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The existence of a preimage attack makes Apple's system completely useless for its nominal purpose. The NeuralHash collider allows the producers and distributor

The existence of a preimage attack makes Apple's system completely useless for its nominal purpose. The NeuralHash collider allows the producers and distributors of CSAM material to ensure that nearly all of the next generation of CSAM will suffer from hash collisions with perfectly innocent images. If these new images never make it to the NCMEC database, then new CSAM content will be completely NeuralHash-proof. However, if these images eventually make their way into the NCMEC database, then everybody who has the perfectly innocent originals will be dealing with an adversarial environment.

SiempreViernes 5y ago
> If these new images never make it to the NCMEC database The remark that an image might not be in the database applies equally to all CSAM pictures, and so is not actually dependent on any technical aspect of the hash at all. The fact that you can modify an image to the point that it gets a different hash isn't important compared to the (separate) issue of how you keep your database up to date. And detecting old CSAM is in any case not as important as tracking and interdicting production of new images. The second remark is good, but mainly because it reminds us to demand Apple ensures that additions are scanned for malicious images before being added to the central database. If the operator determines that a certain images collides with some known public image they can notify Apple. Apple in turn modifies the hasher to dissolve the collision, roll out a patch, and can then update the database.
Someone 5y ago
> ensure that nearly all of the next generation of CSAM will suffer from hash collisions with perfectly innocent images. Even then, for that to affect _John Doe_, they would have to make 30+ images whose hash matches that of images in _John Doe’s_ iCloud account. I think that means they could target individuals, but only if they knew or could guess what photos they have in their account. They also might be able to target groups of individuals, say people who went on holiday to Paris. It would be interesting to see whether such people have enough overlap in the sets of Neuralhashes of photos they took there.

SiempreViernes 5y ago

> If these new images never make it to the NCMEC database The remark that an image might not be in the database applies equally to all CSAM pictures, and so is not actually dependent on any technical aspect of the hash at all. The fact that you can modify an image to the point that it gets a different hash isn't important compared to the (separate) issue of how you keep your database up to date. And detecting old CSAM is in any case not as important as tracking and interdicting production of new images. The second remark is good, but mainly because it reminds us to demand Apple ensures that additions are scanned for malicious images before being added to the central database. If the operator determines that a certain images collides with some known public image they can notify Apple. Apple in turn modifies the hasher to dissolve the collision, roll out a patch, and can then update the database.

Someone 5y ago

> ensure that nearly all of the next generation of CSAM will suffer from hash collisions with perfectly innocent images. Even then, for that to affect _John Doe_, they would have to make 30+ images whose hash matches that of images in _John Doe’s_ iCloud account. I think that means they could target individuals, but only if they knew or could guess what photos they have in their account. They also might be able to target groups of individuals, say people who went on holiday to Paris. It would be interesting to see whether such people have enough overlap in the sets of Neuralhashes of photos they took there.