Due to some iCloud struggles, I had recently occasion to sign into and out of iCloud on OS X a few times recently. Interestingly, when I have 2FA enabled on my iCloud account, OS X asked for the screen lock passcode to my iPhone when signing in to iCloud, and would not sign in without it (no . After the initial sign in succeeds, it prompts for the iCloud password again, and this time asks for the 2FA code.

This was a surprising and unexpected part of the authentication flow. Does anyone know why iCloud / OS X / iOS interact in this way?

  • I don't like it. A desktop OS is more likely to have malware and visual collection would be easier. I think entering your iPhone passcode on any device other than the iPhone itself is a security risk in itself, they just doubled the number of available targets for an attack. – MetaGuru Jun 22 '17 at 18:02

It just seems to be an extra security measure, so that somebody who steals your iphone in an unlocked state can not quickly use the 2FA to change your iCloud account.

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