International Association for Cryptologic Research

# IACR News Central

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2012-06-04
00:17 [Pub][ePrint]

We construct the first public-key encryption scheme whose chosen-ciphertext (i.e., IND-CCA) security can be proved under a standard assumption and does not degrade in either the number of users or the number of ciphertexts. In particular, our scheme can be safely deployed in unknown settings in which no a-priori bound on the number of encryptions and/or users is known.

As a central technical building block, we devise the first structure-preserving signature scheme with a tight security reduction. (This signature scheme may be of independent interest.) Combining this scheme with Groth-Sahai proofs yields a tightly simulation-sound non-interactive zero-knowledge proof system for group equations. If we use this proof system in the Naor-Yung double encryption scheme, we obtain a tightly IND-CCA secure public-key encryption scheme from the Decision Linear assumption.

We point out that our techniques are not specific to public-key encryption security. Rather, we view our signature scheme and proof system as general building blocks that can help to achieve a tight security reduction.

00:17 [Pub][ePrint]

Recently, Chien et al. proposed a gateway-oriented password-based authenticated key exchange (GPAKE) protocol, through which a client and a gateway could generate a session key for future communication with the help of an authentication server. They also demonstrated that their scheme is provably secure in a formal model. However, in this letter, we will show that Chien et al.\'s protocol is vulnerable to the off-line password guessing attack. To overcome the weakness, we also propose an efficient countermeasure.

00:17 [Pub][ePrint]

The concept of proxy signature was introduced in 1996, up to now many proxy signature schemes have been proposed. In order to protect the proxy signer\'s privacy, the concept of anonymous proxy signature, which is also called proxy ring signature, was introduced in 2003. Some anonymous proxy signature schemes, which are provable secure in the random oracle model, have been proposed. However, provable security in the random oracle model is doubtful when the random oracles are instantiated with hash functions in their implementation. Hence, we propose the first secure anonymous proxy signature scheme without random oracles.

00:17 [Pub][ePrint]

The nonlinear feedback shift registers (NLFSR) are used to construct pseudorandom generators for stream ciphers. Their theory is not so complete as that of the linear feedback shift registers (LFSR). In general, it is not known how to construct NLFSRs with maximum period. The direct method is to search for such registers with suitable properties. We used the implementation of NLFSRs in Field Programmable Gate Arrays (FPGA) to perform a corresponding search. We also investigated local statistical properties of the binary sequences ganerated by NLFSRs of order 25 and 27.

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

We prove three optimal transference theorems on lattices possessing $n^{\\epsilon}$-unique shortest vectors which relate to the successive minima, the covering radius and the minimal length of

generating vectors respectively. The theorems result in reductions

between GapSVP$_{\\gamma\'}$ and GapSIVP$_\\gamma$ for this class of

lattices. Furthermore, we prove a new transference theorem giving an

optimal lower bound relating the successive minima of a lattice with

its dual. As an application, we compare the respective advantages of

current upper bounds on the smoothing parameter of discrete Gaussian

measures over lattices and show a more appropriate bound for lattices whose duals possess $\\sqrt{n}$-unique shortest vectors.

21:17 [Pub][ePrint]

Pollard\'s rho algorithm, along with parallelized, vectorized, and negating variants, is the standard method to compute discrete logarithms in generic prime-order groups.

This paper presents two reasons that Pollard\'s rho algorithm

is farther from optimality than generally believed.

First, higher-degree local anti-collisions\'\'

make the rho walk less random than the predictions made by the conventional Brent--Pollard heuristic.

Second, even a truly random walk is suboptimal,

because it suffers from global anti-collisions\'\' that can at least partially be avoided.

For example, after (1.5+o(1))\\sqrt(l) additions in a group of order l (without fast negation),

the baby-step-giant-step method has probability 0.5625+o(1)

of finding a uniform random discrete logarithm;

a truly random walk would have probability 0.6753\\ldots+o(1);

and this paper\'s new two-grumpy-giants-and-a-baby method has probability 0.71875+o(1).

21:17 [Pub][ePrint]

We present a formalisation of a category of schemes which we call \\emph{Broadcast-enhanced Key Predistribution Schemes}.

These schemes can be used instead of a key predistribution scheme in any network which has access to a trusted base station and broadcast channel.

In such networks, broadcast-enhanced key predistribution schemes can provide advantages over key predistribution schemes including flexibility and more efficient revocation.

There are many possible applications and ways to implement broadcast-enhanced key predistribution schemes, and we propose a framework for describing, comparing and analysing them.

In their paper From key predistribution to key redistribution\', Cicho\\\'{n}, Go{\\l}\\c{e}biewski and Kuty{\\l}owski propose a scheme for redistributing\' keys to a wireless sensor network using a broadcast channel after an initial key predistribution.

We classify this as a broadcast-enhanced key predistribution scheme and analyse it in that context.

We provide simpler proofs of some results from their paper, give a precise analysis of the resilience of their scheme, and discuss modifications based on defining a suitable keyring intersection threshold.

In the latter half of the paper we suggest two particular scenarios where broadcast-enhanced key predistribution schemes may be particularly desirable and the relevant design goals to prioritise in each case.

For each scenario we propose a suitable family of broadcast-enhanced key predistribution schemes and our analysis demonstrates their effectiveness in achieving their aims in resource-constrained networks.

21:17 [Pub][ePrint]

This paper is a short summary of a real world AES key extraction performed on a military grade FPGA marketed as \'virtually unbreakable\' and \'highly secure\'. We demonstrated that it is possible to extract the AES key from the Actel/Microsemi ProASIC3 chip in a time of 0.01 seconds using a new side-channel analysis technique called Pipeline Emission Analysis (PEA). This new technique does not introduce a new form of side-channel attacks (SCA), it introduces a substantially improved method of waveform analysis over conventional attack technology. It could be used to improve upon the speed at which all SCA can be performed, on any device and especially against devices previously thought to be unfeasible to break because of the time and equipment cost. Possessing the AES key for the ProASIC3 would allow an attacker to decrypt the bitstream or authenticate himself as a legitimate user and extract the bitstream from the device where no read back facility exists. This means the device is wide open to intellectual property theft, fraud and reverse engineering of the design to allow the introduction of a backdoor or Trojan. We show that with a very low cost hardware setup made with parts obtained from a local electronics distributor you can improve upon existing SCA up to a factor of x1,000,000 in time and at a fraction of the cost of existing SCA equipment.

21:17 [Pub][ePrint]

It is notoriously difficult to create hardware that is immune from side channel and tampering attacks. A lot of recent literature, therefore, has instead considered \\emph{algorithmic} defenses from such attacks.

In this paper, we show how to algorithmically secure any cryptographic functionality from continual split-state leakage and tampering attacks. A split-state attack on cryptographic hardware is one that targets separate parts of the hardware separately. Our construction does not require the hardware to have access to randomness. In contrast, prior work on protecting from continual combined leakage and tampering required true randomness for each update. Our construction is in the common reference string (CRS) model; the CRS must be hard-wired into the device. We note that prior negative results show that it is impossible to algorithmically secure a cryptographic functionality against a combination of arbitrary continual leakage and tampering attacks without true randomness; therefore restricting our attention to the split-state model is justified.

Our construction is simple and modular, and relies on a new construction, in the CRS model, of non-malleable codes with respect to split-state tampering functions, which may be of independent interest.

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.