[c#] Password masking console application

I tried the following code...

string pass = "";
Console.Write("Enter your password: ");
ConsoleKeyInfo key;

do
{
    key = Console.ReadKey(true);

    // Backspace Should Not Work
    if (key.Key != ConsoleKey.Backspace)
    {
        pass += key.KeyChar;
        Console.Write("*");
    }
    else
    {
        Console.Write("\b");
    }
}
// Stops Receving Keys Once Enter is Pressed
while (key.Key != ConsoleKey.Enter);

Console.WriteLine();
Console.WriteLine("The Password You entered is : " + pass);

But this way the backspace functionality doesn't work while typing the password. Any suggestion?

This question is related to c# passwords console-application user-input masking

The answer is


Console.Write("\b \b"); will delete the asterisk character from the screen, but you do not have any code within your else block that removes the previously entered character from your pass string variable.

Here's the relevant working code that should do what you require:

var pass = string.Empty;
ConsoleKey key;
do
{
    var keyInfo = Console.ReadKey(intercept: true);
    key = keyInfo.Key;

    if (key == ConsoleKey.Backspace && pass.Length > 0)
    {
        Console.Write("\b \b");
        pass = pass[0..^1];
    }
    else if (!char.IsControl(keyInfo.KeyChar))
    {
        Console.Write("*");
        pass += keyInfo.KeyChar;
    }
} while (key != ConsoleKey.Enter);

 string pass = "";
 Console.WriteLine("Enter your password: ");
 ConsoleKeyInfo key;

 do {
  key = Console.ReadKey(true);

  if (key.Key != ConsoleKey.Backspace) {
   pass += key.KeyChar;
   Console.Write("*");
  } else {
   Console.Write("\b \b");
   char[] pas = pass.ToCharArray();
   string temp = "";
   for (int i = 0; i < pass.Length - 1; i++) {
    temp += pas[i];
   }
   pass = temp;
  }
 }
 // Stops Receving Keys Once Enter is Pressed
 while (key.Key != ConsoleKey.Enter);

 Console.WriteLine();
 Console.WriteLine("The Password You entered is : " + pass);

If I understand this correctly, you're trying to make backspace delete both the visible * character on screen and the cached character in your pass variable?

If so, then just change your else block to this:

            else
            {
                Console.Write("\b");
                pass = pass.Remove(pass.Length -1);
            }

I found a bug in shermy's vanilla C# 3.5 .NET solution which otherwise works a charm. I have also incorporated Damian Leszczynski - Vash's SecureString idea here but you can use an ordinary string if you prefer.

THE BUG: If you press backspace during the password prompt and the current length of the password is 0 then an asterisk is incorrectly inserted in the password mask. To fix this bug modify the following method.

    public static string ReadPassword(char mask)
    {
        const int ENTER = 13, BACKSP = 8, CTRLBACKSP = 127;
        int[] FILTERED = { 0, 27, 9, 10 /*, 32 space, if you care */ }; // const


        SecureString securePass = new SecureString();

        char chr = (char)0;

        while ((chr = System.Console.ReadKey(true).KeyChar) != ENTER)
        {
            if (((chr == BACKSP) || (chr == CTRLBACKSP)) 
                && (securePass.Length > 0))
            {
                System.Console.Write("\b \b");
                securePass.RemoveAt(securePass.Length - 1);

            }
            // Don't append * when length is 0 and backspace is selected
            else if (((chr == BACKSP) || (chr == CTRLBACKSP)) && (securePass.Length == 0))
            {
            }

            // Don't append when a filtered char is detected
            else if (FILTERED.Count(x => chr == x) > 0)
            {
            }

            // Append and write * mask
            else
            {
                securePass.AppendChar(chr);
                System.Console.Write(mask);
            }
        }

        System.Console.WriteLine();
        IntPtr ptr = new IntPtr();
        ptr = Marshal.SecureStringToBSTR(securePass);
        string plainPass = Marshal.PtrToStringBSTR(ptr);
        Marshal.ZeroFreeBSTR(ptr);
        return plainPass;
    }

