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2013-08-30
09:17 [Pub][ePrint]

It is a common wisdom that servers should better store the one-way hash of their clients\' passwords, rather than storing the password in the clear. This paper introduces Catena, a new one-way function for that purpose. Catena is sequentially memory-hard, which hinders massively parallel attacks on cheap memory-constrained hardware, such as recent \"graphical processing units\", GPUs. Furthermore, Catena has been designed to resist cache-timing attacks. This distinguishes Catena from scrypt, which is also sequentially memory-hard, but which we show to be vulnerable to cache-timing attacks. Additionally, Catena supports (1) client-independent updates (the server can increase the security parameters and update the password hash without user interaction or knowing the password), (2) a server relief protocol (saving the server\'s resources at the cost of the client), and (3) a variant Catena-KG for secure key derivation (to securely generate many cryptographic keys of arbitrary lengths such that compromising

some keys does not help to break others).

09:17 [Pub][ePrint]

In June 2013 the U.S. National Security Agency proposed two families of ultra-lightweight block ciphers, called Simon and Speck. In this paper we present the first cryptanalysis of round-reduced versions of Simon. We mount differential distinguishers and key-recovery attacks on up to 14/32, 17/36, 21/44, 26/54, and 32/72 rounds, for the 32-, 48-, 64-, 96-, and 128-bit versions, respectively. Furthermore, we briefly consider impossible-differential and rotational attacks. While our attacks are mostly academic, they demonstrate the drawback of the aggressive optimizations in Simon which allow powerful differential cryptanalysis.

09:17 [Pub][ePrint]

Helper data schemes are a security primitive used for privacy-preserving biometric databases and Physical Unclonable Functions.

One of the oldest known helper data schemes is the Code Offset Method (COM).

We propose an extension of the COM: the helper data is accompanied by many instances of fake helper data that is drawn from the same distribution as the real one.

While the adversary has no way to distinguish between them, the legitimate party has more information and *can* see the difference.

We use an LDPC code in order to improve the efficiency of the legitimate party\'s selection procedure.

Our construction provides a new kind of trade-off: more effective use of the source entropy, at the price of increased helper data storage.

We give a security analysis in terms of Shannon entropy and order-2 Renyi entropy.

09:17 [Pub][ePrint]

We present the first anonymous hierarchical identity based encryption (HIBE) scheme using

Type-3 pairings with adaptive security based on standard assumptions. Previous constructions

of anonymous HIBE schemes did not simultaneously achieve all these features.

The new construction uses dual pairing vector spaces using an identity hash earlier used by Boneh, Boyen and Goh.

The proof of security follows dual system approach based on decisional subspace assumptions

which are implied by Symmetric eXternal Diffie-Hellman (SXDH) assumption in Type-3 pairing groups.

09:17 [Pub][ePrint]

Secure Multiparty Computation (MPC) protocols allow a set of distrusting participants to securely compute a joint function

of their private inputs without revealing anything but the output of the function to each other. In 1991 Ostrovsky

and Yung introduced the \\emph{proactive security model}, where faults spread throughout the network, analogous

to the spread of a virus or a worm. More specifically, in the proactive security model, the adversary is not limited in the number of

parties it can corrupt but rather in the {\\em rate} of corruption with respect to a rebooting\'\' rate. In the same

paper, Ostrovsky and Yung showed that constructing a general purpose MPC protocol in the proactive security model is indeed feasible

when the rate of corruption is a constant fraction of the parties. Their result, however, was shown

only for stand-alone security and incurred a large polynomial communication overhead for each gate of the

computation. In contrast, protocols for classical\'\' MPC models (where the adversary is limited to corrupt in total up to a fixed

fraction of the parties) have seen dramatic progress in reducing communication complexity in recent years.

The question that we consider in this paper is whether continuous improvements of communication overhead in

protocols for the classical\'\' stationary corruptions model in the MPC literature can lead to communication complexity reductions in the

proactive security model as well. It turns out that improving communication complexity of proactive MPC protocols using modern

techniques encounters two fundamental roadblocks due to the nature of the mobile faults model: First, in the

proactive security model there is the inherent impossibility of bulk pre-computation\'\' to generate cryptographic material

that can be slowly consumed during protocol computation in order to amortize communication cost (the adversary can easily

discover pre-computed values if they are not refreshed, and refreshing is expensive); second, there is an apparent need for

double-sharing (which requires high communication overhead) of data in order to achieve proactive security guarantees.

Thus, techniques that were used to speed up classical MPC do not work, and new ideas are needed. That is exactly what we do in this paper: we show

a novel MPC protocol in the proactive security model that can tolerate a $\\frac13-\\epsilon$ (resp. $\\frac12-\\epsilon$) fraction of moving faults, is perfectly (resp. statistically) UC-secure, and

achieves near-linear communication complexity for each step of the computation. Our results match the asymptotic communication complexity of the best known results in the classical\'\' model

of stationary faults \\cite{DIK10}. One of the important building blocks that we introduce is a new near-linear

packed\'\' proactive secret sharing (PPSS) scheme, where the amortized communication and computational cost of maintaining

each individual secret share is just a constant. We believe that our PPSS scheme might be of independent interest.

2013-08-26
14:13 [Event][New]

Submission: 15 September 2013
Notification: 15 January 2014
From February 28 to February 28
More Information: http://cfc-crypt.weebly.com/index.html

14:12 [Event][New]

Submission: 15 September 2013
Notification: 15 January 2014
From February 28 to February 28
More Information: http://cfc-crypt.weebly.com/index.html

11:01 [Event][New]

Submission: 1 January 2014
Notification: 15 April 2014
From August 26 to October 1
More Information: http://www.di.ens.fr/~fouque/cfp-cc

07:09 [Event][New]

Submission: 31 July 2014
From August 31 to July 31
More Information: http://www.ijiss.org

2013-08-25
22:42 [Service]

I'm looking for a volunteer to edit the videos from TCC 2013. The data consists of about 30 DVDs, or about 100GB of video data. There are two DVDs for each session (the stage and the presentation screen), and they need to be re-encoded for streaming distribution on youtube. If we decide that this is too much, we might opt for only the presentation screen videos from the invited talks, but ideally I'd like to do the following: 1. split the VOB files into one file per talk. The files should be named in such a way that they can be matched to cryptodb, e.g., 24520.mp4 for http://www.iacr.org/cryptodb/data/paper.php?pubkey=24520 2. encode each file as AAC-LC audio with H.264 video, as described on https://support.google.com/youtube/answer/1722171?hl=en. 3. upload the resulting files to www.iacr.org so that they can be archived and uploaded to the IACR youtube channel. If interested, contact cryptodb@iacr.org.

2013-08-24
08:59 [Event][New]

Submission: 10 September 2013
Notification: 31 October 2013
From November 27 to November 29
Location: Berlin, Germany
More Information: http://cardis.sec.t-labs.tu-berlin.de/index.html