Thanks to Ian Firns that has implemented custom output formating (sancp like), pcap indexing and pcap capturing (daemonlogger-style)…!
Starting from commit 6b32fb24db, cxtracker can now, additional to writing flowdata, also do packet-capturing and outputting indexing data about where in the pcap(s) the flow starts and ends. This should potentially bring down the time needed to carve a session out of a big pcap. Right now, all this is just in beta, but the functionality is there, and there is also an example perl-script to carve out a session based on index-data.
Output fields of interest:
%spf pcap file containing start packet in session
%spo pcap file offset of start packet in session
%epf pcap file containing last packet in session
%epo pcap file offset of last packet in session
Example on a indexed pcap output, using: “%spf|%spo|%epf|%epo”
So, basically, if you have a 1 GB pcap file, normally you could use tcpdump with a BPF filter to care out the session you where looking for, reading and searching the whole 1 GB pcap file.
With this addition to cxtracker, you would now be able to spool right to the start-byte off the session and start carving from there until the end-byte of the session. So if the session is placed say 450 MB into the pcap, and ends at 550 MB into the pcap, you basically only have to read and carve in 100 MB of pcap data. In the example perl script (cxt2pcap.pl), the file handle for the file is opened, it would seek to the right place in the pcap (_not_ reading 450 MB of data from your disk) and start reading 100 MB data from your disk and carving+filtering and then close the file handle.
We would love to have some feedbacks here, and to have people test it. Again, it is still beta, so be aware 🙂
Note: Idexing pcap files is nothing new, the sancp project did add alike features, but was never properly released.