Simple Comments Release Notes: v.950 (2/2) | WebReference

Simple Comments Release Notes: v.950 (2/2)

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Simple Comments Release Notes: v.950

Introducing ReCAPTCHAS

In our previous release of Simple Comments, we introduced CAPTCHA-based identification--the ability to distinguish between bots and humans by requiring the entry of graphically displayed characters. If you're unfamiliar with the Simple Comments CAPTCHA system or captchas in general, you might wish to review the v.930 release notes now.

Our initial implementation of captchas for Simple Comments was based on the system deployed over at Captchas.net, which is free, simple to deploy and also includes audio captchas for the visually impaired. With v.950, we also support the use of reCAPTCHAS.

A sample reCAPTCHA display.
A sample reCAPTCHA entry box.

reCAPTCHAS are captchas with a twist: Instead of supplying any old random graphical characters or words to be typed into the submission form, the reCAPTCHA form instead displays words that have been scanned from books but could not be properly recognized by OCR technology--i.e., words that the computer itself literally cannot understand or make out. By typing in the correct characters for these mis-scanned words, your visitors are not only validating themselves to your forms, but are also helping to digitize older texts for electronic representation. Have a look at this page of the reCAPTCHA site for further details on the project and the captcha mechanism.

To use reCAPTCHAS in Simple Comments, you must first (as is the case with Captchas.net) register for an account at the reCAPTCHA site mentioned above. As a result of that registration, you'll be provided with several pieces of information, which you can incorporate within your config.xml file, including your own unique public and private key (which can be used only on your Web site). To enable reCAPTCHAs in Simple Comments, you need to set the captcha_enabled parameter to 1, and set the captcha_system parameter--new in v.950--to recaptcha. The previous captcha system (from Captchas.net) is also still available in v.950; to use it, you simply set captcha_system to captchas.net.

Submission Thresholds

A clear danger with any CGI script which allows users to submit information that will be written to your hard drive is the potential for misuse; i.e., bad guys can bombard your site with submissions in an attempt to fill your disk and/or slow your site response times. This is also a concern with the new release of Simple Comments; since visitor profile registrations are written to the disk in a one-profile-per-disk-file architecture. Even if the visitors never bother confirming their profile registrations (and it's doubtful that Mr. or Mrs. Bad Guy would bother to confirm), they can still generate thousands of files on your drive--by submitting bogus visitor profiles--in a relatively short period of time.

To combat this and other DoS-related possibilities in Simple Comments, I've added a submission threshold feature. In brief, the submission threshold will prevent any submitter from supplying comments or visitor registrations faster than a predetermined rate, which can be set by the administrator. In its default deployment, Simple Comments restricts submitters to one comment or profile every 30 seconds. Such a limitation is a minor inconvenience for legitimate users (most won't even notice the feature), while providing an effective deterrent for all but the most determined of Bad Guys. You can adjust the 30 second interval to anything you like; or if you're confident your system is Bad Guy proof (via some other means) you can disable the feature entirely (by setting the threshold to zero).

Other Adjustments

Other enhancements, adjustments, and outright fixes finding their way into this version of Simple Comments include:

That last point deserves a bit more detail. Previously, we simply hashed the admin passwords and stored them directly within the users.xml file, which provided good protection--but it could have been better. Salting the hashed passwords--i.e., combining the password with a value unique to each password entry and user before hashing--can strengthen the overall password file if it (the file) ever gets into the hands of crackers.

To break a hashed password, a cracker typically takes a dictionary of common words, phrases, or character combinations, hashes each of those entries in the same manner that the program using the hashes did, and then compares the results to the actual encoded hashes in the user list (such as the password encodings stored in the users.xml file). If all the passwords in the file were salted with the same value (or unsalted), then the cracker can quickly compare the results of their encoded dictionary to all the entries in the file without having to re-encrypt their dictionary between password checks. While this might seem like a minor deterrent, forcing the cracker to reencrypt the dictionary between password checks can slow them down a tremendous amount--perhaps even enough to warrant moving on to another malicious project and abandoning your password file altogether.

In Simple Comments we've now chosen to salt the stored passwords with the user's ID; fulfilling our requirements that each password is salted with a separate value (that both we and the administrator supplying the password knows, and that can be somehow linked to the user themselves for subsequent authentication checks) and therefore forcing the cracker to re-hash their dictionary on each password cracking attempt. You might be tempted to salt the password with the password itself before storing it--but that would be a serious mistake. Doing so offers no deterrence to the would-be cracker (who can just encrypt their whole dictionary once using the dictionary words themselves; since the dictionary word itself is the salt), and with some functions--such as Perl's crypt function on most systems--the salt itself is stored literally as part of the encrypted string that is returned. If your crypt-based script salts the password with the password itself, you'll be giving away two literal characters of the password to any would-be attacker! I.E.:

my $password = "Testing";
# Don't do this
my $encoded = crypt($password, $password);
print $encoded, "\n";
# Above prints "TeakRFRsTNc6E"
# Note that the first two characters are 
# the first two characters of the password
# Instead do something like this
$encoded = crypt($password,
                 join('', ('A'..'Z', 'a'..'z')[rand 52, rand 52]));
print $encoded, "\n";
# Above uses a random salt; the salt itself appears
# as the first two characters of the encoded string
# for subsequent verifications

And while we're on the topic, remember that crypt typically only encrypts the first 8 characters of a string; meaning that password1 and password2 will create identical encodings

print crypt('password1', 'DR'), "\n";
print crypt('password2', 'DR'), "\n";
# Both statements above print "DRSA07ZWOpRt6"

and can therefore be used interchangeably (i.e., a person could authenticate with 'password1,' 'password2,' or even 'password-smashword,' for that matter). For more crypt related details, have a look at the perldoc entry on your system (perldoc -f crypt) or visit perldoc.perl.org.

Conclusion

What's next from Simple Comments? On my radar screen are multiple potential enhancements inspired by the new visitor registration capabilities; including support for OpenID and hopefully single sign on (where perhaps a single comment script can serve as the login point for multiple independent sites, or multiple sections of a single site). Also, the comment display and submission interaction templates--including the new login process--could use some updating; perhaps with AJAX-based controls so the user doesn't have to flip from page to page to login or post new comments (i.e., the entire comment posting process could conceivably be performed within the page, instead of requiring multiple script hits).

More importantly, what do you think the next key feature of Simple Comments should be? Drop us a note with your ideas and we'll be sure to consider them for possible inclusion in future Simple Comments releases!


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Created: November 12, 2007
Revised: November 12, 2007

URL: http://webreference.com/programming/perl/comments/v.950/2.html