C# Security Functions

I need to create a c# function which will create a secure token.
string genSharedComplaintToken(staff username, complaint ID, date) return string eg Ed#*l23Aq! This string should only be decripted by another method.
Create a c# function which will accept a secure token and return the following.
new function
DecryptSharedComplaintToken(string Token "Ed#*l23Aq!") returns the following
Bolean AccessAllowed =True|False String = staff username String = complaint ID Date = date the token was created
The date must not be older than 8 weeks. if it is then AccessAllowed = false.
I have not used security functions before ,How can I do this