IMO - Passkey in iCloud Keychain

IMO = In My Opinion is a blog format where a author reflects his own opinion

With the recent announcement of Apple at their annual Worldwide Developers Conference (WWDC) 2021, our perception of how secure authentication should work will gradually shift towards a passwordless future.

The new(est) innovation from Apple to get rid of passwords and second factors is called “Passkeys in iCloud Keychain”. It basically works with the WebAuthN API by utilizing the FIDO2 specification (CTAP2) to create a private / public key pair for each login system. This is normally identified by its domain name of the server challenging your device for authentication. For this to work across devices it is necessary to synchronize the private key in some way.

But wait … synchronizing a private key across your devices with a cloud solution does not sound exactly … sane!
Well, ok. Let's argue for a minute what the “normal” user does anyway. Many users today rely on password managers to synchronize their passwords and sometimes even their second factors. By doing so, they already expose their secrets to some provider, for example Google, Apple, Microsoft, 1Password, and so on. Even if those providers claim that the secrets are encrypted, it is not a penny better from a security perspective than the synchronization of a private key with the same process. In the end, all private keys, passwords and OTP seed secrets are all secrets which allow access to your resources.

But then again, some of you might argue: “I totally control the sync process with a software I run on my own!”
Well that does not really change the statement above because you end up using a device from one of those vendors anyway and most of them are closed source, so you have absolutely no guarantees that they don’t steal your credentials on the OS level anyway (some exceptions apply - looking at you Linux and to some degree Android).
To make things worse on an OS or even browser level. Something, like a malicious browser extension or trojan horse, could steal things like access_token or cookies, which broadens the threat model a lot towards OS and browsers.

Oh and to make things worse… Out of band processes like OTP, SMS-TAN and email codes don’t help this effort. If you gain access to either the user's device, OS, or browser, then your whole security model is broken anyway. This is because a lot of today's users just use one device in which they login and also store, receive or generate their second factor.

Ah and yes don't even get me started about those pesky banking authentication apps!

So with this in mind is it still a bad thing to sync the private key?

Well, in my opinion, even with all the downsides like synchronization of private keys (secrets in general) we still gain an improved user experience and phishing resistance, which I find important these days without any additional risk (remember you have them anyway). Also, we reduce the attack surface by preventing credential reuse by the user.

So if you ask me: The tradeoff made here by Apple does outweigh the risk. And if you think this risk is too high for you, then just do not use iCloud Passkeys (and password managers in general) and stick to hardware keys.
If you really care about security you would end up with mTLS (mutual TLS) anyway because this is the only way to mutually authenticate connections and mitigate Man-in-the-middle risk more or less completely (which FIDO2 does not). But this is a topic for another time.

If you want to test iCloud Passkeys today you are best off to use iOS 15, iPadOS 15 or macOS Monterey. Optimally you have multiple devices to see whether the keys get synced across your devices with iCloud Keychain.

As of today more and more systems and services offer the use of passwordless authentication methods. For example your Microsoft Login can be used in this way. Popular Open Source IAM Solutions like Keycloak also give you the option to use passwordless. Our IAM as a Service project ZITADEL does also provide support for the password authentication future.

But remember: Passkeys in iCloud Keychain are not production ready yet (technology preview) and are intended for testing only. So for your own sake, please register a fallback hardware key like the ones from our friends at SoloKeys or YubiKey. We recommend you to register multiple keys anyway.