Here's the whitepaper about iOS security: https://www.apple.com/business/docs/iOS_Security_Guide.pdf

There is a reference for this as Apple published a security white-paper about it prior to the release of TouchID. Unfortunately, I'm not at a point where I can search for it. If I find the time today, I will update this post with a link.

Cheers. I'd appreciate it.

Edit to add: I came across this one:

https://www.apple.com/business/docs/iOS_Security_Guide.pdf

It was linked from an article in 2014[1], though this PDF document is dated March 2017.

[1]: http://www.biometricupdate.com/201402/apple-publishes-whitep...

Yeah, that's the updated one. Prior to the release of TouchID, something similar was released.