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XSDecode -- the X-Stop list codebreaker

Used to determine that X-Stop has an error rate of 68% in blocking student home pages

(See also the analysis of the first 50 blocked URL's in the .edu domain. 34 out of 50 blocked sites were classified as errors.)

XSDecode was the tool that we used to decrypt the database of sites blocked by X-Stop as "obscene". After extracting the first 50 URL's in the ".edu" domain that were still valid, we visited those pages and found that 34 of them, or 68%, were obviously errors in X-Stop's list.

The 50 sites that we tested are listed here, classified as "obvious errors", "marginal errors" and "not errors".

You can follow the instructions below to download a copy of X-Stop's blocked-site list. (Of course, after X-Stop has viewed this page, some of the more embarrassing errors may no longer be on the list.)

We had already decrypted X-Stop's blocked-site list by the time XSDecode was sent to us anonymously, but we are posting this version of XSDecode since the source code is cleaner. Download XSDecode here or get the source code here.

Then, download the latest full version of the list of sites blocked by X-Stop from this URL:
(c. 4 megabyte download) Please email me and let me know once you've downloaded the file -- we may need confirmation from multiple "witnesses" in case X-Stop disputes the "smoking gun" evidence contained in this file. (That is to say, it would be fairly easy for X-Stop to remove the embarrassing errors from the list, and claim that we fabricated the report.)

This is a binary file in DC Micro's Crusher format. It is the file that the X-Stop client program downloads when you tell it to update its blocked site list. To extract the file, download arq.exe and run the command

arq -x xfexf.bin
to extract the archive. One of the resulting files -- by far the largest, at 17 M -- will be named "~ldcsvr.exf". This is X-Stop's list of "obscene" sites. To decrypt the file, run XSdecode with the command
xsdecode ~ldcsvr.exf > output.txt
The resulting output.txt file will still be very large, about 13 M. To extract the list of blocked URL's in the ".edu" domain, grep for the string .edu/