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29 November 2018
Simon-Philipp Merz, Christophe Petit
ePrint ReportOur decomposition algorithm yields a universal forgery attack on WalnutDSA^TM, which is one of the 20 proposed signature schemes that are being considered by NIST for standardization of quantum-resistant public-key cryptographic algorithms. Our attack on WalnutDSA^TM can universally forge signatures within seconds for both the 128-bit and 256-bit security level, given one random message-signature pair. The attack worked on 99.8% and 100% of signatures for the 128-bit and 256-bit security levels in our experiments.
Furthermore, we show that the decomposition algorithm can be used to solve instances of the conjugacy search problem and decomposition search problem in braid groups. These problems are at the heart of other cryptographic schemes based on braid groups.
Muslum Ozgur Ozmen, Rouzbeh Behnia, Attila A. Yavuz
ePrint ReportAntonio Faonio
ePrint ReportIn this paper we show two new constructions in the standard model where the above limitation is avoided. Specifically, the first scheme achieves slack parameter $O(1/\lambda)$ where $\lambda$ is the security parameter and it is based on standard number theoretic assumptions, the second scheme achieves optimal slack parameter (i.e. $\gamma = 1$) and it is based on knowledge of the exponent assumptions. Our constructions are efficient and have leakage rate $1 - o(1)$, most notably our second construction has signature size of only 8 group elements which makes it the leakage-resilient signature scheme with the shortest signature size known to the best of our knowledge.
Kexin Hu, Zhenfeng Zhang, Kaiven Guo
ePrint Report28 November 2018
Ashutosh Kumar, Raghu Meka, Amit Sahai
ePrint ReportWe give an unconditional compiler that transforms any standard secret sharing scheme with arbitrary access structure into a $p$-party leakage-resilient one for $p$ logarithmic in the number of parties. This yields the first secret sharing schemes secure against adaptive and joint leakage for more than two parties.
As a natural extension, we initiate the study of leakage-resilient non-malleable secret sharing} and build such schemes for general access structures. We empower the computationally unbounded adversary to adaptively leak from the shares and then use the leakage to tamper with each of the shares arbitrarily and independently. Leveraging our $p$-party leakage-resilient schemes, we also construct such non-malleable secret sharing schemes: any such tampering either preserves the secret or completely `destroys' it. This improves upon the non-malleable secret sharing scheme of Goyal and Kumar (CRYPTO 2018) where no leakage was permitted. Leakage-resilient non-malleable codes can be seen as 2-out-of-2 schemes satisfying our guarantee and have already found several applications in cryptography [LL12,ADKO15,GKPRS18,GK18,CL18,OPVV18].
Our constructions rely on a clean connection we draw to communication complexity in the well-studied number-on-forehead (NOF) model and rely on functions that have strong communication-complexity lower bounds in the NOF model (in a black-box way). We get efficient $p$-party leakage-resilient schemes for $p$ upto $O(\log n)$ as our share sizes have exponential dependence on $p$. We observe that improving this dependence from $2^{O(p)}$ to $2^{o(p)}$ will lead to progress on longstanding open problems in complexity theory.
Jasper Scholten
ePrint ReportS. Sharmila Deva Selvi , Arinjita Paul, C. Pandu Rangan
ePrint ReportSébastien Andreina, Jens-Matthias Bohli, Ghassan O. Karame, Wenting Li, Giorgia Azzurra Marson
ePrint ReportNicholas Stifter, Philipp Schindler, Aljosha Judmayer, Alexei Zamyatin, Andreas Kern, Edgar Weippl
ePrint ReportFurthermore, by applying this new technique to Litecoin and its child cryptocur rencies, we are able to provide the first extensive view and lower bound on the stale block and fork rate in the Litecoin network. Finally, we outline that a recovery of other important metrics and blockchain characteristics through merged mining may also be possible.
Vamshi Krishna Kammadanam, Virendra R. Sule, Yi Hong
ePrint ReportThomas Kerber, Markulf Kohlweiss, Aggelos Kiayias, Vassilis Zikas
ePrint ReportArinjita Paul, Varshika Srinivasavaradhan, S. Sharmila Deva Selvi, C. Pandu Rangan
ePrint ReportAshwin Jha, Mridul Nandi
ePrint ReportJean-Sebastien Coron, Hilder V. L. Pereira
ePrint ReportAs an application, we describe the first concrete implementation of non-interactive Diffie-Hellman key exchange secure against existing attacks. Key exchange was originally the most straightforward application of multilinear maps; however it was quickly broken for the three known families of multilinear maps (GGH13, CLT13 and GGH15). Here we describe the first implementation of key exchange based on CLT13 that is resistant against the Cheon et al. attack. For N=4 users and a medium (62 bits) level of security, our implementation requires 8 GB of public parameters, and a few minutes for the derivation of a shared key. Without Kilian's randomization of encodings our construction would be completely unpractical, as it would require more than 100 TB of public parameters.
Kang Yang, Liqun Chen, Zhenfeng Zhang, Chris Newton, Bo Yang, Li Xi
ePrint ReportP. Arun Babu, Jithin Jose Thomas
ePrint ReportDingfeng Ye, Danping Shi, Peng Wang
ePrint ReportMassimo Bartoletti, Roberto Zunino
ePrint Report27 November 2018
CWI Amsterdam
Job PostingRequirements:
You should hold a Master degree (or expect to obtain it soon) in mathematics or computer science (or a comparable subject) with excellent grades, and you should have successfully demonstrated your research abilities, e.g. by completion of an (undergraduate) research project with outstanding results. Furthermore, preferably, you:
- have some background in cryptography;
- enjoy mathematics;
- possess good academic writing and presentation skills;
- are fluent in spoken and written English.
Application:
Your application should include the following information:
- a curriculum vitae;
- a letter of motivation (at most 1 page) explaining why you are interested in this position;
- a list of all university courses taken, including a transcript of grades;
- a report from an undergraduate research project you have done;
- the name and contact details (including email address) of two to three referees who can provide details about your profile (one of whom should be the main supervisor of your Master thesis).
The applications will be reviewed upon receipt and until the position is filled.
Closing date for applications: 1 February 2019
Contact: Please send your application to Ronald Cramer (CWI & Leiden U) and Serge Fehr (CWI & Leiden U), using ``Application CWI PhD Position`` as subject. Email: {cramer,fehr} (at) cwi.nl
University Clermont Auvergne, LIMOS, Clermont-Ferrand, France
Job PostingYour Profile:
A PhD in Computer Science, Applied Mathematics, Cryptography or related field.
Competitive research record in symmetric cryptography or in constraint programming.
Commitment, team working and a critical mind.
Fluent written and verbal communication skills in English are essential
Closing date for applications: 1 September 2019
Contact: email your cover letter, your CV, your PhD, reports of the reviewers of your PhD, a selection of your best papers related to the post-doc offer, some recommandation
letters, contact information for 3 referees and any information that might help us to choose you.
More information: http://sancy.univ-bpclermont.fr/~lafourcade/post-doc-LIMOS.pdf