*15:17* [Pub][ePrint]
Indistinguishability Obfuscation vs. Auxiliary-Input Extractable Functions: One Must Fall, by Nir Bitansky and Ran Canetti and Omer Paneth and Alon Rosen
We show that if there exist indistinguishability obfuscators for all circuits then there do not exist auxiliary-input extractable one-way functions. In particular, the knowledge of exponent assumption withrespect to adversaries with auxiliary input is false in any group where computing discrete logarithms is intractable. The proof uses the \"punctured programs\" technique of [Sahai-Waters 2013].

*15:17* [Pub][ePrint]
Multiparty Key Exchange, Efficient Traitor Tracing, and More from Indistinguishability Obfuscation, by Dan Boneh and Mark Zhandry
In this work, we show how to use indistinguishability obfuscation (iO) to build multiparty key exchange, efficient broadcast encryption, and efficient traitor tracing. In addition to being the first constructions of these primitives from iO, our schemes also enjoy several interesting properties that have not been achievable before: - Our multiparty key exchange protocol does not require a trusted setup. Moreover, the size of the published value from each user is independent of the total number of users.

- Our broadcast encryption schemes support distributed setup, where users choose their own secret keys. The broadcast ciphertext size is independent of the number of users.

- Our traitor tracing system is fully collusion resistant and provides ciphertexts that are logarithmic in the number of users and constant-sized secret keys. This construction resolves an open problem relating to differential privacy.

Our proof of security for traitor tracing introduces a new tool for iO proofs: the construction makes use of a key-homomorphic symmetric cipher which plays a crucial role in the proof of security.

*15:17* [Pub][ePrint]
FlexDPDP: FlexList-based Optimized Dynamic Provable Data Possession, by Ertem Esiner and Adilet Kachkeev and Samuel Braunfeld and Alptekin K\\\"up\\c{c}\\\"u and \\\"Oznur \\\"Ozkasap
With popularity of cloud storage, efficiently proving the integrity of data stored at an untrusted server has become significant. Authenticated Skip Lists and Rank-based Authenticated Skip Lists (RBASL) have been used in cloud storage to provide support for provable data update operations. In a dynamic file scenario, an RBASL falls short when updates are not proportional to a fixed block size; such an update to the file, however small, may translate to O(n) many block updates to the RBASL, for a file with n blocks. To overcome this problem, we introduce FlexList: Flexible Length-Based Authenticated Skip List. FlexList translates even variable-size updates to O(u) insertions, removals, or modifications, where u is the size of the update divided by the block size. We present various optimizations on the four types of skip lists (regular, authenticated, rank-based authenticated, and FlexList). We compute one single proof to answer multiple (non-)membership queries and obtain efficiency gains of 35%, 35% and 40% in terms of proof time, energy, and size, respectively. We also deployed our implementation of FlexDPDP (DPDP with FlexList instead of RBASL) on PlanetLab, demonstrating that FlexDPDP performs comparable to the most efficient static storage scheme (PDP), while providing dynamic data support.

*22:35* [Job][New]
PhD Scholarship, *Centre for Secure Information Technologies (CSIT), Queen’s University Belfast, UK*
The Government Communications Headquarters (GCHQ) in Cheltenham has agreed in principle to sponsor a PhD/Doctoral Studentship at CSIT, Queens University Belfast in the area of Detection, Mitigation and Prevention of Emerging Application Layer DDoS Attacks. This GCHQ-sponsored PhD studentship provides funding for 3.5 years and can commence as soon as possible. GCHQ will cover the costs of university fees and will provide an annual stipend to the student corresponding to the National Minimum Stipend (currently £13,590 per annum) plus an additional sum of £7,000 per annum (both tax free). For comparison this is **equivalent to approx. £26,555 annual salary**. A further £5k of funding will also be available per annum for travel to conferences, collaborative partners, and GCHQ visits. The studentship is **only open to UK nationals** and the successful candidate will be required to spend in the region of 2 - 4 weeks per year at GCHQ headquarters in Cheltenham. To be considered for this studentship, candidates must **therefore be prepared to undergo GCHQ\\\'s security clearance procedures**.

