Cryptex: how a custom iPhone is changing macOS updates – The Eclectic Light Company

December 8, 2022

Cryptex: how a custom iPhone is changing macOS updates – The Eclectic Light Company:

Big Sur brought us the immutable boot volume, signed and sealed, with the SSV. This makes it almost impossible for malicious software to change anything in the System, as it’s a snapshot with every last bit verified using its tree of hashes. Its downside is that making wanted changes to update macOS or any components on the SSV is cumbersome: changes have to be written to the System volume, a snapshot made, the tree of hashes rebuilt and verified against Apple’s setting for that build of macOS, and macOS rebooted from the new snapshot.

Initially, the solution for apps like Safari, security data such as that for XProtect, and other components like Rosetta 2 that need to be installed separately from macOS, was to store them on the Data volume, where they can only be protected by SIP. That’s how Big Sur and Monterey worked, but this started to change in late versions of Monterey (in 12.6.1, if not before), and Ventura, with the introduction of the cryptex.

Cryptexes first appeared on Apple’s customised iPhone, its Security Research Device, which uses them to load a personalised trust cache and a disk image containing corresponding content. Without the cryptex, engineering those iPhones would have been extremely difficult.

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