*16:30* [Job][New]
Two PhD Positions, *University of Bristol*
The Government Communications Headquarters (GCHQ) in Cheltenham has agreed in principle to sponsor two PhD/Doctoral Studentships at Bristol University in the area of Cryptography. See the link below for the two project descriptions. The studentships are 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.

The studentships will be funded for a period of 3.5 years. GCHQ will cover the costs of university fees (currently £ 3828 per annum) and will provide an annual stipend to the student corresponding to the National Minimum Stipend (currently £ 13,590 per annum) plus an additional stipend of £ 7,000 per annum. Making a total tax-free stipend of £ 20,590 per annum. A generous travel budget is also provided to enable attendance at international conferences and workshops.

*13:03* [Job][New]
Two Post-Docs, *Nanyang Technological University, Singapore*
We are looking for two Post-Docs in coding and lattice based cryptography. Contact us if you have (or will have soon) a PhD in Cryptography or a related subject, an excellent publication record and would like to work in a fun environment in Singapore. More information on Coding and Crypto Research Group at Nanyang Technological University can be found at http://www1.spms.ntu.edu.sg/~ccrg/index.html

The applications will be considered immediately. The positions are for 1 year, but renewable up to 3 years.

*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.