Date: 26 Jun 2005

A hidden cryptographic assumption in no-transferable indentification schemes

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A 4-move perfect zero-knowledge argument for quadratic residuosity is discussed and the identification scheme based on this protocol is shown to be no-transferable. Note that the soundness of all known previous no-transferable protocols require no computational assumption, while our proposed protocol assumes a restriction of the power of cheating provers. Furthermore, a new notion of practical soundness is introduced and the relationship between practical soundness and no-transferable is investigated. An important consequence is that perfect zero-knowledge arguments does not always satisfy no-transferable nor practical soundness.