ipscrub is an IP address anonymizer for nginx log files. It’s an nginx module that generates an IP-based hash. You can use this hash to link requests from the same source, without identifying your users by IP address.
HASH(ngx_random() ++ timestamp).
HASH(salt ++ IP address).
ngx_random to generate random nonces.
ngx_random is defined as the C
random() function on non-Windows platforms, and
rand() on Windows. NOTE: this is not a cryptographically secure RNG, but for the following threat model, that is ok.
ALSO NOTE: the generated hash WILL change on each
PERIOD transition, so you will only have continuity within each
PERIOD. But because users can transition between networks at any time (e.g. wifi -> cellular), you’d have this type of issue even if you were storing raw IPs.
In threat scenario (1), the goal is to compute the masked IP corresponding to a target IP address. This will only be possible if the demand is made before the end of the current
Scenario (2) is defended against because the server operator does not know the salt, and cannot infer it based on the request timestamp, because the salt is generated from a nonce that is only stored in memory. The server operator would have to be an accomplice in this case, but that is more simply accomplished by the server operator just recording the unmasked IP. So this security/threat model does not defend against a malicious server operator, but that is not the point. It does defend against an honest server operator being compelled in threat scenarios (1) and (2).
ipscrub can be built statically with nginx or as a dynamic module. See the
Makefile for examples of both ways.
load_module ngx_ipscrub_module.so;(NOTE: only if you built as a dynamic module).
ipscrub_period_seconds <NUM SECONDS PER PERIOD>;(optional).
NOTE: nginx may still leak IP addresses in the error log. If this is a concern, disable error logging or wipe the log regularly.
GDPR goes into effect on May 25, 2018. It legislates the handling of personal data about your users, including IP addresses.
What constitutes personal data? Any information related to a natural person or ‘Data Subject’, that can be used to directly or indirectly identify the person. It can be anything from a name, a photo, [...], or a computer IP address.
The hashes generated by
ipscrub let you correlate nginx log entries by IP address, without actually storing IP addresses, reducing your GDPR surface area.
Copyright 2018 Mason Simon
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