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No, he's not. Read the documentation. The hash database your photos are compared to will live on your device, and scanning happens entirely on-device. "Apple f

No, he's not. Read the documentation. The hash database your photos are compared to will live on your device, and scanning happens entirely on-device. "Apple further transforms this database into an unreadable set of hashes, which is securely stored on users’ devices."

josephcsible 5y ago
Read further down: > the blinding step using the server-side secret is not possible on device because it is unknown to the device. The goal is to run the final step on the server and finish the process on server. This ensures the device doesn’t know the result of the match, but it can encode the result of the on-device match process before uploading to the server.
- willseth 5y ago
  This is a confusing paragraph, but the "final step" is not matching per se. The final step reveals whether a match occurred - but it's clear that the database exists on-device and the database lookup occurs on-device. Note the last part: "... but it can encode the result of the on-device match process before uploading to the server." The result of the match already exists before it is uploaded to the server. This is also made clear in the diagram. Depending on how you define "matching," it either occurs on-device or no explicit matching actually occurs. The server gets a payload for each uploaded image and attempts to use its server-side secret to derive its decryption key from the header. If (and only if) the image was a match - as determined by the blinded on-device comparison - it will now have a key to decrypt the rest of the payload (for review). Note that neither client nor server explicitly compare the real database hash to the image hash. The comparison is absorbed into crypto "properties."
  - josephcsible 5y ago
    Do you agree with these two statements? 1. For every image that's scanned, whether matching or non-matching, some data will be sent to the server. 2. Your phone never learns and has no way to tell which images match and which ones don't.
    - willseth 5y ago
      Ugh. Feel free to expound any of your vague replies in this thread with actual explanations that make sense under any reasonable interpretation of "on device."

josephcsible 5y ago

Read further down: > the blinding step using the server-side secret is not possible on device because it is unknown to the device. The goal is to run the final step on the server and finish the process on server. This ensures the device doesn’t know the result of the match, but it can encode the result of the on-device match process before uploading to the server.

willseth 5y ago
This is a confusing paragraph, but the "final step" is not matching per se. The final step reveals whether a match occurred - but it's clear that the database exists on-device and the database lookup occurs on-device. Note the last part: "... but it can encode the result of the on-device match process before uploading to the server." The result of the match already exists before it is uploaded to the server. This is also made clear in the diagram. Depending on how you define "matching," it either occurs on-device or no explicit matching actually occurs. The server gets a payload for each uploaded image and attempts to use its server-side secret to derive its decryption key from the header. If (and only if) the image was a match - as determined by the blinded on-device comparison - it will now have a key to decrypt the rest of the payload (for review). Note that neither client nor server explicitly compare the real database hash to the image hash. The comparison is absorbed into crypto "properties."
- josephcsible 5y ago
  Do you agree with these two statements? 1. For every image that's scanned, whether matching or non-matching, some data will be sent to the server. 2. Your phone never learns and has no way to tell which images match and which ones don't.
  - willseth 5y ago
    Ugh. Feel free to expound any of your vague replies in this thread with actual explanations that make sense under any reasonable interpretation of "on device."