International Association for Cryptologic Research

International Association
for Cryptologic Research


Yong Ho Hwang

Affiliation: The Johns Hopkins University


Certificateless Public Key Encryption Secure against Malicious KGC Attacks in the Standard Model
Yong Ho Hwang Joseph K. Liu
We introduce the first secure Certificateless Public Key Encryption (CL-PKE) scheme against a malicious Key Generation Center (KGC) in the standard model. Recently, Au \textit{et al.} \cite{AuChLiMuWoYa07} pointed out that the previous security models for CL-PKE schemes cannot guarantee the security against a malicious KGC. They also showed that although some schemes are secure against malicious KGC, they require the random oracle model to prove the security. In this paper, we first show that previous CL-PKE schemes in the standard model are not secure against malicious KGC. And then, we construct a new CL-PKE scheme with rigorous security proof against the attacks of a malicious KGC in the standard model, which is the first in the literature.
Efficient Broadcast Encryption Scheme with Log-Key Storage
Yong Ho Hwang Pil Joong Lee
In this paper, we present a broadcast encryption scheme with efficient transmission cost under the \emph{log-key} restriction. Given $n$ users and $r$ revoked users, our scheme has the transmission cost of $O(r)$ and requires the storage of $O(\log n)$ keys at each receiver. These are optimal complexities in broadcast encryptions using one-way hash functions (or pseudo-random generators.) To achieve these complexities, the stratified subset difference (SSD) scheme and the $\overline{B1}$ scheme were introduced by Goodrich et al. and Hwang et al. respectively. However, their schemes have the disadvantage that transmission cost increases linearly according to the number of stratifications. By assigning the related keys between stratifications, our scheme remedies the defect and achieves very efficient transmission cost even in an environment where the key storage is restricted. To the best of our knowledge, our scheme has the most efficient transmission cost in the existing schemes with log-key storage. In addition, our result is comparable to other schemes that allow a large key storage.


Chong Hee Kim (1)
Pil Joong Lee (2)
Joseph K. Liu (1)