It says GDPR compliant and no cookies on the project page. How are unique visitors calculated? And I'm assuming it can't link conversions to campaigns without some cookie-alternative?
> Instead of tagging users with cookies, we count the number of unique IP addresses that accessed your website. Counting IP addresses is an old-school method that was used before the modern age of JavaScript snippets and tracking cookies.
Since IP addresses are considered personal data under GDPR, we anonymize them using a one-way cryptographic hash function. This generates a random string of letters and numbers that is used to calculate unique visitor numbers for the day. Old salts are deleted to avoid the possibility of linking visitor information from one day to the next. We never store IP addresses in our database or logs.
Um... hashing IPv4 addresses, even with salt, does literally nothing to anonymise (assuming the output space is at least ~32 bits, which I think is safe to assume): they’ll still be PII. IPv6 addresses I’m not so confident about; maybe it would be sufficient for some parts, but it’s definitely inadequate for some concerns.
(For IPv4, enumerating all four billion inputs is so completely practical that “one-way” is nonsense.)
I’m almost certain this is legal theatre.
If I tell you the value is either 1 or 2, but I hashed it with sha256 to make it secure, that's bullshit, right? You can just hash both and see which it is.
Same concept applies regardless of the hash algo, and still applies if you have more than 2 possible values, 4 billion or so possible ipv4 addresses is _not_ that many values to a computer.
Other common places this problem occurs is with any other restricted set of values, eg phone numbers and email addresses (most are at like 5 domains and are easy to guess/know).
Lossless techniques do nothing to dilute that taint.
Lossy techniques are necessary to get anywhere, such as disregarding certain bits of the address, or Bloom filters.
Information-theory-wise, this is no different to just storing the actual IP addresses (and deleting them daily after tallying, as before). It does mean that you need to obtain two things instead of just one, but if you get access to it all, it’s straightforward to reverse the lot (though computationally a little expensive), and easy to check a single value for a match.
The technique may be considered reasonable effort at protecting against casual abuse, but it’s not technically effective of itself, and it doesn’t stop the data from being PII. The important aspect is that the PII is deleted within 24 hours. My personal opinion is that the hashing part should probably be considered snake oil and whitewash, at least for what they’re claiming—I don’t say it’s useless, but it definitely doesn’t do what they’re touting it for.
Unless they’re actually keeping the hashed values for some reason after one day, and associating them with other records? In which case, disregard part of what I say, it’s obviously better than persisting IP addresses long-term! But also it’s extremely dubious to call that anonymisation as they do, because you can so often tie things together, behavioural patterns and such, to deanonymise. It’s frighteningly effective.
That said, the whole IP thing is weird to me. Not only are we allowed to log IPs directly for security reasons, we even *have* to log IPs in certain cases (newsletter subscriptions).
The point of designating something as PII isn't that we then _never_ store or use it, it's to carefully consider if we actually need it or not (and what protections we can add for the values we do need to store/use).
We're meant to stop the practice of just collecting and storing all data, without consideration for the harms that causes.
When I researched this topic it was strange to me that no one seems to agree. Is it just arm-chair internet answers? Or is it actually that the letter of the law is actually ambiguous? What are the real world consequences of using this when it’s possible it violates GDPR? Or, what are the chances there would be consequences?