International Association for Cryptologic Research

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2012-06-03
21:17 [Pub][ePrint]

We define and propose an efficient and provably secure construction of blind signatures with attributes. Prior notions of blind signatures did not yield themselves to the construction of anonymous credential systems, not even if we drop the unlinkability requirement of

anonymous credentials. Our new notion in contrast is a convenient building block for anonymous

credential systems. The construction we propose is efficient: it requires just a few exponentiations in a prime-order group in which the decisional Diffie-Hellman problem is hard. Thus, for

the ﬁrst time, we give a provably secure construction of anonymous credentials that can work in

the elliptic group setting without bilinear pairings. In contrast, prior provably secure constructions were based on the RSA group or on groups with pairings, which made them prohibitively

inefficient for mobile devices, RFIDs and smartcards. The only prior efficient construction that

could work in such elliptic curve groups, due to Brands, does not have a proof of security.

21:17 [Pub][ePrint]

Stream cipher ZUC plays a crucial role in the next generation of mobile communication as it has already been included by the 3GPP LTE-Advanced, which is a candidate standard for the 4G network. Through a long-time evaluation program, ZUC algorithm is thought to be robust enough to resist many existing cryptanalyses, but not for DPA, one of the most powerful threat of SCAs(Side Channel Analysis).Up to the present, almost all the work on DPA is for block ciphers, such as DES and AES, a very few work has been done on stream ciphers, such as ZUC algorithm, for particular reasons that would be illustrated in the later section. In this paper, we generally study the security of unprotected ZUC hardware implementation against DPA. Our theoretical analysis and experimental results show that ZUC algorithm is potentially vulnerable to this kind of attack. Furthermore, kinds of common countermeasures are discussed when we try to apply them to ZUC hardware implementations, both the security and tradeoffs are considered. The experiments are given in the last section to verify our conclusions, which would undoubtedly provide some guidance to the corresponding designers.

21:17 [Pub][ePrint]

Side-channel attacks have proven many hardware implementations of cryptographic algorithms to be vulnerable.

A recently proposed masking method, based on secret sharing and multi-party computation methods, introduces a set of sufficient requirements for implementations to be provably resistant against first-order DPA with minimal assumptions on the hardware.

The original paper doesn\'t describe how to construct the Boolean functions that are to be used in the implementation. In this paper, we derive the functions for all invertible $3 \\times 3$, $4 \\times 4$ S-boxes and the $6 \\times 4$ DES S-boxes. Our methods and observations can also be used to accelerate the search for sharings of larger (e.g. $8 \\times 8$) S-boxes. Finally, we investigate the cost of such protection.

21:17 [Pub][ePrint]

In TCC 2007, Adida and Wikstr\\\"{o}m proposed a novel approach to

shuffle, called a public shuffle,

in which a shuffler can perform shuffle publicly without needing information kept secret.

Their scheme uses an encrypted permutation matrix to shuffle

ciphertexts publicly.

This approach significantly reduces the cost of constructing a mix-net

to verifiable joint decryption. Though their method is successful in making

shuffle to be a public operation, their scheme

still requires that some trusted parties should choose a permutation

to be encrypted and construct zero-knowledge proofs on the

well-formedness of this permutation.

In this paper, we propose a method to construct a public shuffle

without relying on permutations and randomizers generated privately: Given an

$n$-tuple of ciphertext $(c_1,\\dots,c_n)$, our shuffle algorithm

computes $f_i(c_1,\\dots,c_n)$ for $i=1,\\dots,\\ell$ where each

$f_i(x_1,\\dots,x_n)$ is a symmetric polynomial in $x_1,\\dots,x_n$.

Depending on the symmetric polynomials we use, we propose two concrete constructions.

One is to use ring homomorphic encryption with constant ciphertext

complexity and the other is to use simple ElGamal encryption with

linear ciphertext complexity in the number of senders. Both

constructions are free of zero-knowledge proofs and publicly

verifiable.

21:17 [Pub][ePrint]

The UC approach of Canetti offers the advantage of stand-alone analysis while keeping security guaranties for arbitrary complex environment. When we implement by this approach first we have to ensure secure instance separation and based on this condition, we are allowed to carry out a stand-alone analysis. In this report we propose three issues related to instance separation in UC-context:

We consider the problem of universal composability in cases, when we cannot assume independence of instances. Next we formalize the interleaving attack and a related security notion. In time-aware protocols time-based separation of instances is one of the standard implementation techniques. We propose an event-driven clock model towards purely symbolic analysis of time-aware protocols.

21:17 [Pub][ePrint]

Despite the fact that we evidently have very good block ciphers at hand today, some fundamental questions on their security are still unsolved. One such fundamental problem is to precisely assess the security of a given block cipher with respect to linear cryptanalysis. In by far most of the cases we have to make (clearly wrong) assumptions, e.g., assume independent round-keys. Besides being unsatisfactory from a scientific perspective, the lack of fundamental understanding might have an impact on the performance of the ciphers we use. As we do not understand the security sufficiently enough, we often tend to embed a security margin -- from an efficiency perspective nothing else than wasted performance. The aim of this paper is to stimulate research on these foundations of block ciphers. We do this by presenting three examples of ciphers that behave differently to what is normally assumed. Thus, on the one hand these examples serve as counter examples to common beliefs and on the other hand serve as a guideline for future work.

21:17 [Pub][ePrint]

We provide the first two-party protocol allowing Alice and Bob to evaluate privately even against active adversaries any completely positive, trace-preserving map given as a quantum circuit upon their joint quantum input state. Our protocol leaks no more to any active adversary than an ideal functionality for the map, provided Alice and Bob have the cryptographic resources for active secure two-party classical computation.

15:06 [Conf][Crypto]

The list of accepted papers has been posted on the CRYPTO 2012 website.
http://www.iacr.org/conferences/crypto2012/acceptedpapers-2012.html

2012-06-01
13:45 [Event][New]

Submission: 1 July 2012
From October 25 to October 26

2012-05-30
02:23 [Conf][Crypto]

Crypto 2012 online registration is now open.

Registration website --
http://www.iacr.org/conferences/crypto2012/registration-2012.html

Early registration deadline: July 8, 2012

2012-05-29
21:17 [Pub][ePrint]

The Rainbow Signature Scheme is a non-trivial generalization of the well known Unbalanced Oil and Vinegar Signature Scheme (Eurocrypt \'99) minimizing the length of the signatures. Recently a new variant based on non-commutative rings, called NC-Rainbow, was introduced at CT-RSA 2012 to further minimize the secret key size.

We disprove the claim that NC-Rainbow is as secure as Rainbow in general and show how to reduce the complexity of MinRank attacks from 2^288 to 2^112 and of HighRank attacks from 2^128 to 2^96 for the proposed instantiation over the ring of Quaternions. We further reveal some facts about Quaternions that increase the complexity of the signing algorithm. We show that NC-Rainbow is just a special case of introducing further structure to the secret key in order to decrease the key size. As the results are comparable with the ones achieved by equivalent keys, which provably do not decrease security, and far worse than just using a PRNG, we recommend not to use NC-Rainbow.