The first good news is that for many practical cases, full packet capture is not necessary. This rationale stems from the well-known law of heavy tailed traffic: from an analysis standpoint, most of the interesting features found in network traffic—such as a network attack, although not limited to it—are found in a very small fraction of it. Further, in some cases full packet capture is not only unnecessary but could represent a liability as sensitive information is kept in non-ephemeral storage. The second good news is that all the heavy lifting done by Zeek in processing network traffic can be leveraged to overcome both the intractability and the liability problems. Indeed, Zeek can be brought into the loop to perform selective packet capture (SPC), a process by which the Zeek workers themselves decide which traffic must be stored into disk in a selective and fine granular manner.
In this talk Reservoir Labs will present a workflow to perform selective packet capture using the Zeek sensor at very high speed rates. The workflow allows Zeek scripts to directly trigger packet captures based on the real time analysis of the traffic itself. We will describe key data structures needed to efficiently perform this task and introduce several Zeek scripts and use cases illustrating how SPC can be used to capture just the necessary packets to enable meaningful forensic analysis while minimizing the exposure to the liability risk.
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