International Association for Cryptologic Research

# IACR News Central

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2013-06-09
21:17 [Pub][ePrint]

We show that public-key bit encryption schemes which support weak (i.e., compact) homomorphic evaluation of any sufficiently \"sensitive\" collection of functions cannot be proved message indistinguishable beyond AM intersect coAM via general (adaptive) reductions, and beyond statistical zero-knowledge via reductions of constant query complexity. Examples of sensitive collections include parities, majorities, and the class consisting of all AND and OR functions.

Our techniques also give a method for converting a strong (i.e., distribution-preserving) homomorphic evaluator for essentially any boolean function (except the trivial ones, the NOT function, and the AND and OR functions) into a rerandomization algorithm: This is a procedure that converts a ciphertext into another ciphertext which is statistically close to being independent and identically distributed with the original one. Our transformation preserves negligible statistical error.

21:17 [Pub][ePrint]

Masking is a well-known technique used to prevent block cipher implementations from side-channel attacks. Higher-order side channel attacks (e.g. higher-order DPA attack) on widely used block cipher like AES have motivated the design of efficient higher-order masking schemes. Indeed, it is known that as the masking order increases, the difficulty of side-channel attack increases exponentially. However, the main problem in higher-order masking is to design an efficient and secure technique for S-box computations in block cipher implementations. At FSE 2012, Carlet et al. proposed a generic masking scheme that can be applied to any S-box at any order. This is the first generic scheme for efficient software implementations. Analysis of the running time, or \\textit{masking complexity}, of this scheme is related to a variant of the well-known problem of efficient exponentiation (\\textit{addition chain}), and evaluation of polynomials.

In this paper we investigate optimal methods for exponentiation

in $\\mathbb{F}_{2^{n}}$ by studying a variant of addition chain,

which we call \\textit{cyclotomic-class addition chain}, or \\textit{CC-addition chain}. Among several interesting properties, we prove lower bounds on min-length CC-addition

chains. We define the notion of \\GFn-polynomial chain, and use it to count the number of \\textit{non-linear} multiplications required while evaluating polynomials over $\\mathbb{F}_{2^{n}}$. We also give a lower bound on the length of such a chain for any polynomial. As a consequence, we show that a lower bound for the masking complexity of DES S-boxes is three, and that of PRESENT S-box is two. We disprove a claim previously made by Carlet et al. regarding min-length CC-addition chains. Finally, we give a polynomial evaluation method, which results into an improved masking scheme (compared to the technique of Carlet et al.) for DES S-boxes. As an illustration we apply this method to several other S-boxes and show significant improvement for them.

21:17 [Pub][ePrint]

In this paper we describe an attack against nonce leaks in 384-bit ECDSA using an FFT-based attack due to Bleichenbacher. The signatures were computed by a modern smart card. We extracted the low-order bits of each nonce using a template-based power analysis attack against the modular inversion of the nonce. We also developed a BKZ-based method for the range reduction phase of the attack, as it was impractical to collect enough signatures for the collision searches originally used by Bleichenbacher. We confirmed our attack by extracting the entire signing key using a 5-bit nonce leak from 4000 signatures.

21:17 [Pub][ePrint]

The problem of securing data present on USB memories and SD cards has not been adequately addressed in the cryptography literature. While the formal notion of a tweakable enciphering scheme (TES) is well accepted as the proper primitive for secure data storage, the real challenge is to design a low cost TES which can perform at the data rates of the targeted memory devices. In this work, we provide the first answer to this problem. Our solution, called STES, combines a stream cipher with a XOR universal hash function. The security

of STES is rigorously analyzed in the usual manner of provable security approach. By carefully defining appropriate variants of the multi-linear hash function and the pseudo-dot product based

hash function we obtain controllable trade-offs between area and throughput. We combine the hash function with the recent hardware oriented stream ciphers, namely Mickey, Grain and Trivium. Our implementations are targeted towards two low cost FPGAs -- Xilinx Spartan~3 and Lattice ICE40. Simulation results demonstrate

that the speed of encryption/decryption matches the data rates of different USB and SD memories. We believe that our work opens up the possibility of actually putting FPGAs within controllers of such memories to perform low-level in-place encryption.

03:17 [Pub][ePrint]

We describe a comparatively simple fully homomorphic encryption (FHE) scheme based on the learning with errors (LWE) problem. In previous LWE-based FHE schemes, multiplication is a complicated and expensive step involving \"relinearization\". In this work, we propose a new technique for building FHE schemes that we call the \"approximate eigenvector\" method. In our scheme, for the most part, homomorphic addition and multiplication are just matrix addition and multiplication. This makes our scheme both asymptotically faster and (we believe) easier to understand.

