
Research
Abstracts  2006 
Proxy ReSignatures: New Definitions, Algorithms, and ApplicationsGiuseppe Ateniese & Susan HohenbergerAbstract.In 1998, Blaze, Bleumer, and Strauss (BBS) proposed proxy resignatures, in which a semitrusted proxy acts as a translator between Alice and Bob. To translate, the proxy converts a signature from Alice into a signature from Bob on the same message. The proxy, however, does not learn any signing key and cannot sign arbitrary messages on behalf of either Alice or Bob. Since the BBS proposal, the proxy resignature primitive has been largely ignored, but we show that it is a very useful tool for sharing web certificates, forming weak group signatures, and authenticating a network path. We begin our results by formalizing the definition of security for a proxy resignature. We next substantiate the need for improved schemes by pointing out certain weaknesses of the original BBS proxy resignature scheme which make it unfit for most practical applications. We then present two secure proxy resignature schemes based on bilinear maps. Our first scheme relies on the Computational DiffieHellman (CDH) assumption; here the proxy can translate from Alice to Bob and viceversa. Our second scheme relies on the CDH and 2Discrete Logarithm (2DL) assumptions and achieves a stronger security guarantee  the proxy is only able to translate in one direction. Constructing such a scheme has been an open problem since proposed by BBS in 1998. Furthermore in this second scheme, even if the delegator and the proxy collude, they cannot sign on behalf of the delegatee. Both schemes are efficient and secure in the random oracle model. Funding.Susan is extremely grateful to be funded by an NDSEG Fellowship. References:[1] Giuseppe Ateniese (Johns Hopkins) and Susan Hohenberger. Proxy ReSignatures: New Definitions, Algorithms, and Applications. In The Proceedings of the ACM Conference on Computer and Communication Security (CCS), pp. 310319, Alexandria, VA, USA, Nov 2005. Full version on eprint. 

