Paper 2008/324

RSA-TBOS Signcryption with Proxy Re-encryption.

Varad Kirtane and C. Pandu Rangan

Abstract

The recent attack on Apple iTunes Digital Rights Management \cite{SJ05} has brought to light the usefulness of proxy re-encryption schemes for Digital Rights Management. It is known that the use of proxy re-encryption would have prevented the attack in \cite{SJ05}. With this utility in mind and with the added requirement of non-repudiation, we propose the first ever signcryption scheme with proxy re-encryption that does not involve bilinear maps. Our scheme is called RSA-TBOS-PRE and is based on the RSA-TBOS signcryption scheme of Mao and Malone-Lee \cite{MM03}. We adapt various models available in the literature concerning authenticity, unforgeability and non-repudiation and propose a signature non-repudiation model suitable for signcryption schemes with proxy re-encryption. We show the non-repudiability of our scheme in this model. We also introduce and define a new security notion of Weak-IND-CCA2, a slightly weakened adaptation of the IND-CCA2 security model for signcryption schemes and prove that RSA-TBOS-PRE is secure in this model. Our scheme is Weak-IND-CCA2 secure, unidirectional, extensible to multi-use and does not use bilinear maps. This represents significant progress towards solving the open problem of designing an IND-CCA2 secure, unidirectional, multi-use scheme not using bilinear maps proposed in \cite{CH07}\cite{SXC08}.

Note: This is the full version of the paper that is to be published in ACM DRM 2008.