 The GNU C library , a set of standard routines available for use in computer programming , contains a function — <unk> ( ) — which has a similar purpose to ROT13 , although it is intended for use with arbitrary binary data . The function operates by combining each byte with the binary pattern <unk> ( 42 ) using the exclusive or ( XOR ) operation . This effects a simple XOR cipher . Like ROT13 , XOR ( and therefore <unk> ( ) ) is self @-@ reciprocal , and provides a similar , virtually absent , level of security . 
