@jpsachse : or when your account gets pwned and the attacker does a better job proving that they are you than you - after all, *they* have access to your account - while you do not.

ANDROID PASSKEY BLACK HOLE
*Or* when you press a button "Clear data" (at the bottom of https://chrome.google.com/sync) which is accompanied by the text:

« This will clear your Chrome data that has been saved in your Google Account. This might clear some data from your devices. »

For you to subsequently find out that ALL OF YOUR PASSKEYS on (all of) your Android device(s) are IRRETRIEVABLE GONE (I reported this to Google in June 2023 and published it 6 months later in
https://seclists.org/fulldisclosure/2024/Feb/15). It's still unfixed.

WHY NO EXPORT AND NO BACKUP
W.r.t. being able to export and/or backup all private keys belonging to all of your passkeys: that's a big dilemma (depending on your POV).

The main (advertised, not taking into account a possibly desired vendor lock-in) reason is simple: if *you* have direct access to such private keys, *malware* running on your device does too.

The compromise is that they are automatically synced to your cloud account, and from there to other devices (of the same brand, provided they run an OS version that's not too old), including a new device if you brick or lose your old device.

However, if there's serious malware on your device, then, even if the malware authors cannot steal all of your passkeys (that is, their private keys), then you're toast anyway; a RAT such as AnyDesk may fool you into believing that you're logging in to website A while in fact it's B and they steal it's session cookie - and pwn the webaccount.

SYNCING PRIVATE KEYS
BTW it's hardly being discussed, but being able to synchronize secrets between secure hardware enclaves in such a way that *you* are denied access, is quite an achievement (considering that, if you buy a new phone, the only available secrets to the transport system are your definitely weak passcode, and your, potentially weak, cloud password that may be used to encrypt the private keys in transit).

I *know* that it's complicated because I accidentally found out around June 2023 that Android can get confused: passkeys *seem* to sync just fine, but passkeys created on phone 1 do not work on phone 2 and vice versa. Somehow the phones had started using *different* encryption keys used to securily synchronize them (I also mentioned that issue in my reports to Google in the summer of 2023, and I mention it in the FD (seclists.org) message).

I don't know how Apple syncs secrets in iCloud keychain, and neither whether a situation may exist where passkey's private keys sync but are unusable (like may happen when using Android).

APPLE'S OWN PASSKEY MISERY
However, Apple has got their own bunch of problems with passkeys being usable *without* requiring biometrics or a passcode to unlock them from iCloud Keychain, see https://infosec.exchange/@ErikvanStraten/113050312014160350 and follow-up (it gets worse every time I look at it) https://infosec.exchange/@ErikvanStraten/113053761440539290 (more details in earlier toots in that thread).

In short: if you don't use biometrics to unlock your iPhone or iPad (OR you do, but you have -unlikely- disabled a specific configuration setting), then anyone with access to your iDevice in an unlocked condition (*), can sign in to:
https://appleid.apple.com
and/or
https://icloud.com
WITHOUT entering your passcode (or using biometrics).

(*) your child, spouse, someone you don't know (well) who borrows your phone to make a call (because their's battery is dead), NOTABLY including a thief who stole it while you were using it (or saw you type your passcode and can unlock it by themselves: https://youtu.be/QUYODQB_2wQ).

I'm not sure yet, but this may even render Apple's anti-theft system totally moot.

@rmondello @johnbrayton
@agl