Paper 2004/322

Separable and Anonymous Identity-Based Key Issuing

Ai-fen Sui and Sherman S.M. Chow and Lucas C.K. Hui and S.M. Yiu and K.P. Chow and W.W. Tsang and C.F. Chong and K.H. Pun and H.W. Chan

Abstract

In identity-based (ID-based) cryptosystems, a local registration authority (LRA) is responsible for authentication of users while the key generation center (KGC) is responsible for computing and sending the private keys to users and therefore, a secure channel is required. For privacy-oriented applications, it is important to keep in secret whether the private key corresponding to a certain identity has been requested. All of the existing ID-based key issuing schemes have not addressed this anonymity issue. Besides, the separation of duties for authentication and private key computation has not been discussed as well. In this paper, based on a signature scheme similar to a short blind signature, we propose a novel separable and anonymous ID-based key issuing scheme without secure channel. Our protocol supports the separation of duties between LRA and KGC. The private key computed by the KGC can be sent to the user in an encrypted form such that only the legitimate key requester authenticated by LRA can decrypt it, and any eavesdropper cannot know the identity corre-sponding to the secret key.

Note: This is the full version.