Szyfrowanie

Mam taki mały problem....Potrzebuje jakiegoś algorytmu szyfrowania tekstu, który jest odwracalny....Na początku miałem XOR, ale okazało się, że dane liczbowe są źle szyfrowane...I teraz się zastanawiam, jaki algorytm użyć.....Jaki algorytm polecacie i gdzie mogę znaleźć jakieś jego zastosowanie ?? (mile widziany kod)

program cipher;
uses
  SysUtils;

{$APPTYPE CONSOLE}

type
   TParams = record
     inputFile, outputFile : string;
     codeMethode : (cmNone, cmXor, cmAdd, cmRot13);
     key : byte;
   end;


const
  progName = 'cipher';
  progVer  = '1.0';



function Rot13(ch : Char) : Char;
begin
  if (upcase(ch)>='A') and (upcase(ch)<='M') then result:=chr(ord(ch)+13)
   else
  if (upcase(ch)>='N') and (upcase(ch)<='Z') then result:=chr(ord(ch)-13)
   else
  result:=ch;
end;


function xorChar(ch : Char; key : byte) : Char;
begin
    result := chr(ord(ch) xor key);
end;


function addChar(ch : Char; key : shortint) : Char;
begin
    result := chr(ord(ch) + key);
end;



var
  i : byte;
  j : word;
  params : TParams;
  predParam, succParam, lineIn, lineOut : string;
  syntaxError : boolean;
  inputFile, outputFile : text;

begin
    syntaxError := false;
    params.codeMethode := cmNone;

    if paramcount = 0 then
    begin          // gdy nie ma parametrów wyswietl informacje
      writeLn(progName +' '+ progVer +' '+ ' - (c) Andrzej Tomicki 2003 [email protected]');
      writeLn;
      writeLn(' -i input_file    (eg: C:\myFile.txt)');
      writeLn(' -o output_file   (eg: C:\myCodedFile.txt)');
      writeLn(' -c code_methode  ([rot13], [xor], [add])');
      writeLn(' -i key           (eg: 13)');
      writeLn;
      writeLn('eg :  cipher -i in.txt -o out.txt -c xor -k 30');
    end
    else
    begin
      for i := 1 to paramcount do   // zczytaj parametry do rekordu
      begin
        try
          predParam := lowerCase(paramstr(i));
          succParam := lowerCase(paramstr(i+1));
          if predParam = '-i' then params.inputFile := paramstr(i+1);
          if predParam = '-o' then params.outputFile := paramstr(i+1);
          if predParam = '-c' then
            if succParam='xor' then params.codeMethode := cmXor
            else
             if succParam='add' then params.codeMethode := cmAdd
             else
              if succParam='rot13' then params.codeMethode := cmRot13
              else
              begin
                syntaxError := true;
                writeLn('Unknown coding methode : ' + succParam);
              end;
             if predParam = '-k' then params.key := StrToInt(succParam);
        except
          syntaxError := true;
          writeLn('Syntax error...');
        end;

      end;
      if (params.key = 0)and(params.codeMethode<>cmRot13) then  // gdy nie podano klucza (nie dotyczy Rot13)
      begin
        syntaxError := true;
        writeLn('Enter key value [eg : -k 13]');
      end;


      if not syntaxError then
       if fileExists(params.inputFile) then
        if params.outputFile = '' then
         writeLn('Enter output file name..')
        else
        if params.codeMethode = cmNone then
         writeLn('Enter coding methode [eg : -c add]')
        else
        begin  // kodowanie
          assign(inputFile , params.inputFile);
          assign(outputFile, params.outputFile);
          reset(inputFile);
          rewrite(outputFile);

          while not(eof(inputFile)) do
          begin
            lineOut := '';
            readln(inputFile, lineIn);
            for j := 1 to length(lineIn) do
            begin
             if params.codeMethode = cmXor then       // xor
               lineOut := lineOut + xorChar(lineIn[j], params.key) else
             if params.codeMethode = cmRot13 then     // rot13
               lineOut := lineOut + rot13(lineIn[j]) else
             if params.codeMethode = cmAdd then       // add
               lineOut := lineOut + addChar(lineIn[j], params.key)
            end; //for
            writeLn(outputFile, lineOut);
          end;

          close(inputFile);
          close(outputFile);
          writeLn('Done..');
        end
        else // (not fileExists)
        if params.inputFile = '' then
         writeLn('Enter file name to code/decode..')
        else
          writeLn('File '''+params.inputFile+''' doesn''t exists..');

    end;
end.