They put out a new paper [0] describing the security thread model they were working with, and this paragraph on page 9 stood out to me:

The perceptual CSAM hash database is included, in an encrypted form, as part of the signed operating system. It is never downloaded or updated separately over the Internet or through any other mechanism. This claim is subject to code inspection by security researchers like all other iOS device-side security claims.

Could someone tell me how that inspection works? Are there researchers who are given the source code?

[0]: https://www.apple.com/child-safety/pdf/Security_Threat_Model...