Whitelisting: You Set The Rules For Security

By  on  

We all know what blacklisting is when it comes to strings: removing specified "bad" characters. While this helps to secure user input, it isn't as secure as whitelisting. Whitelisting is the process of saying "Let me tell you what you can give me" whereas blacklisting says "If I find this, I'll remove it."

A customer recently asked that I create a whitelisting function that allowed letters, digits, whitespace characters, periods, commas, and dashes. Any other characters were to be replaced with spaces.

The PHP

function make_valid($input) 
{ 
	return preg_replace('/[^A-Za-z0-9.,\(\)\s-]/',' ',$input); 
}

The above function uses preg_match() and a small regular expression to remove the rubbish characters.

Recent Features

  • By
    Send Text Messages with PHP

    Kids these days, I tell ya.  All they care about is the technology.  The video games.  The bottled water.  Oh, and the texting, always the texting.  Back in my day, all we had was...OK, I had all of these things too.  But I still don't get...

  • By
    From Webcam to Animated GIF: the Secret Behind chat.meatspac.es!

    My team mate Edna Piranha is not only an awesome hacker; she's also a fantastic philosopher! Communication and online interactions is a subject that has kept her mind busy for a long time, and it has also resulted in a bunch of interesting experimental projects...

Incredible Demos

Discussion

  1. Your way for whitelisting is quite nice. It’s like in Flash where you can specify exactly what characters are allowed by the user.
    This method may work well as a common security filter that replaces get_magic_quotes_gpc(), strip_tags() and htmlentities().
    Good work as usual!

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!