Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
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Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
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Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#2Barely related, but is CSAM a new acronym? I hadn't heard it until this fiasco.
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#3The question presumes the database leak also comes with the server side secret for blinding the CSAM database, which is unlikely (that’s not how HSMs work) and would be a general catastrophe (it would leak the Neural Hashes of photos in the NCMEC database, which are supposed to remain secret).
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#4Barely related, but is CSAM a new acronym? I hadn't heard it until this fiasco.
No.
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#5The question presumes the database leak also comes with the server side secret for blinding the CSAM database, which is unlikely (that’s not how HSMs work) and would be a general catastrophe (it would leak the Neural Hashes of photos in the NCMEC database, which are supposed to remain secret).
The question doesn't presume that, as the the secret for blinding the CSAM database would only be helpful if a third party were also looking to see which accounts contained CSAM.
In this case, the question assumes that an attacker would more or less be creating their own database of hashes and derived keys (to search for and decrypt known photos and associate them with user accounts, or to bruteforce unknown photos), and would therefore have no need to worry about acquiring the key used for blinding the CSAM hash database.
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#6The question presumes the database leak also comes with the server side secret for blinding the CSAM database, which is unlikely (that’s not how HSMs work) and would be a general catastrophe (it would leak the Neural Hashes of photos in the NCMEC database, which are supposed to remain secret).
Yeah, I've worked with HSMs in the past and to say that it's a challenge to get key material out of them is an understatement. That said, a lot of this depends on the architecture surrounding the HSM - if the key material leaves the HSM at any point, you've basically increased your attack surface from an incredibly secure box to whatever your surrounding interfaces are. At Apple's scale, I have to imagine it's more economical to have some kind of envelope encryption - maybe this is the right attack vector for a malicious actor to hit?
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#7Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#8The question presumes the database leak also comes with the server side secret for blinding the CSAM database, which is unlikely (that’s not how HSMs work) and would be a general catastrophe (it would leak the Neural Hashes of photos in the NCMEC database, which are supposed to remain secret).
The question doesn't presume that, as the the secret for blinding the CSAM database would only be helpful if a third party were also looking to see which accounts contained CSAM. In this case, the question assumes that an attacker would more or less be creating their own database of hashes and derived keys (to search for and decrypt known photos and associate them with user accounts, or to bruteforce unknown photos),…
> What's to stop an attacker from generating a NeuralHash of popular memes, deriving a key, then bruteforcing the leaked data until it successfully decrypts an entry, thus verifying the contents within a specific user's cloud photo library, and degrading their level of privacy?
Decrypting vouchers requires the server blinding key and the NeuralHash derived metadata of the input image (technical summary page 10, Bellare Fig. 1 line 18). This attacker only has the latter.
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#9Earlier quoted context omitted.
No.
What is the difference between CP and CSAM and why is everyone suddenly using the term CSAM instead of CP?
Good link to explain why "CSAM" is being used in lieu of "CP"
https://www.adfsolutions.com/news/what-is-csam
> However, the phrase “child pornography” is almost too sterile and generic to properly exemplify the horrors of what is being created. That is why many advocates, including the National Center for Missing and Exploited Children (NCMEC), believe this phrase to be outdated.
> NCMEC refers to these kinds of material as Child Sexual Abuse Material (CSAM), in order to “most accurately reflect what is depicted- the sexual abuse and exploitation of children”.
> As a result, many organizations and advocates now refer to this material by the new term rather than "child pornography" because it explicitly ties the material to the source of the problem; the abuse that is being perpetuated to create it. Furthermore, children are re-victimized every time a file is shared, sustaining the abuse in a continuous loop.
Re: Apple's New CSAM Protections May Make iCloud Photos Bruteforceable
#10Earlier quoted context omitted.
No.
What is the difference between CP and CSAM and why is everyone suddenly using the term CSAM instead of CP?
CSAM is not necessarily pornographic material, but merely material that becomes objectionable within context.
For example, parents' photos of kids in the bath isn't CP. However _someone else_ having a _quantity_ of bath photos is CSAM, if they have no reasonable reason for possessing them.