Special Aspects of Escrow-based E-Cash Systems

Electronic cash systems are one way to implement digital payments; e-cash schemes can offer user anonymity at the same level as paper-based cash. However, this anonymity can be misused for illegal purposes; therefore, some means to revoke the anonymity under specific circumstances seems desirable. Many ``escrow-based'' schemes have been proposed; the information needed for this is usually escrowed at a trusted third party. In this thesis, we'll take a close look at various escrow-based e-cash schemes and investigate their security for all participants and the assumptions it is based on. The notion of ``self-escrowing'', i.e. replacing the trusted third party by the user himself, will be addressed; finally, by combining some of the techniques presented, we construct an escrow-based e-cash scheme which offers strengthened security against forgery of coins.