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10 December 2019
Sebastian Lauer, Kai Gellert, Robert Merget, Tobias Handirk, Jörg Schwenk
For several years it has been an open question if the same strong security guarantees could be achieved with less message overhead, which is desirable because of the inherent latency in overlay networks. Several publications described CCPs which require only O(n) message exchanges, but significantly reduce the security of the resulting Tor circuit. It was even conjectured that it is impossible to achieve both message complexity O(n) and forward secrecy immediately after circuit construction (so-called immediate forward secrecy).
Inspired by the latest advancements in zero round-trip time key exchange (0-RTT), we present a new CCP protocol Tor 0-RTT (T0RTT). Using modern cryptographic primitives such as puncturable encryption allow to achieve immediate forward secrecy using only O(n) messages. We implemented these new primitives to give a first indication of possible problems and how to overcome them in order to build practical CCPs with O(n) messages and immediate forward secrecy in the future.
Diana Maimut, George Teseleanu
Arasu Arun, C. Pandu Rangan
Alessandro Chiesa, Siqi Liu
This question is intimately related to a recent line of work that builds cryptographic primitives (e.g., hash functions) via constructions that are "friendly" to known probabilistic proofs. This improves the efficiency of probabilistic proofs for computations calling these primitives.
We prove that "non-trivial" probabilistic proofs relative to several natural oracles do not exist. Our results provide strong complexity-theoretic evidence that certain functionalities cannot be treated as black boxes, and thus investing effort to instantiate these functionalities via constructions tailored to known probabilistic proofs may be inherent.
Shion Samadder Chaudhury, Sabyasachi Dutta, Kouichi Sakurai
Shion Samadder Chaudhury, Sabyasachi Dutta, Kouichi Sakurai
Sumanta Sarkar, Kalikinkar Mandal, Dhiman Saha
Boris Ryabko
Zhiguo Wan, Wei Liu, Hui Cui
Chun Guo, François-Xavier Standaert, Weijia Wang, Yu Yu
Nir Drucker, Shay Gueron, Dusan Kostic
Xiong Fan, Joshua Gancher, Greg Morrisett, Elaine Shi, Kristina Sojakova
When proving the (approximate) observational equivalance of protocols, as is required by simulation based security in the style of Universal Composability (UC), a bisimulation is typically performed in order to reason about the nontrivial control flows induced by concurrency. Unfortunately, bisimulations are typically very tedious to carry out manually and do not capture the high-level intuitions which guide informal proofs of UC security on paper. Because of this, there is currently a large gap of formality between proofs of cryptographic protocols on paper and in mechanized theorem provers.
We work towards closing this gap through a new methodology for iteratively constructing bisimulations in a manner close to on-paper intuition. We present this methodology through Interactive Probabilistic Dependency Logic (IPDL), a simple calculus and proof system for specifying and reasoning about (a certain subclass of) distributed probabilistic computations. The IPDL framework exposes an equational logic on protocols; proofs in our logic consist of a number of rewriting rules, each of which induce a single low-level bisimulation between protocols.
We show how to encode simulation-based security in the style of UC in our logic, and evaluate our logic on a number of case studies; most notably, a semi-honest secure Oblivious Transfer protocol, and a simple multiparty computation protocol robust to Byzantine faults. Due to the novel design of our logic, we are able to deliver mechanized proofs of protocols which we believe are comprehensible to cryptographers without verification expertise. We provide a mechanization in Coq of IPDL and all case studies presented in this work.
Nicky Mouha, Christopher Celi
Antonis Aggelakis, Prastudy Fauzi, Georgios Korfiatis, Panos Louridas, Foteinos Mergoupis-Anagnou, Janno Siim, Michal Zajac
We augment the most efficient argument by Fauzi et al. [Asiacrypt 2017] with a distributed key generation protocol that assures soundness of the argument if at least one party in the protocol is honest and additionally provide a key verification algorithm which guarantees zero-knowledge even if all the parties are malicious. Furthermore, we simplify their construction and improve security by using weaker assumptions while retaining roughly the same level of efficiency. We also provide an implementation to the distributed key generation protocol and the shuffle argument.
Ahmet Turan Erozan, Michael Hefenbrock, Michael Beigl, Jasmin Aghassi-Hagmann, Mehdi B. Tahoori
Zi-Yuan Liu, Yi-Fan Tseng, Raylin Tso
Xuejun Fan, Song Tian, Bao Li, Xiu Xu
09 December 2019
The Signal Private Group System and Anonymous Credentials Supporting Efficient Verifiable Encryption
Melissa Chase, Trevor Perrin, Greg Zaverucha
Authentication in our design uses a primitive called a keyed-verification anonymous credential (KVAC), and we construct a new KVAC scheme based on an algebraic MAC, instantiated in a group $\G$ of prime order. The benefit of the new KVAC is that attributes may be elements in $\G$, whereas previous schemes could only support attributes that were integers modulo the order of $\G$. This enables us to encrypt group data using an efficient Elgamal-like encryption scheme, and to prove in zero-knowledge that the encrypted data is certified by a credential. Because encryption, authentication, and the associated proofs of knowledge are all instantiated in $\G$ the system is efficient, even for large groups.
06 December 2019
Avignon, France, 29 June - 1 July 2020
Submission deadline: 18 February 2020
Notification: 23 March 2020
University of York, Department of Computer Science, York, UK
Working with Prof. Kahrobaei (the Director of York Interdisciplinary Centre for Cyber Security) and Prof. Wade (the Director of the Centre for Future Health).
Topic: Fully Homomorphic Encryption for Secure Processing of Sensitive Video Game Data by Artificial Intelligence Systems". Application deadline: January 31, 2020.
Fully Homomorphic Encryption (FHE) promises to revolutionise the way we deal with data. It enables researchers to analyze encrypted datasets and obtain useful outputs - safeguarding the privacy of the data providers and broadening the scope of available datasets at the same time. One of the most promising targets for FHE is video game telemetry - a form of data that has vast commercial and health-related potential but which is often hard to share because of issues relating to privacy, security and consent.
This competitively funded PhD studentship is advertised under the IGGI programme (http://www.iggi.org.uk/) - the largest doctoral training programme in advanced video game technology in the world. The student would focus on the theoretical and practical issues involved in implementing a fast and secure next-generation FHE analysis framework based on recent work from PI Delaram Kahrobaei (https://www.cs.york.ac.uk/research/cyber-security/people/). We will iterate development using test datasets from video games in close collaboration with our partners in the video game industry and focus on the secure, private extraction of data relating to worldwide cognitive health.
The student would engage with a full set of the training opportunities presented under the IGGI programme and would gain a broad understanding of the entire video game ecosystem - including design, analytics and applications. In addition, the work would require a deep understanding of the maths and computer science underlying FHE and the student would be supervised by world experts in the fields of both cryptography (PI Kahrobaei) and cognitive neuroscience and game analytics (PI Wade).
We expect candidate to have excellent mathematical skills and some experience in programming.
Closing date for applications:
Contact: Project enquiries: Professor Delaram Kahrobaei (delaram.kahrobaei@york.ac.uk) Professor Alex Wade (alex.wade@york.ac.uk) Application enquiries: apply@iggi.org.uk
More information: http://iggi.org.uk/apply