Yubico Forum

I'm interested in having a backup Yubico 4 device that I lock in a safe in the event I ever lose mine and need access to my accounts.

I have a couple of questions in regards to this.

1) How do I setup a new Yubico key to act as a 'backup' to my current key? I'm assuming there's some private data embedded on my key that would need to be transferred to another key. I'm mostly using U2F mode as my second form of auth. I'm not sure how that would impact a backup key.

2) In the event my key is ever lost, once I regain access to my accounts with a backup key, I'm guessing I'll need to do something to invalidate the existing keys and "rebuild/reseed" the current keys so my lost one becomes useless. Is there documentation suggesting how this is done anywhere?

Thanks!

By design it's not possible to retrieve private data from a yubikey, the only way is to you program both keys with the same secret, to do that you most know the secret beforehand. Since you can't program U2F (only enable/disable) you can't create a backup with exact same secret, that being said, most sites (I can only guarantee google, dropbox and github) accept multiple keys, I myself have 2 U2F registered on them, if you lost one the keys just go and revoke on every site where you registered.

Now a backup of Yubico OTP can be done, but to do so you need generate a new AES key and program it on the both keys, then upload the key to https://upload.yubico.com/. To avoid "locking yourself out", first create the backup and change the old key from services you use, them overwrite the old secret from your every day key.

On 2014 Yubico shutdown the YubiRevoke service, and so there is no more way to revoke a AES key from Yubicloud. The reasons of why they done this can be found here: https://www.yubico.com/2014/06/lost-yubikey-practices/

when backing up (or cloning) your yubi you have one great problem. at least in HOTP, U2F and YubiOTP modes.

The counter.
while in u2f and YubiOTP the counter just needs to be higher than before, in standard OTP (which I actually have never seen being used on a website before) can desync so you essentially need to know the previous counter value.

when working with U2F I suggest getting something like this http://www.amazon.de/dp/B00OGPO3ZS
set it up as another authorised key and stroe it safely.
it might look cheap and it might not work for a million auths, but unlike a yubi it is goddamn cheap and can work as a U2F backup device

when working with YubiOTP I suggest getting a cheap yubikey (can be older, they pretty much all do YubiOTP but can be less than half the price of a yibi4) and set that that one is another key for authorisation

with HOTP well usually services offering standard OTP in counter mode are a pain since HOTP can easily desync (which actually happens when you set another device with the same seed and try to set the counter too high) and on the yubi there's no way to retrieve the counter so you are out of luck for some just try it, but bruteforcing wont help you because maybe that will lock your account for good.

U2F creds cannot be backed up, that's why any service that utilizes U2F allows you to add ten or more different U2F devices as backups. At one point I was testing GitHub and got up to 28 devices added (I ran out of U2F-capable YubiKeys to test with so I don't know how many are actually allowed, if there is even a limit). Google originally maxed at ten but that number has been lifted, as I have added more than ten during testing. People also seem to forget that services that use U2F, OATH-HOTP, etc. allow backup recovery methods, ways to remove the requirement, etc.

For example:

Google / Dropbox / GitHub - recovery codes, backup via Google Authenticator or SMS, etc.

KeePass (OATH-HOTP) - If counter gets out of sync, devices fails, etc., use the secret key used to program the OATH-HOTP to access your account. You can then configure a replacement YubiKey, remove the protection on the account, then generate a new credential and sync.

of yourse you cannot normally back up a U2F device but if someone sophicated tries to read out the chip and succeeds somehow (greetings from murphy's law) they have a backup, but the point is that one of those 2 will be kicked earlier or later due to the counter.