 In December 1999 , it was found that Netscape Communicator used ROT13 as part of an insecure scheme to store email passwords . In 2001 , Russian programmer Dimitry Sklyarov demonstrated that an eBook vendor , New Paradigm Research Group ( NPRG ) , used ROT13 to encrypt their documents ; it has been speculated that NPRG may have mistaken the ROT13 toy example — provided with the Adobe eBook software development kit — for a serious encryption scheme . Windows XP uses ROT13 on some of its registry keys . ROT13 is also used in the Unix fortune program to encrypt potentially offensive dicta . 
