3 ms·

If you can make one algorithm collide, you can make two collide.

by phyzome 3y ago

astrange 3y ago
You can't because you don't have access to one of the algorithms.
- logi_sko 3y ago
  We don't actually have access to the first algorithm either, but it's been reverse engineered and a binary published. According to article.
  - astrange 3y ago
    I should have said "algorithm deployment" or something. The main point is that on the server side, you can change the hash (or its seed) anytime you want, if the false positive rate is getting too high. It may be possible to do the same thing to the client actually.
- quitit 3y ago
  In online people sometimes write things the way they want them to be, not the way they factually are. In small ways it comes across as wishful thinking, in other ways it's just plain old lying. I didn't feel that the comment trivialising multiple hash collisions was worth a direct reply, because the author is clearly not writing with bona fide intentions, or any real knowledge about an image scanning system. It's the fingers in ears, head in the sand kind of denialism that adds nothing to the conversation. My earlier comment already addressed what happens after the hashes match: a visual comparison. This isn't an original concept, it's a standard approach and part of earlier CSAM scanning proposals. One needs to act rather barefaced to pretend that a matched hash alone will have consequences, when we already have established that false positives are the known downside to using hash-based image matching.
alexfoo 3y ago
If you can make 46 collide you can mint your own bitcoins. The increase in difficulty is multiplicative not additive.
logi_sko 3y ago
It needs to be not just a second algorithm but a parametric hash function. So after an image B has been found which matches illegal image A on f(B)=f(A) then the server picks a random number R and sends the client R,f(A,R) and the client checks if f(B,R) =f(A,R) as well. Do we have such a hash function?

If you can make one algorithm collide, you can make two collide.

astrange 3y ago

You can't because you don't have access to one of the algorithms.

logi_sko 3y ago
We don't actually have access to the first algorithm either, but it's been reverse engineered and a binary published. According to article.
- astrange 3y ago
  I should have said "algorithm deployment" or something. The main point is that on the server side, you can change the hash (or its seed) anytime you want, if the false positive rate is getting too high. It may be possible to do the same thing to the client actually.
quitit 3y ago
In online people sometimes write things the way they want them to be, not the way they factually are. In small ways it comes across as wishful thinking, in other ways it's just plain old lying. I didn't feel that the comment trivialising multiple hash collisions was worth a direct reply, because the author is clearly not writing with bona fide intentions, or any real knowledge about an image scanning system. It's the fingers in ears, head in the sand kind of denialism that adds nothing to the conversation. My earlier comment already addressed what happens after the hashes match: a visual comparison. This isn't an original concept, it's a standard approach and part of earlier CSAM scanning proposals. One needs to act rather barefaced to pretend that a matched hash alone will have consequences, when we already have established that false positives are the known downside to using hash-based image matching.

alexfoo 3y ago

If you can make 46 collide you can mint your own bitcoins. The increase in difficulty is multiplicative not additive.

logi_sko 3y ago

It needs to be not just a second algorithm but a parametric hash function. So after an image B has been found which matches illegal image A on f(B)=f(A) then the server picks a random number R and sends the client R,f(A,R) and the client checks if f(B,R) =f(A,R) as well. Do we have such a hash function?