Click here to close now.

Welcome!

Java Authors: Carmen Gonzalez, Liz McMillan, Yeshim Deniz, Pat Romanski, Elizabeth White

Related Topics: Perl, Java, .NET, Linux, Security

Perl: Article

The Development of a Perl-based Password Complexity Filter

A useful foundation for developers and system administrators to improve password policy compliance

If you watch the news regularly, it is easy to notice that in almost any given week some company seems to have experienced an electronic break-in or in some other way experienced a form of computer or network compromise. While computer security professionals can help to mitigate such risks via the proper configuration of firewalls, careful crafting of Access Control Lists, the application of updates, and the judicious application of file permission, among other measures, it's important that one of the most fundamental ways of improving the security of a computer or network resource not be overlooked - that of a really strong password. To this day passwords remain one of the weaker links in the security of electronic resources, and their potential for exploitation needs to be examined more carefully than ever. With the growing trend of cloud computing-based initiatives, many resources that were formerly enclosed within the wall of a business are now available over a network, thereby mitigating the physical security measures the previously helped to limit access to such resources. Given that many of these cloud-based solutions are accessed via user name and password combinations, a strong password is often the primary form of defense against illicit access.

The Makings of a Strong Password
One of the best ways to ensure that users of any application you develop have a strong password is to validate the strength of the password via the usage of a password complexity filter, which ensures that any proposed password meets certain minimum complexity requirements. In order to get a clear grasp of the requirements considered essential for a strong password, let's first consider several password usage cases. First let's consider a case where we have an application that only utilizes case-insensitive alphabet characters in a password that's four characters long. If we were to compute the number of possible passwords that could fit into such a "password space," we would see that passwords created with these rules in mind would allow for

26 * 26 * 26 * 26 = 264 = 456,976 possible passwords

If we instead now allow passwords to be case sensitive and distinguish upper and lowercase characters as being distinct, you can readily see that we have increased the size of the password space since we would now have

52 * 52 * 52 * 52 = 524 = 7,311,616 possible passwords

Now if we also allow our application to include passwords that contain numbers we would end up with 624 (14,776,336) possible passwords, and if we incorporate a set of special characters the number of possible passwords would be even greater. You can clearly see that for each additional character set we add, the number of possible passwords that could be created expands. The greater the size of this password space, the harder it would be for a person with malicious intentions to obtain the password, since any brute force attack would require the attacker to try an increasingly large number of password possibilities before the correct password was obtained. Thus our demonstrations so far have indicated that we greatly enhance the security of our passwords by requiring users to create passwords with a combination of mixed case letters, numbers, and special characters since this yields the maximum possible variability within each allowed character position.

Increasing the variability at each position is not the only way of expanding the size of this password space, however. This space can be expanded to an even greater degree by increasing the number of allowable positions. For example, if we consider our first usage case of the case-insensitive password and simply add a fifth position to the password, we would now have 265 (11,881,376) possible passwords and for each additional position we add, we would have exponentially more password possibilities. This illustrates that length as well as positional variability is crucial to creating a strong password. Typically, password minimums are set in the 8-10 character range, but for highly secure systems it may be desirable to require even longer passwords.

In addition, while each of these aforementioned techniques can work to reduce the potential for brute force attacks, by helping to ensure that finding the correct password within the entire search space would take an inordinate amount of time, you should not overlook the fact that too many passwords do not require brute force approaches to find. The human aspect should never be forgotten about, and keep in mind that remembering random strings of letters, numbers, and special characters may not be the easiest thing in the world for many users. Because of this, many users seek to use dictionary words or names as passwords and this forms the basis for the use of dictionary attacks, in which a long listing of names and words are tried as passwords, with the hopes that one will match. Likewise, dates such as anniversaries or birthdays are not a good choice either, since they can readily be incorporated into a dictionary style attack as well. Dictionary attacks are such an established threat, that dictionary words should never be used as a password or as a part of a password.

When considering establishing password policies, with regards to dictionary words, you should also consider that many users seek to use dictionary words as a basis for their passwords with some minor modifications to incorporate special characters and/or numbers. For example, a user might take a dictionary word like "password" and modify into "pa$sword" to meet a special character requirement or they may modify "security" into "s3curity" to incorporate a number. Many dictionaries used for dictionary attacks now include such minor word variations in their word listings, and as such it may be prudent to disallow the creation of such passwords.

In this article we'll look at the development of a Perl -based password complexity filter that can be readily adapted for compliance with the most standard password policies. As such the script could serve as a useful basis for checking the strength of passwords users wish to use for access to Web applications.

