The proliferation ofchild sexual abuse materialon the internet is harrowing and sobering.
Who holds the key?
Encryption is one of the best tools for protecting personal information as it traverses the internet.
It’s free, every week, in your inbox.
Can a cloud service provider detect child abuse material if the photos are garbled using encryption?
It depends on who holds the secret key.
But this convenience comes at a big cost.
A cloud provider that stores secret keys mightabuse its accessto your dataor fall prey to adata breach.
In this case, the provider cannot decrypt your photos.
Apples proposed image matchingon iCloud Photos uses cryptographically protected computing to scan photos without seeing them.
Its based on a tool calledprivate set intersectionthat has been studied by cryptographers since the 1980s.
This tool allows two people to discover files that they have in common while hiding the rest.
Heres how the image matching works.
For each photo that you upload to iCloud, your deviceapplies a digital fingerprint, called NeuralHash.
The fingerprinting works even if someone makes small changes in a photo.
Otherwise, the server cannot view any of your photos.
But thats a big caveat.
I care about what it can do!
Apples phone scanning technology is designed to protect privacy.
The threat of mission creep was a risk even with server-based matching.
These public accountability goalscan be achieved using cryptography.
But no technology on its own can fully answer complex social problems.
All options for how to use encryption and image scanning havedelicate, nuanced effectson society.
