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A reasonably efficient password based key exchange (KE) protocol with provable security without random oracle was recently proposed by Katz, et al. [18] and later by Gennaro and Lindell [13]. However, these protocols do not support mutual authentication (MA). The authors explained that this could be achieved by adding an additional flow. But then this(More)
A non-interactive conference key distribution system (or, a NICKDS for short) allows conference members to calculate a shared key without interacting with each other. NICKDSs have been studied in unconditional and computational settings. In both cases security has been evaluated against an adversary who can corrupt participants. In this paper we consider an(More)
A τ-time key agreement system (τ-time KAS) is an unconditionally secure key agreement where an attacker cannot obtain any information about the challenge conference key even if he eavesdrops executions of τ (maybe repetitive) conferences and corrupts a predefined number of users. Here, an eavesdropped conference may contain a corrupted user, who could be(More)
Deniable authentication is a technique that allows one party to send messages to another while the latter can not prove to a third party the fact of communication. In this paper, we first formalize a natural notion of deniable security and naturally extend the basic authenticator theorem by Bellare et al. [2] to the setting of deniable authentication. Of(More)
In this work, we consider the problem of key cloning in attribute-based encryption schemes. We introduce a new type of attribute-based encryption scheme, called token-based attribute-based encryption, that provides strong deterrence for key cloning, in the sense that delegation of keys reveals some personal information about the user. We formalize the(More)