Abstract. We proposed a new public-key traitor tracing scheme with revocation capability using dynamic shares and entity revocation techniques. Our scheme's traitor tracing and revocation programs cohere tightly. The size of the enabling block of our scheme is independent of the number of receivers. Each receiver holds one decryption key only. The distinct feature of our scheme is that when traitors are found, we can revoke their private keys (up to some threshold z) without updating the private keys of other receivers. In particular, no revocation messages are broadcast and all receivers do nothing. Previously proposed revocation schemes need update existing keys and entail large amount of broadcast messages. Our traitor tracing algorithm works in a black-box way. It is conceptually simple and fully k-resilient, that is, it can find all traitors if the number of them is k or less. The encryption algorithm of our scheme is semantically secure assuming that the decisional Diffie-Hellman problem is hard.

Abstract. We proposed a new public-key traitor tracing scheme with revocation capability using dynamic shares and entity revocation techniques. Our scheme's traitor tracing and revocation programs cohere tightly. The size of the enabling block of our scheme is independent of the number of receivers. Each receiver holds one decryption key only. The distinct feature of our scheme is that when traitors are found, we can revoke their private keys (up to some threshold z) without updating the private keys of other receivers. In particular, no revocation messages are broadcast and all receivers do nothing. Previously proposed revocation schemes need update existing keys and entail large amount of broadcast messages. Our traitor tracing algorithm works in a black-box way. It is conceptually simple and fully k-resilient, that is, it can find all traitors if the number of them is k or less. The encryption algorithm of our scheme is semantically secure assuming that the decisional Diffie-Hellman problem is hard.

A conference key protocol allows a group of participants to establish a secret communication (conference) key so that all their communications thereafter are protected by the key. In this paper we consider the distributed conference key (conference key agreement) protocol. We present two round-efficient conference key agreement protocols, which achieve the optimum in terms of the number of rounds. Our protocols are secure against both passive and active adversaries under the random oracle model. They release no useful information to passive adversaries and achieve fault tolerance against any coalition of malicious participants. We achieve the optimal round by transferring an interactive proof system to a non-interactive version, while preserving its security capability.

The secret key of a forward-secure signature scheme evolves at regular intervals, but the public key is fixed during the lifetime of the system. This paper enhances the security of Abdalla and Reyzin's forward-secure signature scheme via threshold and proactive mechanisms. In our threshold forward-secure signature scheme, we combine multiplicative and polynomial secret sharing schemes to form a threshold forward-secure signature scheme. We develop a special proof system to prove robustness of our scheme.

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