3 ms·

A four byte hash is unique to two billion sites. The collision space with non-mainstream sites you might visit is going to be tiny. It’s as good as sending the

A four byte hash is unique to two billion sites. The collision space with non-mainstream sites you might visit is going to be tiny. It’s as good as sending the actual URL, and possibly even the full path to the document you requested, if the browser has previously asked Google for another site and Google has seen a pattern of browsing from Site A to Site B in browsers not using this “security” feature.

lixtra 8y ago
> A four byte hash is unique to two billion sites Due to the birthday paradox collisions happen much earlier.
- Engineering-MD 8y ago
  Yes, but that is (by the nature of the paradox) only true for a small subset of sites. It provides a huge amount of information, and for much the same reason, DoB is often used as part of an identifier.
  - lixtra 8y ago
    Let’s assume that it is indeed the hash of the URL as they wrote. There are much more than 2B URLs on the net. Assume google flagged 2M as malicious (a 8MB db). So on average you get a hit for 1 in thousands URLs. For each hit you query google for the malicious sites with the actual hash. It does feel like some information could leak but at the same time there are literally hundreds of possible URLs that map to each hash value. So there is plausible deniability as well. Again, combined with more information this could be exploited. But probably there are easier attack vectors.
- manicdee 8y ago
  Not the point. You issue quest on hash A then hash B. Google guesses that because of other activity it has seen today, visits to a site marked by hash A followed by visits to site marked hash B means you are following a link from Alex Jones’ blog to a flat earth holocaust denial web site, and thus prepares to serve your IP address ads for tin foil hats and prepper magazines. The chances of your traffic pattern of hash A then hash B colliding with, say, my browsing of the MLP fan club and following a link to cosplay photos from Dragon Con are pretty slim, even though the MLP fan club URL hash collided with the Alex Jones blog hash. Google aren’t just looking at the one thing you viewed, they are following you everywhere.

lixtra 8y ago

> A four byte hash is unique to two billion sites Due to the birthday paradox collisions happen much earlier.

Engineering-MD 8y ago
Yes, but that is (by the nature of the paradox) only true for a small subset of sites. It provides a huge amount of information, and for much the same reason, DoB is often used as part of an identifier.
- lixtra 8y ago
  Let’s assume that it is indeed the hash of the URL as they wrote. There are much more than 2B URLs on the net. Assume google flagged 2M as malicious (a 8MB db). So on average you get a hit for 1 in thousands URLs. For each hit you query google for the malicious sites with the actual hash. It does feel like some information could leak but at the same time there are literally hundreds of possible URLs that map to each hash value. So there is plausible deniability as well. Again, combined with more information this could be exploited. But probably there are easier attack vectors.
manicdee 8y ago
Not the point. You issue quest on hash A then hash B. Google guesses that because of other activity it has seen today, visits to a site marked by hash A followed by visits to site marked hash B means you are following a link from Alex Jones’ blog to a flat earth holocaust denial web site, and thus prepares to serve your IP address ads for tin foil hats and prepper magazines. The chances of your traffic pattern of hash A then hash B colliding with, say, my browsing of the MLP fan club and following a link to cosplay photos from Dragon Con are pretty slim, even though the MLP fan club URL hash collided with the Alex Jones blog hash. Google aren’t just looking at the one thing you viewed, they are following you everywhere.