Ordinary security

These security types are mainly treated in Section 5.4.3. With the ordinary type of security, known from ordinary digital signature schemes, the requirement of the recipient on disputes is guaranteed with the high degree of security, whereas the court may wrongly decide for the recipient in extreme situations. To its right, a type of security dual to ordinary security is shown. 

The fail-stop property is stronger than both these types One can simulate ordinary security by identifying broken with TRUE and dual security by identifying broken with FALSE. 

Ordinary security is the type of security that ordinary digital signature schemes offer The requirement of the signer on disputes is fulfilled computationally only, that of the recipient information-theoretically, and there is no fail-stop property. If transferability is required, the effectiveness of transfers also holds information-theoretically. 

With ordinary security, the recipient may or may not be secure without an error probability. (In ordinary digital signature schemes, he is.)... 

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 structure of authentication and disputes in existing dual invisible signature schemes resembles that of existing invisible signature schemes with ordinary security, not that of fail-stop signature schemes. The protocol carried out during authentication is of the following restricted form ... 

This section discusses possible benefits of the new types of signature schemes in applications. It resumes Section 3.1, where some problems with ordinary digital signature schemes were sketched, which can now be described as problems with ordinary security. Hence it is now discussed what advantages other security types may have with respect to the legal and social requirements from Chapter 1. 

To rule out misunderstanding The claim in the first topic is not dual security is better than ordinary security . 

This section gives a short overview of important ideas used in the construction of signature schemes with other than ordinary security. Only abstract ideas are presented the number-theoretic ideas follow in Chapter 8. 

It was sketched under Figure 5.12 and at the end of Section 5.4.3 that fail-stop security is stronger than ordinary security. This is now shown formally for the conventional definition of standard fail-stop signature schemes. Actually, two statements are shown ... 

Full standard fail-stop signature schemes themselves provide ordinary security if the output broken in disputes is replaced with TRUE. The same holds for schemes with special risk bearers if the signer plays the role of a risk bearer, too. 

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