Browsing by Author "Tzeng, ZJ"

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A public-key traitor tracing scheme with revocation using dynamic shares
(2005-04-01)
Tzeng, WG
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Tzeng, ZJ
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資訊工程學系
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Department of Computer Science
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 public-key traitor tracing scheme with revocation using dynamic shares
(2001)
Tzeng, WG
;
Tzeng, ZJ
;
資訊工程學系
;
Department of Computer Science
We proposed a new public-key traitor tracing scheme with revocation capability using the dynamic share and entity revocation techniques. The enabling block of our scheme is independent of the number of subscribers, but dependent on the collusion and revocation thresholds. Each receiver holds one decryption key only. Our traitor tracing algorithm works in a black-box way and is conceptually simple. The distinct feature of our scheme is that when the traitors are found, we can revoke their private keys (up to some threshold z) without updating any private key of the remaining subscribers. Furthermore, we can restore the decryption privilege of a revoked private key later. We can actually increase the revocation capability beyond z with dynamic assignment of shares into the enabling block. This property makes our scheme highly practical. Previously proposed public-key traitor tracing schemes have to update all existing private keys even when revoking one private key only. Our scheme is as efficient as Boneh and Franklin's scheme in many aspects. Our traitor tracing scheme is fully k-resilient such that our traitor tracing algorithm 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. We also proposed a variant traitor tracing scheme whose encryption algorithm is semantically secure against the adaptive chosen ciphertext attack assuming hardness of the decisional Diffie-Hellman problem.
Authentication of mobile users in third generation mobile systems
(2001-01-01)
Tzeng, ZJ
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Tzeng, WG
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資訊工程學系
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Department of Computer Science
The goal of the third-generation mobile systems is to provide worldwide operation, enhance service capabilities, and improve performance over the second-generation mobile systems. In this paper, we propose an authentication procedure for third-generation mobile systems. The authentication procedure is a protocol suite consisting of two subprotocols: a certificate-based authentication (CBA) protocol and a ticket-based authentication (TBA) protocol. Only two parties, MS and VLR, are involved in executing our protocol. Our authentication procedure uses both public- and secret-key cryptosystems. Our authentication procedure not only provides uniform authentication across domains, but also reduces computational costs in the process of repeated authentication. We provide firm proof of our procedure's correctness.
Practical and efficient electronic voting schemes
(2001-11-01)
Tzeng, ZJ
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Tzeng, WG
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資訊工程學系
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Department of Computer Science
We present various types of new electronic voting schemes. including two-way, multi-way and multi-selection election schemes, which guarantee privacy, universal verifiability, and robustness. Initially, a voter registers a polynomial function, his public key, with the election committee, Each voter uses his polynomial function to cast his vote in various elections. The distinct feature is that each term of a polynomial function corresponds to a candidate in a multi-way election. Thus, the final tally is independent among candidates, and the time complexity for searching final results is O(n). In our schemes, each voter contacts the authorities only once; thus, our schemes are practical and suitable for large-scale elections. For robustness, we use the witness indistinguishable technique to construct the proof of validity. Security, then, is based on the discrete logarithm and decisional Diffie-Hellman assumptions.
Robust forward-secure signature schemes with proactive security
(2001)
Tzeng, WG
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Tzeng, ZJ
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資訊工程學系
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Department of Computer Science
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.
Robust key-evolving public key encryption schemes
(2002)
Tzeng, WG
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Tzeng, ZJ
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資訊工程學系
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Department of Computer Science
We propose a key-evolving paradigm to deal with the key exposure problem of public key encryption schemes. The key evolving paradigm is like the one used for forward-secure digital signature schemes. Let time be divided into time periods such that at time period j, the decryptor holds the secret key SKj, while the public key PK is fixed during its lifetime. At time period j, a sender encrypts a message m as , which can be decrypted only with the private key SKj. When the time makes a transit from period j to j + 1, the decryptor updates its private key from SKj to SKj+1 and deletes SKj immediately. The key-evolving paradigm assures that compromise of the private key SKj does not jeopardize the message encrypted at the other time periods. We propose two key-evolving public key encryption schemes with z-resilience such that compromise of z private keys does not affect confidentiality of messages encrypted in other time periods. Assuming that the DDH problem is hard, we show one scheme semantically secure against passive adversaries and the other scheme semantically secure against the adaptive chosen ciphertext attack under the random oracle.
Round-efficient conference key agreement protocols with provable security
(2000)
Tzeng, WG
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Tzeng, ZJ
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資訊工程學系
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Department of Computer Science
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.