Full Homomorphic Encryption (FHE) and CSAM

You sometimes tire of those blogs which push the same old, “You multifactor authentication”, and “Change your password often!”. While the messages are worthy, they hardly stimulate debate and critical thought in cybersecurity. We thus need people like Bruce Schneier and Matthew Green to stir things up a bit, and try and explain complex areas of technology in an interesting and engaging way.

And, so, this week, Matthew published this blog post [here]:

It is a stimulating essay on one of the most difficult technology challenges of the time … how to uncover objectable material (CSAM) without breaking our rights to privacy. For this, he talks about Ashton Kutcher — and who played Steve Jobs in a movie. Matthew outlines that Ashton gave a major speech to EU Parliament members — and which supported the EU’s approach to scanning content. Ashton co-founded Thorn, and which integrates cryptography for CSAM scanning.

As Matthew outlines, Ashton even outlined a method of using FHE (Fully Homomorphic Encryption) to perform matches on content matches. This could work by storing hashes of objectable content, and then encrypting these with a homomorphic public key…