International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Malicious KGC Attacks in Certificateless Cryptography

Man Ho Au
Jing Chen
Joseph K. Liu
Yi Mu
Duncan S. Wong
Guomin Yang
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Abstract: Identity-based cryptosystems have an inherent key escrow issue, that is, the Key Generation Center (KGC) always knows user secret key. If the KGC is malicious, it can always impersonate the user. Certificateless cryptography, introduced by Al-Riyami and Paterson in 2003, is intended to solve this problem. However, in all the previously proposed certificateless schemes, it is always assumed that the malicious KGC starts launching attacks (so-called Type II attacks) only after it has generated a master public/secret key pair honestly. In this paper, we propose new security models that remove this assumption for both certificateless signature and encryption schemes. Under the new models, we show that a class of certificateless encryption and signature schemes proposed previously are insecure. These schemes still suffer from the key escrow problem. On the other side, we also give new proofs to show that there are two generic constructions, one for certificateless signature and the other for certificateless encryption, proposed recently that are secure under our new models.
  title={Malicious KGC Attacks in Certificateless Cryptography},
  booktitle={IACR Eprint archive},
  keywords={public-key cryptography / certificateless cryptography},
  note={ASIACCS 2007 13508 received 26 Jul 2006, last revised 26 Dec 2006},
  author={Man Ho Au and Jing Chen and Joseph K. Liu and Yi Mu and Duncan S. Wong and Guomin Yang},