InfoSec Seminar: Limitations of black-box constructions in cryptography

Speaker: Dr Mohammad Hajiabadi

Date/Time: 23-Feb-2017, 16:00 UTC

Venue: Gordon Street (25) - Maths 505



Since much of modern cryptography is based on unproven assumptions a central goal in crypto is to base primitives on the weakest possible assumptions. Most cryptographic constructions are black-box in the sense that the constructed object uses the base object as an oracle, without assuming anything beyond the input-output behavior of the base object. Starting with the seminal paper of Impagliazzo and Rudich (1989) there has been a large body of work showing that certain cryptographic primitives cannot be built based on certain others in a black-box way.

Moreover, we currently have a rich theory for proving lower-bounds for the efficiency of blackbox cryptographic constructions and lower-bounds for the tightness of underlying reductions.

I'll give an overview of some of the black-box separation models and techniques used in the literature. If time permits, I'll discuss two of my recent results, proving a blackbox separation between certain forms of key-dependent-message-secure (KDM-secure) encryption from semantically-secure encryption, and proving separations between different enhancements of trapdoor permutations.



Mohammad Hajiabadi has recently (September 2016) joined the security group of UCL, working with Jens Groth. He completed his PhD in Computer Science at the University of Victoria, Canada, under the supervision of Bruce Kapron. His main areas of research include foundations of cryptography and applications of formal methods in cryptography.

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