4 ms·

Thanks, that's really helpful. Followup questions though: - Does this mean if I buy 2 of these devices at the same time, it's possible for me to get the same a

Thanks, that's really helpful. Followup questions though: - Does this mean if I buy 2 of these devices at the same time, it's possible for me to get the same attestation keys on both devices? I guess depends on how many batches at a time a company is producing. - Doesn't this mean that attestation keys will get more unique over time as devices from the pool fall out of circulation and become rarer? Are keys rotated to prevent that (ie, would a manufacturer ever re-release a new pool with the same keys as an old one)?

md_ 5y ago
- Yes. - To my (limited) knowledge, yes, you are right that keys will get more unique over time. That's a very good point. Keys are not rotated nor (generally) are they rotatable; they are usually read-only. If you are using a very old FIDO device and worried it has too much entropy now--like, if it's a "rare" or "vintage" device!--then you should buy a new one, I guess? (I honestly have not thought about your second point before, but I am not really deep in the FIDO stuff. So take my answer with a grain of salt.)
- fuckyouriotshit 5y ago
  Manufacturers don't necessarily have to rotate the keys on older devices; they could rotate the keys on newer devices such that it's difficult to reliably tell what batch/generation a newer device is from, because it could be using a newer or older key. Such behavior would require some way of revoking old keys from newer devices to prevent a situation where a compromised and blacklisted old key is selected and causes the CAPTCHA to fail, seemingly at random.
  - md_ 5y ago
    I don't totally follow. The key is baked into each device, so if you sold a mix of devices where some had the old key and some the new, revocation of the old key would brick the new devices with that old key.
gjvr 5y ago
I understand from [0] that the attestation key is shared across all instances (SNs) of the same model (PN): "...For example, all YubiKey 4 devices would have the same attestation certificate; or all Samsung Galaxy S8’s would have the same attestation certificate". So you would not need to to buy them at the same time. But of course, despite this, still a unique key is generated for each identity upon sign up [0]. I am not sure (as in 'have no knowledge of') the entropy for these devices. [0] https://fidoalliance.org/fido-technotes-the-truth-about-attestation/ https://fidoalliance.org/fido-technotes-the-truth-about-atte...

md_ 5y ago

- Yes. - To my (limited) knowledge, yes, you are right that keys will get more unique over time. That's a very good point. Keys are not rotated nor (generally) are they rotatable; they are usually read-only. If you are using a very old FIDO device and worried it has too much entropy now--like, if it's a "rare" or "vintage" device!--then you should buy a new one, I guess? (I honestly have not thought about your second point before, but I am not really deep in the FIDO stuff. So take my answer with a grain of salt.)

fuckyouriotshit 5y ago
Manufacturers don't necessarily have to rotate the keys on older devices; they could rotate the keys on newer devices such that it's difficult to reliably tell what batch/generation a newer device is from, because it could be using a newer or older key. Such behavior would require some way of revoking old keys from newer devices to prevent a situation where a compromised and blacklisted old key is selected and causes the CAPTCHA to fail, seemingly at random.
- md_ 5y ago
  I don't totally follow. The key is baked into each device, so if you sold a mix of devices where some had the old key and some the new, revocation of the old key would brick the new devices with that old key.

gjvr 5y ago

I understand from [0] that the attestation key is shared across all instances (SNs) of the same model (PN): "...For example, all YubiKey 4 devices would have the same attestation certificate; or all Samsung Galaxy S8’s would have the same attestation certificate". So you would not need to to buy them at the same time. But of course, despite this, still a unique key is generated for each identity upon sign up [0]. I am not sure (as in 'have no knowledge of') the entropy for these devices. [0] https://fidoalliance.org/fido-technotes-the-truth-about-attestation/ https://fidoalliance.org/fido-technotes-the-truth-about-atte...