unit Unit2;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm2 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    memoEncrypt: TMemo;
    memoDecrypt: TMemo;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form2: TForm2;

implementation

{$R *.dfm}

function GetStr(var str: String): String;
var
  i: Integer;
  newStr: String;
begin
  for i := 1 to Length(str) do
  begin
    if (ord(str[i]) >= 1072) and (ord(str[i]) <= 1103) or (ord(str[i]) = 1105)then
      newStr := newStr + str[i];
    result := newStr;
  end;
end;

function LowerCase(Str: string): string;
var
  i: integer;
begin
  Result := Str;
  for i := 1 to length(Result) do
  begin
     if (Result[i] in ['А'..'Я']) then
        Result[i] := chr(ord(Result[i]) + 32);
     if Result[i] = 'Ё' then
        Result[i] := 'ё';
  end;
end;

function Encrypt(str: string; const Coolkey: string):string;
const
   SizeAlphabet = 33;
   Alphabet = 'абвгдеёжзийклмнопрстуфхцчшщъыьэюя';
var
   i, j, Position, KeyCounter, Offset: integer;
   temp, key: string;
begin
   str := GetStr(Str);
   Key := Coolkey;
   KeyCounter := 0;
   for i := 1 to length(str) do
   begin
      inc(KeyCounter);
      if KeyCounter > length(key) then
      begin
         KeyCounter := 1;
         for  j := 1 to Length(Key) do
            Key[j] := Alphabet[pos(Key[j], Alphabet) + 1];
      end;
      Position := pos(str[i], Alphabet) + pos(key[KeyCounter], Alphabet) - 1;
      if Position > SizeAlphabet then
         Position := Position - SizeAlphabet;
      Result:=Result + Alphabet[Position];
   end;
end;


function Decrypt(str, key: string): string;
const
   SizeAlphabet = 33;
   Alphabet = 'абвгдеёжзийклмнопрстуфхцчшщъыьэюя';
var
   i, j, Position, KeyCounter: integer;
   Temp: string;
begin
   Str := GetStr(Str);
   Str := LowerCase(str);
   Key := LowerCase(key);
   KeyCounter := 0;
   for i := 1 to length(str) do
   begin
      inc(KeyCounter);
      if KeyCounter > length(Key) then
      begin
         KeyCounter := 1;
         for  j := 1 to Length(Key) do
            Key[j] := Alphabet[pos(Key[j], Alphabet) + 1];
      end;
      Position := pos(Str[i], Alphabet) - pos(Key[KeyCounter], Alphabet) + 1;
      if Position <= 0 then
         Position := Position + SizeAlphabet;
      Result := Result + Alphabet[Position];
   end;
end;

procedure TForm2.Button1Click(Sender: TObject);
begin
   memoDecrypt.Text := Encrypt(memoEncrypt.Text,edit1.Text);
end;

procedure TForm2.Button2Click(Sender: TObject);
begin
   memoDecrypt.Text := Decrypt(memoDecrypt.Text,edit1.Text);
end;

procedure TForm2.Button3Click(Sender: TObject);
begin
   memoEncrypt.Lines.Clear;
   memoDecrypt.Lines.Clear;
   edit1.Text:='';
end;

end.