Here's a version that adds support for the Escape key (which returns a null string)

public static string ReadPassword()
{
    string password = "";
    while (true)
    {
        ConsoleKeyInfo key = Console.ReadKey(true);
        switch (key.Key)
        {
            case ConsoleKey.Escape:
                return null;
            case ConsoleKey.Enter:
                return password;
            case ConsoleKey.Backspace:
                if (password.Length > 0) 
                {
                    password = password.Substring(0, (password.Length - 1));
                    Console.Write("\b \b");
                }
                break;
            default:
                password += key.KeyChar;
                Console.Write("*");
                break;
        }
    }
}

I have updated Ronnie's version after spending way too much time trying to enter a password only to find out that I had my CAPS LOCK on!

With this version what ever the message is in _CapsLockMessage will "float" at the end of the typing area and will be displayed in red.

This version takes a bit more code and does require a polling loop. On my computer CPU usage about 3% to 4%, but one could always add a small Sleep() value to decrease CPU usage if needed.

    private const string _CapsLockMessage = " CAPS LOCK";

    /// <summary>
    /// Like System.Console.ReadLine(), only with a mask.
    /// </summary>
    /// <param name="mask">a <c>char</c> representing your choice of console mask</param>
    /// <returns>the string the user typed in</returns>
    public static string ReadLineMasked(char mask = '*')
    {
        // Taken from http://stackoverflow.com/a/19770778/486660
        var consoleLine = new StringBuilder();
        ConsoleKeyInfo keyInfo;
        bool isDone;
        bool isAlreadyLocked;
        bool isCapsLockOn;
        int cursorLeft;
        int cursorTop;
        ConsoleColor originalForegroundColor;

        isDone = false;
        isAlreadyLocked = Console.CapsLock;

        while (isDone == false)
        {
            isCapsLockOn = Console.CapsLock;
            if (isCapsLockOn != isAlreadyLocked)
            {
                if (isCapsLockOn)
                {
                    cursorLeft = Console.CursorLeft;
                    cursorTop = Console.CursorTop;
                    originalForegroundColor = Console.ForegroundColor;
                    Console.ForegroundColor = ConsoleColor.Red;
                    Console.Write("{0}", _CapsLockMessage);
                    Console.SetCursorPosition(cursorLeft, cursorTop);
                    Console.ForegroundColor = originalForegroundColor;
                }
                else
                {
                    cursorLeft = Console.CursorLeft;
                    cursorTop = Console.CursorTop;
                    Console.Write("{0}", string.Empty.PadRight(_CapsLockMessage.Length));
                    Console.SetCursorPosition(cursorLeft, cursorTop);
                }
                isAlreadyLocked = isCapsLockOn;
            }

            if (Console.KeyAvailable)
            {
                keyInfo = Console.ReadKey(intercept: true);

                if (keyInfo.Key == ConsoleKey.Enter)
                {
                    isDone = true;
                    continue;
                }

                if (!char.IsControl(keyInfo.KeyChar))
                {
                    consoleLine.Append(keyInfo.KeyChar);
                    Console.Write(mask);
                }
                else if (keyInfo.Key == ConsoleKey.Backspace && consoleLine.Length > 0)
                {
                    consoleLine.Remove(consoleLine.Length - 1, 1);

                    if (Console.CursorLeft == 0)
                    {
                        Console.SetCursorPosition(Console.BufferWidth - 1, Console.CursorTop - 1);
                        Console.Write(' ');
                        Console.SetCursorPosition(Console.BufferWidth - 1, Console.CursorTop - 1);
                    }
                    else
                    {
                        Console.Write("\b \b");
                    }
                }

                if (isCapsLockOn)
                {
                    cursorLeft = Console.CursorLeft;
                    cursorTop = Console.CursorTop;
                    originalForegroundColor = Console.ForegroundColor;
                    Console.ForegroundColor = ConsoleColor.Red;
                    Console.Write("{0}", _CapsLockMessage);
                    Console.CursorLeft = cursorLeft;
                    Console.CursorTop = cursorTop;
                    Console.ForegroundColor = originalForegroundColor;
                }
            }
        }