The Password Complexity Filter
Before the coding of the password complexity filter is delved into, a dictionary of words should first be created for use by the password complexity filter script in order to flag any password that's based on a dictionary word as being a poor choice. In order to do this, we will make use of a modified form of the "words.txt" file that comes standard with most Linux distributions, but with a minor modification. The words.txt file will be modified to eliminate all words of less than three characters, because the presence of small words in the dictionary such as "I," "a," "at," etc., can lead to many false positive identifications of passwords as being poor password choices because they are based on dictionary words. One other important consideration to keep in mind when running this script is that code itself is portable between both Linux and Windows, but in order for the code to function properly, the list of dictionary words needs to be saved in the text formatting that is used by the platform the code is being run on due to differences in encoding line endings.

Now that the dictionary is established, we can begin to look at the Perl code, which begins by first declaring the Perl modules that it makes use of and opens the file that stores the dictionary list as follows:

use strict;
use Fcntl qw(:seek);
#words.txt file is derived from the linux ditionary file with all words of 3 characters
#or less removed, since small words like "at" and "I" can trigger false positives
open(WORDS, "words2.txt") or die("Cannot open words.txt \n");

The "use strict" pragma is used to help ensure the quality of the Perl code by forcing all variables to be explicitly declared, and the Fcntrl module will be utilized to navigate around the dictionary list file. The dictionary file is assumed to be in the same directory as the Perl script by this code and is opened with the file handle WORDS.

Next the script declares its variables as follows:

my $word;
my $passwd;
my $dc=1;
my $count=0;
my $len=8; #sets the minimum password length
my $minnum=1; #sets the minimum number of digits
my $minup=1; #sets the minimum number of uppercase letters
my $minlow=1; #sets the minimum number of lowercase letters
my $minspec=1; #sets the minimim number of special characters
my @FuzzyStrings;
my $regexp;
my $char;
my $stringpos;
my $i;
my $j;

The functions of each variable will be discussed as they are utilized, but the main variables of interest to those who seek to customize the password complexity filter to suit their respective password policies are the variables that each begin with "$min" since these are used to set the minimum lengths of each password and the minimum amounts of each character type as indicated in the code comments.

The script then seeks to compare the provided password to a list of dictionary words to make sure that none of the passwords contain dictionary words by using the following segment of code:

$passwd=join(" ", @ARGV);

while($word=<WORDS>){
chomp($word);
if($passwd=~/$word/i){
print "Password Contains A Dictionary Word: FAIL \n";
$dc=0;
last;
}
}
if($dc==1){print "Dictionary Check: PASS \n";}

Note that in the variable list above, the variable $dc was set equal to 1, since this variable will serve as our indicator of whether or not the user-provided password contains a dictionary word. The above segment of code loops through each word in the dictionary file and uses case-insensitive regular expression-based pattern matching to determine if the password contains a dictionary word. If the password ($passwd) matches any of the words in the dictionary, the variable $dc is set to 0 and a failure warning printed to STDOUT. If $dc remains equal to 1, a pass message is displayed.

The next check is a straightforward password length check, wherein the length of the password is compared to the minimum required password length ($len), as demonstrated below:

if(length($passwd)<$len){
print "Password Is Too Short: FAIL \n";
}
else{print "Length Check: PASS \n";}

Following this, the script will check to ensure the password contains at least the minimum number of upper and lower case characters, numbers, and special characters by using the following code segments:

while($passwd=~/\d/g){
$count=$count+1;
}
if($count<$minnum){
print "Password Does Not Contain $minnum Number(s): FAIL  \n";
}
else{print "Contains Number Check: PASS \n";}

$count=0;

while($passwd=~/[a-z]/g){
$count=$count+1;
}
if($count<$minlow){
print "Password Does Not Contain $minlow Lowercase Letter(s): FAIL \n";
}
else{print "Contains Lowercase Letter Check: PASS \n";}

$count=0;

while($passwd=~/[A-Z]/g){
$count=$count+1;
}
if($count<$minup){
print "Password Does Not Contain $minup Uppercase Letter(s): FAIL \n";
}
else{print "Contains Uppercase Letter Check: PASS \n";}

$count=0;

while($passwd=~/!|"|#|\$|%|&|'|\(|\)|\*|\+|,|-|\.|\/|:|;|<|=|>|\?|@|\[|\\|]|\^|_|`|\{|\||}|~/g){
$count=$count+1;
}
if($count<$minspec){
print "Password Does Not Contain $minspec Special Character(s): FAIL \n";
}
else{print "Contains Special Character Check: PASS \n";}

In each case, the script counts the number of times the character type of interest appears by making use of global pattern matching (/g), and comparing this count to the specified minimums. One thing to keep in mind is that not all software platforms support the full range of special characters listed here, so that particular regular expression may require some editing. If that's the case, be sure to pay attention to which special characters are metacharacters and keep them prefixed with a backslash to ensure proper compilation and functionality. A sample output using the checks discussed so far can be seen in Figure 1.

