It's all on pages 4 and 5 of https://www.apple.com/child-safety/pdf/CSAM_Detection_Technical_Summary.pdf https://www.apple.com/child-safety/pdf/CSAM_Detection_T

It's all on pages 4 and 5 of https://www.apple.com/child-safety/pdf/CSAM_Detection_Technical_Summary.pdf https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni... > The main purpose of the hash is to ensure that identical and visually similar images result in the same hash, and images that are different from one another result in different hashes. For example, an image that has been slightly cropped or resized should be considered identical to its original and have the same hash. The system generates NeuralHash in two steps. First, an image is passed into a convolutional neural network to generate an N-dimensional, floating-point descriptor. Second, the descriptor is passed through a hashing scheme to convert the N floating-point numbers to M bits. Here, M is much smaller than the number of bits needed to represent the N floating-point numbers. NeuralHash achieves this level of compression and preserves sufficient information about the image so that matches and lookups on image sets are still successful, and the compression meets the storage and transmission requirements Just like a human fingerprint is a lower-dimensional representation of all the atoms in your body that's invariant to how old you are or the exact stance you're in when you're fingerprinted... technically Federighi is being accurate about the "exact fingerprint" part. The thing that has me and others concerned isn't necessarily the hash algorithm per se, but rather: how can Apple promise to the world that the data source for "specific known child sexual abuse images" will actually be just that over time? There are two attacks of note: (1) a sophisticated actor compromising the hash list handoff from NCMEC to Apple to insert hashes of non-CSAM material, which is something Apple cannot independently verify as it does not have access to the raw images, which at minimum could be a denial-of-service attack causing e.g. journalists' or dissidents' accounts to be frozen temporarily by Apple's systems pending appeal (2) Apple no longer being able to have a "we don't think we can do this technically due to our encryption" leg to stand on when asked by foreign governments "hey we have a list of hashes, just create a CSAM-like system for us" That Apple must have considered these possibilities and built this system anyways is a tremendously significant breach of trust.