        Console.WriteLine();

        return consoleLine.ToString();
    }

Mine ignores control characters and handles line wrapping:

public static string ReadLineMasked(char mask = '*')
{
    var sb = new StringBuilder();
    ConsoleKeyInfo keyInfo;
    while ((keyInfo = Console.ReadKey(true)).Key != ConsoleKey.Enter)
    {
        if (!char.IsControl(keyInfo.KeyChar))
        {
            sb.Append(keyInfo.KeyChar);
            Console.Write(mask);
        }
        else if (keyInfo.Key == ConsoleKey.Backspace && sb.Length > 0)
        {
            sb.Remove(sb.Length - 1, 1);

            if (Console.CursorLeft == 0)
            {
                Console.SetCursorPosition(Console.BufferWidth - 1, Console.CursorTop - 1);
                Console.Write(' ');
                Console.SetCursorPosition(Console.BufferWidth - 1, Console.CursorTop - 1);
            }
            else Console.Write("\b \b");
        }
    }
    Console.WriteLine();
    return sb.ToString();
}

Reading console input is hard, you need to handle special keys like Ctrl, Alt, also cursor keys and Backspace/Delete. On some keyboard layouts, like Swedish Ctrl is even needed to enter keys that exist directly on US keyboard. I believe that trying to handle this using the "low-level" Console.ReadKey(true) is just very hard, so the easiest and most robust way is to just to disable "console input echo" during entering password using a bit of WINAPI.

The sample below is based on answer to Read a password from std::cin question.

    private enum StdHandle
    {
        Input = -10,
        Output = -11,
        Error = -12,
    }

    private enum ConsoleMode
    {
        ENABLE_ECHO_INPUT = 4
    }

    [DllImport("kernel32.dll", SetLastError = true)]
    private static extern IntPtr GetStdHandle(StdHandle nStdHandle);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool GetConsoleMode(IntPtr hConsoleHandle, out int lpMode);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool SetConsoleMode(IntPtr hConsoleHandle, int dwMode);

    public static string ReadPassword()
    {
        IntPtr stdInputHandle = GetStdHandle(StdHandle.Input);
        if (stdInputHandle == IntPtr.Zero)
        {
            throw new InvalidOperationException("No console input");
        }

        int previousConsoleMode;
        if (!GetConsoleMode(stdInputHandle , out previousConsoleMode))
        {
            throw new Win32Exception(Marshal.GetLastWin32Error(), "Could not get console mode.");
        }

        // disable console input echo
        if (!SetConsoleMode(stdInputHandle , previousConsoleMode & ~(int)ConsoleMode.ENABLE_ECHO_INPUT))
        {
            throw new Win32Exception(Marshal.GetLastWin32Error(), "Could not disable console input echo.");
        }

        // just read the password using standard Console.ReadLine()
        string password = Console.ReadLine();

        // reset console mode to previous
        if (!SetConsoleMode(stdInputHandle , previousConsoleMode))
        {
            throw new Win32Exception(Marshal.GetLastWin32Error(), "Could not reset console mode.");
        }

        return password;
    }

Jeez guys

    static string ReadPasswordLine()
    {
        string pass = "";
        ConsoleKeyInfo key;
        do
        {
            key = Console.ReadKey(true);
            if (key.Key != ConsoleKey.Enter)
            {
                if (!(key.KeyChar < ' '))
                {
                    pass += key.KeyChar;
                    Console.Write("*");
                }
                else if (key.Key == ConsoleKey.Backspace && pass.Length > 0)
                {
                    Console.Write(Convert.ToChar(ConsoleKey.Backspace));
                    pass = pass.Remove(pass.Length - 1);
                    Console.Write(" ");
                    Console.Write(Convert.ToChar(ConsoleKey.Backspace));
                }
            }
        } while (key.Key != ConsoleKey.Enter);
        return pass;
    }

Here is my simple version. Every time you hit a key, delete all from console and draw as many '*' as the length of password string is.

int chr = 0;
string pass = "";
const int ENTER = 13;
const int BS = 8;

do
{
   chr = Console.ReadKey().KeyChar;
   Console.Clear(); //imediately clear the char you printed