Figure 1: "password123" tested against the complexity filter. It is properly detected as a dictionary word and its character composition is correctly assessed.

At this point we have one remaining check to complete and that is the check to see if the entered password is just a minor modification of a dictionary word, which is carried out as shown below:

if($dc==1){
seek(WORDS, 0, SEEK_SET);
my $length=length($passwd);

for($i=0;$i<=$length-1;$i++){
pos($passwd)=0;
while($passwd=~/(\w)/gc){
$char=$1;
$stringpos=pos($passwd)-1;
if($stringpos==$i){
$FuzzyStrings[$i]=$FuzzyStrings[$i] . '.';
}
else{
$FuzzyStrings[$i]=$FuzzyStrings[$i] . $char;
}
}
if($i==0){
$regexp=$FuzzyStrings[$i];
}
else{
$regexp=$regexp . '|' . $FuzzyStrings[$i];
}
}
while($word=<WORDS>){
chomp($word);
if($word=~/$regexp/i){
print "Password Contains A Dictionary Word with Minor Substitution: FAIL \n";
$dc=0;
last;
}
}
if($dc==1){print "Dictionary Word with Minor Substitution Check: PASS \n";}
}

This check will only run if the earlier dictionary check did not find the password to be an exact dictionary word ($dc==1). It initially sets the dictionary word file back to its starting point and computes the length of the password. A nested set of loops and conditional statements is then used to create an array of @FuzzyStrings in which each character within the password is individually sequentially replaced with the "." character. "." is a special character within Perl regular expressions that can be used to match any other character. The result of this nested control structure yields a regular expression that is stored in the $regexp variable, such that a password "abc" would be turned into the regular expression ".bc|a.c|ab.". This means that a password that consists of a substitution of a dictionary word at any single position, to any type of character, will match the created regular expression. Once this regular expression is created, it's then matched against every word in the dictionary list to determine if the password is just a minor variant of any dictionary word (see Figure2). The fuzziness of the regular expression can also be readily enhanced by using quantifiers in conjunction with the ".", as the presence of quantifiers would allow for more than single character substitutions to be discovered. In particular the presence of a quantifier may be desirable for when the first and last character positions are ".", since this will allow for the detection of a partial word being appended to some additional characters.

Figure 2: Demonstration of how the password complexity filter picks up "pas$word" as being a dictionary word with a minor substitution.

Conclusion
This above script illustrates various techniques that can be used to create password complexity filters for use in verifying that existing passwords comply with an organization's password complexity requirements (see Figure 3). Moreover, this script can be run in its current command-line form or readily modified into a CGI application to provide a Web-based interface for making use of the programs functionality. As such, the article and example script should provide a useful foundation for developers and system administrators to improve password policy compliance within their organization.

Figure 3: A password that passes all checks.

