Regular Expression in Javascript for password validation

Question

I am trying to create a regular expression that validates a user's password when they create it. The password needs to be:

at least 6 characters long and can be any type of character
each character that is used needs to appear in the password exactly 3 times.

Good examples:

AAABBB
ABABBA
+++===
+ar++arra
myyymm
/Arrr/AA/

Does anyone know which regex would accomplish this?

I can give you an answer, but please explain first why you would want to have passwords with three times less entropy than necessary...? — Tim Pietzcker
– Tim Pietzcker, Commented Dec 15, 2016 at 7:48
Thinking about it a bit more, I'm not quite sure that this can be accomplished with just a regex; definitely not with a JavaScript regex with its very limited capabilities. You'd need two steps: Sort the password first, then use a regex to check that each character occurs exactly three times. — Tim Pietzcker
– Tim Pietzcker, Commented Dec 15, 2016 at 7:54
This is not a great match for regex (and a terrible password scheme). If you're targeting ES6 you can toss all the characters in a map and count them. Less efficiently, you can sort the string and then check it contains runs of 3 (which you could come up with a regex for but it would be more convoluted than almost any other alternative). — pvg
– pvg, Commented Dec 15, 2016 at 7:55
This looks like homework, no one would demand such stupid restrictions on a password — Fallenhero
– Fallenhero, Commented Dec 15, 2016 at 7:55
@sabithpocker - Almost all password strength checkers are obsolete and useless. Nowadays the conditions for a good password are only two: sufficient length (more is better) and resistance to dictionary attacks (which is the problem itself). Tips as "use capital an small letters, numbers and special symbols" have no value, even for average hackers. — MarianD
– MarianD, Commented Dec 15, 2016 at 8:22

Thomas Ayoub · Accepted Answer · 2016-12-15 08:55:50Z

2

You can ease yourself by sorting the password before testing it:

$('button').on('click', function(){
var s = $('#password').val();
var split = s.split("").sort().join("");
if(/^(?:(.)\1{2}(?!\1)){2,}$/.test(split))
   console.log("Valid password");
else
   console.log("Invalid password");
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>
<input id="password">
<button>Test me</button>

edited Dec 15, 2016 at 8:55

answered Dec 15, 2016 at 8:20

Thomas Ayoub

29.6k16 gold badges98 silver badges149 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

laurenmc34 Over a year ago

this doesn't account for the overall length of 6 characters, correct?

Fallenhero Over a year ago

minimum of 6 not exactly 6 :)

Fallenhero Over a year ago

:) @ThomasAyoub

Tim Pietzcker Over a year ago

This will validate passwords like AAAAAA - it only checks for multiples of threes, not exactly three instances of each character.

Rjoydip · Accepted Answer · 2016-12-15 09:02:53Z

0

For 1st option you have to check without regex.

var str = "your password";
var pattern = /(.)(.*\1){3}/;
if(str.length >= 6){
   // It will give you boolean as return
   // If it is match then it return true else false
   pattern.test(str);
}

answered Dec 15, 2016 at 9:02

Rjoydip

663 bronze badges

1 Comment

pvg Over a year ago

You should try this with some of the test expressions provided.

SamWhan · Accepted Answer · 2016-12-15 09:54:59Z

An alternative solution since you're allowing code (which your question imply you wouldn't ;)

Using a function like verifyPass below should do the trick. It gradually replaces any valid three letter combination with an empty string. Checking that this is done in more than one iteration (it's at least 6 characters) and ending up with an empty string in the end, means it's a valid password.

function verifyPass(pass) {
  var re = /^(.)((?:(?!\1).)*)\1((?:(?!\1).)*)\1((?:(?!\1).)*)$/,
      cnt=0;

  while(re.test(pass)) {
    pass = pass.replace(re, '$2$3$4');
    cnt++;
  }
  return pass==='' && cnt>1;
}

var testItems = [
      '123123123',
      'AAABBB',
      'AAABBBAAA',
      'Qwerty',
      'ABABBA',
      '+++===',
      '111',
      'qweqwd',
      'sdcjhsdfkj',
      '+ar++arra',
      'mYYYmms',
      '/Arrr/AA/'
  ];
  
  testItems.forEach(function(item) {
    document.write('<span style="color:' + (verifyPass(item) ? 'green' : 'red') + ';">' + item + '</span> <br/>');
  });

Collectives™ on Stack Overflow

Regular Expression in Javascript for password validation

3 Answers 3

4 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related