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06:17 [Pub][ePrint] DAC-MACS: Effective Data Access Control for Multi-Authority Cloud Storage Systems, by Kan Yang and Xiaohua Jia and Kui Ren

  Data access control is an effective way to ensure the data security in the cloud. However, due to data outsourcing and untrusted cloud servers, the data access control becomes a challenging issue in cloud storage systems. Existing access control schemes are no longer applicable to cloud storage systems, because they either produce multiple encrypted copies of the same data or require a fully trusted cloud server.

Ciphertext-Policy Attribute-based Encryption (CP-ABE) is a promising technique for access control of encrypted data. It requires a trusted authority manages all the attributes and distributes keys in the system. In cloud storage systems, there are multiple authorities co-exist and each authority is able to issue attributes independently.

However, existing CP-ABE schemes cannot be directly applied to the access control for multi-authority cloud storage systems, due to the inefficiency of decryption and revocation. In this paper, we propose DAC-MACS (Data Access Control for Multi-Authority Cloud Storage), an effective and secure data access control scheme with efficient decryption and revocation. Specifically, we construct a new multi-authority CP-ABE scheme with efficient decryption and also design an efficient attribute revocation method that can achieve both forward security and backward security. The analysis and the simulation results show that our DAC-MACS is highly efficient and provably secure under the security model.

16:31 [Event][New] FC13: Financial Crypto

  Submission: 13 October 2012
Notification: 17 December 2012
From April 1 to April 5
Location: Okinawa, Japan
More Information:

06:17 [Pub][JoC] A Comparison of Cryptanalytic Tradeoff Algorithms


Abstract  Three time-memory tradeoff algorithms are compared in this paper. Specifically, the classical tradeoff algorithm by Hellman, the distinguished point tradeoff method, and the rainbow table method, in their non-perfect table versions, are treated. We show that, under parameters and assumptions that are typically considered in theoretic discussions of the tradeoff algorithms, the Hellman and distinguished point tradeoffs perform very close to each other and the rainbow table method performs somewhat better than the other two algorithms. Our method of comparison can easily be applied to other situations, where the conclusions could be different. The analysis of tradeoff efficiency presented in this paper does not ignore the effects of false alarms and also covers techniques for reducing storage, such as ending point truncations and index tables. Our comparison of algorithms fully takes into account success probabilities and precomputation efforts.

  • Content Type Journal Article
  • Pages 1-79
  • DOI 10.1007/s00145-012-9128-3
  • Authors

    • Jin Hong, Department of Mathematical Sciences and ISaC, Seoul National University, Seoul, 151-747 Korea
    • Sunghwan Moon, Department of Mathematics, Texas A&M University, College Station, TX 77843-3368, USA

    • Journal Journal of Cryptology
    • Online ISSN 1432-1378
    • Print ISSN 0933-2790

From: Wed, 25 Jul 2012 14:55:57 GMT

07:33 [Job][New] Security Expert for Smart Card and Embedded Devices, Samsung Electronics, Republic of Korea (South Korea)

  Samsung is opening the job position for the smart card security expert. The detailed job description is as follows:

- Participate to the specification of the next generation security devices in collaboration with the design team, propose new security features

- Customer support for security and security promotion

- Support CC/EMV certification

- Attend & follow-up the smart card security related standard & organization (JHAS...)

- Survey and study the up-to-date attack/countermeasure techniques and the relevant result from crypto/security research communities

The successful candidates are expected to have expertise in one or more of the following areas:

- strong experience in smart card security and more generally embedded device security (SW or HW)

- security architecture specification

- security evaluation and the attack technologies including various side channel analysis attacks

- firmware design

- EMVco / Common Criteria certifications.

The candidates are preferred to work in South Korea but it is negotiable.

The application should include the current curriculum vitae.

14:30 [Job][New] Research and PhD positions, Information Security Group, Royal Holloway, University of London, United Kingdom

  We have several doctoral and research associate positions within ASECOLAB, Adaptive Security and Economics Lab, founded at Royal Holloway, University of London by Prof Dusko Pavlovic. Some of the research directions of the Lab are indicated in the article \\\"Gaming security by obscurity\\\", NSPW 2011. Candidates with interests in the broad area of mathematical and economic models of security processes are encouraged to apply. Salaries will be competitive. The positions are for fixed term, under the standard academic conditions.

