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18:17 [Pub][ePrint] On Necessary and Sufficient Conditions for Private Ballot Submission, by D. Bernhard and O. Pereira and B. Warinschi

  We exhibit the precise security guarantees that a public key encryption scheme needs to satisfy to guarantee ballot privacy when used in a large class of voting systems. We also identify new security notions for public key encryption that characterize the number of times that a public key can be used in different elections, and show that the most common ballot preparation approach that consists in encrypting the vote and adding a NIZK proof of its validity is sound, even without hardwiring the voter identity in the proof. Our results provide important steps towards proving the privacy of the ballot submission procedure in the widely deployed Helios voting system.

18:17 [Pub][ePrint] In the point of view security, An efficient scheme in IBE with random oracle, by Rkia Aouinatou1, Mostafa Belkasmi2

  We present in these papers a scheme, which bypasses the weakness presented in the existed scheme of IBE with random oracle. We propose, a secure scheme which project into Zp contrary to elliptic

curve as with Boneh and Franklin. More, our scheme is basing in its study of simulation in the problem 4-EBDHP which is more efficient than q-BDHIP used by Skai Kasarah. We provide the prove of security of our scheme and we show its efficiency by comparison with the scheme declared

above. Even if it we have a little cost in complexity, but as in the field cryptography we are more interested to the security, this makes our proposition more efficient.

18:17 [Pub][ePrint] The Boomerang Attacks on the Round-Reduced Skein-512, by Hongbo Yu and Jiazhe Chen and XIaoyun Wang

  The hash function Skein is one of the five finalists of the NIST SHA-3 competition;it is based on the block cipher Threefish which only uses three primitive operations: modular addition, rotation and bitwise XOR (ARX). This paper studies the boomerang attacks on Skein-512. Boomerang distinguishers on the compression function reduced to 32 and 36 rounds are proposed, with complexities 2^{104.5} and 2^{454} respectively. Examples of the distinguishers on 28-round and 31-round are also given. In addition, the boomerang distinguishers are applicable to the key-recovery attacks on reduced Threefish-512. The complexities for key-recovery attacks reduced to 32-/33-/34-round are about 2^{181}, 2^{305} and 2^{424}. Because Laurent et al. [14] pointed out that the previous boomerang distinguishers for Threefish-512 are in fact not compatible, our attacks are the first valid boomerang attacks for the final round Skein-512.

18:17 [Pub][ePrint] Zero-Knowledge for Multivariate Polynomials, by Valerie Nachef and Jacques Patarin and Emmanuel Volte

  In~\\cite{SSH} a Zero-Knowledge scheme $ZK(2)$ was designed from a solution of a set of multivariate quadratic equations over a finite field. In this paper we will give two methods to generalize this construction for polynomials of any degree $d$, i.e. we will design two Zero-Knowledge schemes $ZK(d)$ and $\\tilde {ZK}(d)$ from a set of polynomial equations of degree $d$. We will show that $\\tilde {ZK} (d)$ is optimal in term of the number of computations to be performed and that $ZK(d)$ is optimal in term of the number of bits to be send. Moreover this

property is still true for all kinds of polynomials: for example if the polynomials are sparse or dense. Finally, we will present two examples of applications: with

Brent equations, or with morphisms of polynomials.

18:17 [Pub][ePrint] Ring Switching in BGV-Style Homomorphic Encryption, by Craig Gentry and Shai Halevi and Nigel P. Smart

  BGV-style homomorphic encryption schemes over polynomial rings, rely for their security on rings of very large dimension. This large dimension is needed because of the large modulus-to-noise ratio in the key-switching matrices that are used for the top few levels of the evaluated circuit. However, larger noise (and hence smaller modulus-to-noise ratio) is used in lower levels of the circuit, so from a security standpoint it is permissible to switch to lower-dimension rings. Switching to a smaller ring, if possible, can help speeding up the homomorphic operations for the lower levels of the circuit. However, implementing such ring-switching is nontrivial, since these schemes rely on the ring algebraic structure for their homomorphic properties.

A basic ring-switching operation was introduced by Brakerski, Gentry and Vaikuntanathan, in the context of bootstrapping over polynomial rings of the form $\\Z[X]/(X^{2^n}+1)$. In this work we first extend this technique to work over any cyclotomic ring. Then we build on the extended technique and show how it can be used not only for bootstrapping but also during the computation itself, in conjunction with the ``packed ciphertext\'\' techniques of Gentry, Halevi and Smart.

18:17 [Pub][ePrint] Key distribution system and attribute-based encryption , by Masahiro Yagisawa

  I propose the new key distribution system and attribute-based encryption scheme on non-commutative ring where the complexity required for enciphering and deciphering is small. As in this system encryption keys and decryption keys involve the attributes of each user, the system is adaptive for cloud computing systems. The security of this system is based on the complexity for solving the multivariate algebraic equations of high degree over finite field, that is, one of NP complete problems. So this system is immune from the Gröbner basis attacks. The key size of this system becomes to be small enough to handle.

18:17 [Pub][ePrint] Less is More: Relaxed yet Composable Security Notions for Key Exchange, by C. Brzuska and M. Fischlin and N.P. Smart and B. Warinschi and S. Williams

  Although they do not suffer from clear attacks, various key agreement protocols (for example that used within the TLS protocol) are deemed as insecure by existing security models for key exchange. The reason is that the derived keys are used within the key exchange step, violating the common key indistinguishability requirement.

