ACE Seminar: Short Group Signatures via Structure-Preserving Signatures: Standard Model Security from Simple Assumptions

Speaker: Dr Thomas Peters

Date/Time: 15-Oct-2015, 15:00 UTC

Venue: Birkbeck B30



Group signatures are a central cryptographic primitive which allows users to sign messages while hiding their identity within a crowd of group members. In the standard model (without the random oracle idealization), the most efficient constructions rely on the Groth-Sahai proof systems (Eurocrypt'08). The structure-preserving signatures of Abe et al. (Asiacrypt'12) make it possible to design group signatures based on well-established, constant-size number theoretic assumptions, a.k.a. 'simple assumptions'. While much more efficient than group signatures built on general assumptions, these constructions incur a significant overhead w.r.t. constructions secure in the idealized random oracle model. Indeed, the best known solution based on simple assumptions requires 2.8 kB per signature for currently recommended parameters. Reducing this size and presenting techniques for shorter signatures are thus natural questions. In this seminar, I will present recent progresses to significantly reduce this overhead. Namely, we will see how we can obtain the first fully anonymous group signatures based on simple assumptions with signatures shorter than  2 kB at the 128-bit security level. In dynamic (resp. static) groups, our signature length drops to 1.8 kB (resp. 1 kB). This improvement is enabled by two technical tools: a new structure-preserving signature based on simple assumptions which shortens the best previous scheme by 25% and a new method for attaining anonymity in the strongest sense using a new CCA2-secure encryption scheme which is simultaneously a Groth-Sahai commitment.


Dr Thomas Peters is currently a CNRS researcher in the Department of Informatics, Ecole Normale Supérieure, France. He also has a pending post-doctoral fellowship granted by the FNRS for doing researcher within the crypto group at the Université catholique de Louvain, Belgium. Dr Peters received his Ph.D. in April 2014 from the Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université catholique de Louvain, Belgium. Recently, he received the IBM Innovation Award 2015, from IBM Belgium and the FNRS, for his thesis entitled 'Privacy Enhancing Cryptographic Mechanisms with Public Verifiability'. Thomas Peters' research interests focus on public-key cryptography, privacy protocols with provable security, electronic voting systems and efficient multi-party computation for the Cloud.



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