CID Question

J B

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Jan 19, 2023, 9:13:42 PM1/19/23

to FIDO Dev (fido-dev)

I see that there is a CID that should be used for broadcasting, but I don't see any other requirements about the CID that devices should be using. Should devices be assigned CIDs according to any spec? Should devices try to have unique CIDs? What's the guidance around this?

J B

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Jan 24, 2023, 12:03:04 PM1/24/23

to FIDO Dev (fido-dev), J B

I found some more info in the CTAP2.0 spec that I had previously missed:

"8.1.3. Concurrency and channels: A channel identifier is allocated by the FIDO authenticator to ensure its system-wide uniqueness. The actual algorithm for generation of channel identifiers is vendor specific and not defined by this specification."

Can this just be a sequentially increasing ID or serial number? What happens if there are multiple devices with the same CID?

Fujimi Bentley

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Sep 5, 2023, 2:05:28 AM9/5/23

to FIDO Dev (fido-dev), J B

I'm adding this to a list of things to try when I get around to implementing FIDO on my own device(s).... I will definitely have duplicate CID's. Still trying to make sure that the behaviour I'm getting is actually correct or if it is actually an "error state".

As a guess I think duplicate CID's are not an issue for authenticators on multiple devices since each should have unique device codes reported by the OS, at a lower level to CID.