Password masking console application

Question

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

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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  gt  0                                         password   password Substring 0   password Length - 1                        Console Write   b  b                                      break              default                  password    key KeyChar                  Console Write                       break

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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             lt summary gt          Like System Console ReadLine    only with a mask           lt  summary gt           lt param name  mask  gt a  lt c gt char lt  c gt  representing your choice of console mask lt  param gt           lt returns gt the string the user typed in lt  returns gt      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  amp  amp  consoleLine Length  gt  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

User · Answer

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

User · Answer

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

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Jeez guys     static string ReadPasswordLine                 string pass    quot  quot           ConsoleKeyInfo key          do                       key   Console ReadKey true               if  key Key    ConsoleKey Enter                                if    key KeyChar  lt                                              pass    key KeyChar                      Console Write  quot   quot                                      else if  key Key    ConsoleKey Backspace  amp  amp  pass Length  gt  0                                        Console Write Convert ToChar ConsoleKey Backspace                        pass   pass Remove pass Length - 1                       Console Write  quot   quot                        Console Write Convert ToChar ConsoleKey Backspace                                              while  key Key    ConsoleKey Enter           return pass

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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

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Console Write  quot  b  b quot    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  amp  amp  pass Length  gt  0                Console Write  quot  b  b quot            pass   pass 0   1             else if   char IsControl keyInfo KeyChar                 Console Write  quot   quot            pass    keyInfo KeyChar          while  key    ConsoleKey Enter

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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  amp  amp  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  lt  pass Length  i               Console Write                while  chr    ENTER    Console Write   n    Console Write pass    Console Read      just to see the pass

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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  amp  amp  pass Length  gt  0                    pass RemoveAt pass Length - 1                   Console Write   b  b                                         Stops Receving Keys Once Enter is Pressed     while  key Key    ConsoleKey Enter       return pass

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Complete solution  vanilla C   net 3 5   Cut  amp  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 lt Password gt  0  lt  Password gt    password                    Console ReadLine                                       namespace Orb App                    lt summary gt              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               lt  summary gt          static public class Console                            lt summary gt                  Like System Console ReadLine    only with a mask                   lt  summary gt                   lt param name  mask  gt a  lt c gt char lt  c gt  representing your choice of console mask lt  param gt                   lt returns gt the string the user typed in  lt  returns gt              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 lt char gt                     char chr    char 0                   while   chr   System Console ReadKey true  KeyChar     ENTER                                        if  chr    BACKSP                                                if  pass Count  gt  0                                                        System Console Write   b  b                                pass Pop                                                                        else if  chr    CTRLBACKSP                                                while  pass Count  gt  0                                                        System Console Write   b  b                                pass Pop                                                                        else if  FILTERED Count x   gt  chr    x   gt  0                          else                                               pass Push  char chr                           System Console Write mask                                                            System Console WriteLine                     return new string pass Reverse   ToArray                                     lt summary gt                  Like System Console ReadLine    only with a mask                   lt  summary gt                   lt returns gt the string the user typed in  lt  returns gt              public static string ReadPassword                                 return Orb App Console ReadPassword

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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                     amp  amp   securePass Length  gt  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    amp  amp   securePass Length    0                                               Don t append when a filtered char is detected             else if  FILTERED Count x   gt  chr    x   gt  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

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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  gt  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

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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  amp    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

User · Answer

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  lt  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

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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  amp  amp  sb Length  gt  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

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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

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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

[c#] Password masking console application

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