並存簽章(Concurrent Signatures)的概念由公平交換簽章(Fair Exchange of Signatures)的概念衍生而來，其目標在於，為互不信任但需公平地交換簽章的兩人，提供(相較於以往)更具可行性的解法。 並存簽章的實際系統，最初乃是根基於環簽章(Ring Signatures)的 概念上；環簽章所擁有的種種性質，使得這兩個概念有著相當完美的 配合。然而，這往往不會是唯一的可能；根基於與環簽章相異概念的 並存簽章系統，亦有被公開發表。 在本論文中，對於上述根基於不同建構方式的並存簽章系統，我 們提出了詳實的分析，指出了其中的謬誤，與可能具有的潛在危險。 此外，由詳實分析作為出發點的延伸性研究，諸如尚未被強調的重要 安全性概念，以及對於並存簽章系統是否可根基於某概念的建構議題 上，我們亦作了進一步的探討 The notion of concurrent signatures, which is evolved from the notion of fair exchange of digital signatures, is aimed to provide an (even more) practical solution to the problem of fair exchange of signatures between parties that are mutually distrustful. Concurrent signature schemes are originally based on the notion of ring signatures; features of a ring signature seems perfectly match the notion of concurrent signatures. Nevertheless, this cannot be the only case; concrete schemes based on other ways of construction have also been published. In this thesis, analysis of concurrent signature schemes that are based on different approaches is conducted. Moreover, extended investigation regarding implicit but important security notions of concurrent signatures which were never stressed before, as well as the possibility of taking a particular way to construct a concurrent signature scheme have also been made.