In this paper we propose a new security definition for key exchange

protocols that offers two important benefits. Our notion is weaker than the more established ones and thus allows the analysis of a larger class of protocols. Furthermore, security in the sense that we define enjoys rather general composability properties. In addition our composability properties are derived within game based formalisms, and do not appeal to any simulation based paradigm.

Specifically, for protocols whose security relies exclusively on some underlying symmetric primitive we show that they can be securely composed with key exchange protocols provided that two main requirements hold: 1) no adversary can break the underlying {\\em primitive}, even when the primitive uses keys obtained from executions of the key exchange protocol in the presence of the adversary (this is essentially the security requirement that we introduce and formalize in this paper), and 2) the security of the protocol can be reduced to that of the primitive, no matter how the keys for the primitive are distributed. Proving that the two conditions are satisfied, and then applying our generic theorem, should be simpler than performing a monolithic analysis of the composed protocol. We exemplify our results in the case of a profile of the TLS protocol. Our definition and results are set entirely within the framework of cryptographic games (and thus avoid the use of simulation).

16:55 [Job][New] Ph.D. scholarship, Center for Advanced Security Research Darmstadt (CASED)

  CASED offers PhD Scholarships in Cybersecurity (Resilient Critical Infrastructures) at the CASED lab under the authority of Technische Universität Darmstadt and Prof. Dr. Max Mühlhäuser with funding from AGT Germany.

Relevant research topics in Cybersecurity range from adversary detection to network resilience, including mitigation and healing. Regarding the application domains, a main emphasis is put on critical infrastructures with Internet backbones. This comprises Smart Cities, Smart Grids, Smart Transport,and large-scale industrial sites.

Experience in IT security, preferably with a focus on Cybersecurity, as well as profound knowledge in computer science, distributed systems and networks are mandatory. Candidates should hold a Diploma or Master degree and should have an excellent command of English and preferably some command of German.

What we offer is an international environment and contact to experienced researchers and other PhD students working on related topics in the area of IT security. Candidates obtain a 3 year scholarship and become members of the CASED graduate school, which supports them during their entire PhD research. This includes professional courses for transferable skills like trainings in giving scientific presentations or writing scientific papers.

Your application should include your Curriculum Vitae, M.Sc./Diploma certificates and grades, a letter of motivation stating your interest in the position as well as your research interests. Furthermore, you should attach at least one letter of recommendation.

Please send your complete application by email to Prof. Dr. Max Mühlhäuser (max (at)

16:55 [Job][New] Post-Doc, Technical University Denmark, Copenhagen


Postdoc within the area of Symmetric Cryptography

Applications are invited for an 18 month (with a possible extension of 6 months) Postdoc position at the Danish-Chinese Center for Applications of Algebraic Geometry in Coding and Cryptology. The center is located at the Department of Mathematics at the Technical University of Denmark. The position is available from July 2012 or earliest thereafter.


The candidate should have a PhD degree or academic qualifications equivalent to the PhD level, and should have a strong background in symmetric cryptography. This is usually demonstrated by having publications in well established journals and/or conferences.

As it is essential for the project to establish research connections with China, applicants are expected to be willing to actively establish these connections. This ideally includes one or several visits to the East China Normal University.

Salary and terms of employment

The appointment will be based on the collective agreement with the Confederation of Professional Associations. The allowance will be agreed with the relevant union.

The period of employment is 18 months.

Further information

Further information about the project may be reached by contacting Associate Professor Gregor Leander, tel. (+45) 4525 3055, g.leander (at)


We must have your online application no later than 31 May 2012. See for details.

21:47 [Event][New] ACM STC: The Seventh ACM Workshop on Scalable Trusted Computing

  Submission: 16 July 2012
Notification: 13 August 2012
From October 15 to October 15
Location: Raleigh, USA
More Information:

12:09 [PhD][Update] Kazuo Sakiyama: Secure Design Methodology and Implementation for Embedded Public-key Cryptosystems

  Name: Kazuo Sakiyama
Topic: Secure Design Methodology and Implementation for Embedded Public-key Cryptosystems

Description: Efficient embedded systems are implemented taking into account both hardware and software (HW/SW). In the security domain, cryptosystems need to be resistant against Side-Channel Attacks (SCAs) to protect secret information. Therefore trade-offs between cost, performance and security need to be explored when implementing cryptosystems. The goal for this thesis is to find the best architecture by investigating the trade-offs. The first contribution of this thesis focuses on a HW/SW architecture for Public-Key Cryptography (PKC). We introduce a new scalable and flexible Modular Arithmetic Logic Unit (MALU) that can be used for both RSA and curve-based cryptosystems such as Elliptic Curve Cryptography (ECC) and Hyper-Elliptic Curve Cryptography (HECC). The MALU is the main block in the hardware coprocessor and can accelerate modulo n operations and modular operations over GF(2^m) efficiently. We conclude that the proposed HW/SW platform can be used commonly for developing public-key cryptosystems. The second part of this thesis deals with several case studies that explore the cost and performance trade-offs based on the proposed platform. Two extreme examples of public-key implementations will be introduced; one offers very high performance that is necessary for powerful security systems such as banking servers. By exploiting multi-level parallelism, the proposed ECC processor can perform more than 80 000 point multiplications per second. Another one is targeting a low-power application such as passive RFID tags. We show that the compact version of the MALU consumes less than 30 uW @500 kHz. In addition, we discuss a system-level design flow that can be used for evaluating the security level of hardware implementations against power analysis attacks. The design flow offers an environment to get a quick and correct evaluation of the first order attacks. In this way, we can take the cost for SCA resistance into account in an early stage of the design.[...]