Threshold Proxy Re-Signature

The focus of this paper is to design an efficient and secure solution addressing the key escrow problem in proxy re-signature schemes, i.e., the proxy knows the user\´s private key, which damages the essential requirement - "non-repudiation" property of proxy re-signature schemes. In this paper, we first define the security model for threshold proxy re-signature scheme, and then propose two threshold proxy re-signature schemes based on Ateniese\´s (see ACM CCS, p.310-319, 2005) and Shao Jun\´s (see Progress in Cryptology - INDOCRYPT 2007, vol.4859 of LNCS, p.197-209, 2007) approach. To our knowledge, there is no threshold proxy re-signature scheme that has been formally presented yet.