   //if the char is not 'return' or 'backspace' add it to pass string
   if (chr != ENTER && chr != BS) pass += (char)chr;

   //if you hit backspace remove last char from pass string
   if (chr == BS) pass = pass.Remove(pass.Length-1, 1);

   for (int i = 0; i < pass.Length; i++)
   {
      Console.Write('*');
   }
} 
 while (chr != ENTER);

Console.Write("\n");
Console.Write(pass);

Console.Read(); //just to see the pass

This masks the password with a red square, then reverts back to the original colours once the password has been entered.

It doesn't stop the user from using copy/paste to get the password, but if it's more just about stopping someone looking over your shoulder, this is a good quick solution.

Console.Write("Password ");
ConsoleColor origBG = Console.BackgroundColor; // Store original values
ConsoleColor origFG = Console.ForegroundColor;

Console.BackgroundColor = ConsoleColor.Red; // Set the block colour (could be anything)
Console.ForegroundColor = ConsoleColor.Red;

string Password = Console.ReadLine(); // read the password

Console.BackgroundColor= origBG; // revert back to original
Console.ForegroundColor= origFG;

I made some changes for backspace

        string pass = "";
        Console.Write("Enter your password: ");
        ConsoleKeyInfo key;

        do
        {
            key = Console.ReadKey(true);

            // Backspace Should Not Work
            if (key.Key != ConsoleKey.Backspace)
            {
                pass += key.KeyChar;
                Console.Write("*");
            }
            else
            {
                pass = pass.Remove(pass.Length - 1);
                Console.Write("\b \b");
            }
        }
        // Stops Receving Keys Once Enter is Pressed
        while (key.Key != ConsoleKey.Enter);

        Console.WriteLine();
        Console.WriteLine("The Password You entered is : " + pass);

(My) nuget package to do this, based on the top answer:

install-package PanoramicData.ConsoleExtensions

Usage:

using PanoramicData.ConsoleExtensions;

...

Console.Write("Password: ");
var password = ConsolePlus.ReadPassword();
Console.WriteLine();

Project URL: https://github.com/panoramicdata/PanoramicData.ConsoleExtensions

Pull requests welcome.


For this you should use the System.Security.SecureString

public SecureString GetPassword()
{
    var pwd = new SecureString();
    while (true)
    {
        ConsoleKeyInfo i = Console.ReadKey(true);
        if (i.Key == ConsoleKey.Enter)
        {
            break;
        }
        else if (i.Key == ConsoleKey.Backspace)
        {
            if (pwd.Length > 0)
            {
                pwd.RemoveAt(pwd.Length - 1);
                Console.Write("\b \b");
            }
        }
        else if (i.KeyChar != '\u0000' ) // KeyChar == '\u0000' if the key pressed does not correspond to a printable character, e.g. F1, Pause-Break, etc
        {
            pwd.AppendChar(i.KeyChar);
            Console.Write("*");
        }
    }
    return pwd;
}

You could append your keys to an accumulating linked list.

When a backspace key is received, remove the last key from the list.

When you receive the enter key, collapse your list into a string and do the rest of your work.


Complete solution, vanilla C# .net 3.5+

Cut & Paste :)

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

    namespace ConsoleReadPasswords
    {
        class Program
        {
            static void Main(string[] args)
            {
                Console.Write("Password:");

                string password = Orb.App.Console.ReadPassword();

                Console.WriteLine("Sorry - I just can't keep a secret!");
                Console.WriteLine("Your password was:\n<Password>{0}</Password>", password);