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.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
The 4th International Internet of @ThingsExpo, co-located with the 17th International Cloud Expo - to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA - announces that its Call for Papers is open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal today!
In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect at GE, and Ibrahim Gokcen, who leads GE's advanced IoT analytics, focused on the Internet of Things / Industrial Internet and how to make it operational for business end-users. Learn about the challenges posed by machine and sensor data and how to marry it with enterprise data. They also discussed the tips and tricks to provide the Industrial Internet as an end-user consumable service using Big Data Analytics and Industrial Cloud.
Sensor-enabled things are becoming more commonplace, precursors to a larger and more complex framework that most consider the ultimate promise of the IoT: things connecting, interacting, sharing, storing, and over time perhaps learning and predicting based on habits, behaviors, location, preferences, purchases and more. In his session at @ThingsExpo, Tom Wesselman, Director of Communications Ecosystem Architecture at Plantronics, will examine the still nascent IoT as it is coalescing, including what it is today, what it might ultimately be, the role of wearable tech, and technology gaps stil...
The explosion of connected devices / sensors is creating an ever-expanding set of new and valuable data. In parallel the emerging capability of Big Data technologies to store, access, analyze, and react to this data is producing changes in business models under the umbrella of the Internet of Things (IoT). In particular within the Insurance industry, IoT appears positioned to enable deep changes by altering relationships between insurers, distributors, and the insured. In his session at @ThingsExpo, Michael Sick, a Senior Manager and Big Data Architect within Ernst and Young's Financial Servi...
17th Cloud Expo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterprises are using some form of XaaS – software, platform, and infrastructure as a service.
The Workspace-as-a-Service (WaaS) market will grow to $6.4B by 2018. In his session at 16th Cloud Expo, Seth Bostock, CEO of IndependenceIT, will begin by walking the audience through the evolution of Workspace as-a-Service, where it is now vs. where it going. To look beyond the desktop we must understand exactly what WaaS is, who the users are, and where it is going in the future. IT departments, ISVs and service providers must look to workflow and automation capabilities to adapt to growing demand and the rapidly changing workspace model.
Since 2008 and for the first time in history, more than half of humans live in urban areas, urging cities to become “smart.” Today, cities can leverage the wide availability of smartphones combined with new technologies such as Beacons or NFC to connect their urban furniture and environment to create citizen-first services that improve transportation, way-finding and information delivery. In her session at @ThingsExpo, Laetitia Gazel-Anthoine, CEO of Connecthings, will focus on successful use cases.
One of the biggest impacts of the Internet of Things is and will continue to be on data; specifically data volume, management and usage. Companies are scrambling to adapt to this new and unpredictable data reality with legacy infrastructure that cannot handle the speed and volume of data. In his session at @ThingsExpo, Don DeLoach, CEO and president of Infobright, will discuss how companies need to rethink their data infrastructure to participate in the IoT, including: Data storage: Understanding the kinds of data: structured, unstructured, big/small? Analytics: What kinds and how responsiv...
Building low-cost wearable devices can enhance the quality of our lives. In his session at Internet of @ThingsExpo, Sai Yamanoor, Embedded Software Engineer at Altschool, provided an example of putting together a small keychain within a $50 budget that educates the user about the air quality in their surroundings. He also provided examples such as building a wearable device that provides transit or recreational information. He then reviewed the resources available to build wearable devices at home including open source hardware, the raw materials required and the options available to power s...
How do APIs and IoT relate? The answer is not as simple as merely adding an API on top of a dumb device, but rather about understanding the architectural patterns for implementing an IoT fabric. There are typically two or three trends: Exposing the device to a management framework Exposing that management framework to a business centric logic Exposing that business layer and data to end users. This last trend is the IoT stack, which involves a new shift in the separation of what stuff happens, where data lives and where the interface lies. For instance, it's a mix of architectural styles ...
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal an...
DevOps tends to focus on the relationship between Dev and Ops, putting an emphasis on the ops and application infrastructure. But that’s changing with microservices architectures. In her session at DevOps Summit, Lori MacVittie, Evangelist for F5 Networks, will focus on how microservices are changing the underlying architectures needed to scale, secure and deliver applications based on highly distributed (micro) services and why that means an expansion into “the network” for DevOps.
The 3rd International @ThingsExpo, co-located with the 16th International Cloud Expo – to be held June 9-11, 2015, at the Javits Center in New York City, NY – is now accepting Hackathon proposals. Hackathon sponsorship benefits include general brand exposure and increasing engagement with the developer ecosystem. At Cloud Expo 2014 Silicon Valley, IBM held the Bluemix Developer Playground on November 5 and ElasticBox held the DevOps Hackathon on November 6. Both events took place on the expo floor. The Bluemix Developer Playground, for developers of all levels, highlighted the ease of use of...
We’re no longer looking to the future for the IoT wave. It’s no longer a distant dream but a reality that has arrived. It’s now time to make sure the industry is in alignment to meet the IoT growing pains – cooperate and collaborate as well as innovate. In his session at @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, will examine the key ingredients to IoT success and identify solutions to challenges the industry is facing. The deep industry expertise behind this presentation will provide attendees with a leading edge view of rapidly emerging IoT oppor...
Connected devices and the Internet of Things are getting significant momentum in 2014. In his session at Internet of @ThingsExpo, Jim Hunter, Chief Scientist & Technology Evangelist at Greenwave Systems, examined three key elements that together will drive mass adoption of the IoT before the end of 2015. The first element is the recent advent of robust open source protocols (like AllJoyn and WebRTC) that facilitate M2M communication. The second is broad availability of flexible, cost-effective storage designed to handle the massive surge in back-end data in a world where timely analytics is e...
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
For years, we’ve relied too heavily on individual network functions or simplistic cloud controllers. However, they are no longer enough for today’s modern cloud data center. Businesses need a comprehensive platform architecture in order to deliver a complete networking suite for IoT environment based on OpenStack. In his session at @ThingsExpo, Dhiraj Sehgal from PLUMgrid will discuss what a holistic networking solution should really entail, and how to build a complete platform that is scalable, secure, agile and automated.