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But wouldn't the TouchID be creating a secure password that only the user knows (by hashing the fingerprint data)?
I am thinking Apple recommends the 6 digit only because they know most users can't remember a long secure password. That is why Apple created TouchID.
Thus I am sorry, but I think you are incorrect on this issue.
I do think Apple uses a separate password to control which s/w you can install, which I detest, but that is an orthogonal issue.
TouchID. has already been long since being cracked.
https://www.ccc.de/en/updates/2013/ccc-breaks-apple-touchid I mean seriously someone's phone is not going to have their fingerprints on it? Giving people a false sense of security in order to sell security theater is detestable.
Edit: Remembering a well chosen secure password can actually be easier than remembering a six digit number.