International Association for Cryptologic Research

# IACR News Central

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2012-04-23
00:17 [Pub][ePrint]

Public-key encryption schemes rely for their IND-CPA security on per-message fresh randomness. In practice, randomness may be of poor quality for a variety of reasons, leading to failure of the schemes. Expecting the systems to improve is unrealistic. What we show in this paper is that we can, instead, improve the cryptography to offset the lack of possible randomness. We provide public-key encryption schemes that achieve IND-CPA security when the randomness they use is of high quality, but, when the latter is not the case, rather than breaking completely, they achieve a weaker but still useful notion of security that we call IND-CDA. This hedged public-key encryption provides the best possible security guarantees in the face of bad randomness. We provide simple RO-based ways to make in-practice IND-CPA schemes hedge secure with minimal software changes. We also provide non-RO model schemes relying on lossy trapdoor functions (LTDFs) and techniques from deterministic encryption. They achieve adaptive security by establishing and exploiting the anonymity of LTDFs which we believe is of independent interest.

00:17 [Pub][ePrint]

We consider secure multi-party computation (MPC) in a setting where

the adversary can separately corrupt not only the parties (nodes) but

also the communication channels (edges), and can furthermore choose

selectively and adaptively which edges or nodes to corrupt. Note that

if an adversary corrupts an edge, even if the two nodes that share

that edge are honest, the adversary can control the link and thus

deliver wrong messages to both players. We consider this question in

the information-theoretic setting, and require security against a

In a fully connected network the above question is simple (and we

that is optimal up to a constant factor). What makes the problem

more challenging is to consider the case of sparse networks.

Partially connected networks are far more realistic than fully

connected networks, which led Garay and Ostrovsky [Eurocrypt\'08] to

formulate the notion of (unconditional) \\emph{almost everywhere (a.e.)

secure computation} in the node-corruption model, i.e., a model in

which not all pairs of nodes are connected by secure channels and the

adversary can corrupt some of the nodes (but not the edges). In such a setting,

MPC amongst all honest nodes cannot be guaranteed due

to the possible poor connectivity of some honest nodes with other

honest nodes, and hence some of

them must be given up\'\' and left out of the

computation. The number of such nodes is a function of the underlying

communication graph and the adversarial set of nodes.

In this work we introduce the notion of \\emph{almost-everywhere secure

computation with edge corruptions}, which is exactly the same problem as

completely control some of the communication channels between two

correct nodes---i.e., to corrupt\'\' edges in the network. While it is

easy to see that an a.e. secure computation protocol for the original

node-corruption model is also an a.e. secure computation protocol tolerating

edge corruptions (albeit for a reduced fraction of edge corruptions

with respect to the bound for node corruptions), no polynomial-time

protocol is known in the case where a {\\bf constant fraction} of the edges can be corrupted (i.e., the maximum that can be tolerated)

and the degree of the network is sub-linear.

We make progress on this front, by constructing graphs of degree

$O(n^\\epsilon)$ (for arbitrary constant $0 2012-04-22 09:17 [Pub][ePrint] The Gr{\\o}stl hash function is one of the 5 final round candidates of the {\\shathree} competition hosted by NIST. In this paper, we study the preimage resistance of the Gr{\\o}stl hash function. We propose pseudo preimage attacks on Gr{\\o}stl hash function for both 256-bit and 512-bit versions, i.e. we need to choose the initial value in order to invert the hash function. Pseudo preimage attack on 5(out of 10)-round Gr{\\o}stl-256 has a complexity of$(2^{244.85},2^{230.13})$(in time and memory) and pseudo preimage attack on 8(out of 14)-round Gr{\\o}stl-512 has a complexity of$(2^{507.32},2^{507.00})\$. To the best of our knowledge, our attacks are the first (pseudo) preimage attacks on round-reduced Gr{\\o}stl hash function, including its compression function and output transformation. These results are obtained by a variant of meet-in-the-middle preimage attack framework by Aoki and Sasaki. We also improve the time complexities of the preimage attacks against 5-round Whirlpool and 7-round AES hashes by Sasaki in FSE~2011.

