Comment by crote
8 days ago
There is no truly secure options for this, unfortunately. Passkeys have to be online to enroll additional keys, so any kind of software or smartphone solution is going to depend completely on cloud sync. Any form of offline copy stored in a physical safe will quickly be outdated.
It gets even worse when you want to have separate passkeys, so that you have the possibility of knowing which one was compromised and doing a partial revocation: the cloud sync now requires every device to have access to every copy, so that you can individually enroll them during registration.
Yubikey of course suffers most from this, as their hardware tokens are physically incapable of any kind of sync, so a Yubikey passkey is very quickly a single-point-of-failure. They proposed[0] a system which would allow enrolling a "backup key" (which could then be safely locked in a vault, far away from day-to-day use), but with the various Big Tech companies pushing their own proprietary cloud-synced passkey implementations that of obviously went nowhere.
[0]: https://www.yubico.com/blog/yubico-proposes-webauthn-protoco...
> Passkeys have to be online to enroll additional keys
No they don't? A passkey is fundamentally just a private key pair, which can be copied around just like a very long password. Of course if you store it inside one hardware enclave and want to move it to another hardware enclave you have a problem, but for software implementations it's simply a client UX issue.
I think "online" here means "loaded in a device", as opposed to "sitting in a safe".
The protocol requires additional keys to sign a challenge during registration, so at best you have to load a pre-generated key from the safe when creating a new account. In practice, you generate a new key for every account, so between generating the key and storing it in your safe there's no backup but cloud sync.
This prevents using backup storage that is safer but inconvenient to access, and also prevents registering accounts on-the-go.
> "Online" in the sense of "loaded in a device", as opposed to "sitting in my safe".
The "device" can be entirely virtual. I've written a passkey-compatible OIDC provider for use on my homelab and it uses passkeys. But the passkeys are just in a SQLite database, which can be copied wherever.
That's not advisable for security, which is one reason I've not released the provider for others to use, but passkeys can operate just fine with that.
If I wanted, the private key itself just be in something like AWS KMS instead of a SQLite database, and it would all still work fine. Nothing about passkeys itself requires a hardware device or that the key be unexportable.
6 replies →
Most website implementations that support passkeys have to support multiple key enrollment. It's the only long-term reliable way for the many, many users that are cross-ecosystem, which especially means Windows users in the age of no Windows Phone. Every Windows user has either an Android or iPhone. You can bootstrap with Bluetooth LTE access to your phone for a Passkey, but it's a rough web experience if the user needs to do that every time they access a page, so most good flows ask the user the enroll a Windows PC passkey in addition to their phone's passkey and really good ones make use of a passkey auto-enrollment option designed for this scenario (Bluetooth passkey to "local" passkey auto-enrollment).
Perhaps surprisingly, Windows has helped keep Passkeys from being "proprietary" lock-in because Microsoft no longer has users in a single ecosystem.
There is no dedicated auto-enrollment for "backup" keys, but most consumer sites make it very easy to enroll "backup" keys yourself.
Also, Passkeys don't have to be "online" to enroll additional keys. Each key is independent, enrolling is just generating new keys. The trouble is that web browsers generate lots of Passkeys (at least one per domain, at the very least) so if you in theory want to print them all and store them in a physical vault it might be a hefty book you are printing.
Cloud sync isn't required. Most users want it so that they don't have a single-point-of-failure.
As an implementation detail some Passkeys have a master key that is then used in some key derivation function (KDF) to generate the hundreds or thousands of individual passkeys (at least one per domain), and that's what most Yubikey passkey implementations need to do because Yubikeys weren't designed to store lots of keys, so it is devices like Yubikey that makes it seem like Passkeys are less independent than they really are.
I am not sure I completely understand.
> so a Yubikey passkey is very quickly a single-point-of-failure
It is a single point of failure when there is one. As soon as you use two, then it's not a single point a failure anymore, is it?
The counter argument I usually read is: "Yeah but it is not practical, because you need 3 yubikeys: the first 2 with you, that you enroll everywhere, and one in a safe. And every time you add a new passkey, you need to go get the one in the safe, replace it by another one, and enroll the one of the safe. You can't spend your life driving between your desk and your safe".
But I have been using multiple Yubikeys for... 8 years now I think? I don't remember the last time I enrolled and important key. Sure, once in a while I add a website, and it is a bit annoying to have to enroll the other Yubikeys at a different time. But it really doesn't happen that often, and anyway most of those websites allow me to recover my account with my email. So it is actually practical to have a "convenience yubikey" for websites that don't matter so much, and in case this Yubikey dies... well those websites were not so important, and anyway I can recover from my email.
The difference for the important websites (and really, I don't think I have really important websites in my life that don't allow me to recover by going in person with my ID, but for the sake of the argument) is that I actually do have multiple Yubikeys, one of which is stored away.
Whereas the master password of my Bitwarden account is a single point of failure, and the security of my online Bitwarden account is as well.
That's a clever setup that I hadn't seen before. Some extra downsides:
- Relying on emails for account recovery prevents creation of anonymous accounts.
- Have you ever lost your "convenience yubikey"? People underestimate how painful mass account recovery can be.
- The cost of 3 yubikeys can be substantial for some demographics.
- Important accounts are not properly backed up until you drive to your safe. That can be many days for a bank deposit box, or even longer if you're traveling.
Overall that's a lot of compromises for what should have been just "put this recovery key/password in a safe and forget about it until needed", if the protocol was better. And definitely not something that can be widely recommended.
> ... just "put this recovery key/password in a safe and forget about it until needed"...
Surely that is also impacted by:
> Important accounts are not properly backed up until you drive to your safe. That can be many days for a bank deposit box, or even longer if you're traveling.
6 replies →
> I have been using multiple Yubikeys for... 8 years now I think? I don't remember the last time I enrolled and important key.
This probably makes your use case somewhat unusual...
> I actually do have multiple Yubikeys, one of which is stored away.
...and this probably puts you in the 0.0001th or so percentile of users. It's really a great security strategy if you can pull it off, but practically almost nobody can.
Not sure what you mean. "Normal people" have to enroll important keys much more often, and cannot use multiple Yubikeys?
My feeling would be that "normal people" can always recover their accounts from their main email, which makes the main email the only "important" account. So having a Yubikey always plugged in is a "nice convenience".
Now to be honest, I would expect that "normal people" are absolutely fine with passkeys on their smartphone, and don't consider it a "trap".
I would just expect that people who consider it a trap are able to use a Yubikey the way I do.
1 reply →
I use Yubikeys for WebAuthn 2FA (not as passkeys). Keeping them in sync is not a big issue in practice: I just don't sign up for new services that often. There's a stable set of services I'm using and it is rare that I actively look for something new. Usually it is the other way around--how do I use this thingamajig without creating an account.
Why would cloud sync never be "truly secure" (no such thing btw – security is always a tradeoff, availability also matters etc.)? A hardware root of trust and credential synchronization are not mutually exclusive.
True, most solutions today don't do this, which makes onboarding of fraudulent additional instances to some cloud-synced vault a big security concern, but I don't think it's fundamentally impossible.
Not mutually exclusive, as long as you have a trusted mechanism for establishing mutual trust between hardware roots. How do you achieve this when one of the roots is a distributed cloud service, provided by a third party?
A cloud synced passkey is still better than a cloud synced password, and that is the alternative.