Replace a part of string containing Password

Question

Slightly similar to this question, I want to replace argv contents:

string argv = "-help=none\n-URL=(default)\n-password=look\n-uname=Khanna\n-p=100";

to this:

"-help=none\n-URL=(default)\n-password=********\n-uname=Khanna\n-p=100"

I have tried very basic string find and search operations (using IndexOf, SubString etc.). I am looking for more elegant solution so as to replace this part of string:

-password=AnyPassword

to:

-password=*******

And keep other part of string intact. I am looking if String.Replace or Regex replace may help.

What I've tried (not much of error-checks):

var pwd_index = argv.IndexOf("--password=");

string converted;

if (pwd_index >= 0)
{
     var leftPart = argv.Substring(0, pwd_index);
     var pwdStr = argv.Substring(pwd_index);
     var rightPart = pwdStr.Substring(pwdStr.IndexOf("\n") + 1);

     converted = leftPart + "--password=********\n" + rightPart;
}
else
     converted = argv;

Console.WriteLine(converted);

Community · Accepted Answer · 2017-05-23 10:34:01Z

Solution

Similar to Rubens Farias' solution but a little bit more elegant:

string argv = "-help=none\n-URL=(default)\n-password=\n-uname=Khanna\n-p=100";
string result = Regex.Replace(argv, @"(password=)[^\n]*", "$1********");

It matches password= literally, stores it in capture group $1 and the keeps matching until a \n is reached.

This yields a constant number of *'s, though. But telling how much characters a password has, might already convey too much information to hackers, anyway.

Working example: https://dotnetfiddle.net/xOFCyG

Regular expression breakdown

(              // Store the following match in capture group $1.
  password=    // Match "password=" literally.
)    
[              // Match one from a set of characters.
  ^            // Negate a set of characters (i.e., match anything not
               //   contained in the following set).
    \n         // The character set: consists only of the new line character.
]
*              // Match the previously matched character 0 to n times.

Elegant and readable solution. And thanks for parameter-breakdown! :)
Add RegexOptions.IgnoreCase to make it case-insensitive. Regex.Replace(argv, @"(Password=)[^\n]*", "$1********", RegexOptions.IgnoreCase);

Rubens Farias · Accepted Answer · 2016-06-09 12:26:58Z

3

This code replaces the password value by several "*" characters:

string argv = "-help=none\n-URL=(default)\n-password=look\n-uname=Khanna\n-p=100";
string result = Regex.Replace(argv, @"(password=)([\s\S]*?\n)",
    match => match.Groups[1].Value + new String('*', match.Groups[2].Value.Length - 1) + "\n");

You can also remove the new String() part and replace it by a string constant

edited Jun 9, 2016 at 12:26

answered Jun 9, 2016 at 11:52

Rubens Farias

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2 Comments

3615 Over a year ago

Seems that it also cuts \n from \n-uname=K

Ajay Over a year ago

This would work for me. But it is adding one more extra *. For look, it is creating *****

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