A New Security Definition for Proxy Re-Signature Schemes

Jonas Özgan (University of Bonn)

Thursday 14 July 2011, 15.00, b-it 1.25 (cosec meeting room)

In a proxy re-signature scheme a semi trusted proxy who has access to a re-signature key translates the signature of Aylin into a signature of Boris. This cryptographic primitive which was introduced in 1998, by Blaze, Bleumer and Strauss recieved renewed interest in 2005 with publication of Ateniese and Hohenberger. The security definition proposed in this publication was also used in other proxy re-signature proposals such as the uni-directional multi-use scheme of Libert and Vergnaud. Unfortunately this security definition is very complex and lacks of completenes which was mentioned in our thesis and also in the publication of Shao et al. In this talk we propose a new security definition for proxy re-signature schemes which is very intuitive and avoids the unnatural splitting of the security definition. Further, we believe that our new security definition provides the necessary flexibility to be used for other signature schemes as well.