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function MyInputBox(Title,Text,Standart:String):String;
begin
with InputForm do
  begin
    Caption:=Title;
    Label1.Caption:=text;
    Edit1.Text:=Standart;
    ShowModal;
  end;
  result:=InputForm.Edit1.Text;
end;					

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const
  InputBoxMessage = WM_USER + 200;

implementation

{$R *.DFM}

procedure TForm1.InputBoxSetPasswordChar(var Msg: TMessage);
var
  hInputForm, hEdit, hButton: HWND;
begin
  hInputForm := Screen.Forms[0].Handle;
  if (hInputForm <> 0) then begin
    hEdit := FindWindowEx(hInputForm, 0, 'TEdit', nil);
    {
      // Change button text:
      hButton := FindWindowEx(hInputForm, 0, 'TButton', nil);
      SendMessage(hButton, WM_SETTEXT, 0, Integer(PChar('Cancel')));
    }
    SendMessage(hEdit, EM_SETPASSWORDCHAR, Ord('*'), 0);
  end;
end;


procedure TForm1.Button1Click(Sender: TObject);
var
  InputString: string;
begin
  PostMessage(Handle, InputBoxMessage, 0, 0);
  InputString := InputBox('Input Box', 'Please Enter a Password', '');
end;					

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unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

const
  WM_SetPwdChar = WM_USER +200;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure InputBoxSetPasswordChar(var Msg: TMessage); message WM_SetPwdChar; // vergessen...
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.InputBoxSetPasswordChar(var Msg: TMessage);
  var
    hInputForm, hEdit: HWND;
begin
  hInputForm := Screen.Forms[0].Handle;
  if (hInputForm <> 0) then begin
    hEdit := FindWindowEx(hInputForm, 0, 'TEdit', NIL);
    SendMessage(hEdit, EM_SETPASSWORDCHAR, Ord('*'), 0);
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
  var
    InputString: String;
begin
  PostMessage(Handle, WM_SetPwdChar, 0, 0);
  Application.ProcessMessages; // schon geht´s nicht mehr...
  InputString := InputBox('Authentifikation', 'Kennwort: ', '');
end;

end.