An identity based cryptosystem is a novel type of public cryptographic scheme in which the public keys of the users are their identities or strings derived from their identities. In a (t, n) proxy signature scheme, the original signer can delegate his/her signing capability to n proxy signers such that any t or more proxy signers can sign messages on behalf of the former, but t-1 or less of them cannot do the same thing. However, in many situations we want to enjoy confidentiality, authenticity and non-repudiation of message simultaneously. In this paper we propose an identity based threshold proxy signcryption scheme using bilinear pairings. The security of the scheme is also analyzed.
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