Mere authentication scheme

Mere authentication schemes also serve to ensure the authenticity of messages The recipient of a message with correct authentication can also be sure that the supposed sender has sent or agreed to send exactly this message. However, he cannot make anybody else believe this. In particular, the authentication does not help him in court. More precisely, from the point of view of a third party, the recipient could usually have produced the authenticated message just as well as the supposed sender. The purpose of these schemes is therefore to help people who trust each other to ensure that their messages have not been modified or forged by outsiders. 

This symmetry between senders and recipients is usually reflected in the system structure the schemes are then called symmetric authentication schemes (see Section 2.1). In contrast, digital signature schemes are sometimes called asymmetric authentication schemes. However, schemes exist that provide mere authentication and are not symmetric in this sense [OkOh91] (called non-transitive signature schemes there). 

From every authentication scheme (mere authentication or signatures), a corresponding identification scheme can be constructed for instance, authenticated messages I am now.here,. .. , with a time stamp, can be sent. The reverse... 

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