Overview of Existing Schemes with Other than Ordinary Security

This chapter presents an overview of existing schemes with other than ordinary security. Recall that existing means that a concrete constraction has been proposed in the literature. Section 6.1 contains an overview of these schemes within the classification from Chapter 5, i.e., their service, structural, and security properties, and the complete bibliography of these schemes. Section 6.2 discusses possible benefits of the new schemes in applications. Section 6.3 presents ideas for actual constructions in an informal way and contains references to the remaining chapters. 

The security types considered are fail-stop, dual, and information-theoretic security. In other words, the schemes considered here offer information-theoretic security for signers, i.e., either the requirement or the fail-back requirement of the signer on disputes is fulfilled information-theoretically. 

It is not useful to consider all possible combinations of service, structure, and degree of security one by one, because there are far more possible combinations than existing schemes. (However, one could try to do so in future, i.e., either invent a scheme, or prove impossibility, or explain why the combination only has disadvantages even if one takes efficiency into account.) Instead, classes are defined according to a few important criteria, and within each class, the existing schemes with their remaining properties are listed. 

The next two levels of the classification will be the presence or absence of 

The reason is that these two properties, like the security types, have always been seen as so clear deviations from ordinary digital signature schemes that, if present in a signature scheme, they are mentioned in the name. In fact, invisibility makes quite a difference to the legal environment needed for signatures (see Section 5.2.8, 

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Overview of Existing Schemes with Other than Ordinary Security... 

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