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12:17 [Pub][ePrint] A Three-Level Sieve Algorithm for the Shortest Vector Problem, by Feng Zhang and Yanbin Pan and Gengran Hu

  In AsiaCCS 2011, Wang et al. proposed a two-level heuristic sieve algorithm for the shortest vector problem in lattices, which improves the Nguyen-Vidick sieve algorithm. Inspired by their idea, we present a three-level sieve algorithm in this paper, which is shown to have better time complexity. More precisely, the time complexity of our algorithm is $2^{0.3778n+o(n)}$ polynomial-time operations and the corresponding space complexity is $2^{0.2833n+o(n)}$ polynomially many bits.

12:17 [Pub][ePrint] Inter-FSP Funds Transfer Protocol, by Amir Herzberg and Shay Nachmani

  We present the first decentralized secure funds transfer protocol with multiple participants. The protocol ensures that a participant can only lose money, if a peer it trusted is corrupted. Furthermore, the loss is

bounded by the credit allocated to this partner. The protocol supports expiration times for payment orders, and realistic network queuing delay.We achieve this using model and techniques from the Quality of Service area to guarantee delays and avoid payment order expiration. We present rigorous security proof.

12:17 [Pub][ePrint] Practical Issues with TLS Client Certificate Authentication, by Arnis Parsovs

  The most widely used secure Internet communication standard TLS (Transport Layer Security) has an optional client certificate authentication feature that in theory has significant security advantages over HTML form-based password authentication. In this paper we discuss practical security and usability issues related to TLS client certificate authentication stemming from the server side and browser implementations. In particular we analyze Apache mod_ssl implementation on server side and the most popular browsers - Mozilla Firefox, Google Chrome and Microsoft Internet Explorer on client side. We complement our paper with a case study performed in Estonia where TLS client certificate authentication is widely used. We present our recommendations for TLS implementations on the client and server side to improve the security and usability of TLS client certificate authentication.

12:17 [Pub][ePrint] Rebound attacks on Stribog, by Riham AlTawy and Aleksandar Kircanski and Amr M. Youssef

  In August 2012, the Stribog hash function was selected as the new Russian hash standard (GOST R 34.11-2012). Stribog is an AES-based primitive and is considered as an asymmetric reply to the new SHA-3. In this paper we investigate the collision resistance of the Stribog compression function and its internal cipher. Specifically, we present a message differential path for the internal block cipher that allows us to efficiently obtain a 5-round free-start collision and a 7.75 free-start near collision for the internal cipher with complexities $2^8$ and $2^{40}$, respectively. Finally, the compression function is analyzed and a 7.75 round semi free-start collision, 8.75 and 9.75 round semi free-start near collisions are presented along with an example for 4.75 round 49 out of 64 bytes near colliding message pair.

09:17 [Pub][ePrint] Multiple Limited-Birthday Distinguishers and Applications, by Jérémy Jean and María Naya-Plasencia and Thomas Peyrin

  In this article, we propose a new improvement of the rebound techniques, used for cryptanalyzing AES-like permutations during the past years. Our improvement, that allows to reduce the complexity of the attacks, increases the probability of the outbound part by considering a new type of differential paths. Moreover, we propose a new type of distinguisher, the multiple limited-birthday problem, based on the limited-birthday one, but where differences on the input and on the output might have randomized positions. We also discuss the generic complexity for solving this problem and provide a lower bound of it as well as we propose an efficient and generic algorithm for solving it. Our advances lead to improved distinguishing or collision results for many AES-based functions such as AES, ECHO, Grøstl, LED, PHOTON and Whirlpool.

09:17 [Pub][ePrint] The Resistance of PRESENT-80 Against Related-Key Differential Attacks, by Sareh Emami, San Ling, Ivica Nikolic, Josef Pieprzyk and Huaxiong Wang

  We examine the security of the 64-bit lightweight block cipher PRESENT-80 against related-key differential attacks. With a computer search we are able to prove that no related-key differential characteristic exists with probability higher than $2^{-64}$ for the full-round PRESENT-80.

To overcome the exponential (in the state and key sizes) computational complexity we use truncated differences, however as the key schedule is not nibble oriented, we switch to actual differences and apply early abort techniques to prune the tree-based search.

With a new method called extended split approach we are able to make the whole search feasible and we implement and run it in real time.

Our approach targets the PRESENT-80 cipher however, with small modifications can be reused for other lightweight ciphers as well.

