secure two-party computation with respect to black-box proofs of security. They prove that 5 rounds are necessary for secure two-party protocols (4-round are sufficient if only one party receives the output) and provide a protocol that matches such lower bound. The main challenge when designing such protocol is to parallelize the proofs of consistency provided by both parties - necessary when security against malicious adversaries is considered- in 4 rounds. Toward this goal they employ specific proofs in which the statement can be unspecified till the last round but that require non-black-box access to the underlying primitives.

A rich line of work [IKLP06, Hai08, CDSMW09, IKOS07, PW09] has shown that the non- black-box use of the cryptographic primitive in secure two-party computation is not necessary by providing black-box constructions matching basically all the feasibility results that were previously demonstrated only via non-black-box protocols.

All such constructions however are far from being round optimal. The reason is that they are based on cut-and-choose mechanisms where one party can safely take an action only after the other party has successfully completed the cut-and-choose phase, therefore requiring additional rounds.

A natural question is whether round-optimal constructions do inherently require non-black- box access to the primitives, and whether the lower bound shown by Katz and Ostrovsky can only be matched by a non-black-box protocol.

In this work we show that round-optimality is achievable even with only black-box access to the primitives. We provide the first 4-round black-box oblivious transfer based on any enhanced trapdoor permutation. Plugging a parallel version of our oblivious transfer into the black- box non-interactive secure computation protocol of [IKO+11] we obtain the first round-optimal black-box two-party protocol in the plain model for any functionality.





2015-06-13
17:11 [News] Deadline approaching for IACR School proposals

  The IACR has recently started sponsoring select Cryptology Schools. If you would like to propose an IACR-sponsored school that takes place on/before February 2016, then your last chance to submit proposals is June 30. The next round of proposals is not until December 31. More information about the application process can be found at http://www.iacr.org/schools/.



2015-06-12
21:17 [Pub][ePrint] Quantum homomorphic encryption for circuits of low $T$-gate complexity, by Anne Broadbent and Stacey Jeffery

  Fully homomorphic encryption is an encryption method with the property that any computation on the plaintext can be performed by a party having access to the ciphertext only.

Here, we formally define and give schemes for \\emph{quantum} homomorphic encryption, which is the encryption of \\emph{quantum} information such that \\emph{quantum} computations can be performed given the ciphertext only. Our schemes allow for arbitrary Clifford group gates, but become inefficient for circuits with

large complexity, measured in terms of the non-Clifford portion of the circuit (we use the ``$\\pi/8$\'\' non-Clifford group gate, also known as the $T$-gate).

More specifically, two schemes are proposed: the first scheme has a decryption procedure whose complexity scales with the square of the \\emph{number} of $T$-gates (compared with a trivial scheme in which the complexity scales with the total number of gates); the second scheme

uses a quantum evaluation key of length given by a polynomial of degree exponential in the circuit\'s

$T$-gate depth, yielding a homomorphic scheme for quantum circuits with constant $T$-depth. Both schemes build on a classical fully homomorphic encryption scheme.

A further contribution of ours is to formally define the security of encryption schemes for quantum messages: we define \\emph{quantum indistinguishability under chosen plaintext attacks} in both the public- and private-key settings. In this context, we show the equivalence of several definitions.

Our schemes are the first of their kind that are secure under modern cryptographic definitions, and can be seen as a quantum analogue of classical results establishing homomorphic encryption for circuits with a limited number of \\emph{multiplication} gates. Historically, such results appeared as precursors to the breakthrough result establishing classical fully homomorphic encryption.



04:08 [Event][New] PRIVAGEN 2015: Privacy-Aware Computational Genomics 2015

  Submission: 30 June 2015
Notification: 20 July 2015
From September 8 to September 8
Location: Tokyo, Japan
More Information: http://aistcrypt.github.io/Privacy-Aware-Computational-Genomics/




2015-06-11
21:17 [Forum] [2014 Reports] 2015/468 FHE for plaintexts from Z_p, with prime p, do not work? by movax

  From: 2015-11-06 21:11:12 (UTC)

17:37 [Event][New] PETS: Privacy Enhancing Technologies Symposium (PETS)

  From June 30 to July 2
Location: PHILADELPHIA, United States
More Information: https://petsymposium.org/2015/


15:16 [Job][New] Doctoral Research Fellows, University of Passau

  Two 0.5 full-time equivalent (FTE) positions are offered as part of the DFG funded project Algebraic Fault Attacks.

These positions are remunerated pro rata at salary band E13 of the German public-sector wage agreement (TV-L E13). Candidates may combine these positions with one 0.25 FTE teaching assistantship each.

The successful candidates will participate in an area of the project which uses Computer Algebra techniques and their integration with SAT solvers to break cryptographic hardware primitives based on the information obtained from fault attacks. The interdisciplinary, state-of-the-art approach requires rigorous and broad-based mathematical knowledge and an openness towards computer science methods.

Detailed job requirements are listed in the link below.

06:37 [Job][New] Post-Doc, Ruhr University Bochum

  The Ruhr University Bochum is offering a 2-year post-doc position in theoretical cryptography, working on the ERC project \"Efficient Resource Constrained Cryptography\". Required is a PhD in cryptography and excellence in research, proven for example by publications in IACR conferences and workshops.

Applicants interested in the positions should provide the following information in pdf format with the application:

- Motivation letter

- CV

- List of publications, mark your top 2

This position will be filled as soon as possible, late applications will be considered.

06:37 [Job][New] PhD Research Fellowship in Secure Networking Technologies, Norwegian University of Science and Technology (NTNU), Trondheim, Norway

  The researcher will work on a project entitled “Securing emerging network technologies with homomorphic encryption”. The overall aim of the project is to design methods for secure processing of network data in emerging networks using practical variants of homomorphic encryption. Recent advances in cryptography will be applied to secure the virtualization of the ICT infrastructure (such as “cloud” processing and storage) and new flexible networking technologies such as software defined networks (SDN) and network function virtualization (NFV). Work tasks will include: analysis of suitable network functions for homomorphic processing; analysis of practical homomorphic encryption algorithms; secure protocol design and analysis; and experimental implementations.