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Using PHP to Enhance Password Security

Converting a phrase to a seemingly random password using PHP

When dictating password policies to users, it is common for such policies to require that users generate passwords that contain a combination of uppercase and lowercase letters, as well as numbers and special characters. Moreover, it is well established that the strengths of such passwords are further enhanced if the passwords do not in any way resemble dictionary words, since minor substitutions of dictionary words and names are often included in the dictionaries used in dictionary-based attacks and in some rainbow table variants. Thus "D3veloper" would be a less than ideal password since potentially it's an easily guessed variant of the word "developer."

A common recommendation for dealing with this issue is to suggest the use of randomly generated passwords such as "0Y=/S?tV". However, such passwords often pose great difficulty for many users to remember, which can lead to passwords being written down and hence result in a decrease rather than an increase in security. To resolve this issue, a technique has recently been suggested whereby the user turns an easily remembered phrase into a seemingly random password by taking the first letter of each word in the phrase and then performing character substitutions in order to introduce other character types such as numbers and special characters.

Thus, the user would take a phrase such as "The quick brown fox jumped over the lazy dog" and turn it into the character string "Tqbfjotld." They could then pick a character and replace it with an easily remembered number and then pick a second character and replace it with an easily remembered special character. Thus if the person's "b"irthday was on the 5th, perhaps they would associate "b" with number "5," and if they liked the J# programming language, perhaps they would associate "j" with "#."  Thus "b" and "j" could be replaced with their associated characters to make the password "Tq5f#otld"; a seemingly random password that can be recalled by the user using easy to remember mnemonic tricks.

This article demonstrates a small PHP5 script that can be used to convert user supplied phrases into such a seemingly random password. Before the PHP code itself is executed, however, an HTML form is initially used to allow the user to supply the phrase they are interested in, via text box, and specify their choice in character substitutions, via drop down boxes. The HTML code can be found in Listing 1 and a screenshot of the HTML form found in Figure 1.

Figure 1: The HTML interface used to accept user inputs

It is important to note that the HTML script uses the post action to submit the various HTML control values to the PHP script as follows. The text box element is named "Text" and is used to allow the user to enter his phrase of choice. Four drop down boxes are also used, where the drop down box "NumLet" allows the user to specify the letter that the user wants to replace with the number found in the drop down box "Num." Likewise, the "SpecLet" drop down box allows the user to specify the letter that the user wants to replace with the special character found in the drop down box "Spec."

Upon Execution, the PHP script accepts the values of these HTML controls and assigns them to like named variables as follows:

$passwd="";
$Phrase=$_POST['Text'];
$NumLet=$_POST['NumLet'];
$Num=$_POST['Num'];
$SpecLet=$_POST['SpecLet'];
$Spec=$_POST['Spec'];

Next, the PHP script uses the explode function to split the $Phrase string into an array of individual words (substrings), by using a space as the delimiter.  A for loop is then used to loop through all of the substrings and a regular expression, which makes use of the predefined "\w" subpattern used to identify the first letter of each substring.  The identified letter is then appended to the string stored in the variable $passwd to produce a string the consists of the first letter found in each substring as demonstrated below:

$words=explode(" ", $Phrase);
foreach($words as $word){
preg_match('/\w/', $word, $matches);
$passwd=$passwd . $matches[0];
}

Two additional regular expressions are then utilized to perform a match and replace operation, whereby the two user-specified letters are replaced with the respective user-selected number and special character, as shown below:

$passwd=preg_replace("/($NumLet)/i", "$Num", $passwd);
$passwd=preg_replace("/($SpecLet)/i", "$Spec", $passwd);

The password is then printed to the screen and to yield output like the representative one shown in Figure 2.

Figure 2: The seemingly random password that results from the information specified in Figure 1.

All in all, this article demonstrates a PHP5 script that can be used to automate the conversion of any user-specified phrase into a seemingly random password. Both the HTML code and the PHP5 code (see Listing 2 for complete code) can be easily modified to enhance compliance with organizational policies and as such can provide a useful tool for enhancing password policy compliance and password security throughout any organization. A version of the software is also being hosted at http://www.insilicobiotechnologies.com/PasswdMkr/PhrasetoPassIn.html for anyone who wishes to make use of the application in the format specified here.

More Stories By Christopher Frenz

Christopher Frenz is the author of "Visual Basic and Visual Basic .NET for Scientists and Engineers" (Apress) and "Pro Perl Parsing" (Apress). He is a faculty member in the Department of Computer Engineering at the New York City College of Technology (CUNY), where he performs computational biology and machine learning research.

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