Royal Holloway is located in Egham, in the convenient and attractive area between London Heathrow and Windsor Great Park.

Please apply at The screening of the candidates will begin on August 20th, and will continue until the positions are filled. Please email Dusko.Pavlovic (at) for informal discussions about the posts. For inquiries about the application process please contact Claire.Hudson (at)

21:17 [Pub][ePrint] MDPC-McEliece: New McEliece Variants from Moderate Density Parity-Check Codes, by Rafael Misoczki and Jean-Pierre Tillich and Nicolas Sendrier and Paulo S. L. M. Barreto

  Recently, several variants of the McEliece cryptosystem based on low-density parity-check (LDPC) codes have been proposed. When combined with quasi-cyclic structure, these proposals provide much smaller key sizes than the original McEliece cryptosystem. LDPC codes are characterized by the existence of low weight dual codewords, used to perform an efficient iterative decoding. In order to avoid attacks aimed at recovering such codewords, these last proposals suggested to replace the permutation matrix used by McEliece by a matrix of small constant row and column weight, in order to increase the dual codeword weight. In this paper, we introduce the moderate density parity-check codes (MPDC, for short), which provide a better decoding process than the aforementioned LDPC variants. It also recovers the possibility to use permutation equivalent private and public codes. As a result, we present two new McEliece variants (one using quasi-cyclic MDPC codes and other employing generic MDPC codes). One of the main benefits of our variants is that both key-recovery and message decoding attacks boil down to the same coding-theory problem: low weight codeword finding. Therefore we present a security reduction much closer to the general decoding problem than any other code-based encryption scheme. Regarding each variant separately, while the QC-MDPC variant is mainly focused on allowing smaller public keys (e.g., for 80-bits of security, only 4800 bits), the MDPC variant further reduces the ways for structural attacks. Finally, we evaluate several kind of attacks, resulting in practical parameters quite competitive to conventional cryptography.

21:17 [Pub][ePrint] Cryptanalysis of an Identity-Based Multiple Key Agreement Scheme, by Qingfeng Cheng

  Multiple key agreement (MKA) protocols allow two parties to generate two or more session keys in one session, which will be used for future secure communications in public network. In recent years, many MKA protocols have been proposed. However, most of them do not

consider ephemeral key compromise resilience, and some of them still exists security flaws. In this paper, we analyze the scheme proposed by Dehkordi and Alimoradi in 2011, which is announced with stronger security. We will present ephemeral key compromise attack and impersonation attack against Dehkordi and Alimoradi\'s protocol. For overcoming these security flaws, we also propose an improvement of Dehkordi and Alimoradi\'s protocol.

21:17 [Pub][ePrint] Infinite Secret Sharing -- Examples, by Alexander Dibert and Laszlo Csirmaz

  The motivation for extending secret sharing schemes to cases when either the

set of players is infinite or the domain from which the secret and/or the

shares are drawn is infinite or both, is similar to the case when switching

to abstract probability spaces from classical combinatorial probability. It

might shed new light on old problems, could connect seemingly unrelated

problems, and unify diverse phenomena.

Definitions equivalent in the finitary case could be very much different

when switching to infinity, signifying their difference. The standard

requirement that qualified subsets should be able to determine the secret

has different interpretations in spite of the fact that, by assumption, all

participants have infinite computing power. The requirement that unqualified

subsets should have no, or limited information on the secret suggests that

we also need some probability distribution. In the infinite case events with

zero probability are not necessarily impossible, and we should decide

whether bad events with zero probability are allowed or not.