09:17 [Pub][ePrint]

Hummingbird is a lightweight encryption and message authentication primitive published in RISC\'09 and WLC\'10. In FSE\'11, Markku-Juhani O.Saarinen presented a differential divide-and-conquer method which has complexity upper bounded by 264 operations and requires processing of few megabytes of chosen messages under two related nonces (IVs). The improved version, Hummingbird-2, was presented in RFIDSec 2011. Based on the idea of differential collision, this paper discovers some weaknesses of the round function WD16 combining with key loading algorithm and we propose a related-key chosen-IV attack which can recover the full secret key. Under 24 pairs of related keys, the 128 bit initial key can be recovered, with the computational complexity of O(232.6) and data complexity of O(232.6). The result shows that the Hummingbird-2 cipher can\'t resist related key attack.

2012-04-18
18:01 [PhD][New]

Name: Tolga Acar
Topic: High-Speed Algorithms & Architectures For Number-Theoretic Cryptosystems
Category: implementation

Description: Computer and network security systems rely on the privacy and authenticity of information, which requires implementation of cryptographic functions. Software implementations of these functions are often desired because of their flexibility and cost effectiveness. In this study, we concentrate on developing high-speed and area-efficient modular multiplication and exponentiation algorithms for number-theoretic cryptosystems.\r\nThe RSA algorithm, the Diffie-Hellman key exchange scheme and Digital Signature\r\nStandard require the computation of modular exponentiation, which is broken into a series\r\nof modular multiplications. One of the most interesting advances in modular exponentiation has been the introduction of Montgomery multiplication. We are interested in two aspects of modular multiplication algorithms: development of fast and convenient methods on a given hardware platform, and hardware requirements to achieve high-performance\r\nalgorithms.\r\nArithmetic operations in the Galois field GF(2^k) have several applications in coding\r\ntheory, computer algebra, and cryptography. We are especially interested in cryptographic applications where k is large, such as elliptic curve cryptosystems.[...]

16:52 [Event][Update]

From March 11 to March 13
Location: Singapore, Singapore

08:17 [Event][New]

From March 11 to March 13
Location: Singapore, Singapore

2012-04-17
21:12 [Event][New]

Submission: 25 May 2012
From September 13 to September 14
Location: Pisa, Italy

18:42 [News]

The IACR fellows of 2012 have been selected: The IACR fellow programme was started in 2002. Within this programme, we recognize outstanding IACR members for technical and professional contributions that:
• Advance the science, technology, and practice of cryptology and related fields
• Promote the free exchange of ideas and information about cryptology and related fields
• Develop and maintain the professional skill and integrity of individuals in the cryptologic community
• Advance the standing of the cryptologic community in the wider scientific and technical world and promote fruitful relationships between the IACR and other scientific and technical organizations

2012-04-16
23:01 [News]

Minutes for the Eurocrypt 2011 and Crypto 2011 meetings of the IACR Board of Directors, as well as minutes and slides of the corresponding membership meetings, are now available online.

08:05 [News]

The number of publication at IACR conferences hardly changed over the last 15 years. At the same time, the number of submissions increased by nearly 60% while the quality of submissions stayed the same - at least according to members of the programme committees. To worsen things, the IACR community has grown and there are many more researchers active in our domain than used to be 15 years ago.
Detailed statistics on submissions and acceptance rates: http://www2.mat.dtu.dk/people/Lars.R.Knudsen/accrates.html

To better serve our community, the Board of Directors expressed its with that Conference Programme Chairs (for Eurocrypt, Crypto, and Asiacrypt) to accept substancially more papers then used to be the case and to work with their General Chair for the logistics to make this possible (using extra slots, shorter talks, and parallel sessions).