Abstract:

The past three decades have witnessed a tremendous
progress in the field of Cryptography. During these years, many
cryptographic tasks have been put under rigorous treatment and
numerous constructions realizing these tasks have been proposed.
By now, the scope of cryptographic constructions ranges from
simple schemes that realize ``atomic" tasks such as
authentication, identification, and encryption, to fairly
complex protocols that realize ``high-level" tasks such as
secure multi-party computation.

The original setting in which cryptographic protocols were
investigated consisted of one execution of the protocol at a
time. While this served as a good starting point, it did not
really provide a meaningful security guarantee in a large
network scenario, where multiple executions of protocols are
taking place concurrently. Such scenarios have become
increasingly relevant in the late 90's, with the advent of large
distributed networks (such as the Internet). This state of
affairs has called for the re-establishment of the known
feasibility results in settings that are closer to the "real
world".

In this talk I will give an account of the progress made in the
area of concurrent protocol execution (a.k.a. protocol
composition). The talk will focus on the special case of
zero-knowledge protocols, and on the pivotal role that they have
played in the conceptualization and realization of more general
(and "ambitious") cryptographic tasks.