Non Repudiation

Don't non repudiation of origin and non repudiation of receipt 
imply that the recipient has to keep a persistent copy of the message for some 
rather long period of time (typically of the order of years)?

 

Is this duration implicit (i.e., has the same value for all 
cases) or should it be represented explicitly in the CPA?

 

Another related question is whether the logging functionality 
to support non repudiation belongs above or below the Message Service 
Interface.

 

-Arvola