zebra barcode printer c# 14: Web Site Security in Objective-C

Draw Data Matrix ECC200 in Objective-C 14: Web Site Security

CHAPTER 14: Web Site Security
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$_ =~ s/[^$ok_chars]//go; param($param_name,$_); }
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Be mindful that using this code will not guarantee security in situations where you re protecting your Perl scripts with the T switch. If you use the Perl command line to test syntax, you can still do so by using perl cT scriptname.pl.
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Securing robots.txt
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If you have a web site, you can assume that search engines will find it and index the text and code of your site, adding it into their extensive catalog of sites for users to search. Many administrators do not want their sites to appear in search engines for a variety of reasons. The robots.txt file is a simple text file script at the root of your web host that tells a robot whether it has access to a certain file or directory. It is designed for companies that want to keep their data from being scanned by bots, preventing search engines from scanning or crawling their web site. It s flexible, in that different rules can be specified based on the robot s user agent. A sample robots.txt is as follows:
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User-agent: * Disallow: /secret-files/
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This simple file tells all robots not to enter the /secret-files folder. A more complex robots.txt or robots(AllowRoot).txt file looks like this:
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User-agent: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: Disallow: * /_vti_bin/ /clienthelp/ /exchweb/ /remote/ /tsweb/ /aspnet_client/ /images/ /_private/ /_vti_cnf/ /_vti_log/ /_vti_pvt/ /_vti_script/ /_vti_txt/
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Allow All traffic: User-agent: * Disallow: /
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Blocking Hosts Based on robots.txt
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This is all well and good, and most robots, such as those of Google and Yahoo, respect your rules. But what happens when a robot blatantly ignores your rules The simple answer is, it does whatever it wants. Because it s up to the robot to obey or ignore the rules, any disreputable robot can download your entire site.
CHAPTER 14: Web Site Security
The solution is to proactively block wayward robots. There are a few different ways to do this, such as blocking known bad robot user agents and blocking IPs. Blocking certain user agents is easy, but it s also easy for the robot to spoof its user agent, so you ll find that you have to continuously update your list of bad user agents. Blocking IP addresses is effective too, but you ll also need to consistently update your blocked IP list. The best solution involves a combination of techniques that, once implemented, requires little or no maintenance and lays a trap for bad robots. First, put a hidden link into the main page of your site. This hidden link is a zero-by-zeropixel image that links to a script within /secret-files/.
<a href="/secret-files/robot.cgi"><img border="0" width="0" length="0" src="images/ spacer.gif"></a>
Because this image isn t viewable in a browser, the only way it s ever likely to be accessed is if a robot is crawling your site. Because your robots.txt file is blocking access to that folder, the only time this script will actually get called is if a robot is crawling the site while ignoring robots.txt. Once the script within /secret-files/ is run, it blocks the user s IP. Of course, it s possible that an inquisitive user viewing the source of your site (using the View Source option available in most modern browsers) might find that link, follow it, and find herself blocked. When you re devising methods of blocking bad traffic, you should always consider the potential for collateral damage. TIP: Typically, sites have more than one entry point, so it s a good idea to place this hidden link in more than one page. If you take advantage of server-side includes (SSIs), then placing it inside the header.html or footer.html file offers excellent protection. The following are the contents of the robot.cgi script (big thanks to Erin Scott for whipping this up):
#!/usr/bin/perl -w $htaccess = "/path/to/web/root/.htaccess"; open (HTACCESS, ">> $htaccess") or die $!; print HTACCESS "deny from $ENV{REMOTE_ADDR}\n"; close (HTACCESS); # needs to be the full path
Another benefit to this script is that it stops robots from crawling your site before they download anything more than your front page. If you have other domains that are using Apache s mod_rewrite module in the root of your web folder, they will also be inaccessible by the bad robot s IP address. Ninetynine percent of the time, this is preferable.
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