this post was submitted on 04 Jul 2023
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You Should Know
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The hash function would still need to be public to share data between instances.
That's the point of a hash function. You have a public hash function, say SHA-256. It's easy to check a username against it's hash, but virtually impossible to reverse the hash back to the username.
Edit: Instead of storing, say,
eddie, we'd store3b9d8298f1b5086d012618feebb2da1a394357c1dab7523443c9f6a743c4c84d. Then when the instance gets aLikefromeddie, it hashes his username to get3b9d8298f1b5086d012618feebb2da1a394357c1dab7523443c9f6a743c4c84d, realizes there's a match, and doesn't update the count.Note that when given
3b9d8298f1b5086d012618feebb2da1a394357c1dab7523443c9f6a743c4c84d, it would take millions of CPU years to compute the original username from it. Therefore, we can check for duplicates without actually checking the name itself (a similar method is used for checking passwords; Lemmy is open source, we know the hashing algorithm, but we can't unhash user passwords, only check them).While there is an enormous amount of possible passwords, there is only a limited (and quite small) amount of users. Couldn't you just hash all the usernames one by one and map the hashes to the usernames? So you could still reverse engineer the usernames of those who voted on a post.
Edit: Salting with the post id would make this attacking process harder, but still realistic. Probably the only real solution is to hide the votes table from federated instances, I'm not sure if that brings technical problems.
If anything, wouldn't that make vote abuse even easier? Just send 100 upvotes with 100 random hashes.
That was what I was implying, yes.
Just hash each username and store it. Then just check the usernames hash to see if it matches.
I was more comnenting that you could still reverse engineer the users who voted on a post
Actually, you’re not really wrong.
All the more reason to give out limited data to all other instances. Why do these instances really need this data? Mastodon doesn’t need it, not quite sure why Lemmy does it.
Yeah I don't understand why every instance can't keep track of their own votes privately. Sure, voting manipulation is a thing, but it's possible regardless.
Honestly I really hope Lemmy does something to address this issue. Otherwise it's kind of a dealbreaker for me.