Strong requirement of the signer on disputes

The dotted line indicates the period of time where the signer must not have authenticated m for the result acc = FALSE to be guaranteed. 

The following Table 5.2 shows all variants that seem moderately sensible, including a command agree for a signer to agree to having authenticated the message.  

Earlier Start of dispute Possible sets of permitted results 

The most important distinction is in bold type. No restriction formally means the set Dispute results. 

One scheme from the literature, [Fu0091], is not covered by this table, because the signer can both agree and disavow in one dispute. However, I cannot imagine an application. 

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Before the requirements that remain from Section 7.1.3 are formalized, the additional service properties that standard fail-stop signature schemes should have according to Section 6.1.2 are considered. It turns out that most of these requirements are automatically fulfilled according to the assumed structure of the entities around the algorithms from Definition 7.1 or 7.2, respectively. The only remaining one, the strong requirement of the signer on disputes in the case with special risk bearers, can be fulfilled by similar structural measures. 

As mentioned in Section 5.2.9, Combinations , it is usefiil in practice to add the strong requirement of the signer on disputes for the degree low to the minimal requirements. This means that on a computational assumption, the following is required even if the signer does not take part in a dispute ... 

Lemma 7.8. A secure full standard fail-stop signature scheme, i.e., one that fulfils all the minimal requirements, also fulfils the strong requirement of the signer on disputes computationally. ... 

Hence the strong requirement of the signer on disputes is not mentioned again. 

Strong fail-back requirement of the recipient on disputes. Once a recipient has accepted a certain message as authenticated by a certain signer, a court should obtain a result acc 6 (TRUE, broken ] in a dispute about this... 

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