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 -^s"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 [1] and Shao Jun's [6] approach. To our knowledge, there is no threshold proxy re-signature scheme that has been formally presented yet.
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