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SubjectRe: tcp/ip filtering
On Mon, 20 May 1996, Hartmut Niemann wrote:

> omnilord wrote:
> > If someone writes it and puts it into the kernel, and someone else uses
> > it, then that means someone has found the module useful. The internet is
> That is right. But what you do and discuss seems strange to mw for some
> reasons:
> (1) searching for offending _words_ does not work or hits the wrong horse.
> Words can and should not be censored.
> Words get their meaning in context. Look up all the meanings og "gay",
> if you want to and read some old english madrigal texts from 16xx!
> You probably had to censor them, along with most modern song lyrics.

We aren't going to censor "gay" obviously... There are some words that
most people find offensive (and which teachers regularly punish students
for speaking) which will be the ones that will be filtered.. And of
course if a student has trouble with a file transfer, I'll help them
out.. (also giving me knowledge to how many times the filter is on
target, which hopefully will be pretty high... no use debating until its

> (2) searching for _words_ can crash a ftp on a compressed file. Or it can not.
> but this does not depend on the content of the uncompressed file!

True, but unlike people are saying, just "sex" wouldn't trip anything, it
would have to be surrounded by non alphabetic characters (and the word
"sex" won't be filtered anyhow)... In the end, like I said, I hope to
duplicate the abilities of SurfWatch, but for free, and on the server end..

> (3) You can not easiliy (without supervising every user) allow users to download
> pictures without implicitly allowing them to download pictures you would
> like/have to censor. If somebody downloads jeff222.gif - how could you
> say whether this is a new linux logo or a naked girl?

No way to know :), but our other filtering methods will hopefully make up
for this defficiency... Its an unsolved problem, definetly, but there are
still MANY things that will be caught by the filter..

> (4) packet filtering based on packet contents will cause problems on compressed
> and pictures

Yeah, IF the data has an "offensive" (chosen by the teacher) word,
separated by non alphabets... It isnt very often that you would find
something like:
df8y*^9dfa65675 SEX ds8fhare5&;:78ad
in a binary file... and on the slim chance that that happens, then "df" "y"
"dfa" "SEX" "ds" "fhare" or "ad" would all be checked against banned
words, and if we were maniac enough to put sex in the list, then it would
trip the filter... But this is VERY rare... (I know I often cat binary
files for the heck of it:).. but like I said, when it actually starts
working then I'll know for sure..

> => Your plan most probably has to fail for systematic reasons. So if you want
> to discuss linux-specific - go on. But whether or not? does not belong here.

SurfWatch seems to be a very popular filtering tool, and if they managed,
I can find a way too :)... And yes, this is a tool that I wanted to
implment specifically on Linux, and had been hoping someone from the
mailing list could help me...

> > > Michael "Tired" Riepe <>

> I do not want to offend anybody, but with 500+ messages in my mailbox I would like
> them to be more kernel-related, or at least linux-related...

May we discuss things that we want to implement into the linux kernel? I
thought that was linux-related..

> Hartmut Niemann
> Zum Aussichtsturm 18 D-91080 Marloffstein

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