International Association for Cryptologic Research

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2012-08-13
15:17 [Pub][ePrint]

In this paper, we study timed-release cryptography with information-theoretic security. As fundamental cryptographic primitives with information-theoretic security, we can consider key-agreement, encryption, and authentication codes. Therefore, in this paper, we deal with information-theoretic timed-release security for all those primitives. Specifically, we propose models and formalizations of security for information-theoretic timed-release key-agreement, encryption, and authentication codes, and we present constructions of those ones. In particular, information-theoretic timed-release encryption and authentication codes can be constructed from information-theoretic timed-release key-agreement in a generic and simple way. Also, we derive tight lower bounds on sizes of secret-keys and show optimal constructions for information-theoretic timed-release key-agreement and encryption. Furthermore, we investigate a relationship of mechanisms between information-theoretic timed-release key-agreement and information-theoretic key-insulated key-agreement. It turns out that there exists a simple algorithm which converts the former into the latter, and vice versa. In the sense, we conclude that these two mechanisms are essentially close.

12:17 [Pub][ePrint]

In the face of an untrusted cloud infrastructure, outsourced data

needs to be protected. Fully homomorphic encryption is one solution

that also allows performing operations on outsourced data. However,

the involved high overhead of today\'s fully homomorphic encryption

techniques outweigh cloud cost saving advantages, rendering it

impractical. We present EPiC, a practical, efficient protocol for

the privacy-preserving evaluation of a fundamental operation on data

sets: frequency counting. In an IND-CPA encrypted outsourced data

set, a cloud user can specify a pattern, and the cloud will count

the number of occurrences of this pattern in a completely oblivious

manner. EPiC\'s main idea is, first, to reduce the problem of

counting to polynomial evaluation. Second, to efficiently evaluate

polynomials in a privacy-preserving manner, we extend previous work

on the Hidden Modular Group Order assumption and design a new

\\emph{somewhat homomorphic} encryption scheme. This scheme is highly

efficient in our particular counting scenario with a relatively

small number of possible patterns. Besides a formal analysis where

we prove EPiC\'s privacy, we also present implementation and

evaluation results. We specifically target Google\'s prominent

MapReduce paradigm as offered by major cloud providers. Our

evaluation performed both locally and in Amazon\'s public cloud with

data sets sizes of up to 1 TByte shows only modest overhead compared

to non-private counting, attesting to EPiC\'s efficiency.

12:17 [Pub][ePrint]

This paper shows a generic method of constructing CCA-secure public key encryption schemes with leakage resilience on the secret key. It is based on a new kind of universal$_2$ hash proof system which accepts an auxiliary parameter. Specifically, two schemes are presented, basing on the DCR assumption and DLIN assumption respectively.

07:37 [Event][New]

Submission: 1 September 2012
Notification: 1 December 2012
From March 3 to March 6
Location: Tokyo, Japan
More Information: http://tcc2013.com/

2012-08-11
01:26 [Event][New]

Submission: 30 September 2012
Notification: 15 November 2012
From January 11 to January 12
Location: Greater Noida, India
More Information: http://qshine.org/2013/show/home

2012-08-09
16:00 [Job][New]

The APSIA Group (APplied Security and Information Assurance), led by Prof P Y A Ryan, along with the University of Applied Science in Berne, has recently been awarded a joint INTER project (funded by the FNR in Luxembourg and the SNF in Switzerland), to study verifiable, secure internet voting. The APSIA Group is seeking a highly qualified post-doctoral researcher for this project.

The VIVO project, a joint project with Prof Rolf Haenni of the University of Applied Sciences in Berne, will develop and evaluate novel approaches to ensuring the security (verifiability, coercion-resistance etc.) of internet voting. You will be working with Prof Ryan and members of the APSIA team as well as collaborating with Prof Haenni and members of the Berne e-voting group (http://e-voting.bfh.ch/).

15:50 [Event][New]

Submission: 7 October 2012
Notification: 5 November 2012
From December 14 to December 16
Location: Washington DC, USA
More Information: http://www.securityengineeringforum.org/rise12/

15:49 [Event][New]

Submission: 27 March 2012
Notification: 7 July 2012
From September 13 to September 13
Location: Leuven, Belgium
More Information: http://www.proofs-workshop.org/

2012-08-08
06:17 [Pub][ePrint]

At CRYPTO 2008 Stam conjectured that if an $(m\\!+\\!s)$-bit

to $s$-bit compression function $F$ makes $r$ calls to a primitive $f$

of $n$-bit input, then a collision for $F$ can be obtained (with high

probability) using $r2^{(nr-m)/(r+1)}$ queries to $f$, which is sometimes

less than the birthday bound. Steinberger (Eurocrypt 2010) proved Stam\'s

conjecture up to a constant multiplicative factor for most cases in

which $r = 1$ and for certain other cases that reduce to the case

$r = 1$. In this paper we prove the general case of Stam\'s conjecture

(also up to a constant multiplicative factor). Our result is

qualitatively different from Steinberger\'s, moreover, as we show the

following novel threshold phenomenon: that exponentially many (more

exactly, $2^{s-2(m-n)/(r+1)}$) collisions are obtained with high

probability after $O(1)r2^{(nr-m)/(r+1)}$ queries. This in particular

shows that threshold phenomena observed in practical compression

functions such as JH are, in fact, unavoidable for compression

functions with those parameters. (This is the full version of the

same-titled article that appeared at CRYPTO 2012.)

2012-08-07
21:17 [Pub][ePrint]

In this paper, we focus on the problem of minimizing ciphertext overhead, and discuss the (im)possibility of constructing key encapsulation mechanisms (KEMs) with low ciphertext overhead. More specifically, we rule out the existence of algebraic black-box reductions from the (bounded) CCA security of a natural class of KEMs to any non-interactive problem. The class of KEMs captures the structure of the currently most efficient KEMs defined in standard prime order groups, but restricts an encapsulation to consist of a single group element and a string. This result suggests that we cannot rely on existing techniques to construct a CCA secure KEM in standard prime order groups with a ciphertext overhead lower than two group elements. Furthermore, we show how the properties of an (algebraic) programmable hash function can be exploited to construct a simple, efficient and CCA secure KEM based on the hardness of the decisional Diffie-Hellman problem with the ciphertext overhead of just a single group element. Since this KEM construction is covered by the above mentioned impossibility result, this enables us to derive a lower bound on the hash key size of an algebraic programmable hash function, and rule out the existence of algebraic $({\\sf poly},n)$-programmable hash functions in prime order groups for any integer $n$. The latter result answers an open question posed by Hofheinz and Kiltz (CRYPTO\'08) in the case of algebraic programmable hash functions in prime order groups.

21:17 [Pub][ePrint]

Sensitive electronic data may be required to remain confidential for long periods of time. Yet encryption under a computationally secure cryptosystem cannot provide a guarantee of long term confidentiality, due to potential advances in computing power or cryptanalysis. Long term confidentiality is ensured by information theoretically secure ciphers, but at the expense of impractical key agreement and key management.

We overview known methods to alleviate these problems, whilst retaining some form of information theoretic security relevant for long term confidentiality.