                Console.ReadLine();
            }
        }
    }

    namespace Orb.App
    {
        /// <summary>
        /// Adds some nice help to the console. Static extension methods don't exist (probably for a good reason) so the next best thing is congruent naming.
        /// </summary>
        static public class Console
        {
            /// <summary>
            /// Like System.Console.ReadLine(), only with a mask.
            /// </summary>
            /// <param name="mask">a <c>char</c> representing your choice of console mask</param>
            /// <returns>the string the user typed in </returns>
            public static string ReadPassword(char mask)
            {
                const int ENTER = 13, BACKSP = 8, CTRLBACKSP = 127;
                int[] FILTERED = { 0, 27, 9, 10 /*, 32 space, if you care */ }; // const

                var pass = new Stack<char>();
                char chr = (char)0;

                while ((chr = System.Console.ReadKey(true).KeyChar) != ENTER)
                {
                    if (chr == BACKSP)
                    {
                        if (pass.Count > 0)
                        {
                            System.Console.Write("\b \b");
                            pass.Pop();
                        }
                    }
                    else if (chr == CTRLBACKSP)
                    {
                        while (pass.Count > 0)
                        {
                            System.Console.Write("\b \b");
                            pass.Pop();
                        }
                    }
                    else if (FILTERED.Count(x => chr == x) > 0) { }
                    else
                    {
                        pass.Push((char)chr);
                        System.Console.Write(mask);
                    }
                }

                System.Console.WriteLine();

                return new string(pass.Reverse().ToArray());
            }

            /// <summary>
            /// Like System.Console.ReadLine(), only with a mask.
            /// </summary>
            /// <returns>the string the user typed in </returns>
            public static string ReadPassword()
            {
                return Orb.App.Console.ReadPassword('*');
            }
        }
    }

Taking the top answer, as well as the suggestions from its comments, and modifying it to use SecureString instead of String, test for all control keys, and not error or write an extra "*" to the screen when the password length is 0, my solution is:

public static SecureString getPasswordFromConsole(String displayMessage) {
    SecureString pass = new SecureString();
    Console.Write(displayMessage);
    ConsoleKeyInfo key;

    do {
        key = Console.ReadKey(true);

        // Backspace Should Not Work
        if (!char.IsControl(key.KeyChar)) {
            pass.AppendChar(key.KeyChar);
            Console.Write("*");
        } else {
            if (key.Key == ConsoleKey.Backspace && pass.Length > 0) {
                pass.RemoveAt(pass.Length - 1);
                Console.Write("\b \b");
            }
        }
    }
    // Stops Receving Keys Once Enter is Pressed
    while (key.Key != ConsoleKey.Enter);
    return pass;
}

Examples related to c#

How can I convert this one line of ActionScript to C#? Microsoft Advertising SDK doesn't deliverer ads How to use a global array in C#? How to correctly write async method? C# - insert values from file into two arrays Uploading into folder in FTP? Are these methods thread safe? dotnet ef not found in .NET Core 3 HTTP Error 500.30 - ANCM In-Process Start Failure Best way to "push" into C# array

Examples related to passwords

Your password does not satisfy the current policy requirements Laravel Password & Password_Confirmation Validation Default password of mysql in ubuntu server 16.04 mcrypt is deprecated, what is the alternative? What is the default root pasword for MySQL 5.7 MySQL user DB does not have password columns - Installing MySQL on OSX Changing an AIX password via script? Hide password with "•••••••" in a textField How to create a laravel hashed password Enter export password to generate a P12 certificate

Examples related to console-application

How to run .NET Core console app from the command line ASP.NET Core configuration for .NET Core console application How to keep console window open How to navigate a few folders up? How to stop C# console applications from closing automatically? Could not load file or assembly ... An attempt was made to load a program with an incorrect format (System.BadImageFormatException) Can I write into the console in a unit test? If yes, why doesn't the console window open? What is the command to exit a Console application in C#? Can't specify the 'async' modifier on the 'Main' method of a console app Why is the console window closing immediately once displayed my output?

Examples related to user-input

Simple InputBox function Asking the user for input until they give a valid response Converting String Array to an Integer Array How to save user input into a variable in html and js Command line input in Python Javascript - User input through HTML input tag to set a Javascript variable? Simulate user input in bash script How to scanf only integer and repeat reading if the user enters non-numeric characters? How to get input from user at runtime Why can't I enter a string in Scanner(System.in), when calling nextLine()-method?

Examples related to masking

Easiest way to mask characters in HTML(5) text input Masking password input from the console : Java Password masking console application