Como inverter essa function?

 

var 
  Yoa  : String = ´*[+*/$SYHDUS-854231$\*+]´;

...

function DesCript(Src : String) : String;
var
  KLen    : integer;
  KPos    : integer;
  setG    : integer;
  dest      : String;
  SPos    : integer;
  SAsc    : integer;
  TmSAsc : integer;
begin
  dest := ´´;
  KLen := Length(Yoa);
  KPos := 0;
  SPos := 0;
  SAsc := 0;
 
 setG := StrToInt(´$´+ copy(src,1,2));
  SPos := 3;
  repeat
    SAsc := StrToInt(´$´+ copy(src,SPos,2));
    if KPos < KLen then
      KPos := KPos + 1
    else
      KPos := 1;
 
    TmSAsc := SAsc xor Ord(Yoa[KPos]);
 
    if TmSAsc <= setG then
      TmSAsc := 255 + TmSAsc - setG
    else
      TmSAsc := TmSAsc - setG;
 
    dest := dest + chr(TmSAsc);
    setG := SAsc;
    SPos := SPos + 2;
  until SPos >= Length(Src);
 
  DesCript := dest;
end;