[Oisf-devel] filemd5?

Nikolay Denev ndenev at gmail.com
Thu Feb 16 14:59:26 UTC 2012

On Feb 16, 2012, at 4:21 PM, Victor Julien wrote:

> So I guess the best development happens when you're actually doing
> boring stuff and you allow yourself to spend 30 minutes on a hunch. Of
> course the 30 minutes becomes a couple of hours, but who cares :)
> Anyway, the hunch here was integrating libnss' md5 calculation code into
> the Suricata file inspection/extraction code, calculating the md5
> checksum of files on the fly.
> Turns out it works and at decent speeds too. In a test pcap I extract
> 8393 files in 16.9 seconds. With md5 on the fly it's 17.6 seconds.
> Sounds acceptable, no?
> Right now all I have is writing the md5 to the .meta file, like so:
> TIME:              10/02/2009-21:35:10.556990
> PCAP PKT NUM:      6225
> SRC IP:  
> DST IP:  
> PROTO:             6
> SRC PORT:          80
> DST PORT:          1091
> FILENAME:          /ww/aa7.exe
> MAGIC:             PE32 executable for MS Windows (GUI) Intel 80386 32-bit
> STATE:             CLOSED
> MD5:               e148eaaadceecb2e3e25fd25809cb5db
> SIZE:              25712
> But obviously this needs to be made available to the rule language. I
> was thinking a simple filemd5 keyword to start, allowing matching on
> single md5's. But the real value is probably in a keyword that allows
> you to check an entire db of md5's all at once. I'm sure there are ppl
> sitting on large collections of known bad md5.
> Does this all make sense? Any other ideas?
> -- 
> ---------------------------------------------
> Victor Julien
> http://www.inliniac.net/
> PGP: http://www.inliniac.net/victorjulien.asc
> ---------------------------------------------

Very cool!

This seems that can be also used to provide DLP functionality, i.e. keep a database with md5 checksums of files with sensitive data and
alert if the data is leaked (regardless of filename). I've heard at least of one DLP vendor that uses similar method to detect unauthorized data leaks.

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