09:17 [Pub][ePrint] White-Box Security Notions for Symmetric Encryption Schemes, by Cécile Delerablée and Tancrède Lepoint and Pascal Paillier and Matthieu Rivain

  White-box cryptography has attracted a growing interest from researchers in the last decade. Several white-box implementations of standard block-ciphers (DES, AES) have been proposed but they have all been broken. On the other hand, neither evidence of existence nor proofs of impossibility have been provided for this particular setting. This might be in part because it is still quite unclear what

{white-box} cryptography really aims to achieve and which security properties are expected from white-box programs in applications. This paper builds a first step towards a practical answer to this question by translating folklore intuitions behind white-box cryptography into concrete security notions. Specifically, we introduce the notion of white-box compiler that turns a symmetric encryption scheme into randomized white-box programs, and we capture several desired security properties such as one-wayness, incompressibility and traceability for white-box programs. We also give concrete examples of white-box compilers that already achieve some of these notions. Overall, our results open new perspectives on the design of white-box programs that securely implement symmetric encryption.

09:17 [Pub][ePrint] Threshold Secret Image Sharing, by Teng Guo, Feng Liu, ChuanKun Wu, ChingNung Yang, Wen Wang and YaWei Ren

  A (k; n) threshold secret image sharing scheme, abbreviated as (k; n)-TSISS, splits a secret image into n shadow images in such a way

that any k shadow images can be used to reconstruct the secret image

exactly. In 2002, for (k; n)-TSISS, Thien and Lin reduced the size of each

shadow image to 1/k of the original secret image. Their main technique

is by adopting all coefficients of a (k-1)-degree polynomial to embed the secret pixels. This benet of small shadow size has drawn many researcher\'s attention and their technique has been extensively used in

the following studies. In this paper, we rst show that this technique

is neither information theoretic secure nor computational secure. Furthermore, we point out the security defect of previous (k; n)-TSISSs for

sharing textual images, and then fix up this security defect by adding an

AES encryption process. At last, we prove that this new (k; n)-TSISS is

computational secure.

09:17 [Pub][ePrint] Catena: A Memory-Consuming Password Scrambler, by Christian Forler and Stefan Lucks and Jakob Wenzel

  It is a common wisdom that servers should better store the one-way hash of their clients\' passwords, rather than storing the password in the clear. This paper introduces Catena, a new one-way function for that purpose. Catena is sequentially memory-hard, which hinders massively parallel attacks on cheap memory-constrained hardware, such as recent \"graphical processing units\", GPUs. Furthermore, Catena has been designed to resist cache-timing attacks. This distinguishes Catena from scrypt, which is also sequentially memory-hard, but which we show to be vulnerable to cache-timing attacks. Additionally, Catena supports (1) client-independent updates (the server can increase the security parameters and update the password hash without user interaction or knowing the password), (2) a server relief protocol (saving the server\'s resources at the cost of the client), and (3) a variant Catena-KG for secure key derivation (to securely generate many cryptographic keys of arbitrary lengths such that compromising

some keys does not help to break others).

09:17 [Pub][ePrint] Differential Cryptanalysis of Reduced-Round Simon, by Farzaneh Abed and Eik List and Stefan Lucks and Jakob Wenzel

  In June 2013 the U.S. National Security Agency proposed two families of ultra-lightweight block ciphers, called Simon and Speck. In this paper we present the first cryptanalysis of round-reduced versions of Simon. We mount differential distinguishers and key-recovery attacks on up to 14/32, 17/36, 21/44, 26/54, and 32/72 rounds, for the 32-, 48-, 64-, 96-, and 128-bit versions, respectively. Furthermore, we briefly consider impossible-differential and rotational attacks. While our attacks are mostly academic, they demonstrate the drawback of the aggressive optimizations in Simon which allow powerful differential cryptanalysis.

09:17 [Pub][ePrint] The Spammed Code Offset Method, by Boris Skoric and Niels de Vreede

  Helper data schemes are a security primitive used for privacy-preserving biometric databases and Physical Unclonable Functions.

One of the oldest known helper data schemes is the Code Offset Method (COM).

We propose an extension of the COM: the helper data is accompanied by many instances of fake helper data that is drawn from the same distribution as the real one.

While the adversary has no way to distinguish between them, the legitimate party has more information and *can* see the difference.

We use an LDPC code in order to improve the efficiency of the legitimate party\'s selection procedure.

Our construction provides a new kind of trade-off: more effective use of the source entropy, at the price of increased helper data storage.

We give a security analysis in terms of Shannon entropy and order-2 Renyi entropy.