You can read more of his iPhone-related writing here: https://blog.cryptographyengineering.com/category/apple/ https://blog.cryptographyengineering.com/category

You can read more of his iPhone-related writing here: https://blog.cryptographyengineering.com/category/apple/ https://blog.cryptographyengineering.com/category/apple/ I'm not sure how concerned he is that it's closed source, I think in this case he was just surprised that the implementation details and security considerations weren't documented anywhere: https://twitter.com/matthew_d_green/status/1443382207838621703 https://twitter.com/matthew_d_green/status/14433822078386217... Note that he was relatively positive about this feature when it came out two years ago: https://blog.cryptographyengineering.com/2019/06/05/how-does-apple-privately-find-your-offline-devices/ https://blog.cryptographyengineering.com/2019/06/05/how-does.... It seems like the motivation for this tweet was "wow I do a lot of iPhone security research and I didn't know this worked when the phone is off, I'm surprised Apple doesn't document the details of this anywhere." Remember that it's hard to interpret tone through the internet, and as someone that doesn't get a ton of engagement on Twitter, he probably doesn't feel like he's writing for a mass audience.