*14:17* [Job][New]
Tenured, Tenure-track Faculty positions, *Sejong University, Seoul, Korea*
The Department of Computer and Information Security at Sejong University, Seoul, South Korea invites applications for a tenure-track faculty position in all levels (full professor, associate professor, assistant professor) from Computer and Information Security. Those who have an outstanding research record in applicant\\\'s own research area are encouraged to apply. Applicant must have a doctoral degree in computer science or in a related field and must provide 4 necessary documents. (See below URL) Applicants must also arrange for three recommendation letters and send them to *isdpt (at) sejong.ac.kr*

The application deadline is Oct. 18, 2013 5 p.m. KST (UTC+9). To ensure full consideration, application documents and recommendation letters should be received no later than this date.

Successful candidate is expected to establish an independent research program while contributing to Department\\\'s teaching program in undergraduate and graduate level. Chosen candidate is expected to start his/her duty in Mar. 1, 2014.

Apply online at http://facultyjob.sejong.ac.kr/2013/index.html

*14:16* [Job][New]
Researcher (postdoc) in Cryptography (or Quantum Crypto), *Institute of Computer Science, University of Tartu, Estonia, EU*
The Cryptography group at the University of Tartu, Estonia, is looking for a researcher (postdoc) in cryptography, preferably with strengths on one of the following topics:- Theory of cryptography
- Quantum cryptography
- Mathematics (applied to cryptography)
- Verification
- Any other area that complements the existing team

The Cryptography group in Tartu (senior members: Dominique Unruh, Helger Lipmaa, Sven Laur) does research on a variety of cryptography related topic, such as quantum cryptography, verification, foundations of cryptography, cryptographic protocols, e-voting, etc. On the coding theory side, we also have Vitaly Skachek.

Researchers at U Tartu are full faculty members. Salary is 2000 euro (cost of living in Estonia is quite low, see e.g. http://www.expatistan.com/cost-of-living), with an employment contract for three years.

A successful candidate should:

- Hold a phd degree
- Have a strong background in cryptography or a relevant related field
- Have an international publication record at outstanding venues

To apply, please submit the following documents (by email):

- Letter of motivation
- Research plan
- Two letters of reference (make sure they reach us by the application deadline)
- Curriculum vitae
- Publication list
- Phd degree

Deadline for applications: 1 November 2013

Do not hesitate to contact us in case of questions.

*15:17* [Pub][ePrint]
Improved Linear Sieving Techniques with Applications to Step-Reduced LED-64, by Itai Dinur and Orr Dunkelman and Nathan Keller and Adi Shamir
In this paper, we describe new techniques in meet-in-the-middle attacks. Our basic technique is called a \\emph{linear key sieve} since it exploits as filtering conditions linear dependencies between key bits that are guessed from both sides of the attack. This should be contrasted with related previous attacks, which only exploiteda \\emph{linear state sieve} (i.e., linear dependencies between state bits that are computed from

both sides of the attack). We apply these techniques to the lightweight block cipher LED-64, and improve some of the best known attacks on step-reduced variants of this cipher in all attack models. As a first application of the linear key sieve, we describe a chosen plaintext attack on 2-step LED-64, which reduces the time complexity of the

best previously published attack on this variant from $2^{56}$ to $2^{48}$. Then, we present the first attack on 2-step LED-64 in the \\emph{known plaintext model}. In this attack, we show for the first time that the splice-and-cut technique (which inherently requires chosen messages) can also be applied in the known plaintext model, and we use the linear key sieve in order to obtain an attack with the same time complexity as our chosen plaintext attack. Finally, we describe a related-key attack on 3-step LED-64 which improves the best previously published attack (presented at Asiacrypt 2012) in all the complexity parameters of time/data/memory from $2^{60}$ to $2^{49}$. As our first two single-key attacks, the related-key attack is also based on the linear key sieve, but it uses additional techniques in differential meet-in-the-middle which are interesting in their own right.