Conceptual attribution

This project implements several well-known techniques from first principles. No code was copied from copyleft or unlicensed sources; this file records the prior art each idea derives from and why our implementation is original.

Rotating-salt visitor hashing

• Prior art: Publicly documented by Plausible Analytics ("data policy" docs) and Fathom Analytics; the underlying idea (keyed, time-boxed pseudonymisation) is standard privacy-engineering practice discussed in GDPR/WP29 anonymisation guidance.
• Our implementation: SHA-256(dailySalt ‖ ip ‖ userAgent ‖ siteId) truncated to 8 bytes, salt rotated on a configurable window (default 24 h) with the prior salt destroyed. Written from the description of the technique only; no source code from Plausible (AGPL-3.0) or any other implementation was read or used.
• Deliberate consequence: cross-day re-identification is impossible, so multi-day "unique visitor" figures are on a daily-unique basis and are labelled as such in the UI.

HyperLogLog cardinality estimation

• Prior art: Flajolet, Fusy, Gandouet, Meunier, "HyperLogLog: the analysis of a near-optimal cardinality estimation algorithm" (2007), and the sparse-representation refinement in Heule, Nunkesser, Hall, "HyperLogLog in Practice" (Google, 2013). Both are published papers; algorithms as such are not copyrightable.
• Our implementation: original pure-PHP implementation in src/uniques/Hll.php (phase 3), written from the papers, with a custom binary serialisation format. Redis's PFADD/PFMERGE commands are used via their public API where Redis is available; Redis source code (BSD-3-Clause anyway) was not consulted.

Server-side capture after response flush

• Prior art: fastcgi_finish_request() is documented PHP behaviour; the pattern of doing deferred work after flushing is folk knowledge (PHP manual, Symfony kernel.terminate).
• Our implementation: built on Yii's Response::EVENT_AFTER_SEND as exposed by Craft CMS.