In this paper, rather than giving precise definitions, we enlist an abundance

of hopefully interesting infinite secret sharing schemes. These

schemes touch quite diverse areas of mathematics such as projective

geometry, stochastic processes and Hilbert spaces. Nevertheless our main

tools are from probability theory. The examples discussed here serve as

foundation and illustration to the more theory oriented companion paper ``Probabilistic Infinite Secret Sharing.\'\'

21:17 [Pub][ePrint] Probabilistic Infinite Secret Sharing, by Laszlo Csirmaz

  The study of probabilistic secret sharing schemes using arbitrary

probability spaces and possibly infinite number of participants lets us

investigate abstract properties of such schemes. It highlights important

properties, explains why certain definitions work better than others,

connects this topic to other branches of mathematics, and might yield new

design paradigms.

A {\\em probabilistic secret sharing scheme} is a joint probability

distribution of the shares and the secret together with a collection of {\\em

secret recovery functions} for qualified subsets. The scheme is measurable

if the recovery functions are measurable. Depending on how much information

an unqualified subset might have, we define four scheme types: {\\em

perfect}, {\\em almost perfect}, {\\em ramp}, and {\\em almost ramp}. Our main

results characterize the access structures which can be realized by schemes

of these types.

We show that every access structure can be realized by a non-measurable

perfect probabilistic scheme. The construction is based on a paradoxical

pair of independent random variables which determine each other.

For measurable schemes we have the following complete characterization. An

access structure can be realized by a (measurable) perfect, or almost

perfect scheme if and only if the access structure, as a subset of the

Sierpi\\\'nski space $\\{0,1\\}^P$, is open, if and only if it can be realized

by a span program. The access structure can be realized by a (measurable)

ramp or almost ramp scheme if and only if the access structure is a

$G_\\delta$ set (intersection of countably many open sets) in the

Sierpi\\\'nski topology, if and only if it can be realized by a Hilbert-space


21:17 [Pub][ePrint] Highly Secure Strong PUF based on Nonlinearity of MOSFET Subthreshold Operation, by Mukund Kalyanaraman and Michael Orshansky

  Silicon physical unclonable functions (PUFs) are security primitives relying on intrinsic randomness of IC manufacturing. Strong PUFs have a very large input-output space which is essential for secure authentication. Several proposed strong PUFs use timing races to produce a rich set of responses. However, these PUFs are vulnerable to machine-learning attacks due to linear separability of the output function resulting from the additive nature of timing delay along timing paths. We introduce a novel strong silicon PUF based on the exponential current-voltage behavior in subthreshold region of FET operation which injects strong nonlinearity into the response of the PUF. The PUF, which we term subthreshold current array (SCA) PUF, is implemented as a two-dimensional nxk transistor array with all devices subject to stochastic variability operating in subthreshold region. Our PUF is fundamentally different from earlier attempts to inject nonlinearity via digital control techniques, which could also be used with SCA-PUF. Voltages produced by nominally identical arrays are compared to produce a random binary response.

SCA-PUF shows excellent security properties. The average inter-class Hamming distance, a measure of uniqueness, is 50.3%. The average intra-class Hamming distance, a measure of response stability, is 0.6%. Crucially, we demonstrate that the introduced PUF is much less vulnerable to modeling attacks. Using a machine-learning technique of support-vector machine with radial basis function kernel for best nonlinear learnability, we observe that \"information leakage\" (rate of error reduction with learning) is much lower than for delay-based PUFs. Over a wide range of the number of observed challenge-response pairs, the error rate is 3-35X higher than for earlier designs.

05:22 [Job][New] M.Sc. and Ph.D. in Cryptography, Security, and Privacy, Koç University, Turkey

  Want to store your data online securely? Want a fair Internet? What about outsourcing your job while still being assured of the result? Want to work on cryptography, game theory, peer-to-peer networks, or similar fields?

If you want to secure the cloud through the use of provable cryptographic techniques, then you should definitely apply to the Cryptography, Security & Privacy Research Group at Koç University, Istanbul, Turkey. We have multiple openings for both M.Sc. and Ph.D. level applications. All accepted applicants will receive competitive scholarships.

For more information about our group, visit

For application material, visit

The application deadline has passed, but top-quality candidates will still be considered as long as open positions remain. TOEFL and GRE scores must be submitted. Do NOT apply online, since the deadline has passed. Send your documents via email, specifically indicating our research group as your interest.