11/4/2015

By **Prof. Pooya Farshim**, Queen's University Belfast, UK.

**Abstract**. The talk will be about a new security model for hash functions, known as Universal computational Extractors (UCEs), which captures many random oracle (RO) like properties of hash functions. UCEs give rise to standard model instantiations of many simple and efficient RO-model schemes. I will then show how the existence of indistinguishability obfuscators (iO) can be used to rule out the existence of a strong form of UCEs and go on to present a weakening of UCEs which doesn’t fall suffer from iO attacks. In the second part, I will be talking about applying the iO attack directly to RO-model transforms, and hence show their uninstantiability in the standard model. This talk is based on joint works with Christina Brzuska (MS Research) and Arno Mittelbach (TU Darmstadt) at CRYPTO 2013 and TCC 2014.

**Keywords**. Hash Functions, Random Oracles, Obfuscation, Provable Security.

**About the speaker**. Pooya Farshim is a lecturer in Computer Science at Queen’s University Belfast, UK. Previously, he spent some time as postdoc at TU Darmstadt (Germany), Royal Holloway, University of London (UK), and University of Minho (Portugal). He completed his Ph.D at the Department of Computer Science, University of Bristol (UK). His research interests lie in the area of provable security and in particular those of basic symmetric primitives, such as blockciphers, and advanced asymmetric schemes, such as functional encryption schemes. Pooya has a high record of top tier publications in his field. He served as PC member in several conferences and workshops in his area of research and he organised a summer school on Black-Box Impossibility Results in Cryptography. He also teaches, and used to teach, courses in security and cryptography at University of Minho and Queen’s University Belfast.

**Address: **University of Minho, Gualtar campus, Braga, Portugal.

**Building. **Departamento de Informatica, Building 07.

**Coffee session**: at 1:30PM-2PM, Sala de Estar, 4th floor

**Talks session**: at 2PM-3PM, Auditório A2, 1st floor