Threshold key issuing in identity-based cryptosystems

Secure key issuing in identity-based cryptosystems is a challenging task due to the inherent drawback of key escrow. Several protocols have been proposed for key issuing which do not require secure channel and eliminate key escrow problem. However, the existing secure and efficient protocol requires all the participating authorities to be mandatorily available for constructing the user's private key. We present a secure and robust protocol for key issuing in identity-based cryptosystems by using the concept of threshold cryptosystems, which avoids the practical limitation.