On the security of mix-nets and hierarchical group signatures

Author:

Wikström, Douglas [claim]

Description:

In this thesis we investigate two separate cryptographic notions: mix-nets and hierarchical group signatures. The former notion was introduced by Chaum (1981). The latter notion is introduced in this thesis, but it generalizes the notion of group signatures which was introduced by Chaum and Heyst (1991). Numerous proposals for mix-nets are given in the literature, but these are presented with informal security arguments or at best partial proofs. We illustrate the need for a rigorous treatment of the security mix-nets by giving several practical attacks against a construction of Golle et al. (2002). Then we provide the first definition of security of a mix-net in the universally composable security framework (UC-framework) introduced by Canetti (2001). We construct two distinct efficient mix-nets that are provably secure under standard assumptions in the UC-framework against an adversary that corrupts any minority of the mix-servers and any set of senders. The first construction is based on the El Gamal cryptosystem (1985) and is secure against a static adversary, i.e., an adversary that decides which parties to corrupt before the execution of the protocol. This is the first efficient UC-secure mix-net in the literature and the first sender verifiable mix-net that is robust. The second construction is based on the Paillier cryptosystem (1999) and secure against an adaptive adversary, i.e., an adversary that decides which parties to corrupt during the execution of the protocol. This is the first efficient adaptively secure mix-net in any model. An important subprotocol in the above constructions is a zero-knowledge proof of knowledge of a witness that a party behaves as expected. There are two known approaches for constructing such a protocol given by Neff (2002) and Furukawa and Sako (2002) respectively. We present a third independent approach. We introduce the notion of hierarchical group signatures. This is a generalization of group signatures. There are several group managers, and the signers and group ...

Publisher:

KTH, Numerisk Analys och Datalogi, NADA ; Stockholm : Numerisk analys och datalogi

Year of Publication:

2005

Document Type:

Doctoral thesis, monograph ; info:eu-repo/semantics/doctoralThesis ; text ; [Doctoral and postdoctoral thesis]

Language:

eng

Subjects:

Computer Sciences ; Datavetenskap (datalogi)

DDC:

005 Computer programming, programs & data (computed)