Privacy-Preserving Network Flow Recording

Network flow recording is an important tool with applications that range from legal compliance and security auditing
to network forensics, troubleshooting, and marketing. Unfortunately, current network flow recording technologies
do not allow network operators to enforce a privacy policy on the data that is recorded, in particular how this
data is stored and used within the organization. Challenges to building such a technology include the public
key infrastructure, scalability, and gathering statistics about the data while still preserving privacy.

We present a network flow recording technology that addresses these challenges by using Identity Based Encryption in combination with privacy-preserving semantics for on-the-fly statistics. We argue that our implementation
supports a wide range of policies that cover many current applications of network flow recording. We also
characterize the performance and scalability of our implementation and find that the encryption and statistics scale
well and can easily keep up with the rate at which commodity systems can capture traffic, with a couple of interesting
caveats about the size of the subnet that data is being recorded for and how statistics generation is affected
by implementation details. We conclude that privacy preserving network flow recording is possible at 10 gigabit
rates for subnets as large as a /20 (4096 hosts).

Because network flow recording is one of the most serious threats to web privacy today, we believe that developing
technology to enforce a privacy policy on the recorded data is an important first step before policy makers
can make decisions about how network operators can and should store and use network flow data. Our goal in
this paper is to explore the tradeoffs of performance and scalability vs. privacy, and the usefulness of the recorded
data in forensics vs. privacy.



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