While passkeys are not ready: Yubikey for OTP

[brasilik]

Hey @Steve and audience,

After the recent discussions around passkeys on the podcast, I wanted to share and get feedback on my approach.

As many other listeners, I also have a Yubikey at home and one with me.
But I have never stored a passkey on them. I use the Yubikey Authenticator app for iOS to store OTP secrets on the keys. I always set up both keys at the same time for any service.

Passwords are stored in Bitwarden, Bitwarden is secured by OTP codes from the Yubikeys as well.

With the almost universal availability is OTP, this is a pragmatic way that I have found to secure my accounts by something “physical”.
The Yubikey I carry has also set a password for additional security.

Any downsides to this approach that I might be missing not seeing?


The process in detail below:

Setup of OTP:
1. Ask the site for an OTP qrcode
2. Stick Yubikey A into the phone and scan the code with the Yubikey Authenticator App
3. Stick Yubikey B into the phone and scan the code with the Yubikey Authenticator App
4. Geberate an OTP from either key and put it in the site for confirmation

Get an OTP
1. Stick the Yubikey into the phone
2. Open Yubikey Authenticator App
3. Generate a code an put it in



Happy for any feedback and love the show

 

[PHolder]

Well the possible downside is any weakness in the Yubikey Authenticator App. Depending on how it's coded, it might be possible to bypass the requirement for the key. It's clearly storing its data on the phone, not on the key, so it may be that it merely checks for the existence of the key before decoding the data on the phone. (I would need to know more about the design of the app.)

 

[brasilik]

Well the possible downside is any weakness in the Yubikey Authenticator App. Depending on how it's coded, it might be possible to bypass the requirement for the key. It's clearly storing its data on the phone, not on the key, so it may be that it merely checks for the existence of the key before decoding the data on the phone. (I would need to know more about the design of the app.)

Yea, true about possible vulnerabilities in the app.

It’s not storing anything in there tho. It’s all on the key, which of course is important if I loose my phone. I verified that by using it from a second phone and works great

 

[PHolder]

using it from a second phone and works great

Oh, okay then. I guess it must be storing the OTP seeds on the key, which is safer (shouldn't suffer the issue I thought it had above), but should have limits to how many it can store. Do you know the limits?

 

[brasilik]

Oh, okay then. I guess it must be storing the OTP seeds on the key, which is safer (shouldn't suffer the issue I thought it had above), but should have limits to how many it can store. Do you know the limits?

I was not able to find the limits. If I am not mistaken, this is the doc: https://developers.yubico.com/OATH/

My best guess is that it takes up one of the 20 slots the Yubikey 4 and 5 have.

I am not affected by it, as I only store crucial second factors there: Bitwarden and email.

For most other services, I store them in Bitwarden