In previous schemes, the homomorphic evaluator needs to obtain the user\'s \"evaluation key\", which consists of a chain of encrypted secret keys. Our scheme has no evaluation key. The evaluator can do homomorphic operations without knowing the user\'s public key at all, except for some basic parameters. This fact helps us construct the first identity-based FHE scheme. Using similar techniques, we show how to compile a recent attribute-based encryption scheme for circuits by Gorbunov et al. into an attribute-based FHE scheme that permits data encrypted under the same index to be processed homomorphically.

2013-06-07
21:14 [Event][New]

Submission: 24 June 2013
From October 21 to October 23
Location: Knoxville, USA

18:17 [Pub][ePrint]

TLS is the most widely-used cryptographic protocol on the Internet. It comprises the TLS Handshake Protocol, responsible for authentication and key establishment, and the TLS Record Protocol, which takes care of subsequent use of those keys to protect bulk data. TLS has proved remarkably stubborn to analysis using the tools of modern cryptography. This is due in part to its complexity and its flexibility. In this paper, we present the most complete analysis to date of the TLS Handshake protocol and its application to data encryption (in the Record Protocol). We show how to extract a key-encapsulation mechanism (KEM) from the TLS Handshake Protocol, and how the security of the entire TLS protocol follows from security properties of this KEM when composed with a secure authenticated encryption scheme in the Record Protocol. The security notion we achieve is a variant of the ACCE notion recently introduced by Jager et al. (Crypto \'12). Our approach enables us to analyse multiple different key establishment methods in a modular fashion, including the first proof of the most common deployment mode that is based on RSA PKCS #1v1.5 encryption, as well as Diffie-Hellman modes. Our results can be applied to settings where mutual authentication is provided and to the more common situation where only server authentication is applied.

2013-06-06
09:30 [Conf][Crypto]

The Conference on the Selected Areas in Cryptography in 2012 (SAC 2012) was held at University of Windsor, Windsor, Canada on August 15-16, 2012.

SAC 2012 received 87 submissions. Each submission was reviewed by at least three reviewers. 24 papers were selected for publication in the proceedings and acceptance rate was 24/87=27.6%. Two invited talks were given by Vincent Rijmen (KU Leuven) and Ian Goldberg (University of Waterloo) on the topics "Extracts from the SHA-3 competition" and "Privacy Enhancing Technologies for the Internet", respectively.

A digital version of the pre-proceedings was provided to the 55 attendees. Revised versions of the accepted papers were published in the LNCS 7707 by Springer. Most presentation slides for the technical sessions including the invited talks can be found on the conference website at http://www.uwindsor.ca/sac2012/.

The program co-chairs were Lars R. Knudsen and Huapeng Wu, who wish to thank the sponsors of SAC 2012, including the Vice President (Research) Office, Faculty of Engineering, and the Department of Electrical and Computer Engineering, University of Windsor for their enthusiastic and generous support.

03:47 [Event][New]

From October 1 to October 3

2013-06-04
16:48 [Conf][Crypto]

Crypto 2012 was held August 19-23 on the beautiful campus of the University of California, Santa Barbara. The Program Co-chairs were Rei Safavi-Naini and Ran Canetti, and the General Chair was Yiqun Lisa Yin.

A total of 225 papers were submitted, and 48 were accepted for publication, a record number for IACR flagship conferences. For the Best Paper Award, the PC overwhelmingly selected “Efficient Dissection of Composite Problems, with Applications to Cryptanalysis, Knapsacks and Combinatorial Search Problems” by Itai Dinur, Orr Dunkelman, Nathan Keller, and Adi Shamir.

There were two invited talks and one tutorial session at the conference. Professor Jonathan Zittrain from Harvard gave a talk entitled “The End of Crypto”. Dr. Ernie Brickell from Intel spoke about “Recent Advances and Existing Research Questions in Platform Security”. Professor Adam Smith from Penn State delivered a tutorial on “Pinning Down ‘Privacy’ in Statistical Databases”. Dan Bernstein and Tanja Lange co-chaired yet another entertaining Rump Session. Almost all of the talks were video recorded. These videos, along with author's slides and full versions of the papers, are available on the conference program webpage.

Generous donations were given by five industry sponsors Google, Microsoft Research, Qualcomm, RIM, and Voltage Security, as well as the Marconi Fund. In addition, the conference applied and received a special funding of \$10,000 from the National Science Foundation (NSF). With all the financial support, stipends were offered to over 40 students, both domestic and international.

The Chairs of Crypto 2012 were very grateful for the wonderful work of Sally Vito and the UCSB conference services staff.

12:36 [Pub]

At the ePrint forum (http://eprint.iacr.org/forum/list.php?14), there is currently a discussion going on about possible changes to the IACR publication system.
Some of the latest postings:
• Assigning Papers to Talks (cbw)
• Some issues + Counter proposal (Orr)
• Change is needed, but slow change is important (lindell)
• How to handle resubmissions? (ivandamgard)
• Questions (nigel)
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