developers.google.com/safe-browsing/ is good documentation on how the Safe Browsing API used by browsers (Chromium, Firefox, Safari, etc.) works. It searches a database based on a truncated hash (4 bytes) of a canonicalized URL. It leaks some information, but doesn't send URLs directly.
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Safe Browsing isn't currently supported by GrapheneOS and won't be enabled by default with the standard approach. It leaks too much. I haven't done anything to intentionally break it and wouldn't mind it as an optional feature, but the default mobile approach uses Play Services.
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Some work would need to be done to set up the alternate mobile implementation. Enumerating badness is not a workable approach to security so this hasn't been a priority. I also don't think the attempt at providing privacy is good enough. How large is the entire database anyway?
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I'm curious if it's feasible to just regular scrape the entire Safe Browsing database and then download the full database from a GrapheneOS server on a regular basis. The standard approach seems to trend towards that anyway... and updates to the database can be done via deltas.
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This webpage seems to show that the truncated URL is the most significant 4 to 32 bytes of a SHA256 hash. 32 bytes means the entire hash. 🙄
The page gives 2 examples for 4 an 6 bytes.
The ball seems to be in the browsers camp. Less bytes = more privacy = larger list in return.
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I think 4 bytes is what gets used in practice by most browsers, but I'm not familiar with all of them.
