Cryptology ePrint Archive: Report 2008/006

Joint State Theorems for Public-Key Encryption and Digital Signature Functionalities with Local Computation

Ralf Kuesters and Max Tuengerthal

Abstract: In frameworks for universal composability, complex protocols can be built from sub-protocols in a modular way using composition theorems. However, as first pointed out and studied by Canetti and Rabin, this modular approach often leads to impractical implementations. For example, when using a functionality for digital signatures within a more complex protocol, parties have to generate new verification and signing keys for every session of the protocol. This motivates to generalize composition theorems to so-called joint state (composition) theorems, where different copies of a functionality may share some state, e.g., the same verification and signing keys. In this paper, we present a joint state theorem which is more general than the original theorem of Canetti and Rabin, for which several problems and limitations are pointed out. We apply our theorem to obtain joint state realizations for three functionalities: public-key encryption, replayable public-key encryption, and digital signatures. Unlike most other formulations, our functionalities model that ciphertexts and signatures are computed locally, rather than being provided by the adversary. To obtain the joint state realizations, the functionalities have to be designed carefully. Other formulations proposed in the literature are shown to be unsuitable. Our work is based on the IITM model. Our definitions and results demonstrate the expressivity and simplicity of this model. For example, unlike Canetti's UC model, in the IITM model no explicit joint state operator needs to be defined and the joint state theorem follows immediately from the composition theorem in the IITM model.

Category / Keywords: cryptographic protocols / simulation-based security, joint state theorem

Original Publication (with major differences): Version from 2008 has been published in CSF 2008.

Date: received 3 Jan 2008, last revised 30 Aug 2013

Contact author: kuesters at uni-trier de

Available format(s): PDF | BibTeX Citation

Note: The major difference to the version from 2008 is that we now use the new IITM model: http://eprint.iacr.org/2013/025/

Version: 20130830:074929 (All versions of this report)

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