動作環境

Windows 7 Pro (32bit)
Microsoft Visual Studio 2017 Community
Sublime Text 2

関連 http://qiita.com/7of9/items/58590852bb07e7e489a1

https://www.youtube.com/watch?v=SBeDgl7CX6E&list=PLaYqF7AnyNPfTfZiGqTwedIKW_FkZv4Xj&index=8
PasswordBoxが紹介されている。

MaxLengthプロパティと組み合わせて、指定長さのパスワードを入力するInterfaceを用意できる。

MainWindow.xaml

<Window x:Class="_170509_t0708_passwordBox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:_170509_t0708_passwordBox"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <PasswordBox x:Name="PB_pass" HorizontalAlignment="Left" Margin="47,43,0,0" VerticalAlignment="Top" Width="100" MaxLength="8"/>
        <Button Content="Button" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Margin="176,39,0,0" Click="Button_Click"/>

    </Grid>
</Window>

MainWindow.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace _170509_t0708_passwordBox
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show(PB_pass.Password);
        }
    }
}

3.1415926535と入力。

Buttonクリック時 (MaxLength=8での表示)