how to encrypt a string ?

hi

i have a WebDynpro url which i have a parameter in it

http://us7211.wdf.sap.corp:50021/sap/bc/webdynpro/sap/othello?p_parameter=123123.

i want to prevent the user to edit the value and might get different data, ao i want to encrypt the value '123123' so the user will get some thing like that   

http://us7211.wdf.sap.corp:50021/sap/bc/webdynpro/sap/othello?p_parameter=az%wl

and in the winint method the value will be dncrypt to 123123 again.

is there a method/FM that can ENCRYPT and DNCRYPT a string?

thanks

Elad