International Association for Cryptologic Research

# IACR News Central

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2014-05-10
09:17 [Pub][ePrint]

PANDA is a family of authenticated ciphers submitted to CARSAR, which consists of two ciphers: PANDA-s and PANDA-b. In this work we present a

state recovery attack against PANDA-s with time complexity about $2^{41}$ under the known-plaintext-attack model, which needs 137 pairs of known plaintext/ciphertext and about 2GB memories. Our attack is practical in a small workstation. Based on the above attack, we further deduce a forgery attack against PANDA-s, which can forge a legal ciphertext $(C,T)$ of an arbitrary plaintext $P$. The results show that PANDA-s is insecure.

2014-05-08
09:17 [Pub][ePrint]

Recently, Juels and Rivest proposed honeywords (decoy pass-

words) to detect attacks against hashed password databases. For each

user account, the legitimate password is stored with several honeywords in order to sense impersonation. If honeywords are selected properly, an adversary who steals a file of hashed passwords cannot be sure if it is the real password or a honeyword for any account. Moreover, entering with a honeyword to login will trigger an alarm notifying the administrator about a password file breach. At the expense of increasing storage requirement by 20 times, the authors introduce a simple and effective solution to detection of password file disclosure events. In this study, we scrutinize the honeyword system and present some remarks to highlight possible weak points. Also, we suggest an alternative approach that selects honeywords from existing user passwords in the system to provide

realistic honeywords - a perfectly flat honeyword generation method - and also to reduce storage cost of the honeyword scheme.

2014-05-07
18:21 [News]

The IACR Board of Directors is searching for volunteers to help with the website, the Cryptology ePrint Archive, and other IACR online services. Maintenance and future expansion of the online services of the IACR are crucial part for the interaction among cryptographers. We are interested in motivated cryptographers who would like to exploit their systems skills in a LAMP environment.

If you are interested in serving the community in this way, please contact the President of the IACR at president@iacr.org.

09:17 [Pub][ePrint]

We show a construction of a quantum ramp secret sharing scheme from a nested pair of linear codes. Necessary and sufficient conditions for qualified sets and forbidden sets are given in terms of combinatorial properties of nested linear codes. An algebraic geometric construction for quantum secret sharing is also given.

2014-05-06
12:17 [Pub][ePrint]

The notion of non-malleable codes was introduced as a relaxation of standard error-correction and error-detection. Informally, a code is non-malleable if the message contained in a modified codeword is either the original message, or a completely unrelated value.

In the information theoretic setting, although existence of such codes for various rich classes of tampering functions is known, explicit constructions exist only for highly structured family of tampering functions. Prior explicit constructions of non-malleable codes rely on the compartmentalized\'\' structure of the tampering function, i.e. the codeword is partitioned into {\\em a priori fixed} blocks and each block can {\\em only} be tampered independently. The prominent examples of this model are the family of bit-wise independent tampering functions and the split-state

model.

We consider an infinitely large natural class of non-compartmentalized tampering functions. In our model, the tampering function can permute the bits of the encoding and (optionally) perturb them. In the information theoretic setting, we provide an {\\em explicit} and {\\em efficient}, {\\em rate-1} non-malleable code for {\\em multi-bit messages}.

Lack of explicit constructions of non-malleable codes for non-compartmentalized tampering functions severely inhibits their utility in cryptographic protocols. As a motivation for our construction, we show an application of non-malleable codes to cryptographic protocols. In an idealized setting, we show how string commitments can be based on one-bit commitments, if non-malleable codes exist. Further, as an example of a non-trivial use of non-malleable codes in standard cryptographic protocols (not in an idealized model), we show that if explicit non-malleable codes are obtained for a slightly larger class of tampering functions than we currently handle, one can obtain a very simple non-malleable commitment scheme, under somewhat strong assumptions.

12:17 [Pub][ePrint]

This paper presents a thorough security analysis of the AEAD scheme NORX,

focussing on differential and rotational properties of the core permutation.

To examine its differential properties, we first introduce mathematical models

that describe differential propagation with respect to the non-linear operation

of NORX. Then we adapt the framework previously proposed for ARX designs,

which allows us to automatise the search for differentials and differential

characteristics. We give upper bounds on the differential probability of a

small number of steps of the NORX core permutation, and show how we found the

best characteristics for four rounds, which have probabilities of $2^{-584}$

($32$-bit) and $2^{-836}$ ($64$-bit), respectively. Finally, we discuss some

rotational properties of the core permutation which can be used as a basis for

future studies.

12:17 [Pub][ePrint]

We discuss how to apply Gaudry\'s index calculus algorithm for abelian varieties to solve the discrete logarithm problem in the trace zero variety of an elliptic curve. We treat in particular the practically relevant cases of field extensions of degree 3 or 5. Our theoretical analysis is compared to other algorithms present in the literature, and is complemented by results from a prototype implementation.

12:17 [Pub][ePrint]

In August 2012, the Stribog hash function was selected as the new Russian cryptographic hash standard (GOST R 34.11-2012). Stribog employs twelve rounds of an AES-based compression function operating in Miyaguchi-Preneel mode. In this paper, we investigate the preimage resistance of the Stribog hash function. Specifically, we apply a meet in the middle preimage attack on the compression function which allows us to obtain a 5-round pseudo preimage for a given compression function output with time complexity of $2^{448}$ and memory complexity of $2^{64}$. Additionally, we adopt a guess and determine approach to obtain a 6-round chunk separation that balances the available degrees of freedom and the guess size. The proposed chunk separation allows us to attack 6 out of 12 rounds with time and memory complexities of $2^{496}$ and $2^{112}$, respectively. Finally, employing $2^t$ multicollision, we show that preimages of the 5 and 6-round reduced hash function can be generated with time complexity of $2^{481}$ and $2^{505}$, respectively. The two preimage attacks have equal memory complexity of $2^{256}$.

12:17 [Pub][ePrint]

Simon and Speck are families of lightweight block ciphers designed by the U.S. National Security Agency and published in 2013. Each of the families contains 10 variants, supporting a wide range of block and key sizes. Since the publication of Simon and Speck, several research papers analyzed their security using various cryptanalytic techniques. The best previously published attacks on all the 20 round-reduced ciphers are differential attacks, and are described in two papers (presented at FSE 2014) by Abed et al. and Biryukov et al.

In this paper, we focus on the software-optimized block cipher family Speck, and describe significantly improved attacks on all of its 10 variants. In particular, we increase the number of rounds which can be attacked by 1, 2, or 3, for 9 out of 10 round-reduced members of the family, while significantly improving the complexity of the previous best attack on the remaining round-reduced member. Our attacks use an untraditional key recovery technique for differential attacks, which resembles techniques typically used in attacks based on self-similarity.

Despite our significantly improved attacks, they do not seem to threaten the security of any member of Speck.

12:17 [Pub][ePrint]

We show how to extend hash-tree based data signatures to server-assisted personal digital signature schemes. The new signature scheme does not use trapdoor functions and is based solely on cryptographic hash functions and is thereby, considering the current state of knowledge, resistant to quantum computational attacks. In the new scheme, we combine hash-tree data signature (time- stamping) solutions with hash sequence authentication mechanisms. We show how to implement such a scheme in practice.

06:40 [Event][New]

From March 26 to April 30
Location: Sofia, Bulgaria
More Information: https://www.cosic.esat.kuleuven.be/eurocrypt_2015/index.shtml