International Association for Cryptologic Research

# IACR News Central

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2015-02-22
05:37 [Event][New]

Submission: 20 March 2015
Notification: 13 April 2015
From June 15 to June 17
Location: Paris, France

05:37 [Event][New]

Submission: 20 March 2015
Notification: 13 April 2015
From June 15 to June 17
Location: Paris, France

2015-02-21
13:07 [Event][New]

Submission: 10 April 2015
Notification: 30 May 2015
From August 24 to August 25
Location: Heraklion, Crete, Greece

2015-02-20
08:08 [Event][New]

From October 12 to October 16
Location: Paris, France

2015-02-16
07:17 [Pub][ePrint]

MAC striping has been suggested as a technique to authenticate encrypted payloads using short tags. For an idealized MAC scheme, the probability of a selective forgery has been estimated as $\\binom{\\ell+m}{m}^{-1}\\cdot 2^{-m}$, when utilizing MAC striping with $\\ell$-bit payloads and $m$-bit tags. We show that this estimate is too optimistic. For $m\\le\\ell$ and any payload, we achieve a selective forgery with probability $\\ge \\binom{\\ell+m}{m}^{-1}$, and usually many orders of magnitude more than that.

07:17 [Pub][ePrint]

In this paper, we show structural cryptanalyses against two popular networks, i.e., the Feistel Network and the Substitute-Permutation Network (SPN). Our cryptanalyses are distinguishing attacks by an improved integral distinguisher. The integral distinguisher is one of the most powerful attacks against block ciphers, and it is usually constructed by evaluating the propagation characteristic of integral properties, e.g., the ALL or BALANCE property. However, the integral property does not derive useful distinguishers against block ciphers with non-bijective functions and bit-oriented structures. Moreover, since the integral property does not clearly exploit the algebraic degree of block ciphers, it tends not to construct useful distinguishers against block ciphers with low-degree functions. In this paper, we propose a new property called {\\it the division property}, which is the generalization of the integral property. It can effectively construct the integral distinguisher even if the block cipher has non-bijective functions, bit-oriented structures, and low-degree functions. From viewpoints of the attackable number of rounds or chosen plaintexts, the division property can construct better distinguishers than previous methods. Although our attack is a generic attack, it can improve several integral distinguishers against specific cryptographic primitives. For instance, it can reduce the required number of chosen plaintexts for the 10-round distinguisher on Keccak-f from $2^{1025}$ to $2^{515}$. For the Feistel cipher, it theoretically proves that Simon 32, 48, 64, 96, and 128 have 9-, 11-, 11-, 13-, and 13-round integral distinguishers, respectively.

07:17 [Pub][ePrint]

We present a forgery attack on Prøst-OTR in a related-key setting. Prøst is a family of authenticated encryption algorithms proposed as candidates in the currently ongoing CAESAR competition, and Prøst-OTR is one of the three variants of the Prøst design. The attack exploits how the Prøst permutation is used in an Even-Mansour construction in the Feistel-based OTR mode of operation. Given the ciphertext and tag for any two messages under two related keys K and K + Delta with related nonces, we can forge the ciphertext and tag for a modified message under K. If we can query ciphertexts for chosen messages under K + Delta, we can achieve almost universal forgery for K. The computational complexity is negligible.

06:26 [Job][New]

2 Research Fellow Openings, Department of Computer Science, Faculty of Computing and Mathematical Sciences

We have two fixed-term positions available to be a part of an exciting new MBIE-funded Cyber Security STRATUS (Security Technologies Returning Accountability, Transparency and User-centric Services to the Cloud) project, led by the Faculty’s CROW (Cyber Security Researchers of Waikato) Research Group (https://crow.org.nz).

STRATUS will deliver a platform of user-empowering cloud security software, human capability and technical resources easily accessible by a broad range of NZ industry and government organisations.

You will have a PhD in Computer Science or a related field in an active area of research and will have demonstrated the ability to sustain a successful quality research programme. You will be expected to enhance the Department’s research environment, technology commercialisation process, and to produce high quality research and publications in computer security and Cloud computing as a part of this externally funded programme.

In addition to the requirements above, preference will be given to those with experience in data provenance, network security, digital forensics, linked data visualisation, data mining, applied cryptography and/or related areas.

Current salary range for Research Fellows is NZ$67,477 to$82,383 per year.

Fixed-term for three years.

Closing date: 6 March 2015 (NZ time) Vacancy number: 350045

For more information and to apply, visit http://www.jobs.waikato.ac.nz

2015-02-14
10:17 [Pub][ePrint]

In this note, we present our key recovery attacks against NTRU-type somewhat homomorphic encryption schemes.

10:17 [Pub][ePrint]

Pairing-based cryptography (PBC) has many elegant properties. It is claimed that PBC can offer a desired security level with smaller parameters as the general elliptic curve cryptography (ECC). In the note, we remark that this view is misleading. Suppose that an elliptic curve $E$ is defined over the field $\\mathbb{F}_q$. Then ECC is working with elements which are defined over $\\mathbb{F}_q$. But PBC is working with the functions and elements defined over $\\mathbb{F}_{q^k}$, where $k$ is the \\emph{embedding degree}.

The security of PBC depends directly on the intractable level of either elliptic curve discrete log problem (ECDLP) in the group $E(\\mathbb{F}_q)$ or discrete log problem (DLP) in the group $\\mathbb{F}_{q^k}^*$. That means PBC protocols have to work in a running environment with parameters of 1024 bits so as to offer 80 bits security level. The shortcoming makes PBC lose its competitive advantages significantly.

10:17 [Pub][ePrint]

This paper investigates the effect of affine transformations of the Sbox on the maximal expected differential probability MEDP and linear potential MELP over two rounds of a substitution-permutation network, when the diffusion layer is linear over the finite field defined by the Sbox alphabet. It is mainly motivated by the fact that the 2-round MEDP and MELP of the AES both increase when the AES Sbox is replaced by the inversion in $GF(2^8)$. Most notably, we give new upper bounds on these two quantities which are not invariant under affine equivalence. Moreover, within a given equivalence class, these new bounds are maximal when the considered Sbox is an involution. These results point out that different Sboxes within the same affine equivalence class may lead to different two-round MEDP and MELP. In particular, we exhibit some examples where the basis chosen for defining the isomorphism between $GF(2)^m$ and $GF(2^m)$ affects these values.

For Sboxes with some particular properties, including all Sboxes of the form $A(x^s)$ as in the AES, we also derive some lower and upper bounds for the 2-round MEDP and MELP which hold for any MDS linear layer.