4.14 NIST defines the term cryptoperiod as the time span during which a specific key is
authorized for use or in which the keys for a given system or application may remain
in effect. One document on key management uses the following time diagram for a
shared secret key.
Explain the overlap by giving an example application in which the originator's usage
period for the shared secret key begins before the recipient's usage period and also
ends before the recipient's usage period.