Paper 2019/1073

iUC: Flexible Universal Composability Made Simple

Jan Camenisch, Stephan Krenn, Ralf Kuesters, and Daniel Rausch


Proving the security of complex protocols is a crucial and very challenging task. A widely used approach for reasoning about such protocols in a modular way is universal composability. A perfect model for universal composability should provide a sound basis for formal proofs and be very flexible in order to allow for modeling a multitude of different protocols. It should also be easy to use, including useful design conventions for repetitive modeling aspects, such as corruption, parties, sessions, and subroutine relationships, such that protocol designers can focus on the core logic of their protocols. While many models for universal composability exist, including the UC, GNUC, and IITM models, none of them has achieved this ideal goal yet. As a result, protocols cannot be modeled faithfully and/or using these models is a burden rather than a help, often even leading to underspecified protocols and formally incorrect proofs. Given this dire state of affairs, the goal of this work is to provide a framework for universal composability which combines soundness, flexibility, and usability in an unmatched way. Developing such a security framework is a very difficult and delicate task, as the long history of frameworks for universal composability shows. We build our framework, called iUC, on top of the IITM model, which already provides soundness and flexibility while lacking sufficient usability. At the core of iUC is a single simple template for specifying essentially arbitrary protocols in a convenient, formally precise, and flexible way. We illustrate the main features of our framework with example functionalities and realizations.

Available format(s)
Publication info
A major revision of an IACR publication in ASIACRYPT 2019
Universal ComposabilityModels
Contact author(s)
ralf kuesters @ sec uni-stuttgart de
daniel rausch @ sec uni-stuttgart de
jan @ dfinity org
stephan krenn @ ait ac at
2019-09-23: received
Short URL
Creative Commons Attribution


      author = {Jan Camenisch and Stephan Krenn and Ralf Kuesters and Daniel Rausch},
      title = {iUC: Flexible Universal Composability Made Simple},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1073},
      year = {2019},
      note = {\url{}},
      url = {}
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