How to wite encrypt and decrypt function

Question

 Hi,

I want when user opens the registration form he should be redirected to following page 

http://localhost:50605/empid=?

 

here in the above line empid should be presented in the encryted form so for that i need to write a function for the same.

please help  

 

Once the registration form is opened and when user will enter the emp id automaticaly details should be filled against that particular emp id 

 

when user clickson edit button then only he can fill the entire form and submit the same by clicking on submit button