Stealth and Decryption neither give you an sleaze/attack rating nor are they on the list of cyber programs that a rigger can use on their RCC.
They state that they add +1 to your Sleaze/Attack rating (respectively), which if you don't have one, can't add to it.
Still, it would be cool to have "cyberdeck upgrade" rules, if only so the decker can piecemeal into a better deck instead of replacing the whole thing at outrageous expense (which will never occur, given the price)