Как можно из шифратора сделать дешифратор и как лучше записать ключ?

Question

Alertoso @Alertoso

Как можно из шифратора сделать дешифратор и как лучше записать ключ?

Program Encryption;

{$APPTYPE CONSOLE}

Type
  MyArrayType = array of array of Char;
  DirectionType = (dRight, dDown, dLeft, dUp);

Var
  Matrix: MyArrayType;
  LenMyS, I, J: Integer;
  MyString: String;
  SizeArray: Integer;
  InputText, OutputText, KeyText: TextFile;

Procedure Spiral(var M: MyArrayType; SpirWrite: Boolean; var S: String);
Var
  CurStep, Step, PosX, PosY: Integer;
  Direction: DirectionType; //îò 1 äî 4 - 1 âïðàâî, 2 âíèç, 3 âëåâî, 4 ââåðõ
  I: integer;
Begin
  Randomize;
  I:=1;
  PosX:=round(SizeArray/2)+1;
  PosY:=round(SizeArray/2)+1;
  CurStep:=1;
  Step:=1; //÷åðåç ñêîëüêî øàãîâ ïîâåðíóòü
  Direction:=dRight; //íàïðàâëåíèå ñïèðàëè íà ïåðâîì øàãå
  if Not SpirWrite {çíà÷èò ÷òåíèå èç ìàññèâà} then S := '';
  while (PosX>0) and (PosX<=SizeArray) and (PosY>0) and (PosY<=SizeArray) do
  Begin
    if SpirWrite then
      M[PosX, PosY]:=S[I]
    else
      S:=S+M[PosX, PosY];
    //äâèæåíèå ìàòðèöû ïî ñïèðàëè
    case Direction of
      dRight: Begin
                PosY:=PosY+1;
                if CurStep=Step then
                Begin
                  CurStep:=1;
                  Direction:=dDown;
                  writeln(KeyText, 'R ',PosY,',',PosX);
                End
                else
                  CurStep:=CurStep+1
              End;
       dDown: Begin
                PosX:=PosX+1;
                if CurStep=Step then
                Begin
                  CurStep:=1;
                  Direction:=dLeft;
                  Step:=Step+1;
                  writeln(KeyText, 'D ',PosY,',',PosX);
                End
                else
                  CurStep:=CurStep+1
              End;
       dLeft: Begin
                PosY:=PosY-1;
                if CurStep=Step then
                Begin
                  CurStep:=1;
                  Direction:=dUp;
                  writeln(KeyText, 'L ',PosY,',',PosX);
                End
                else
                  CurStep:=CurStep+1
              End;
         dUp: Begin
                PosX:=PosX-1;
                if CurStep=Step then
                Begin
                  CurStep:=1;
                  Direction:=dRight;
                  Step:=Step+1;
                  writeln(KeyText, 'U ',PosY,',',PosX);
                End
                else
                  CurStep:=CurStep+1
              End
    End;
    Inc(I)
  End
End;

Procedure CheckAndFixString(var S: String; NeedLength: Integer);
Begin
  if (NeedLength>=1) or (NeedLength<=255) then
  Begin
    if Length(S)>NeedLength then
      S:=Copy(S,1,NeedLength)
    else
      while length(S)<NeedLength do
        S:=S + ' '
  End
End;

Begin
  AssignFile(InputText, 'D:\Ðàáîòû ïî ÎÀèÏ\2 ñåìåñòð\InputString.txt');
  Reset(InputText);
  AssignFile(KeyText, 'D:\Ðàáîòû ïî ÎÀèÏ\2 ñåìåñòð\Key.txt');
  Rewrite(KeyText);
  Readln(InputText, MyString);
  LenMyS:=length(MyString);
  if Trunc(sqrt(LenMyS)) mod 2 = 0 then
    SizeArray:=Trunc(sqrt(LenMyS))+1
  else
    SizeArray:=Trunc(sqrt(LenMyS))+2;
  writeln('The required size of the matrix = ',SizeArray,'x',SizeArray);
  Setlength(Matrix, SizeArray+1, SizeArray+1);
  WriteLn('The length of the string = ',LenMyS);
  CheckAndFixString(MyString, sqr(SizeArray));
  LenMyS:=length(MyString);
  WriteLn('Required the length of the string = ',LenMyS);
  Spiral(Matrix, True, MyString);
  Assign(OutputText, 'D:\Ðàáîòû ïî ÎÀèÏ\2 ñåìåñòð\SpirOut.txt');
  Rewrite(OutputText);
  for I:=1 to SizeArray do
  Begin
    for J:=1 to SizeArray do
      Write(OutputText, Matrix[i,j]);
    WriteLn(OutputText)
  End;
  Close(OutputText);
  Close(KeyText);
  writeln('Press Enter to exit...');
  readln;
End.