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<H2><A NAME="SECTION00047000000000000000">
Signature Tool</A>
</H2>
<I>sigtool</I> automates signature creation. If you have got an infected
file not recognized by ClamAV and there is an another anti-virus scanner
working in a console that detects the virus you can try to generate
the signature automatically. <A NAME="tex2html77"
HREF="footnode.html#foot461"><SUP>6</SUP></A> <I>Sigtool is only
partially useful because it only detects the last part of a real
signature. It will fail for multipart signatures (and especially for
polymorphic viruses).</I>
Example usage: create a random file (with any content) and insert the
<code>test/test1</code> file content into it. We will use <I>clamscan</I>
to generate the signature. Remember this is only an example - in a real
life you don't need such tricks - just an infected file. Scan it with
<code>clamscan --stdout testfile</code> - the output should be:
<PRE>
testfile: ClamAV-Test-Signature FOUND
----------- SCAN SUMMARY -----------
Known viruses: 21074
Scanned directories: 0
Scanned files: 1
Data scanned: 0.95 MB
Infected files: 1
I/O buffer size: 131072 bytes
Time: 1.245 sec (0 m 0 s)
</PRE>
The unique string in this output is "ClamAV-Test-Signature" so run
<I>sigtool</I> with the following arguments:
<PRE>
$ sigtool -c "clamscan --stdout" -f testfile -s "ClamAV-Test"
</PRE>
The program will concatenate arguments for <code>-c (--command)</code> and
<code>-f (--file)</code> that's why the scanner's options must be given in the
proper order. At the end it will generate a file called <I>testfile.sig</I>,
which should be 100 bytes in size (in our example). It contains the proper
signature.
<PRE>
Detected, decreasing end 20051 -> 16040
Detected, decreasing end 16040 -> 12029
Detected, decreasing end 12029 -> 8018
Not detected at 8018, moving forward.
Detected, decreasing end 10024 -> 8018
Not detected at 8018, moving forward.
Detected, decreasing end 9021 -> 8018
Not detected at 8018, moving forward.
Not detected at 8520, moving forward.
Detected, decreasing end 8771 -> 8520
Not detected at 8520, moving forward.
Not detected at 8646, moving forward.
Not detected at 8709, moving forward.
Detected, decreasing end 8741 -> 8709
Not detected at 8709, moving forward.
Not detected at 8725, moving forward.
Detected, decreasing end 8733 -> 8725
Not detected at 8725, moving forward.
Not detected at 8729, moving forward.
Detected, decreasing end 8731 -> 8729
Not detected at 8729, moving forward.
Detected, decreasing end 8730 -> 8729
Not detected at 8729, moving forward.
Increasing end 8729 -> 8730
*** Signature end found at 8730
Detected at 8680, moving forward.
Detected at 8680, moving forward.
Not detected, moving backward 8693 -> 8680
Detected at 8680, moving forward.
Not detected, moving backward 8687 -> 8680
Detected at 8680, moving forward.
Not detected, moving backward 8684 -> 8680
Detected at 8680, moving forward.
Not detected, moving backward 8682 -> 8680
Detected at 8680, moving forward.
Not detected, moving backward 8681 -> 8680
Detected at 8680, moving forward.
Not detected, moving backward 8681 -> 8680
Detected at 8680, moving forward.
Moving forward 8680 -> 8681
*** Signature start found at 8681
The scanner was executed 33 times.
The signature length is 49 (98 hex)
Saving signature in testfile.sig file.
Saving binary signature in testfile.bsig file.
</PRE>
To make the generated signature complete you only to add the
<code>VirusName=</code> string at the beginning of the hexadecimal signature in
testfile.sig.
<BR> <I><B>TIP:</B> ClamAV scanners read all .db files in the database
directory. You can create your own database files (e.g. local.db) and they
won't be modified by freshclam !</I>
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<ADDRESS>
Tomasz Kojm
2004-06-14
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