The Ideas and their Background

Signatures and keys are regarded as structural details, and not as the service. 

The main novelty about the first idea is that an interface for signature schemes has to be introduced. More precisely, it is an interface for the systems described by the schemes. In the terminology of Section 4.4.1, this means that Step E is separated from Step 

Of course, the placement of an interface is partly a matter of taste, in particular because several other definitions already exist The systems are normally used in certain environments (for instance, systems described by the GMR definition must be used together with a counter keeping track of the number of messages authenticated), and one has some freedom as to where the system ends and where the environment begins. 

Idea 2 now means that this interface is placed very high , so that signatures and keys are only handled within the system, but do not appear in interface events. 

An interesting similar approach was taken in [SyMe93] for key-distribution protocols usually treated with logics of authentication see the remarks on those in Section 5.2.1. 

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